WO2006002478A1

WO2006002478A1 - Disc pair for single handle water mixer tap

Info

Publication number: WO2006002478A1
Application number: PCT/AU2005/000973
Authority: WO
Inventors: David Brian Stewart
Original assignee: David Brian Stewart
Priority date: 2004-07-07
Filing date: 2005-07-05
Publication date: 2006-01-12
Also published as: WO2006002478A8

Abstract

A valve for a single handle mixer valve comprising an adjacent disc pair, one lower fixed disc (3), one upper disc (4), which cooperates with handle for translation and rotation of upper disc, Inlet ports for hot and cold water on underside of lower disc in flow communication with mirrored mixer inlet ports for cold water (7) and hot water (8) on upper surface (5) of lower disc, outlet port (25) on said upper surface in flow communication with outlet port on underside of lower disc for mixing hot and cold. Lower surface of upper disc is in coplanar bearing and sealing engagement with upper surface of lower disc. Upper disc has a mixing throat with opening (9) at lower surface, said mixing throat having an internal upper surface with longitudinal serrations (32), so that mixer inlets ports for cold and hot water in conjunction with said mixing throat opening define particular size, shape and flow passages for incoming flows depending upon translation and rotation of upper disc relative to lower disc. During overlap of mirrored mixer inlet ports for hot and cold water, mixing of these incoming flows occurs firstly at a flow cross-section at constant width apex (36) of lower disc where intersecting incoming flows of hot and cold are defined by a tapered tip (33) beneath said apex (36) and further defining overlap and proportioning of cold water flow aperture (10) and hot water flow aperture (11) depending on rotation of upper disc about central axis of lower disc as the tapered or vertex like entrance end of the mixing throat opening arcs across said apex result in triangular shaped flow apertures (10 & 11) creating efficient mixing, by which infinitely variable adjustment and control of flow rate and temperature is obtained during translation and rotation of upper disc. During overlap and proportioning of the two incoming flows, as flow approaches almost no flow, the apertures approach a triangular shape and there is almost zero water hammer pressure generation at complete closure during any combination of translation and rotation of said upper disc.

Description

DISC PAIR FOR SINGLlE HANDLE WATER MIXER TAP

This invention relates in general to improvements to single handle or single lever mixer valves or taps or faucets for mixing two incoming streams of fluid from closed conduits to foπn one stream of fluid which issues from said single handle mixer tap with a near constant desirable quality which depends ultimately on a ratio of flowrate of said two incoming streams. Λ desirable quality could be, for example, temperature of a water mixture of hot water from a hot water system and cold water from a reticulated water supply to provide a suitable bathing temperature in a shower bath or spa. Moreover, for said shower, flowrate of said water mixture is considered important enough to warrant selection and adjustment to suit individual requirements and similarly after selecting a desired temperature of said water mixture then maintaining a near constant temperature of said water mixture is also considered important. A further example of the convenience of said single handle mixer tap use is at the kitchen sink where said flowrate and said temperature of said water mixture are considered important for individual selection to meet requirements of use, and particularly where after selecting said suitable temperature of said water mixture there may arise the need for several different said flowrates at said selected suitable temperature. Said single handle mixer tap requires small physical effort for hand adjustment of said water mixture flowrate with vertical raising of said handle to increase said water mixture flowrate and vertical lowering of said handle to decrease said water mixture flowrate and during said adjustments of said water mixture flowrate said water mixture temperature remains desirably constant. Likewise, when said desired water mixture flowrate has been selected, horizontal hand movement of said single handle results in adjustment of said water mixture temperature whilst said selected water mixture flowrate remains desirably constant. '.Tie physical ease of making hand movements to said single handle mixer tap to make said adjustments of said water mixture temperature and said water mixture flowrate may give rise to generation of water hammer in the hot and cold water supply pipes more particularly in said hot water supply pipes leading back upstream to said hot water supply when said water mixture flowrate is shut off suddenly by using inadvertently a quick hand speed movement to said single handle. Other desirable qualities sought after in the application of this invention could be a fluid combination being a mixture blend or compound of two fluids to obtain a suitable taste, colour, odour, viscosity, density or other fluid property of said fluid output. In all applications of said single handle mixer tap it is desirable to eliminate said generation of said water hammer in said hot and cold water supply pipes or generation of fluid hammer in other fluid supply pipes whilst forming said water mixture fjowrate or other fluid combination flowratc issueing from said single handle mixer tap during said sudden shutoff or during sudden opening of said water mixture flowrøte or said other fluid combination flowrate for any said adjustment of temperature of said water mixture flowrate or any adjustment of said fluid property of said fluid combination flowrate,

A particular application described here for performing this invention is mixing of said flowing hot water and said flowing cold water from said water supplies in said single handle mixer tap to obtain said desirable temperature and said flowrate of said water mixture for human bathing in said shower bath or spa or at said kitchen sink or for any other purpose and where fluid dynamic mixing in said single handle mixer tap of said incoming streams of hot and cold water supplies provides said near constant temperature of said water mixture flowratc independent, of reasonable pressure changes in said hot and cold water supplies to said single handle mixer tap. Said fluid dynamic mixing of said hot and cold water supplies in a mixing valve has been previously described and defined using mathematical modelling equations representing one dimensional incompressible fluid flow in a fundamental quantitative analysis of said dynamic mixing which may be found in Industrial and Engineering Chemistry - Process Design and Development Volume 3, January 1964 pages 5-7, " Mixing Two Fluids in a Closed Conduit" by D. B. Stewart and A. K. Johnston and also by said Stewart( also author of this specification ) in Commonwealth of Australia Standard Patent No, 521 749 in which claims were made for a single handle mixing valve resulting in control of only water mixture temperature whilst aggregate flowrate of hot and cold water supplies to said mixing valve remained reasonably constant and thus water mixture flowrate remained reasonably constant whereas individual flowrates of said hot and cold water supplies and thus said aggregate flowratc of hot and cold water supplies were controlled by separate means upstream from said mixing valve whose mixing chamber geometry was unlike the geometry of the disc pair described here. In said prior art by said Stewart no claims were made for prevention of said water hammer generation whereas in said specification for said disc pair for said single handle mixer tap said prevention of water hammer generation is incorporated in a first embodiment in which there is integration of geometry for said water hammer prevention and geometry for highly effective said dynamic mixing and a second embodiment which incorporates prior art disc pair geometry giving Jess effective said dynamic mixing where said geometry for prevention of said water hammer generation is superimposed on said prior art disc pair geometry of the flow aperatures for said hot and cold water in a mixer tap incorporating single control means for adjustment of said water mixture temperature and said flowrate. The essence of said fluid dynamic mixing may be explained qualitatively by reference to the simple yoke piece or breeching piece which has the least effective said fluid dynamic mixing but is still used in domestic plumbing where individual upstream stop taps are employed on separate said hot and cold water supplies feeding said breeching piece for example connected Io said shower bath or spa installation. Suppose said stop taps on said hot and cold water supplies are adjusted for said hot water flowrate and said cold water flowrate to result in said desirable shower temperature whereupon if we now consider that the cold water supply pressure to said cold water stop tap decreases consistent with a cold water user elsewhere turning on another cold water stop tap on said common cold water supply and also suppose that supply pressures remain constant to said hot water slop tap and to the shower end fitting. The immediate consequence is that said cold water flowrate will decrease through said cold water stop tap on said shower installation and this causes the pressure at the mixing throat of said breeching piece to decrease whereupon said flowrate through said hot water stop tap will increase and this therefore results in an increase in said shower temperature simply because said cold water flowrate has decreased and said hoi water flowrate has increased. Similar disturbances of said shower temperature occur for any change positive or negative in either said hot water supply pressure or said cold water supply pressure, Thus said breeching piece as a mixer has an undesirable said fluid dynamic mixing effectiveness. Better mixing incorporating more effective said fluid dynamic mixing is achievable when higher fluid flow velocities are employed in the mixer apertures at the entrance to where mixing of said hot and said cold water streams occur. Of course there are constraints on higher magnitudes of said flow velocities that are beneficial since reasoning of the energy equation of fluid flow indicates that when said flow apertures are loo small in cross sectional area ihen said flow velocities are loo large and may result in static pressure too low in the region of said apertures which may cause water cavitation accompanied by unwanted acoustic noise generation and probable material errosion of said mixer tap. Also accompanying said higher fluid flow velocities there may be turbulence structures formed in the mixing flows of said hot and said cold water and said turbulence may generate unwanted acoustic noise. From said quoted reference material and said prior art by said Stewart it may be seen that said dynamic mixing of said flowing hoi and said flowing cold water results in stability of said mixed water temperature of better than twice the stability of said mixed water temperature of said breeching piece for mixing said flowing hot and said flowing cold water. Said invention is now described in detail and said first embodiment of said disc pair is incorporated in an example of prior art single handle mixer tap cartridge according to CICE of France and is shown in figure 1 which is a pictorial drawing partly schematic showing a mixer tap body 1 which houses said cartridge 2 in which said disc pair consisting of lower disc 3 and upper disc 4 are located. Figure 2 shows a plan view of upper face 5 of said disc 3 in engagement and co-operation with said disc 4 in which a section taken at 6 of figure 1 of said disc 4 is superimposed ( no cross hatching is shown for reason of clarity ) on top of said plan view of said disc 3 to enable explanation of said disc pair geometry as this relates to said effective fluid dynamic mixing and said fluid hammer generation and said fluid hammer prevention. Referring to figures 2, 3, 4, 8, enclosure 7 is the shape of the cold water supply port at said upper face 5 of said lower disc 3 and enclosure 8 is the shape of the hot water supply port at said upper face 5 of said lower disc 3 and enclosure 25 is the shape of the mixed water outlet port at said upper face 5 of said lower disc 3. Enclosure 9 is the shape of the mixing throat or passage or blind hole or pocket in said upper disc 4 at said lower surface of said upper disc 4. Thus as shown in figure 2 the co-planer engagement and co-operation of said upper surface 5 of said lower disc 3 and said lower surface of said upper disc 4 provides geometry of engagement co-operation and definition of cold water supply aperture 10 and hot water supply aperture 11 for said cold water supply and said hot water supply entering said mixing throat 9 in said upper disc 4. Translation of said upper disc 4 is always in the direction of the longitudinal axis of said mixing throat 9 which is always co-planer with the longitudinal axis of said single handle 12 in figure I and said translation direction of said disc 4 is shown in figure 2 in the direction of centerline 13 of said disc 3 simply because said longitudinal axis of said mixing throat 9 is aligned with said centerline 13 of figure 2 as one said alignment of rotational position of said upper disc 4 said alignment resulting in said cold water supply aperture 10 being equal in cross-sectional area to said hot water supply aperture 11 and said translation of said disc 4 results from either vertical Upward hand movement of said single handle 12 in upward direction 14 which results in increase of said aperture 10 and said aperture 11 or said translation of said disc 4 results from vertical downward hand movement of said single handle 12 in downward direction 15 which results in decrease of said cross-seclioal area of said aperture 10 and decrease of said cross-sectional area of said aperture 11 , In said first embodiment incorporated in said example prior art cartridge 2 shown in figure 1 said cartridge 2 consists of stem 16 having square cross-section fixed to said single handle 12 by screw means not shown with said stem 16 co-operating with coupling flange 17 via pivoting means 18 with said pivoting means 18 fixed in said coupling flange 17 and said coupling flange 17 having bearing means for its upper cylindrical portion for rotation of said coupling flange 17 inside said cartridge 2 said coupling flange 17 in turn co-operating with disc holder 19 by sliding means not shown for said disc holder 19 to slide in direction 13 of said longitudinal axis of said mixing throat 9 when said stem 16 further co-operates with its lower end as lever means in a slot not shown in said disc holder 19 said disc holder 19 having protruding tongue means on its lower surface engageing with notches in said upper disc 4 upper surface so that lor said upward movement 14 or said downward movement 15 of said single handle 12 there results said translation of said upper disc 4. Similarly when said single handle 12 is rotated in horozontal direction 20 or 21 said single handle 12 co-operates with said stem 16 via said screw means said stem 16 in turn co-operating with said coupling flange 17 via said pivoting means 18 also used as rotøtablc coupling means for said coupling flange 17 in turn said coupling flange 17 rotatably co-operating with said upper disc holder 19 via said sliding means also being rotatable coupling means to rotate said upper disc 4. Said first embodiment is further illustrated in figure 3 showing a similar arrangement of said lower disc 3 in engagement and co-operation with said upper disc 4 said upper disc 4 is shown displaced rotationally through maximum angular displacement as constrained by maximum horizontal movement of said single handle 12 in said horizontal direction 20 resulting in maximum opening of said cold water supply port 7 to said mixing throat 9 said mixing throat 9 now closed off from said hot water supply port 8 said co-ρ!aner engagement and co-operation of said upper surface S of said lower disc 3 and said lower surface of said upper disc 4 now providing geometry of engagement co-operation and definition of said cold water supply aperture 22 at maximum size said longitudinal centerline of said mixing throat 9 is now in direction 23 said lower disc 3 does not rotate since said lower disc 3 co-operates in fixed engagement with said cartridge 2 by notch means in said lower disc 3 engageing with tongue means integral with said cartridge 2 in turn protrusions from the base 24 of said cartridge 2 co-operate and engage with blind holes in said mixer tap body 1 thereby preventing rotation of said cartridge 2. Said cartridge base 24 has openings for sealing means for said cold water supply port 7 and for said hot water supply port 8 and for mixed water outlet port 25 in said lower disc 3 to seal said ports 7, 8 and 25 against the inside lower face of tap body 1 adjacent to and co-operating with said cartridge base 24 said ports 7, 8 and 25 co-operating with openings in said tap body 1 to allow said incoming streams of cold water 26 and hot water 27 and said mixed water output 28 to co-operate with said disc pair lower disc 3 and upper disc 4. Said first embodiment is further illustrated in figure 4 showing a similar arrangement of said lower disc 3 in engagement and co-operation with said upper disc 4 said upper disc 4 is shown displaced rotationally through maximum angular displacement as constrained by maximum horizontal movement of said single handle 12 in said horizontal direction 21 resulting in maximum opening of said hot water supply port S to said mixing throat 9 said mixing throat 9 is now closed off from said cold water supply port 7 said co-planer engagement and co-operation of said upper surface 5 of said lower disc 3 and said lower surface of said upper disc 4 now providing geometry of engagement co-operation and definition of said hot water supply aperture 29 at maximum size said longitudinal centerline of said mixing throat 9 is now in direction 30, Said fluid dynamic mixing is now explained applied to said first embodiment in accordance with said quoted reference material and said prior art by said Stewart. Said dynamic mixing gives a relationship between the three pressures, P_c the pressure of said incoming stream of cold water 26 i.e. cold water supply pressure, Ph the pressure of said incoming stream of hot water 27 i,e. hot water supply pressure, P₈ the pressure of said water mixture 28 to the shower rose or single handle mixer tap spout, and the velocity ratio v - V_c / Vn where V₀ is the velocity of said cold water at said cold water supply aperture 10, and Vt, is the velocity of said hot water at said hot water supply aperture 1 1 , in terms of said geometry of said first embodiment expressed by A= a_c /a₁ where ac is the cross sectional area of said cold water supply aperture 10 and a_t is the cross-sectional area of flow ϋn said mixing throat 9, and the geometry of said first embodiment incorporated in said single handle mixer tap combined with a shower rose or mixer tap spout defined by B = a_m, /a₁ where H_n, is the aggregate cross-sectional area of said mixed water flow at said shower rose or said mixer tap spout whichever is the smaller. Equation 1 defines said fluid dynamic mixing mathematically modelled on said one dimensional incompressible water flow using the energy equation relating potential energy due to pressure with kinetic energy of said water flow, and using the impulse momentum principle and flow continuity for said hot and cold water flow apertures discharging into said mixing throat;

Where

and k_« is assumed pressure loss coefficient for said cold water supply between cold water supply pipe and said cold water supply aperture 10; k₅ is assumed pressure loss coefficient for mixed water flow after said mixing throat in any diffuser and in piping to and including said shower rose or spout; k, is assumed pressure loss coefficient for said mixing throat; and ki, is assumed pressure loss coefficient for said hot water supply between hot water supply pipe and said hot water supply aperture 11.

In said dynamic mixing applied to said first embodiment incorporated in said single handle mixer tap, by way of example;, the volume mixture ratio R of said cold to hot water that is said flowrate of cold water to said flowrate of hot water to obtain said suitable shower temperature is easily obtained since;

o

This value of v together with values of said Joss coefficients which by experiment were found to be k_c = 0.1, k₎, « 0.1, k, = 0.2 eutd k_s ^» 0.25 may be substituted in equaion I as a means for selecting advantageous values of A and B. Alternatively trial values of A and B may be used in equations 1 and 2 to establish the variation in the normalized pressure

for a variation in mixture ratio R which specfies art acceptable shower temperature range. For example, given that said cold water supply is at temperature T_c - 22° C and said hot water supply is at temperature T_h ≡ 53° C then for an energy balance when heat losses in said mixer tap are neglected we have

TcQ_c + T_fcQfc *^» T_ε( Q_c + Q_b )

( 3 ) where Q_c is said cold water flowrate, Qh is said hot water flowrate, and T₆ is said shower temperature, and as stated for equation 2 we may write for said mixture ratio

R. = ηr which when substituted into equation 3 gives

which for said values of T₁, and T_h given and say for said shower temperatures of 38° C

= 1.21 respectively. These values of R when substituted in equation 2 and subsequent substitution of values of v in equation 1 will show that for example increasing B from 2.3 to 3.5 results in better stability of said shower temperature with regard to variation in said pressure parameter yijJT_pjj" from 3.0 to 4.2 for T_F = 38° C which means for example a greater variation in said cold water supply pressure P_c when said hot water supply pressure P_h stays constant say. With reference to equation 1 for given conditions of said hot water supply pressure, said cold water supply pressure and said shower rose supply pressure, then the left hand side of equation 1 as the dependent parameter p* ^" jff is known. The derivation of equation 1 shows said coefficients a, β, y, S, ε, ζ to depend on said geometry parameter A and said geometry parameter B together with said pressure loss coefficients Jk_w kh» kt_» k_B. With the exception of A all of these may be regarded as fixed values in said mixer tap shower installation for this operational example, Variation of A i.e. said ratio of cold water flow aperture 10 area to said mixed water throat 9 cross-sectional flow area results in the analogue solution of equation 1 by said mixing tap installation with a resultant value of v to satisfy equation 1 for each value of A. Equation 2 rearranged to R - γ^y provides a simplified relationship to arrive at said mixture ratio R for each set of values of A and v satisfying equation 1. Said shower temperature may then be determined for each value of R from equation 4 rearranged to;

Thus each value of A results in a unique shower temperature and therefore each setting of said hori-M>ntal movement of said single handle 12 and correspondingly each setting of said rotatable displacement of said first embodiment disc pair results in a unique said shower temperature. In said operational example and based on said prior art by said Stewart the ratio of said cold water aperture to said mixing throat cross-sectional flow area was taken to be A * 0.5 which is reasonable when considering use of mains pressure hot water supply and it follows that said mixing throat cross-sectional flow area is equal to said area of said cold water supply aperture plus said area of said hot water supply aperture to ensure no sudden enlargement or contraction of flow cross-sectional area for said incoming streams entering said mixing throat whose length was found by experiment to be optimally from three to live times the depth of said mixing throat. Said first embodiment is shown further in figure 5 which is a cross-secϋonal view taken at section 31 of figure 2 said figure 5 shows said mixing throat 9 of said upper disc 4 in engagement and co-operation with tapered tip 33 of said lower disc 3 said tapered tip 33 separating said cold water supply aperture 10 from said hot water supply aperture 11 said tapered tip 33 incorporating a tip 36 of constant width of one to two millimetres for separating and sealing purposes at said upper surface 5 of said lower disc 3 the parallel edges of said constant dp width 36 defining the aperture width 34 of said cold water supply aperture 10 and the aperture width 35 of said hot water suply aperture 11 depending on said translation displacement and said rotation displacement of said upper disc 4 of said disc pair. Referring back to figure 2 said constant tip width 36 extends from the concave arcuate inside curved sides nearest the centre of said lower disc 3 of said cold water supply port 7 and said hot water supply port 8 Io the convex arcuate outside curved sides of said cold water supply port 7 and said hot water supply port 8 said mixing throat 9 having a tapered entrance shape explained later where it engages co-operates and defines said cold water supply aperture 10 and said hot water supply aperture 11 the intersections of said arcuate sides with said tapered tip 33 have joining fillets of radius of the order of one-half millimetre to reduce stress concentrations in said lower disc 3 and also to minimise cavitation sites. Said tapered tip 33 shown in figure 5 of said lower disc 3 is one example of shape for controlling the intersecting jet like entry of said incoming streams of cold and hot water to facilitate said dynamic mixing upon entering said mixing throat 9, a further shape for controlling said incoming streams of cold and hot water upon entering said mixing throat 9 is the arcuate tip 37 shown in figure 6 which from considerations of laminar flow provides a smoother water flow pattern for said incoming streams, however said tapered tip 33 provides intersecting jet like trajectories for said incoming streams of cold water and hot water supplies to promote rapid mixing of said incoming streams of cold water and hot water supplies at said entrance to said mixing throat 9 said trajectories having predominant flow velocities directed towards the roof of said mixing throat 9 said roof of said mixing throat 9 having longitudinal serrations 32 as shown in figure 5 and running in said direction of longitudinal axis of said mixing throat and thus in said direction of mixed water flow in said mixing tliroat as shown in figure 7 which is a cross-sectional view taken at section 38 of figure 2 said longitudinal serrations 32 of height two millimetres and pitch two millimetres and with filleted tips and troughs to minimise cavitation sites said serrations 32 have twofold importance firstly reducing turbulent motion of said incoming streams of cold water and hot water having said jet like intersecting trajectories directed towards said serrations 32 and secondly said serrations 32 result in a laminar flow boundary thereby attenuating acoustic noise already generated by said jet .like intersecting trajectories and reducing acoustic noise generation by said mixed water flow in said mixing throat 9, Said tapered entrance shape of said mixing throat 9 of said upper disc 4 taken at section 6 of figure 1 as shown in figure 2 ( no cross hatching is shown for reason of clarity ) defined by angled entrance sides of said mixing throat 9 intersecting with a one millimetre radius joining fillet, said angled entrance sides having an included angle symmetrical about said longitudinal axis of said mixing throat 9 at said entrance to said mixing throat 9 in conjunction with said constant tip width 36 and said arcuate insides of said cold and hot water supply ports 7 and 8 respectively of said lower disc 3 further defining the shapes of said cold water supply aperture 10 and said hot water supply aperture 11 equal in oross-sectional flow area as shown in figure 2 since said longitudinal axis of said mixing throat 9 is in line with said axis 13 of said lower disc 3. Noteworthy about said defined shapes of said cold water supply aperture 10 and said hot water supply aperture 11 arc that each has two intersecting adjacent straight sides having an acute included angle and each having a third arcuate side being said arcuate inside of said coJd water and hot water supply ports 7 and 8 respectively thereby providing a progressive and complementary variation of said cold water supply aperture \ 0 and hot water supply aperture 11 whereby said apertures 10 and 11 increase equally with said vertical movement of said single handle in said direction up to increase said mixed water flowratc or said apertures 10 and 11 decrease equally with said vertical movement of said single handle in said direction down to decrease said mixed water flowrate for said control of said mixed water flowrate, and with said horizontal movement of said single handle likewise providing a progressive and complementary variation of said cold waler supply aperture 10 and said hot water supply aperture 1 1 whereby a positive change to one said supply aperture is accompanied by an equal negative change to other said supply aperture thereby providing control of said mixture ratio of said cold water to said hot water thereby providing control of water mixture temperature, said engagement and cooperation of said disc pair in defining said cold water supply aperture 10 and said hot water supply aperture 11 with close engagement of said intersecting jet like trajectories contributed to by said tapered tip 33 or said arcuate tip 37 providing an optimum configuration and shape of said cold water supply aperture 10 and said hot water supply aperture 11 in combination with said constant tip width 36 providing an intimate mixing zone so that said mixing '/.one significantly governs sai'd dynamic mixing. Water hammer generation may be analysed quantitatively and mathematically modelled for said first embodiment and for said prior art by said CICE of France and for prior art disc pair technology by Hydro Plast of Italy or for any other prior art disc pair technology for example by considering one dimensional unsteady motion of water flow in pipes upstream from said first embodiment and for simplicity without considering compressibility effects of the water because it is widely known that transmission of water hammer pressure puJses occur at die local sonic velocity in said water as a compressible medium and the objective of this analysis is to predict the likely magnitude of water pressure change due to said water hammer generation. Consider a water flowrate Q in a pipe of cross-sectional area A and effective length L when said flowrate is shutoff commencing at time t = 0 and completed at time t ~ T, the water hammer pressure P may be determined by considering the force F due to retardation of water flow during said shutoff where said water hammer pressure may be based on Newton's second law of motion and expressed by

where for simplicity the average water velocity ϋ ^s 7 and.m is the mass of said water flow undergoing shutoff retardation motion taken to be the water in said pipe of length L, equation 6 simplifies to

which upon integration gives

which is the flow versus time relationship for a square or rectangular flow aperture during uniform displacement closure motion with time for assumed simplification of Q varying linearly with t during shutoff and where ΔP becomes the change in magnitude of said water hammer pressure during complete shutoff of said water flowrate Q with water density p in time duration T. Quite simply equation 8 shows quantitatively that for any said flowrate Q said water hammer pressure change ΔP is increased as said shutoff time duration T is decreased thus the shorter said shutoff time duration is tile greater is said water hammer pressure change. Equation 8 shows that for any given installation characterised by said supply pipe length L of said cross-sectional area A then said water hammer pressure change is directly proportional to shutoff flowrøte at commencement of said shutoff and inversly proportional to said shutoff time duration. As a first worked example consider a hot water flowrate of 12 litres per minute shutoff in 0.08 seconds in piping of 17 millimetres internal diameter and said supply pipe length L = 15 metres measured If om shutoff tap to hot water system fitted with the usual check valve on cold water supply Io said hoi water system. The resulting water hammer pressure change generated with water temperature taken at 60° C as determined using equation 8 is 165 kpa or 1.65 bar or 1.65 atm or 24 psi, In said first embodiment said water hammer generation and prevention may be explained in relation to said tapered entrance shape of said mixing throat 9 as shown in figure 8 where said cold water supply aperture 40 has an isosceles triangular, shape as said cold water supply aperture 40 diminshes during said shutoff said shutoff flowrate is therefore a strong function of the time variation of said isosceles triangular shape of said cold water supply aperture 40, It should be noted that said isosceles triangular shape of said cold water supply aperture 40 as shown in figure 8 has an included angle or vertex angle of 90° between said angled entrance sides at said entrance to said mixing throat 9 said included angle is bisected by said longitudinal axis of said mixing throat 9 said longitudinal axis is in line with axis 39 shown in figure 8 said axis 39 is in said direction of displacement of said upper disc 4 resulting from said vertical movement of said single handle 12, said isosceles triangular shape of said cold water supply aperture 40 has a straight base side portion opposite said vertex angle during the latter decrements of said closure leading to said shutoff of said cold water supply aperture 40 said straight base side portion is tangential to and part of said arcuate inside of said cold water supply port 7 said hot water supply port 8 is the mirror shape of said cold water supply port 7 taken about said axis 13 as mirror axis, said isosceles triangular shape of said cold water supply aperture 40 has a cross-sectional flow area being base length multiplied by one-half the height measured along said axis 39 of said mixing throat 9, thus at one*half said shuloff displacement of said upper disc 4 said cold water supply aperture 40 has reduced to approximately ( this is because at said maximum size of said aperture 22 shown in figure 3 the base side consists of said tangential straight side portion and a remaining curved side portion making up said arcuate inside of said cold water supply port 7, and because of said vertex joining fillet ) one-quarter of said maximum area of said cold water supply aperture 22, because said base length has reduced to approximately one-half and said height has reduced Io one-half, likewise at three-quarters shutoff displacement of said upper disc 4 said cold water supply aperture 40 is approximately one-sixteenth of said maximum area of said cold water supply aperture 22, thus as decrements of said closure proceed resulting in a series of similar triangular shapes where said decrement of vertical height of said similar triangular shapes expressed as a fraction of the maximum said vertical height of said series of similar said triangular shapes is equal to the decrement of the base side of said similar triangular shapes expressed as a fraction of the maximum base side of said series of similar triangular shapes and this results in a mathematical relationship for said cold water supply aperture area a₀ given approximately by

where s is closure displacement of said upper disc 4 from maximum displacement S of opening of said upper disc 4, and using a simplifying assumption of average flow velocity over said cold water supply aperture since the mean Reynolds Number of said flow is of the order of 10⁴ which means turbulent flow regime and therefore we may take the relationship for said cold water flowrate Q through said cold water supply aperture 40 to be based on said average flow velocity as was used in equation 6 and also tliat displacement motion of said upper disc 4 occurs at constant velocity, thus

where T is said shutoff time duration and t is time variable during said shutofT displacement starting from said maximum displacement S of opening of said upper disc 4. Differentiation of equation 10 with respect to t gives

which upon substitution into equation 7 gives

)

Equation J 2 provides a mathematical expression applicable to said first embodiment for said water hammer generation pressure P and is applicable to said cold water shutoff and to said hot water shutofϊ. Significantly equation 12 shows at shutoiϊtime t = T at complete shutoff that said water hammer generation pressure P is swsro, farther analysis of equation 12 shows that said water hammer generation pressure is a maximum at t - 7 at one-half shutoff time and at one-half shutoff displacement of said upper disc 4 that is at one-quarter shutoff flowrate. As a second worked example said maximum water hammer generation pressure for said first embodiment is 165 IcPa for a maximum shutoff flowrate of 12 L/min, with shutoff time T ~ 0.08 seconds, in a pipe length of I, ≠= 15 metres and 17 mm internal diameter, said resulting maximum water hammer pressure generated at said one-half closure of said first embodiment is the same magnitude as said water hammer pressure change generated in said worked example one at said complete closure or complete shutoff for said shulolT flowrate varying linearly during said shutoff, however for said first embodiment said water hammer pressure generated is zero at said complete closure or shutoff for said same conditions of said water flowrate, said shutoff time, said pipe length and diameter. The usual textbook criterion for water hammer generation is that valve closure occurs in said shutoff time where c is the sonic velocity or celerity of water considered

which for said hot water at 60° C is 1520.7 metres per second and for both said worked examples where L = 15 metres seconds, thus in both said

worked examples said shutoff time used was greater than said textbook criterion water hammer generation shutoff time. In experimental work conducted on said water hammer pressure generated by said prior art disc pair technology of said ClCB of France and of said Hydro Plast of Italy and by said first embodiment for test conditions the same as for said worked examples showed the following results: Said CICE single handle tap cartridge dated 18 June 2003 tested in a sink mixer lap using medium hand speed closure for:- cold water flow only at temperature of 22° C resulted in slight water hammer; mixed water flow at temperature of 37° C resulted in moderate water hammer; hot water flow only at temperature of 53° C resulted in severe water hammer, Said Hydro Plast single handle lap cartridge dated 16 December 2003, G40-NL, AUSITAL of Italy tested in said single handle sink mixer tap using medium hand speed closure for;- cold water flow only at temperature of 22° C resulted in no water hammer; mixed water flow at temperature of 37° C resulted in moderate water hammer; hoi water flow only at temperature of 53° C resulted in severe water hammer.

Said first embodiment disc pair fitted to said CJCE single handle tap cartridge tested in said single handle sink mixer using medium hand speed closure foπ- cold water flow only at temperature of 22° C resulted in no water hammer; mixed water flow at temperature of 37° C resulted \n no water hammer; hot water flow only at atcmperature of 53° C resulted in no water hammer. Returning to said first embodiment' description and said isosceles triangular shutoff aperture used in deriving said equation 12 said isosceles triangular shutoff aperture in practice has said one millimetre fillet radius at said vertex of said isosceles triangular shutoff aperture said one millimetre fillet radius contributing to an almost imperceptably small amplitude of said water hammer shutoff pressure generation only for the worst case of hot water only shutoff at a quickest hand speed closure of said single handle sink mixer tap said one millimetre fillet radius or smaller is necessary in the .manufacture and use of ceramic material commonly used in said disc pair technology to reduce stress concentrations and to prevent cracking of said ceramic material. Said worked examples one and two and said experimental tests on said prior art single handle tap cartridges and said first embodiment used uniform displacement closure motion with respect to closure time that is constant velocity of said closure and shutoff. All said prior art disc pair technology feature shallow arcuate said inside and said outside curved sides of said hot and cold water supply ports and also arcuate profiles of several shapes at said entrance to said mixing throat thereby defining said water supply apertures for said cold water and said hot water flow featuring said insides arcuate profiles and said outsider arcuate profiles said arcuate profiles on said moving disc at said shutoff inevitably results in said water hammer pressure generation at said complete shutoff. Referring back to said derivation of equation 12 for said wqtcr hammer generation pressure for said first embodiment said mathematical explanation for said zero water hammer generation pressure at complete shutojpf is that the necessary and sufficient condition is for the first derivative with respect to time of said shutoff flowmte must be zero, it follows mathematically that at any time during said shutoff if the first derivative with respect to time of said shutoff flowrate is zero then and only then will said water hammer generation pressure be zero, it also follows mathematically that said isosceles triangular shape for said hot water supply aperture or said cold water supply aperture is not the only triangular shape resulting in said zero water hammer generation pressure at said shutoff, but any triangular shape provided that said hot Water supply aperture and said cold water supply aperture have a vertex forming the final decrements of closure of said triangular shaped apertures because then and only then will said first derivative of shutofT flowrate with respect to time be zero, for example

S referring back to figure 2 said cold water supply aperture IO and said hot water supply aperture 1 1 meet said requirements of having said vertex forming said final decrements of closure of said cold water supply aperture Ϊ0 and said hot water supply aperture 1 1 and therefore said water hammer pressure shall be zero at said shutoff of said cold water supply aperture 10 and said hot water supply aperture 11. Said vertex forming 0 said final decrements of said closure of said apertures 10 and 11 may occur when said upper disc 4 has said translation motion along said axis 13 of said figure 2 said translation motion during said closure of said single handle mixer tap resulting from said motion of said single handle 12 of said figure 1 in said vertical downward direction 15. Said vertex forming said final decrements of said closure of said apertures 10 and 5 H also occurs when said upper disc 4 has said rotation motion during said rotation of said single handle 12 of said figure 1 in said directions 20 and 21. Said vertex forming said final decrements of closure of said apertures 10 and 1 1 also occurs when said upper disc 4 has any simultaneous combination of said rotation and said translation resulting from any simultaneous combination of said rotation of said single handle 12 in 0 said directions 20 and 21 and said closure motion of said single handle 12 in said vertical downward direction 15,

A second embodiment is now explained where said prior art disc pair technology by said CICE and said Hydro Plast are modified by incorporating a notch shape vertex portion of said triangular shape water supply aperture of said first embodiment into said 5 moveable upper discs of said second embodiment which has been shown in experiments on said water hammer pressure generation to be useful in prevention of excessive said water hammer pressure generation. Said modified CICE disc pair co-operates with said CICE single handle mixer tap cartridge and said tap body already described in said first embodiment. Said modified Hydro Plast disc pair cooperates 0 with said Hydro Plast single handle mixer tap cartridge because a different translation and rotation means is used for the upper disc of said Hydro Plast disc pair incorporated within said Hydro Plast single handle tap cartridge said Hydro Plast single handle tap J o

■ cartridge co-operates with said tap body already described in said first embodiment. Details of said Hydro Plast disc pair unmodified and modified arc shown in figures 9, 10, 11_» and 12, said figure 9 is a plan view of the lower surface 41 of said upper movable disc 42 of said unmodified Hydro Plast disc pair, the periphery of mixing throat 43 defines the shape of said mixing tliroat 43 symmetrical about the longidudinaJ axis 44, said figure 11 is a plan view of the upper surface 45 of the stationary lower disc 46 of said unmodified Hydro Plast disc pair said lower disc 46 upper surface 45 incorporates a cold water supply port 47, a hot water supply port 48 and a mixed water outlet port 49 said lower disc 46 has a longitudinal axis 50. Said figure 10 is a plan view of the lower surface 51 of the modified upper movable disc 52 of said modified Hydro Plast disc pair, the periphery of mixing throat 53 incorporates a small said notch modification portion 54 said notch 54 has equal length sides measured on said surface 51 said notch sides intersecting with an included angle of ninety degrees said notch included angle is bisected by longitudinal axis 55 of said modified upper disc 52 said notch sides having a joining fillet of one-half to one millimetre radius said notch having a width of approximately two and one-half millimetres at the junction of said notch and said shape of said unmodified mixing throat 43 said notch 54 integral with said shape of said mixing throat 53 of said modified upper movable disc 52 therby defining in co-operation with said stationary unmodified lower disc 46 the triangular shape of cold water supply aperture 56 as shown in said figure 12 said triangular shape of said cold water supply aperture 56 defining a non-isosceles triangular shape of said cold water supply aperture 56 during the final decrements of said closure of said cold water supply aperture 56 during translation motion of said modified Hydro Plast upper disc 52 said translation motion along said longitudinal axis now at 57 as shown in said figure 12, Similarly to said analysis for said water hammer pressure generation for said first embodiment it follows that said triangular shape of said cold water supply aperture 56 results in said zero water hammer pressure generation at said complete shutoff of said cold water supply aperture 56. Likewise as explained for said first embodiment, said second embodiment notch portion 54 of said modified Hydro Plast movable upper disc 52 after a combination of said translation and said rotation of said upper disc 52 may be located symmetrically about said longitudinal axis 50 of said unmodified Hydro Plast slationaiy lower disc 46 resulting in said equal area triangular shaped apertures for said cold water supply and said hot water supply to said mixing throat 53 and likewise during said final decrements of said closure of said equal area or said unequal area said triangular cold water and hot water supply apertures there shall be said zero water hammer pressure generation at said complete closure of said triangular shaped cold water supply aperture and said triangular shaped hot water supply aperture and likewise after further said translation and said rotation of said modified Hydro Plast upper movable disc 52 said notch portion 54 of said upper movable disc 5.2 may be open only to said hot water supply port 48 thereby forming a triangular shaped hot water supply aperture similar to said triangular shaped cold water supply aperture 56 and likewise during said final decremants of said closure of said triangular shaped hot water supply aperture there shall be said zero water hammer pressure generation at said complete closure of said triangular shaped hot water supply aperture. Details of said ClCE disc pair unmodified and modified arc shown in figures 13, 14, 15, and 16, said figure 13 is a plan view of the lower surface 58 of said upper movable disc 59 of said unmodified CICE disc pair, the periphery of mixing throat 60 defines the shape of said mixing throat 60 symmetrical about the longidudinal axis 61, said figure 15 is a plan view of the upper Surface 62 of the stationary lower disc 63 of said unmodified CICE disc pair said lower disc 63 upper surface 62 incorporates a cold water supply port 64, a hot water supply port 65 and a mixed water outlet port 66 said lower disc 63 has a longitudinal axis 67, Said figure 14 is a plan view of the lower surface 68 of the modified upper movable disc 69 of said modified ClCE disc pair, the periphery of mixing throat 70 incorporates a small said notch modification portion 71 said notch 71 has equal length sides measured on said surface 68 said notch sides intersecting with an included angle of ninety degrees said notch included angle is bisected by longitudinal axis 72 of said modified Upper disc 69 said notch sides having a joining fillet of one-half to one millimetre radius said notch having a width of approximately two and one-half millimetres at the junction of said notch and said shape of said unmodified mixing throat 60 said notch 71 integral with said shape of said mixing throat 70 of said modified upper movable disc 69 thereby defining in co-operation with said stationary unmodified lower disc 63 the triangular shape of cold water supply aperture 73 as shown in said figure 16 said triangular shape of said cold water supply aperture 73 defining a non-isosceles triangular shape of said cold water supply aperture 73 during the final decrements of said closure of said cold water supply aperture 73 during translation motion of said modified CICE upper disc 69 said translation motion alowg said longitudinal axis now at 74 as shown in said figure 16, Similarly to said analysis for said water hammer pressure generation for said first embodiment it follows that said triangular shape of said cold water supply aperture 73 results in said zero water hammer pressure generation at said complete shuloff of said cold water supply aperture 73. Likewise as explained for said first embodiment, said second embodiment notch portion 71 of said modified CICE movable upper disc 69 after a combination of said translation and said rotation of said upper disc 69 may be located symmetrically about said longitudinal axis 67 of said unmodified CICE stationary lower disc 63 resulting in said equal area triangular shaped apertures for said cold water supply and said hot water supply to said mixing throat 70 and likewise during said final decrements of said closure of said equal area or said unequal area said triangular cold water and hot water^' supply apertures there shall be said zero water hammer pressure generation at said complete closure of said triangular shaped cold water supply aperture and said triangular shaped hot water supply aperture and likewise after further said translation and said rotation of said modified CICR upper movable disc 69 said notch portion 71 of said upper movable disc 69 may be open only to said hot water supply port 65 thereby forming a triangular shaped hot water supply aperture similar to said triangular shaped cold water supply aperture 73 and likewise during said final decremants of said closure of said triangular shaped hot water supply aperture there shall be said zero water hammer pressure generation at said complete closure of said triangular shaped hot water supply aperture.

Further applications for performing this invention relate to improvements to said individual hot and cold stop taps as described earlier said individual stop taps are referred to in the plumbing industry as double taps each connected to said upstream separate hot and cold water supplies said double taps are then usually connected downstream to said breeching piece connected to said shower bath spa or kitchen sink installations or for any other purpose. It follows from said detailed descriptions of said first and second embodiments and from said mathematical analysis for said first embodiment that said prevention of water hammer pressure generation may be similarly embodied in the goemetry of disc pairs incorporated in said double taps thereby minimising said water hammer pressure generation ( as herein before defined ) at complete closure of said double taps during rotation of handle means attached to said double taps.

Claims

The claims defining the invention are as follows:

1. A disc pair for a single handle mixer tap comprising a lower disc and an upper disc with means for constraining said lower disc in position and rotation inside a mixer tap cartridge in turn with means for constraining said cartridge in position and rotation inside a mixer tap body, said lower disc including inlet ports for hot and cold water and an outlet port for mixture of hot and cold water located at said lower disc lower surface, said inlet ports and outlet port in co-operatiou with sealing and flow communicating

• means to seal and flow communicate said ports with an inside lower surface of said miκertap body, alternatively said inlet ports and outlet port in co-operation with a first sealing and flow communicating means to seal and flow communicate said ports with an inside lower surface of said cartridge in turn a second sealing and flow communicating means Io seal and How communicate said ports with an outside lower surface of said cartridge and said inside lower surface of said mixer tap body, said lower disc including specially shaped mirror identical inlet ports for hot and cold water and an outlet port for mixture of hot and cold water located at said lower disc upper surface, said mirror identical inlet ports for hot and cold water with mirror axis bisecting said outlet port at said lower disc upper surface, said lower disc having a first main axis co-linear with said mirror axis and a second main axis at right angles to said first main axis said main axes intersecting at the centre of the generally circular said lower disc, said lower disc upper surface co-operating in co-planer engagement hearing and scaling with said upper disc lower surface said upper disc including a mixing throat with opening to said upper disc lower surface said opening symmetrically shaped about a longitudinal axis of said mixing throat for flow communication with said ports located at said lower disc upper surface, said specially shaped mirror identical inlet ports for hot and cold water in conjunction with said mixing throat opening defining size shape proportioning and allocation of apertures for incoming flows of said hot and cold water to said mixing throat during overlap and no overlap of said mixing throat opening with said mirror identical inlet ports for said hot and cold water incoming flows said sbe and shape of apertures during said overlap variable in area of cross-section with dependence on translation of said upper disc in direction both ways of said longitudinal axis of said mixing throat for control of flowrate and with dependence on rotation of said upper disc about said centre of said lower disc during said overlap for control of water mixture temperature, said incoming flows of hot and cold water having flow trajectories during said overlap so that mixing of said incoming flows of hot and cold water takes place firstly at a flow cross-section located at the constant width tip portion or apex separating said mirror identical inlet ports for said incoming flows of hot and cold waier at said lower disc upper surface said apex when located symmetrically about said longitudinal axis of said mixing throat opening during said overlap of said mixing throat opening defining proportioning of equal area and equal shape of said apertures for said incoming flows of hot and cold water said equal areas defined by the tapered or vertex Ijke entrance end of said mixing throat opening bisected by said constant width apex and said equal shapes defined by each having three sides each first side straight and parallel defined by said constant width apex edges each second side straight and making an acute included angle with said first sides said included angle is one-half of the included angle of said tapered or vertex like entrance end sides of said mixing throat, said entrance sides having a joining fillet of radius one millimetre or so, each third side is concave arcuate and part of the concave arcuate shape portion of the insides of said hot and cold water inlet ports on said lower disc upper surface, said apex or constant width tip portion of a tapered tip or concave arcuate tip separating said incoming flows of hot and cold water further defines as intersecting said jet like trajectories of said incoming flows of hot and cold water from said apertures to said mixing throat, during said overlap said apertures of equal area added together whilst at their maximum size with said dependence on translation of said upper disc define the maximum aggregate cross-sectional flow area of said hot and cold water incoming flows to said mixing throat and during said no overlap said apertures for hot and cold water whilst at their maximum size with said dependence on translation of said upper disc define the maximum individual cross-sectional flow areas of said hot and cold water incoming flows, the sum of said aperture maximum individual cross-sectional flow areas of said hot and cold water incoming flows is larger than said aperture maximum aggregate cross-sectional flow area because of said constant width apex, said mixing throat having a cross-sectional flow area equal to said aperture maximum aggregate cross-sectional flow area said mixing throat having a length of between three and five times the minimum depth of said mixing throat measured at right angles to said longitudinal axis of said mixing throat, said engagement and co-operation of said disc pair in defining said intersecting jet like trajectories of incoming flows of hot and cold water from said aperatures providing an optimum and intimate mixing zone governing and ensuring dynamic mixing ( as hereinbefore defined ) of said incoming streams of hot and cold water to provide stability of mixture ratio of said incoming streams thereby providing stability of temperature of mixture of said hot and cold water incoming streams in spite of variations in the supply pressures of said hot and coJd water to said inlet ports, said dependence on rotation of said upper disc about said centre of said lower disc providing proportioning of areas of cross-section of said apertures for said hot and cold water incoming Hows during said overlap providing the range of complete infinitely variable adjustment and control of said mixture ratio and likewise of said water mixture temperature in accordance with said dynamic mixing, said further dependence on rotation of said upper disc about said centre of said lower disc providing finally said allocation of said apertures for hot and cold water incoming flows during . said no overlap when cither only said aperture for hot water incoming flow is allocated and said aperture for incoming flow of cold water is closed to said mixing throat opening or when only said aperture for cold water incoming flow is allocated and said aperture for incoming flow of hot water is closed to said mixing throat opening, said vertex entrance end of said mixing throat opening during said no overlap defining an isosceles triangular shape of said apertures for hot and cold water incoming streams to said mixing throat with the base side of said isosceles triangular shape a straight portion tangential to said concave arcuate inside curved portions of said hot and cold inlet ports at said lower disc upper surface during the closing decrements of said apertures resulting in a scries of similar trianglar shapes defining the decrement of vertical height of said similar triangular shapes as a fraction of the maximum vertical height of said series of similar triangular shapes equal to the decrement of the base side of said series of similar triangular shapes expressed as a fraction of the maximum base side of said series of similar triangular shapes resulting in zero water hammer pressure generation at complete closure of said triangular shaped apertures of said hot and cold water incoming flows during uniform translation velocity of said upper disc ( as hereinbefore defined ), likewise during said overlap said triangular shaped apertures for hot and cold water incoming flows during said closing decrcmants of said apertures resulting in nearly zero water hammer pressure-generation.

2.A disc pair according to claim 1. wherein said mixing throat has a serrated face opposite said mixing throat opening said serrated face comprising longitudinal serrations in direction of said longitudinal axis of said mixing throat said serrations having height of two millimetres and pitch of two millimetres with or without fϊlteted tips and troughs.

3. A disc pair according to claims 1. and 2. installed in a single handle mixertap cartridge comprising stem means with attachment of single handle means to said stem means upper end portion said stem means co-operating with coupling flange means via pivoting means located at said stem means middle portion said pivoting means fixed in said coupling flange means said coupling flange means co-operating with the inside upper portion of said cartridge via bearing means for rotation of said coupling flange means inside said cartridge said rotation resulting from rotation of said single handle means and stem means in turn said pivoting means acting also as rotatable coupling means contributing to said rotation of said coupling flange means said coupling flange means in turn engageing with disc holder means via sliding and rotatable coupling means said disc holder means in turn engaging with said upper disc through notch and tongue means so that when said handle means is part rotated in both directions said disc holder means is likewise part rotated in said both directions said upper disc is part rotated in said both directions in a one-to-one relationship with said single handle means_* likewise when said single handle means is translated in both directions of the axis of rotation of said single handle means said stem means acts as lever means via said pivoling means acting as fulcrum means with said stem means lower end engaging with said disc holder means to translate said upper disc in both directions of said longitudinal axis of said mixing throat and during said translation of said upper disc said longitudinal axis of said mixing throat always passes through said intersection of said axes of said lower disc said stem means including adjustable means to limit said translation of said upper disc to limit said maximum aperture cross-sectional flow areas to limit said maximum fϊowrate of hot water cold water and mixed hot and cold water,

4. A disc pair according to claims 1. to 3. installed in a single handle mixer tap body for use in a bathroom shower, spa, bath or handbasin or for any other purpose in said bathroom or installed in a kitchen sink or a laundry tub or installed in any other application for mixing of hot and cold water.

5. A disc pair according to claims 1. to 4. with, said mixed water output communicating directly via a closed conduit with a dϊlϊuser for pressure recovery which connects directly or by piping to a shower rose outlet or other water faucet.

6, A disc pair according to claim S. wherein said diffuscr is a diverging flow passage,

7.A disc pair according to claim 5. wherein said diffuser is any enlargement in flow passage cross-section.

8.A disc pair according to claims 1. to 7. with flow restricters or pressure adjusters upstream of said disc pair on said hot and cold water supplies.

9.A disc pair constructed, arranged, adapted and combined to operate substantially as hereinbefore described m any single handle mixer tap cartridge with reference to and as illustrated by figures 1 to 8 of the accompanying drawings.

10.A notch modification portion or notch inclusion portion to any disc pair disc with said notch comprising equal or unequal length adjacent notch sides having an included angle between said adjacent notch sides of from sixty degrees to one hundred and twenty degrees and with a joining fillet to said adjacent notch sides of fillet radius between one~ha1f millimetre and one and one-half millimetres said notch modification or inclusion having a notch width of between two and three millimetres at the junction of said adjacent notch sides and any part of an aperture forming a third side of a generally triangular shape of notch aperture for flow of hot water cold water or mixed hot and cold water with said notch aperture forming the final portion of closure of said aperture thereby minimising water hammer pressure generation at complete closure of said notch aperture and said aperture during uniform translation velocity of the moveable disc of said disc pair ( as herein before defined ).

11 A notch modification portion or notch inclusion portion according to claim 10. constructed, arranged, adapted and combined to operate substantially as hereinbefore described with reference to and as illustrated by figures 9. to 16,,

J2.A notch Inclusion portion or notch modification portion to any disc pair aperture with said notch comprising equal or unequal adjacent notch sides having an included angle between said adjacent notch sides of from sixty degrees to one hundred and twenty degrees said adjacent notch sides consisting of a first notch side on a first or second disc of said disc pair and a second notch side on a second disc of said disc pair said notch having a notch width of between two and three millimetres at the junction of said notch first and second sides and any portion of said aperture forming a third side of a generally triangular shape notch aperture for flow of hoi water cold water or mixed hot and cold water said notch aperture forming the final portion of closure of said aperture thereby minimising water hammer pressure generation at complete closure of said notch aperture and said aperture ( as herein before defined ) where the closure motion of said notch aperture and said aperture results from translation motion or rotation motion or any simultaneous combination of translation motion and rotation motion of said discs of said disc pair.