GB2026245A - Pressure control switch - Google Patents

Abstract

A pressure control switch incorporated in fluid flow apparatus for use principally in beer dispensing systems comprises a blind tube 17 connected at its open end to a fluid flow line 13 and occupied by a gas cushion 19 which varies in volume with fluctuations in the line pressure. Two level sensors 22, 28 are provided at spaced locations along the tube, the lower level sensor 28 having contacts at preselected heights associated with a common conductor lead 27 serving to switch the pump on. The upper level sensor serving to switch the pump off, comprises a sealed cushion 19 of gas above a flexible diaphragm 18 and containing a conductive liquid 21 which bridges a pair of fixed contacts 22 in the top of the tube 17. In modifications the upper contact may be threaded and adjustable in heights or the tube 17 may have a top which is adjustably slidable in the side walls. The arrangement may be applied to a beer degassing chamber. <IMAGE>

Description

SPECIFICATION Pressure control switch This invention relates to fluid flow apparatus and is particularly concerned with, but is not restricted to, beer dispensing apparatus.

Atypical beer dispensing system as used in a public house comprises a keg of beer located at a low level, e.g. in a cellar and connected to a cylinder of carbon dioxide under pressure serving to drive the beer out of the keg to the inlet of a pump located at a higher level and to fill the void left in the keg by the outgoing beer. The pump supplies the motive force for lifting the beer to the level of a dispensing outlet located at the bar and controlled by a manually operated tap. The pump normally has a pressuresensitive on-off switch which detects the slight drop in pressure in the outlet line when the hand-tap is operated to open the dispensing outlet. When the tap is closed the pump continues to run until the outlet line is again pressurised sufficiently to operate the pressure switch and cause the pump to be switched off.

One of the problems with such a dispensing system is that the pump switch is of relatively complicated electromechanical construction with a number of moving parts and is therefore prone to failure or inefficient operation. In consequence, when the keg of beer connected to the pump is empty, the pump may run dry until switched off by hand. This can severely damage the pump which thus requires frequent replacement in such dispensing systems. Pump manufacturers have attempted to solve this problem by incorporating a flow switch utilising a movable float. Unfortunately, the float tends to become stuck in position or displaced by vibrations and the problem has remained unsolved.

A further disadvantage of such dispensing systems is that the line pressure of the beer cannot be accurately controlled. The pressure-sensitive on-off switch of the pump does influence the pressure in the outlet line but only to maintain it at a predetermined level when the dispensing outlet is closed.

When the outlet is opened and the pump switched on, the pump runs at a constant speed and the pressure in the outlet line cannot be altered. This is a particular disadvantage with certain kinds of beer which are prone to froth or fob and in warm conditions when such frothing is likely to occur particularly with relatively high dispensing pressures.

Afurther problem is dispensing beer, particularly in warm weather, is to control the frothing or fobbing so that the amount of froth or "head" dispensed with the beer is limited to a small controllable amount. In our co-pending patent application No. 18578/78 we have described a liquid de-gassing unit which is useful in the de-fobbing of baer and operates by breaking down the froth and purging the gas so released. The de-gassing unit is described in detail below since it has application in the context of the present invention. However, quite apart from the provision of a specialised de-gassing unit, a dispensing system of the kind described would also benefit from the provision of a detector for froth or fob.

It is an object of the present invention to provide improved fluid flow apparatus having application in a beer dispensing system as described above, and capable of improving the system in one or more of its aspects to which reference has been made.

It will be appreciated that the fluid flow apparatus of the invention is not intended to be confined in its application to beer dispensing systems but may also find utility in other liquid and gas flow systems in which simple and convenient means are required for sensing a predetermined fluid pressure.

According to the present invention there is provided fluid flow apparatus comprising a fluid flow line and a line pressure sensor in the form of a pressure chamber occupied by a gas cushion arranged to vary in volume with fluctuations in the line pressure and sensing means arranged to emit an electrical signal when the gas volume reaches a predetermined value corresponding to a specified line pressure.

The invention will now be further described by way of example only with reference to the accompanying drawings, in which Figure 1 is a diagram of a first embodiment of beer dispensing system; Figure2 is a detail of Figure 1 to an enlarged scale illustrating the position of the pressure switch relative to the other components of the system; Figures 3 to 8 are diagrammatic illustrations of alternative embodiments of pressure switch; Figure 9 is a diagram of a second embodiment of beer dispensing system; Figure 10 is a diagram of a third embodiment of beer dispensing sytem; Figure ii is a detail of Figure 10 to an enlarged scale; Figures 12 and 13 illustrate the dispensing outlet of a beer dispensing system in two alternative embodiments, and Figure 14 is a diagram of a water distribution system.

The beer dispensing system shown in Figure 1 is of a kind commonly used in a public house. A beer keg 1 stands on the floor 2 of a cellar and is connected by its bung-hole 3 to a carbon dioxide cylinder 4 which fills the void left in the keg 1 by the outgoing beer and which also serves to lift the beer to the level of a pump 5 by means of a connecting pipe 6. The pump 5 is mounted on a wall of the cellar and is of the centrifugal kind. The connecting pipe 6 is attached to the coaxial inlet of the pump and the pump outlet is connected to an outlet line 7 which ascends through a bar room floor 8 to a dispensing outlet 9 at a bar (not shown). The dispensing outlet 9 is controlled by a hand-operated tap 10.

A pressure control switch 11 is mounted on a branch or side limb of the outlet line 7. The arrangement is shown in greater detail in Figure 2.

The pump 5 is connected by an outlet stub 12 to a T-connector 13 via a first check valve 14. The side brance 1 3a of the T-connector is attached to the outlet line 7 via a further check valve 15 and the other limb of the connector 13 mounts the pressure switch 11 which is accordingly in line with the pump outlet.

A bleed valve 16 is provided in the T-connector 13 opposite the second check valve 15. It will be appreciated that the positions of the outlet pipe 7 and the pressure switch 11 could be reversed if desired, i.e. the outlet pipe 7 would be in line with the pump output and the pressure switch 11 would be attached to the connector side branch 1 3a.

However, the illustrated arrangement is preferred because it makes possible a relatively simple construction of the pressure switch 11 and avoids bends in which dirt is likely to collect.

As shown in Figure 3, one embodiment of pressure control switch 11 comprises a tubular casing 17 containing a seal 18 in the form of a dome-shaped plug or bung of rubber or like flexible material which is effective to divide the casing into two compartments 19 and 20. The compartment 19 is closed by the end wall of the casing 17, which is dome-shaped and contains a quantity of electrically-conductive liquid 21 which is supported on the seal 18. The liquid is preferably water although other liquids may be used if desired. A pair of electrical contacts 22 is mounted in the wall ofthe casing 17 and said contacts extend into the compartment 19.

The other compartment 20 is open at the open end of the casing 1 at which a flange 23 is provided for attachment to the T-connector 13 by means of bolts 24 and an interposed gasket 25. Two contacts 26 connected by a conductor lead 27 are mounted in the wall of the casing 17 within the compartment 20 and in the region of the lead 27 a series of further contacts 28 are mounted in the wall of the casing opposite said lead 27.

The drawing shows the pressure control switch in the inoperative condition. If beer is now allowed to rise into the casing 17, the pressure of the CO2 present in the beer will be sufficient to cause the seal 18 to rise in the casing 17 towards the upper end thereof. When the seal 18 reaches the ends of the side wall of the casing 17, the liquid 21 is contained within the dome-shaped end of the casing and serves to bridge the contacts 22. This will normally be arranged to occur when the pressure of gas in the compartment 4 exceeds 0.70 Kg/sq cm (10 p.s.i.).

The contacts 22 are connected to the pump 5 (Figure 1) and when these contacts 22 are bridged by the liquid 21 the pump 5 is switched on to pump beer into the compartment 20. The beer will continue to rise in the compartment 20 and the pressure in the compartmentwill continue to increase until the lowermost contact 28 and the lead 27 are bridged by the beer. The contacts 27 and 28 are also connected to the pump 5 and when bridged by the beer are arranged to switch the pump off. This will normally be arranged to occur when the pressure of air trapped in the compartment 4 by the rising beer exceeds 1.75 Kg/sq. cm (25 p.s.i.).

When beer is called for, the dispensing outlet 9 (Figure 1) is opened and the pressure in the compartment 20 drops as the level of beer in said compartment falls. As soon as the level falls below the contact 28, the pump 5 is switched on and continues to deliver beer until the dispensing outlet 9 is again closed and the pressure and beer level again rise in the compartment 20.

As shown in the drawing, a series of contacts 28 is provided in order that different pressures can be selected by selectively connecting any one of the contacts 28 to the pump 5. Preferably, four such contacts 28 are provided and are arranged to be bridged by the beer and to switch off the pump at 1.76 Kg/sq. cm (25 p.s.i.), 2.11 Kg/sq. cm (30 p.s.i.), 2.46 Kg/sq. cm (35 p.s.i.), and 2.81 Kg/sq. cm (40 p.s.i.). Further adjustment of the pressure can be achieved by locating one or more spacing washers (not shown) between the flange 23 and the Tconnector 13.

When the beer barrel 1 is empty, there will be only gas pressure and accordingly the seal 18 will drop and therewith the liquid 21 so that the contacts 22 are no longer bridged and the pump 5 is switched off altogether.

A manual override button (not shown) is preferably also provided to allow the pump 5 to run until a pressure of 0.70 Kg/sq (10 p.s.i.) has been attained in cases of open flow cask beer (real ale), which is not subjected to gas pressure.

In the further embodiment of pressure switch now to be described, the seal 18 and contacts 22 are omitted and the pressure switch takes the form of a blind tube requiring no movable parts for its operation.

With reference to Figure 4 of the drawings, the pressure control switch comprises a tubular casing 29 having an opening 30 at its lower end. An electrical contact 31 is mounted in the wall of the casing 29 and extends into the interior of the casing.

A lead wire (not shown) is connected to the casing wall itself which is made of electrically conductive material.

A bung or plug 32 of electrically insulative material is provided in an opening in the wall of the casing at the upper end thereof. Located in a bore in said bung or plug 32 is a nut 33 and an adjustable screw 34 is engaged with the screw-thread of the nut 33 and extends into the interior of the casing 29. The screw 34 is provided with a head 35 to which a pointer 36 is attached. A transparent cover 37 is adapted to be fitted over the outwardly projecting end of the screw 35 and to engage with the casing as shown in Figure 1. This cover is provided with a series of graduations 38 which indicate different pressure settings and the screw 34 can be turned until the pointer 36 is opposite a desired graduation 38. Turning the screw 34 has the effect of moving the end remote from the head 35, which end is pointed, towards or away from the opening 30 of the casing 29 depending on the direction in which the screw is turned. A lead wire 33a is connected to the nut 33. The opening 30 is in flanged connection with the T-connector as previously described.

Figure 4 shows the pressure control switch in the inoperative condition. The volume of the interior of the casing is so arranged that beer can rise freely, under the pressure of the CO2 present in the beer and without pumping, in said casing until it reaches the contact 31 and serves to bridge said contact and the casing to establish electrical connection therebetween. The contact 31 is connected to the pump 5 and, when the contact and casing are bridged by the beer, the pump 5 is switched on and pumps beer into the casing 29. At this point, the dispensing outlet 9 is still closed. The beer will continue to rise in the casing 29 and the pressure in the casing 29 will continue to increase until the beer level reaches the point end of the screw 34.Electrical connection between the screw 34 and the casing 29 is now established and the lead wires connected to those components are also connected to the pump 5 so that as the beer touches the screw 34 the pump 5 is switched off.

This will normally be arranged to occur when the pressure of air trapped in the casing by the rising beer exceeds 1.75 Kg/sq. cm (25 p.s.i.). However, the pressure may be adjusted or varied by turning the screw 34 as above described, and thus the precise pressure at which switch-off is required can be very easily and accurately adjusted.

When beer is called for, the dispensing outlet is opened and the pressure in the casing 29 drops as the level of beer in said casing falls. As soon as the beer leaves the screw 34 the pump 5 is switched on and continues to deliver beer until the dispensing outlet 9 is again closed and the pressure and beer level again rise inside the casing 29.

When the beer barrel is empty, there will be only gas pressure and accordingly the level of beer will drop until the contact 31 and casing are no longer bridged and the pump 5 is switched off altogether.

In the embodiment shown in Figure 5, a disc member 39 is provided in a casing 40 and is provided with a rubber sealing skirt 41 which engages the inner surface of the casing wall to provide a liquid-tight seal therewith. In this case, the bung or plug 32 is replaced by a nut 42 and a hollow screw-threaded member 43 has its external screwthread engaged with the screw-thread of the nut 42.

The nut 42 and/or the member 43 is/are made of electrically insulative material and the member 43 is provided with a head 44 at one end, which head may be hexagonal, and is secured at the other end to the disc member 39.

A screw 45 passes through the hollow member 43 and through an aligned bore in the disc member 39 and is engaged with a nut 46 secured to the underside of the disc member 39. Alternatively or in addition, the bore in the hollow member 43 may be screw-threaded and engaged by the screw 45.

Although not shown in Figure 5, a head 47 of the screw 45 is provided with a pointer and a cover marked with graduations is provided to engage with the casing and cover the head 47 as with the embodiment shown in Figure 4. An upper level sensor is provided by the screw 45 and the lower level sensor is provided by a pair of electrical contacts 48 adjacent a bottom opening 49. This embodiment operates in the same manner as the embodiment shown in Figure 4 but with the additional facility that the effective volume of that part of the casing which can receive liquid can be adjusted by turning the hollow member 43 to move the disc member 39 towards or away from the opening 22 depending on the direction in which said member 34 is turned.

The embodiments of pressure switch already described have included various means for adjusting the pressure at which the pump is switched off. in the embodiment of Figure 3 a plurality of contacts was provided at levels corresponding to different cut-off pressures and there was also the possibility of varying the spacing of the casing from the T-connector by the use of spacer washers. In the embodiment of Figure 4 the upper contact was itself adjustable and this was also the case in the embodiment of Figure 5 in which there was the additional facility of varying the volume of the chamber defined by the casing. It will be appreciated that numerous other variations may be made and it will suffice briefly to indicate some of the possibilities. Thus, the upper contact may be fixed but the volume of the chamber be made variable.The adjustability of the upper contact and/or the variation in the volume of the chamber may be achieved by different means.

Thus, the screw 34,45 of Figures 4 and 5 could be replaced by a pin which is slidably mounted in a sleeve and can be secured in any one of a number of stepped positions by means of a cross-pin. To achieve variability of volume, the casing may be constructed in two parts in screw-threaded or other connection for telescopic movement together and apart. As an alternative the casing may incorporate a bellows member to achieve the desired variation in volume. Another possibility is to mount the casing in a pivotal or any other suitable manner enabling it to be tilted out of its vertical position into a horizontal or intermediate inclined position. The volume of beer required to reach the pump cut-off contact reduces with increasing inclination of the casing.

Thus, the upper contact will be reached by the beer at ever decreasing pressures in the casing with increasing angular deviation of said casing from the vertical. Further design modifications may be achieved by constructing the casing with electrically conductive portions providing said level sensors. For example, the casing illustrated in Figure 6 consists of a series of alternate conductive and insulative rings, the rings 50 being made of electrically conductive material and the rings 51 being made of electrically insulative material. A lower end wall 52 of the casing is electrically insulated from a bottom opening 53 by a further ring 54 of electrically insulative material and the upper end of the casing is closed by an end wall 55 of electrically insulative material. A second contact in the form of a probe 56 projects into the casing from said end wall 55.

Desired switch-on and switch-off pressures can be set by connecting selected rings 50 and/or the probe 56 to the pump 5 (Figure 1).

Electronic sensors are being developed which operate in a similar manner to contact sensors, and these sensors may be mounted as probes on the exterior of the casing to replace the contact(s). The circuitry can be arranged in many ways using transformers, relays and/or solid state devices. If semi-conductors on a logic circuit are used, only one probe is required instead of two contacts as with other arrangements. This is extremely efficient as there are no moving parts and with external probes no corrosion occurs.

Two embodiments of pressure switch with more sophisticated sensing means of this kind will now be described with reference to Figures 7 and 8 of the drawings.

The embodiment of Figure 7 has a fixed position lower contact X and a movable tap Y connected to respective inputs of a differential amplifier. A switch S is provided which when closed energises a relay R which in turn energises the pump, causing the liquid to rise to the level of contact X. Thereafter, the pump will continue to run when the switch S is released as current will flow from the supply through the liquid and contact X to the amplifier. The amplifier output will maintain energisation of relay R. However, if the liquid rises to the level of the tap Y and makes contact then current will flow from tap Y to the amplifier. As a result, the amplifier will turn off the relay R, thus stopping the pump. When the pressure drops the liquid level falls to uncover the contactY, whereupon the pump is re-started as a result of energisation of relay R.R is a solid state relay.

The sensing means in Figure 8 is a capacitive circuit including capacitors C1,C2 which are arranged around the tubular casing. The lower capacitor C2 may be fixed in position and the upper capacitor C1 is slidable along the casing to desired positions. Each capacitor C1, C2 is connected to a respective oscillator 1, 02 and the two capacitor/ oscillator circuits are connected by respective resonance detectors D1, D2 to a common differential amplifier A which is in turn connected to a solid state relay Z. A switch S is again provided for starting the pump P. When this switch is operated the relay Z starts the pump P and the liquid level in the casing begins to rise.When the liquid level has risen to the level of the capacitor C2 the detector 1 commands the amplifier A to turn on a zero current switch forming part of the relay Z. The pump motor P is thus held on since the zero current switch is biased into the "on" position. The pump thus continues to run until the liquid reaches the level of the capacitor C1 when the detector 2 acts through the differential amplifierAto turn off the zero current switch thereby stopping the pump motor. When the pressure falls the liquid level drops below the capacitor C1 and the pump is re-started.

It will be appreciated that the pressure switch according to the invention may also be used in other beer dispensing systems. Thus, for example, Figure 9 illustrates a dispensing system for open cask beer, i.e. beer which does not require to be enlivened by pressurised CO2. In this case, a beer barrel 58 is supported on a plinth 59 above the cellar floor 60 to provide a pressure head for gravity feed by a connecting pipe 61 to the pump 62 which stands on the floor. The arrangement on the pressure side of the pump is substantially the same as in Figure 1 with a pressure switch 11, outlet line 7 and dispensing outlet 9.

Figure 10 shows a lay-out similar to that of Figure 1 with like component identified by like reference numerals but including a de-gassing unit 63 of the kind described in our co-pending United Kingdom Patent Application No. 18578/78. Parts corresponding to those in Figure 1 are designated by the same reference numerals. The de-gassing unit is illustrated in detail in Figure 11 and will now be described.

A cylindrical, preferably transparent, agitation chamber 64 has a liquid inlet 65 connected to the pipe 6 and projecting about one third of the height into the chamber 64, to terminate in a nozzle head 66. The head 66 has a series of spray openings 67 directed diagonally upwards which allow beer pumped through the liquid inlet 65 to impinge against the inside walls of the chamber 64. The chamber 64 has a height two to twenty (preferably four to seven) times its diameter and is tapered at least at its lower end which terminates in a central liquid outlet 68 which leads to the pump 5. From the pump 5, the beer is passed to the dispensing outlet 9.

At the upper end of the chamber 64, there is a central gas outlet 69 which leads to a normally closed solenoid valve 70 and a vent pipe 71 which vents to atmosphere.

Towards the upper end of the chamber 64, and well above the nozzle head 66, is preferably provided a permeable wall formed by a condensation gauze 72. The purpose of this gauze is to aid the breakdown of bubbles formed by escaping gas. Mounted in the wall of the chamber 64 a short distance below the gauze 72 are two electrical contacts 73, which operate at low voltage. The contacts 73 may alternatively be positioned at a lower level possibly even below the nozzle head 66. The contacts 73 are arranged so as to be sensitive to liquid when the liquid level in the chamber 64 rises so that the contacts are bridged, but to be insensitive to the presence of mere froth. A further level sensor 74 is provided towards the lower end of the chamber 64 below the contacts 73.

The apparatus operates as follows: initially, the system is connected up with the liquid inlet 65 connected to the barrel containing beer under CO2 pressure and the pump 5 connected to the dispensing outlet 9, which remains closed. In these circumstances, beer enters through the liquid inlet 65, emerges as jets through the nozzle head 66 and impinges forcibly on the inside walls of the agitation chamber 64. This releases gas from the beer which forms bubbles which rise in a froth towards the gas outlet 69. The beer, partially de-gassed, flows down the walls of the chamber and steadily fills up the latter. When the liquid level reaches the lower level sensor 74 the valve 70 opens. As the bubbles and froth reach the gauze 72, the bubbles are broken and the gas escapes upwards while the beer forming the bubbles coagulates and drops back into the chamber.

As the level of beer in the chamber rises, it covers the nozzle head 66 and the beer coming into the chamber then starts to cause strong agitation of the liquid beer therein. The liquid level continues to rise until it reaches the contacts 73 and when this happens, the electrical control system causes the solenoid valve 70 to be closed. Since the chamber 64 then becomes a closed system, the gas pressure above the liquid in the chamber starts to rise until there is pressure equalisation between that gas and the pressure of the liquid entering the chamber At that point, further inflow of beer ceases, the chamber by then containing a supply of de-gassed beer for transmission to the dispensing tap when required.

Once the dispensing tap 10 is opened, the pump 5 is automatically started to dispense beer which is drawn through the liquid outlet 68 at the bottom of the chamber. This will cause the liquid level in the chamber to drop whereupon the pressure from the barrel will cause a fresh flow of beer to enter through the inlet 65. When equilibrium is restored the liquid will be at a lower level if the fresh beer has released excess gas. The falling level caused in this way will ultimately cause the electrical contacts 73 to become uncovered, so that the hold on the valve 70 is released.Thus, the pressure in the top of the chamber 64 as gas is allowed to escape and the pressure from the barrel will cause a fresh flow of beer to start through the liquid inlet 65 and the procedure previously followed will then occur again, the level of beer in the chamber 64 rising until it reaches the contacts which will then shut the valve 70 in the gas outlet line 71. This procedure will occur so often as the contacts 73 become uncovered and then covered again by liquid. The result is to maintain a ready supply in the chamber of beer with a desired gas content ready for dispensing to a customer.

In the normal course of operation the beer level will notfall below the lower level sensor until the barrel is empty whereupon the valve 70 will be closed. The chamber will now be full of gas which must be vented before a new barrel is fitted. For this purpose the solenoid valve 70 has a manual override button or switch (not shown) which is, incidentally, also useful in cleaning to allow through flow of cleaning fluid. When a new barrel is fitted, the override button is operated if necessary to allow beer to enter the chamber until it reaches the bottom sensor 74 which then holds the valve open.

It will be seen that the apparatus has no moving parts, and is thus extremely reliable in operation. It is also constructed so as to be easily cleanable, and the chamber itself has no dirt traps which make maintenance difficult.

It should be noted that the presence of a pump is not essential, since the apparatus is constantly tending to produce a closed system with the solenoid valve closed, at which time it becomes pressurised and this pressure may be sufficient to dispense the beer from the dispensing tap.

For safety reasons, the system is operated at low voltage. The liquid inlet need not be of the form shown and does not have to come into the chamber centrally at the bottom. It is necessary only that the liquid coming into the chamber should be capable of causing strong agitation of the liquid already in the chamber to ensure that any excess gas is caused to come out of solution and to escape. The apparatus can be used for other liquids than beer.

If deliveries of more than a pint are envisaged, the chamber will have a proportionately larger volume.

Depending on the height, the openings 67 for a head 66 as shown can be directed at any suitable angle above the horizontal.

Though separate contacts or probes 73 are shown, the contacts 73 can be provided by existing metallic members in the chamber, for example the liquid inlet 65 and the gauze 72. Thus as soon as the liquid level reaches the gauze, the electrical circuit would be completed through the liquid. It has also been found that the application of a voltage to or across the gauze can help to break down the froth to release the gas.

In an advantageous embodiment the level sensors are provided by capacitors in a circuit such as is described with reference to Figure 8.

In a modified embodiment of the invention, which can be useful for certain liquids of which a froth will conduct electricity, there may be included in the chamber an extra solid sleeve 75, shown dotted. The sleeve has a gauze 76 at the bottom and forms an annular sub-chamber 77 up which in use only liquid rises, and not froth. Thus the contacts 73 are not closed "falsely" by the column of froth which will rise up inside the sleeve 75, but only "correctly" when the actual liquid level reaches them.

It will be appreciated that the incorporation of a de-gassing unit in the pump feed lines does not affect the operation of the pressure switch as already described.

In a further refinement, the beer dispensing system is equipped with a speed control for the beer pump.

The position of the speed control is illustrated at 78 in Figure 9 at bar level adjacent the beer dispensing tap. The speed control will occupy a corresponding position in the other pump operated dispensing systems discussed above. The speed control will now be described with reference to Figures 12 and 13 which illustrate two alternative embodiments thereof. Figure 12 shows a liquid inlet 79 and a liquid outlet 80 controlled by a tap 81 operated by a handle 82 which is arranged so that the tap 81 is closed when the handle 82 is in the upright position shown in full line and is gradually opened as the handle 82 is pivoted counter-clockwise into the fully open position shown in dotted line. The handle 82 is pivotally connected to a slide rod 83 of a variable slide resistance 84 in the pump motor circuit (not otherwise illustrated).The arrangement is such that when the tap 81 is fully closed the pump is operable at maximum r.p.m. and when the tap is fully open the minimum r.p.m. is reached. In this embodiment, the tap varies both the volume and the pressure of the beer dispensed. When the tap is closed the beer line is at maximum pressure to keep the gas in solution. When the tap is open slightly liquid is dispensed at low volume and high pressure and further opening of the tap allows a higher volume to flow at much lower pressure. When the tap is shut again the line is re-pressurised because the pump runs at maximum speed for a shorttime before being switched off.

The embodiment of Figure 13 is basically similar but here the tap is provided by a solenoid valve 85 which is either fully open or fully closed, as is the case for example in dispensing systems using beer meters at the bar. There is therefore no control of delivery volume and pulling of a handle 86 operates the beer meter causing beer to be dispensed at a fixed rate. When such a system is modified by incorporation of the speed control the extent of pivotal movement of the handle 86 will determine the speed of the pump during the dispensing operation. When the handle 86 is in the upright position the valve 85 is closed and the pump is either off or temporarily running at maximum speed to re-pressurise the line after a dispensing operation.

As soon as the handle 86 is operated the valve is moved into a fully open position and the pump runs at maximum speed. As the handle is pivoted further in the anticlockwise direction the speed control causes the pump motor speed to be reduced. Thus if the bar attendant finds that the beer being dispensed is too lively (i.e. gaseous) he merely needs to pull the handle further in the anticlockwise direction thus causing the pump to slow down and the line pressure to fall. The operation of the speed control is substantially the same as in the embodiment of Figure 12 in that a variable slide resistance 87 is incorporated in the pump motor circuit. The solenoid valve 85 is connected to a microswitch 88 which is arranged to be operated by an actuating rod 89 pivotally connected to the handle 86.When the actuating rod 89 is moved to the left as seen in Figure 22 the microswitch 88 operates to open the solenoid valve 85. A return spring 90 is provided for returning the handle 86 and hence the actuating rod 89 to the starting position when the handle is released. Such return movement again operates the microswitch 88 which causes the solenoid valve 85 to move into the closed position. However, the microswitch 88 does not operate to shut the solenoid valve until a measured volume has been dispensed because an interlock is provided in the meter system.

It will be appreciated that the pressure switch of the invention is not confined to beer or other liquid dispensing systems of the kind described above. The pressure switch has application in any fluid flow system in which pressures require ta be sensed either for control purposes or merely for monitoring purposes. Thus, for example, it might be desirable to monitor a fluid circuit for peak pressures with a view to triggering an alarm when such a pressure was reached. The particular value of the pressure switch in monitoring fluid pressures lies in the fact that an electrical output signal can be generated directly in response to the presence or absence of a predetermined pressure without the need for relatively complex electromechanical transducers such as have hitherto been required.The directly obtained output signals can beefed to control equipment or monitoring apparatus which may itself be computerised.

An example of an alternative application of the pressure switch will now be described with reference to Figure 14. This shows a water distribution system in which a water pump 90 is arranged to pump water from a supply reservoir 91 to a service reservoir 92 from which water is distributed through pipe 93 to the ultimate consumers. Previous control systems have involved the use of ballcocks in the service reservoirforsignalling a fall in liquid level to cause operation of the pump. The system is much simplified by positioning a pressure switch 94 according to the invention at the pressure side of the pump. The switch operates in the way already described to switch the pump on and off at predetermined line pressures corresponding to different liquid levels in the switch casing.

A further advantage of the pressure switch according to the invention is that the electrical contacts may be mounted on the outside of the casing thus rendering the switch suitable for use with flammable liquids.

It will be appreciated that the pressure switch of the invention is not confined to the control of liquid pressures but may also be adapted to the control of gas pressures with only slight modification. This is accomplished by extending the tubular casing into the form of a U of which one end is closed and the other end is connected to the gas flow pipe. The bend of the U-shape is filled with an inert liquid the level of which is the blind limb of the tube varies in accordance with the gas pressure. The blind limb of the tube can thus be equipped with electrical contacts in any of the various ways described above.

A further variation of the pressure switch comprises a single level sensor as opposed to the plurality of sensors in the embodiments described above. This variant may be useful in fluid flow systems in which it is only necessary to respond to a single line pressure, e.g. a maximum or minimum pressure above or below which the system should not be operated.

Although the specification and claims are directed to fluid flow apparatus incorporating a line pressure sensor (the pressure switch) and, optionally, a speed control and de-gassing unit, the applicant does in fact contemplate that these three aspects of the invention may be used independently of each other or in any desired combination. Thus, independent protection is sought not only for the pressure switch but also individually for the speed control and de-gassing unit.

Claims (10)

1. Fluid flow apparatus comprising a fluid flow line and a line pressure sensor in the form of a pressure chamber occupied by a gas cushion arranged to vary in volume with fluctuations in the line pressure and sensing means arranged to emit an electrical signal when the gas volume reaches a predetermined value corresponding to a specified line pressure.

2. Apparatus as claimed in claim 1, wherein the fluid is liquid and the pressure chamber is connected to the fluid flow line in such a way as to permit the liquid to rise and fall in the chamber and thereby vary the volume of the gas cushion as the line pressure varies.

3. Apparatus as claimed in claim 1 or 2, wherein the volume of the pressure chamber is variable so as to alter the volume of the gas cushion and hence the line pressure at which the sensing means responds.

4. Apparatus as claimed in any one of the preceding claims, wherein the sensing means comprises a plurality of level sensors at different levels in the pressure chamber for sensing respective line pressures.

5. Apparatus as claimed in claim 4, further comprising a pump arranged to be switched on by a lower level sensor and to be switched off by an upper level sensor thereby causing the pump to operate within a predetermined range of line pressures.

6. Apparatus as claimed in claim 5, wherein a plurality of upper level sensors are selectively connectible to the pump for switching the pump off at predetermined respective line pressures.

7. Apparatus as claimed in claim 5, wherein the upper level sensor is adjustable to alter the line pressure at which the pump is switched off.

8. Apparatus as claimed in any one of claims 5 to 7, wherein the pump is arranged to deliver liquid to a dispensing outlet controlled by a handle operated valve and the speed of the pump is adapted to vary in dependence upon the position of the handle.

9. Apparatus as claimed in any one ofthe preceding claims, further comprising a de-gassing unit including an agitation chamber, an inlet for liquid to be de-gassed, a spray head connected to said inlet for projecting the liquid against the chamber walls with attendant liberation of excess gas therefrom, a gas outlet controlled by a valve, a lower level sensor arranged to open said valve when the liquid level in said chamber reaches a lower level, an upper level sensor arranged to close said valve when the liquid level in said chamber reaches an upper level, and a liquid outlet.

10. Fluid flow apparatus substantially as herein described with reference to and as illustrated in the accompanying drawings.