GB1566229A

GB1566229A - Termostatically-controlled water mixer

Info

Publication number: GB1566229A
Application number: GB14553/78A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1978-04-13
Filing date: 1978-04-13
Publication date: 1980-04-30
Also published as: SE7903067L; DE2914150A1; FR2422886A1; IT7921744A0

Description

(54) THERMOSTATICALLY-CONTROLLED WATER MIXER (71) We, STANDARD TELEPHONES AND CABLES LIMITED, a British Company of 190 Strand, London, W.C.2, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to thermostatically controlled water mixers, such as are used to automatically control the water outputs of showers and water feeds, e.g. for kitchens, where it is necessary to hold the water at a pre-selected temperature with a reasonable degree of accuracy.

With such mixers the device is supplied with both hot and cold water to achieve a range of water temperatures at the output.

In the design of such mixers some factors must be taken into account. One of these is the accuracy with which the temperature can be selected. This depends on the openness of the calibration scale and on any backlash or hysterisis associated with the selection mechanism. Another factor is the accuracy with which the temperature can be controlled. This also depends on the control mechanism and its hysteresis. The selected temperature should not vary due to changes of temperature, pressure or flow of one or both of the hot or cold water feeds.

The response time of both the control and setting mechanisms has to be of the order of 1 second, at least in the case of a shower, to protect the user from thermal shocks or scalding. Further the system should be arranged to shut off if the cold water supply fails, again to avoid subjecting a user to thermal shocks or scalding. Finally the design has to take account of the build up of deposits from the supply water.

An object of the invention is to provide a thermostatically-controlled water mixer which is relatively cheap but which meets the requirements indicated above.

According to the present invention there is provided a thermostatically-controlled water mixer, which has a hot water input and a cold water input, a valve which can be adjusted so as to vary the proportions of hot and cold water which pass from the inputs to a mixing chamber from which the mixed water passes to an output, and a thermostat arrangement which in response to the temperature of the mixed water varies the position of the valve so as to maintain the temperature of the mixed water output substantially at a desired level, wherein the thermostat arrangement includes a stack of capsules interposed between the valve and its controlling member, said capsules being subjected to the temperature of the mixed water, wherein each said capsule is filled with a heat-sensitive filling so that changes of the temperature of the mixed water vary the effective length of the stack, and wherein the changes in dimension of the capsules effects said variation of the position of the valve.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which Fig. 1 is a cross-section of a capsule for use in a water mixer, Fig. 2 is a water mixer embodying the invention and using a stack of capsules such as that shown in Fig. 1, and Figs. 3 and 4 show two alternative forms of capsule.

The capsule shown in Fig. 1 is a waxfilled thermal capsule, in which the wax is enclosed between a corrugated disc 1 and a can or non-corrugated disc 2. The two discs are sealed at their rims using projection welding, i.e. the weld is made to an annular projection or sequence of discrete projections on the can 2. The weld profile for this being indicated at 3, 3. The corrugated disc is made of stainless steel9 although other materials such as precipitationhardening stainless steel, beryllium copper and phosphor bronze can be used. The disc 1 has a thickness of 0.1 mm, the depth of the corrugations is 1 mm and the diameter of the corrugated portion is 24 mm. The other disc or can 2 is for convenience made in annealed nickel, but other materials such as soft mild steel and stainless steel can be used.The choice of material is goverened by weldability: considerations, and the ease with which the weld profile can be stamped into the land. As shown the disc 2 has a central recess which is of a flattened frustoconical form with the central flat 4 mm across and having a depth of 2 mm. The overall diameter of the two discs is 30 mm in the example shown in Fig. 1. Also important in choice of material is corrosion resistance.

Thus the complete capsule is a can and corrugated disc welded together in one simple operation. Wax has to be introduced into the device to completely fill the cavity, which under laboratory conditions has been done by vacuum filling. This could be too time-consuming and expensive for production use, so an alternative method is used under production conditions. In this a wax preform is used which is moulded between thin plastics sheets, e.g. of a polyethylene terephthalate, sold under the Registered Trade Mark Melinex, to be exactly the shape needed to fill the cavity. The Melinex, covering provides easy handling so that the preform can be put into the can during the welding operation.

Various waxes can be used, but the preferred waxes are polyethylene waxes which are loaded with fine particles of copper to improve their thermal conductivity and thus reduce the response time to temperature change. This provides response times of I second over a range of 200 to 70or.

Fig. 2 shows in section a thermostaticallycontrolled water mixer using wax filled cap sules, such as that shown in Fig. 1. This has a differential control valve 5 which cooperates with the hot water input 6 and the cold water input 7. The valve is provided with bias springs 8 one of which acts on the valve rod 9 while the other acts on the valve itself. At the upper end of the valve rod 9 there is a flat plate 10 which supports a stack 11 of wax-filled capsules. Above the stack 11 there is another flat plate 12 having a set of four (in the present example) guide rods 13 equally spaced about the circumference of the capsules. These rods extend downwards towards the plate 10 and locate the capsules in place. The plate 12 has an upward extension 14 on the end of which is a temperature adjusting knob 15.The mixed water passes via the valve 5 past the capsules 11 to the controlled water outlet 16.

Thus the differential control valve 5, which is af double frusto-conical shape, is acted on by a stack of wax-filled capsules each of which provides a relatively small deflection between 0.005" and 0.010,'. Since about 0.080" deflection is needed to provide the desired degree of adjustment, the stack should contain about 10 capsules.

As will have been seen from Fig. 1, the bottoms of the cans 2 of the capsules are so shaped that when one capsule rests on an other there is space between them sufficient for water to circulate freely. The capsules are, as indicated above, located in their stack by the rods such as 13, which, with the upper plate 12, are adjustable to control the output water temperature by manual operation of the knob 15. The bias springs 8 ensure that the capsule stack is so pre loaded that the capsules always remain in contact with each other in the stack.

The valve is shown in a mid-position, which in many cases is its normal operating position. Its rest position is against the hot water seating, in which case the only water which can pass through the valve is cold water. This latter is the position which it as sumes if the cold water fails, in which case the capsules all expand due to the increased water temperature, and cut off the hot water supply.

Adjustment of the temperature control knob 15 moves the capsule stack 11 away from the valve 5, due to the urgence of the springs 8. Hence a higher temperature has to be achieved in the output water before the valve is moved away from the cold water seating. Hence the adjustment has the effect of moving the operating point of the differential control valve up and down the temperature deflection characteristic of the capsule stack.

Note that Fig. 1 is somewhat simplified and that a practical water mixer for use, for instance, for a shower would include various adjustment devices, non-return valves and filters. These latter can follow established practice, and so are not shown herein.

Other forms of capsule can be used in water mixers, and two of these are shown in Figs. 3 and 4.

In Fig. 3 we show a double-sized capsule with corrugated discs 20 and 21 on each side of a central weld ring 22, which has two weld profiles each as in Fig. 1. On each of these discs the middle corrugations are larger than the outer ones to ensure that when stacked the discs are adequately spaced to allow water to circulate between them. Such a capsule would provide twice as much deflection as the capsule shown in Fig. 1, and would be used whenever the volume change of the filling is larger than can be accommodated in the capsule of Fig.

1. Fillings such as vapours which exhibit very large volume changes could be used in such a capsule.

Fig. 4 shows a capsule which is relatively rigid and is needed where the corrugated diaphragms used in the capsules of Figs. 1 and 3 are insufficiently rigid, This lack of rigidity of the corrugated diaphragm could result in loss of deflection when the capsule operates under load. This capsule has a rigid lower plate 30 and a rigid upper plate 31 between which there is a flexible--and cor negated spacer 32. Both of the rigid plates have welding profiles. The space thus defined is filled by the wax or other expansion medium. The upper plate is dished as shown at 33 so that water can circulate between adjacent capsules in the stack.

The loads to which the capsules are subjected arise mainly from the layer difference pressures across the control valve, especially in an unbalanced system. The maximum water pressure can be of the order of 150 p.s.i., and the maximum can be about 7 p.s.i. Hence differential pressure of 143 p.s.i.

can act if one side of the valve and the sensing actuator (i.e. the capsule stack) must provide enough force to open the valve against this pressure.

From perusal of the preceding description it will be seen that the relatively large surface area of the capsules, which is influenced by the water whose temperature is to be controlled, ensures that a high degree of control is achieved.

In the earlier description various methods of filling the wax capsules have been mentioned; another method is to overfill the capsule prior to welding, in which case the welding is effected through the wax, excess wax being squeezed out of the capsule.

WHAT WE CLAIM IS:- 1. A thermostaically-controlled water mixer, which has a hot water input and a cold water input, a valve which can be adjusted so as to vary the proportions of hot and cold water which pass from the inputs to a mixing chamber from which the mixed water passes to an output, and a thermostat arrangement which in response to the temperature of the mixed water varies the position of the valve so as to maintain the temperature of the mixed water output substantially at a desired level, wherein the thermostat arrangement includes a stack of capsules interposed between the valve and its controlling member, said capsules being subjected to the temperature of the mixed water, wherein each said capsule is filled with a heat-sensitive filling so that changes of the temperature of the mixed water vary the effective length of the stack, and wherein the changes in dimension of the capsules effects said variation of the position of the valve.

2. A water mixer as claimed in claim 1 and wherein each said capsule is formed from a corrugated disc which is welded to a shallow circular can-like member the filling being of a wax located between the disc and the can.

3. A water mixer as claimed in claim 1, and wherein each said capsule is formed from two circular corrugated discs each welded to one circular face of a ring-piece, the filling being of a wax located between the discs.

4. A water mixer as claimed in claim 1, and wherein each said capsule is formed from a flat rigid disc to which is welded a partlycorrugated spacer member, a further rigid plate being welded to said spacer member to complete the enclosure within which the filling which is a wax is confined.

5. A water mixer as claimed in claim 2, 3 or 4, and wherein the wax used is loaded with fine particles of an electrically conductive metal to improve its thermal conductivity.

6. A water mixer as claimed in claim 1, 2, 3, 4 or 5, and wherein the valve is a differential valve of double-frusto-conical form with the hot water input controlled by one half of the frusto-cone and the cold water input controlled by the other half of the frusto-cone.

7. A water mixer as claimed in claim 6, wherein the valve has a valve rod which carries a flat plate which supports one end of the stack of capsules, and wherein the other end of the stack of capsules is supported by another flat plate whose distance from the first flat plate is manually adjustable.

8. A water mixer as claimed in claim 7, wherein the second-mentioned flat plate carries a set of rods which extend towards the first-mentioned flat plate, which rods are equally spaced around the second-mentioned flat plate and serve to locate the capsules in the stack.

9. A thermostatically controlled water mixer, substantially as described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. and 3 are insufficiently rigid, This lack of rigidity of the corrugated diaphragm could result in loss of deflection when the capsule operates under load. This capsule has a rigid lower plate 30 and a rigid upper plate 31 between which there is a flexible--and cor negated spacer 32. Both of the rigid plates have welding profiles. The space thus defined is filled by the wax or other expansion medium. The upper plate is dished as shown at 33 so that water can circulate between adjacent capsules in the stack. The loads to which the capsules are subjected arise mainly from the layer difference pressures across the control valve, especially in an unbalanced system. The maximum water pressure can be of the order of 150 p.s.i., and the maximum can be about 7 p.s.i. Hence differential pressure of 143 p.s.i. can act if one side of the valve and the sensing actuator (i.e. the capsule stack) must provide enough force to open the valve against this pressure. From perusal of the preceding description it will be seen that the relatively large surface area of the capsules, which is influenced by the water whose temperature is to be controlled, ensures that a high degree of control is achieved. In the earlier description various methods of filling the wax capsules have been mentioned; another method is to overfill the capsule prior to welding, in which case the welding is effected through the wax, excess wax being squeezed out of the capsule. WHAT WE CLAIM IS:-

1. A thermostaically-controlled water mixer, which has a hot water input and a cold water input, a valve which can be adjusted so as to vary the proportions of hot and cold water which pass from the inputs to a mixing chamber from which the mixed water passes to an output, and a thermostat arrangement which in response to the temperature of the mixed water varies the position of the valve so as to maintain the temperature of the mixed water output substantially at a desired level, wherein the thermostat arrangement includes a stack of capsules interposed between the valve and its controlling member, said capsules being subjected to the temperature of the mixed water, wherein each said capsule is filled with a heat-sensitive filling so that changes of the temperature of the mixed water vary the effective length of the stack, and wherein the changes in dimension of the capsules effects said variation of the position of the valve.