GB2076494A - Snap-acting control for fluid- flow valve - Google Patents

Abstract

A snap-acting device 17 for connection between the temperature- responsive valve-actuating head and the water flow valve of a thermostatically-operated hot water cylinder valve. The device 17 is provided with "lost-motion" means 35 for delaying the operation of the valve by the actuating head over a temperature range of about 8 DEG C to 10 DEG C so as to prevent frequent cyclic operation of the boiler in a domestic central heating system. <IMAGE>

Description

SPECIFICATION Improvements in or relating to fluid-flow control valves This invention relates to fluid-flow control valves, and particularly, although not exclusively, to such valves for controlling the circulatory flow of a heating fluid in a central heating system.

For example, one use of such valves in a central heating system is to control the temperature of the domestic hot water supply stored in a cylinder which is heated indirectly by a circulating liquid in a closed circuit connected with the boiler and a calorifier coil which is immersed in the water in the cylinder.

Codes of practice recommend that, to prevent scalding of a user, the temperature of the stored hot water in the cylinder should not exceed 60"C.

Since the boiler flow temperature of the circulating liquid is likely to be in excess of 800C to provide efficient space heating for the system, it is usual to provide a valve in the calorifier circuit operable in response to the temperature of the water stored in the cylinder. The actuation of such valves on domestic systems is usually by electrical means or by direct thermo-hydraulic means whereby the expansion and contraction of a temperature-sensing medium contained in a sensor probe or phial actuates a diaphragm or bellows in a thermostatic device which in turn actuates a valve to open or close a passageway between the inlet and outlet in a valve body.

Such electrical valve-actuating means usually employs a form of bi-metallic switch which is inherently endowed with switching temperature differential such that when the valve is caused to close at 600C it is not caused to open until the stored water temperature has decreased by about 8 to 1 OOC. This temperature differential, provides that it is not too great, has several advantages, not least of which is that it reduces the frequency with which the boiler is made to cycle to maintain a satisfactory hot water service and with a consequential saving of fuel.

Whilst known thermo-hydraulically actuated valves are cheaper to manufacture than their electrically actuated counterpart, they suffer the disadvantage of not having the desired operating temperature differential. For instance, such valves usually open when the temperature of the hydraulic medium in the probe sensing the temperature of the hot water cylinder drops by about 1 OC. Consequently, unnecessary frequent cycling of the boiler occurs and more fuel is used to provide a satisfactory hot water service.

The invention as claimed is intended to prevent this happening in that it solves the problems of how to design a thermo-hydraulically actuated valve such that, having closed off the primary circulation through the calorifier circuit, when the temperature of the stored hot water in the cylinder had reached a desired maximum, the valve would not open again until the stored hot water temperature in the cylinder had reduced by, for example, 8 to 100C.

The invention as claimed is also intended to solve the problem of how to adapt existing thermo-hydraulically actuated valves so that they exhibit the aforesaid operational advantages.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view of a typical domestic hot water system incorporating a snapacting thermo-hydraulically operated cylinder valve in accordance with the invention, Figure 2 is a vertical sectional elevation of the whole valve showing the intermediate snap-acting adapter part which fits between the lower body part of the valve and the upper thermo-hydraulic head part of the valve, and Figure 3 is an enlarged sectional elevation of the snap-acting adapter part of Figure 2.

Referring first to Figure 1, the hot water system comprises an indirectly heated water storage cylinder 1 whose heating coil 2 is fed by circulating hot water through flow and return pipes 3,4 from a boiler 5 by means of a pump 6.

The snap-acting valve 10, in accordance with the invention, is preferably connected in the flow pipe 3 for controlling the circulatory flow through the calorifier heating coil 2. The valve 10 is actuated thermo-hydraulically by the expansion and contraction of a temperature-sensing medium, contained in a sealed limpet phial 7 (which in use is attached to the cylinder 1) and its capilliary tube 8, in response to the variation in temperature of the stored water in the cylinder.

Referring now to Figure 2, the whole valve 10 consists of; a well known two-port valve body part 11 having a valve spindle 12 and a valve 13 normally urged to a valve-open position by a compression spring 14, a well known temperature-selective head part 1 5 having a spring-loaded spindle 1 6 which is actuable thermo-hydraulically as aforesaid, and an intermediate snap-acting adapter device 1 7. In known directly actuated hot water cylinder valves, the said valve body 11 and temperature selective head 1 5 are connected together so that, in use, thermo-hydraulic actuation of the spindle 16, as aforesaid, causes it to engage or disengage the valve spindle 1 2 for respectively closing or opening the valve 1 3 in a gradual progressive movement with the disadvantageous effect of permitting frequent cyclic boiler operation due to an insufficient operating temperature differential of say between 8 to 1 OOC, the snap-acting adapter device 1 7 is fitted between the head 1 5 and the valve body 11.

Referring also to Figure 3 of the drawings, the snap-acting spindle 1 9 both slidably movable within the bore 21 of a sleeve 22 which is provided with any suitable means 23,24 at the ends thereof for fastening a respective end to the head 1 5 and valve body 11. The upper spindle 18 is urged to engage the spindle 1 6 of the head 1 5 by a compression spring 25. The lower spindle 19 has a transverse aperture 26 in which a pair of balls 27 are resiliently urged outwardly by a compression spring 28 so as selectively to engage either the bore 21 or an annular recess 29 when the spindle is moved vertically within the bore 21.

The lowermost end of the spindle 1 9 will engage the valve spindle 12 for a closing operation of the valve 13. The two spindles 18 and 19 of the adapter 1 7 are loosely linked together by a threaded post 31 which extends upwardly from the lower spindle 1 9. The post 31 protrudes into a hollow portion 32 of the upper spindle 1 8 through a hole 33 formed in its base 34. The upper spindle 18 is held loosely captive with respect to the lower spindle 1 9 by a pair of nuts 35 adjustably screwed onto the post 31 whereby to determine the amount of free relative movement or 'lost motion' between the spindles 1 8 and 1 9 in the bore 21.

In operation of the hot water system, as the temperature-sensing medium in the phial 7 and capilliary tube 8 expands with the rise in temperature of the stored water in cylinder 1, the spindle 1 6 is pushed downwards and simultaneously pushes down the upper spindle 1 8 which compresses the spring 25 and, in turn, pushes down the lower spindle 1 9 from its position shown in Figure 2 until the spring-loaded balls 27 drop into position in the annular recess 29. In this position, the spindles 1 8 and 1 9 will have depressed the valve spindle 12, compressing the spring 14, and closing the valve 13 against its seating to shut off the water circulation to the coil 2.

As the temperature-sensing medium gradually contracts, for example as a result of a draw-off of hot water from the cylinder 1 or a natural cooling of the stored water therein, the spindle 1 6 moves upwards and the upper spindle 18 moves in sympathy with it by the action of the compressed spring 25, but the lower spindle 19 (and therefore the valve 13) are retained in the closed position by the resilient locking action of the spring-loaded balls 27 in the recess 29, the srength in the compressed spring 14 alone not being sufficient at this point to overcome this locking action.

However, it will be seen that the amount of free upward movement of the upper spindle 1 8 relative to the locked lower spindle 19 is determined by the aforesaid 'lost-motion' gap between the inner surface of the spindle base 34 and the lowermost nut 35 on the post 31. Further upward movement of the spindle 1 6 and upper spindle 1 8 will cause its base 34 to engage the nut 35 (the position shown in Figure 3) whereupon the force in the compressed spring 25, acting on the upper spindle 1 8 to lift the lower spindle 1 9, will be added to the force in the valve spring 14. These combined force will then be sufficient to overcome the aforesaid locking action of the spring-loaded balls 27 forcing them inwardly from engagement with the recess 29 as the spindles 1 8 and 19 moves upwardly in the bore 21 thus allowing the valve 1 3 to open and restore circulation to the coil 2 (i.e.

the original position shown in Figure 2).

Thus, it will be appreciated that the 'lost motion' facility just described, the amount of which can be adjusted by altering the positions of the nuts 35, enables a delay in the operation of the valve from a closed position to an open position to be achieved over a required differential temperature range of the stored water in the cylinder so as to reduce the frequency with which the boiler is made to cycle to maintain a satisfactory hot water service.

Claims (6)

1. A lost-motion device adapted, in use, to be fitted between the thermostatic actuator device and the spring-loaded valve of a thermostaticallyoperated fluid-flow control valve for delaying the operation of the valve by the actuator device from one operative mode to another operative mode, the lost-motion device comprising, a tubular housing, first and second members movable within the housing, means for coupling said first and second members loosely but captively together whereby to provide a limited relative free movement or lost-motion therebetween, first biasing means for urging said first member away from said second member to the limit of said lostmotion therebetween, and means for selectively retaining the second member in a static first position within the housing.

2. A lost-motion device according to Claim 1 wherein the retaining means consists of one or more spring-loaded members carried by said second member and arranged, upon a movement of the second member, either to ride against the internal wall of the housing or to snap-engage in a recess formed therein for retaining the second member in said first position.

3. A lost-motion device according to Claim 1 or Claim 2, wherein said lost motion coupling means is provided by a projection extending from one of said first or second members and which projection locates through an aperture in the other of said first or second members which is held loosely captive on the projection by an abutment, the amount of relatively free movement or lost-motion between the first and second members being adjustable by adjustment means.

4. A thermostatically-operated fluid-flow control valve comprising a thermostatic actuator device, amd a spring-loaded valve operable by an actuating member of said thermostatic device for closing or opening a passageway between a fluid inlet and a fluid outlet of the valve; characterised in that said control valve incorporates a lost motion device in accordance with any preceeding Claim fitted between said thermostatic actuator device and said valve, whereby in use, movement of said actuating member in one direction is transmitted to the valve by the mutual engagement of the first and second members against the forces of said first biasing means and the valve spring to move the valve to a first operational mode at which it can be retained by said retaining means, and whereby, in use, an initial reverse movement of said actuating member is absorbed by said lost-motion coupling means so that the valve is retained in its first operational mode until further reverse movement of the actuating member enables the combined forces of said first biasing means and the valve spring acting via the coupling means and the first and second members to overcome the force of said retaining and allow the valve to move to a second operational mode.

5. A lost motion device substantially as shown in and as hereinbefore described with reference to Figure 3 of the accompanying drawings.

6. A thermostatically-operated fluid-flow control valve incorporating a lost-motion device according to Claim 5 substantially as shown in and as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings.