GB1583158A - Fluid pressure operated thermostat - Google Patents

Abstract

The device has a temperature sensor (9), an actuator (10) and an overtemperature protection (1, 4). The temperature sensor (9) and the actuator (10) are filled with an expansion fluid (3c) and are connected to one another operationally in a hydraulic fashion. The overtemperature protection (1, 4) consists of a pressure vessel (4) with a flexible partition (1) which is arranged between the expansion fluid (3c) and a pressurised gas (5). The partition (1) inserted in the pressure vessel (4) consists of a diaphragm, which is bent under stress and consists of a gas-tight plastic film. It is provided with a protrusion (1a), having an undulating profile, which can be pressed into the gas chamber (5) of the pressure vessel (4). This thermostat uses no aid. It guarantees, measured against the known or proposed thermostat systems, the withstanding of substantially higher overtemperatures without in any way impairing the operational reliability and service life. In this arrangement, the overtemperature protection requires a comparatively small installation space and is also, in addition, economic and of simple design. <IMAGE>

Description

(54) A FLUID PRESSURE OPERATED THERMOSTAT (71) We, INDUSIRIE WERKE KARLSRUHE AUGSBURG A.G., a Joint Stock Comapny organised under the laws of Germany (Fed. Rep.) of Postfach 3409, 7500 Karlsruhe 1, Germany (Fed. Rep.), 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:- This invention relates to a fluid pressure operated thermostat.

According to the present invention there is provided a fluid pressure operated thermostat comprising a fluid circuit including (1) a fluid containing temperature sensor (2) a fluid pressure responsive actuator for connection to a flow control valve (3) a reference value adjuster in the form of a chamber which is variable in volume by means incapable of being displaced by fluid pressure and (4) a pressure relief chamber having a restricted fluid inlet/outlet opening and a flexible wall which enables the volume of the pressure relief chamber to increase as fluid enters and which is biased by a gas under a predetermined pressure to return fluid to the circuit on reduction of the pressure therein, said flexible wall being a shaped disc of gas impermeable synthetic plastics material with at least one corrugation whereof the concave surface is directed inwardly of said pressure relief chamber.

Preferably, said shaped disc has a flat central area, a rim trapped between a fixed wall of the pressure relief chamber and a containing wall of a chamber for the pressurized gas, and an intermediate corrugation of annular form.

The fixed wall of the pressure relief chamber and the shaped disc are preferably of complementary shape and the disc in its rest position bears against said fixed wall.

The invention will now be further described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic part sectional view of one embodiment of fluid pressure operated thermostat in accordance with the invention, and Fig. 2 is a diagram to an enlarged scale illustrating the shape of a flexible wall used in the embodiment of Fig. 1.

Referring firstly to Fig. 1, the exemplary thermostat comprises a fluid containing temperature sensor 9, a valve servo drive 10 for moving a valve stem 10a of a valve (not shown), and a reference value adjuster 3 having a body 3a, including a cylinder portion 3b, and a piston 3e together defining a variable volume chamber containing fluid 3c and connected by capillary tubes 8 and 8a to the temperature sensor 9 and the valve servo-drive 10 respectively.

The position of the piston 3a in the cylinder 3b is adjustable manually by means of a setting knob 3d. Once set the piston is incapable of being displaced by fluid pressure.

A bore 3f is formed in the body 3 and is connected at its one end to the cylinder 3b and at its other end is screw threaded to receive a threaded nipple 7 of a pressure relief chamber defined by a fixed wall 6 and a flexible wall 1. A pressure reservoir 4 contains a gas 5, e.g. nitrogen, under a predetermined static pressure acting on one side of the wall 1 to bias it against the fixed wall 6.

The flexible wall 1 is trapped at its edge region between the fixed wall 6 and the containing wall of the pressure reservoir 4 to form a gas tight seal. The reference value adjuster 3 and the pressure reservoir 4 are contained in a casing 2.

As best seen in Fig. 2, the flexible wall 1 is a shaped disc with a central axis ib surrounded by a flat central portion lc between which and an outer rim id is an annular corrugation la whereof the concave surface is directed inwardly of said pressure relief chamber. The shaped disc 1 is made of gas impermeable synthetic plastics material. The fixed wall 6 of the pressure relief chamber has a shape complementary to that of the shaped disc 1 and the disc 1 in its rest position bears against the fixed wall 6.

The mode of operation of the thermostat is as follows.

Exposure of the temperature sensor 9 to an elevated temperature causes the liquid therein to expand and pass through the capillary tube 8 into the chamber of the cylinder 3b and thence via capillary tube 8a to the valve servo drive 10 which causes the valve stem 10a to move and throttle or completely close the associated valve. When the temperature sensor 9 and the sensor fluid therein cool down the valve is reopened. The response of the valve servodrive 10 can be altered to suit different temperature ranges by setting the reference value adjuster 3, by turning the setting knob 3d and displacing the piston 3e in the cylinder 3b thereby changing the volume of the chamber containing the fluid 3c. In normal operating conditions, the flexible wall 1 is prevented from moving by the pressure of the gas 5 in the reservoir 4.If an excessive temperature should occur at the temperature sensor 9 the resultant increase in volume of the liquid 3c is accommodated by flexure of the flexible wall 1 to increase the volume of the pressure relief chamber defined between it and the fixed wall 6. An inadmissible increase in the internal pressure of the system is thus prevented. When the excess temperature reduces again the flexible wall 1 returns to its initial position as a result of the biasing "force of the pressurized gas in the reservoir 4 and fluid is returned to the hydraulic circuit. It will be appreciated that the variations in pressure sufficient to cause movement of the flexible wall 1 do not cause any movement of the piston 3e whose position in the cylinder 3b can only be adjusted manually by way of the setting knob 3d.

WHAT WE CLAIM IS: 1. A fluid pressure operated thermostat comprising a fluid circuit including (1) a fluid-containing temperature sensor (2) a fluid pressure responsive actuator for connection to a flow control valve (3) a reference value adjuster in the form of a chamber which is variable in volume by means incapable of being displaced by fluid pressure and (4) a pressure relief chamber having a restricted fluid inlet/outlet opening and a flexible wall which enables the volume of the pressure relief chamber to increase as fluid enters and which is biased by a gas under a predetermined pressure to return fluid to the circuit on reduction of the pressure therein, said flexible wall being a shaped disc of gas impermeable synthetic plastics material with at least one corrugation whereof the concave surface is directed inwardly of said pressure relief chamber.

2. A thermostat as claimed in claim 1, wherein said shaped disc has a flat central area, a rim trapped between a fixed wall of the pressure relief chamber and a containing wall of a chamber for the pressurized gas, and an intermediate corrugation of annular form.

3. A thermostat as claimed in claim 2, wherein the fixed wall of the pressure relief chamber and the shaped disc are of com plementary shape and the disc in its rest position bears against said fixed wall.

4. A fluid pressure operated thermostat substantially as herein described with reference to and as illustrated in the accompanying drawings.

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

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. capillary tube 8 into the chamber of the cylinder 3b and thence via capillary tube 8a to the valve servo drive 10 which causes the valve stem 10a to move and throttle or completely close the associated valve. When the temperature sensor 9 and the sensor fluid therein cool down the valve is reopened. The response of the valve servodrive 10 can be altered to suit different temperature ranges by setting the reference value adjuster 3, by turning the setting knob 3d and displacing the piston 3e in the cylinder 3b thereby changing the volume of the chamber containing the fluid 3c. In normal operating conditions, the flexible wall 1 is prevented from moving by the pressure of the gas 5 in the reservoir 4.If an excessive temperature should occur at the temperature sensor 9 the resultant increase in volume of the liquid 3c is accommodated by flexure of the flexible wall 1 to increase the volume of the pressure relief chamber defined between it and the fixed wall 6. An inadmissible increase in the internal pressure of the system is thus prevented. When the excess temperature reduces again the flexible wall 1 returns to its initial position as a result of the biasing "force of the pressurized gas in the reservoir 4 and fluid is returned to the hydraulic circuit. It will be appreciated that the variations in pressure sufficient to cause movement of the flexible wall 1 do not cause any movement of the piston 3e whose position in the cylinder 3b can only be adjusted manually by way of the setting knob 3d. WHAT WE CLAIM IS:

1. A fluid pressure operated thermostat comprising a fluid circuit including (1) a fluid-containing temperature sensor (2) a fluid pressure responsive actuator for connection to a flow control valve (3) a reference value adjuster in the form of a chamber which is variable in volume by means incapable of being displaced by fluid pressure and (4) a pressure relief chamber having a restricted fluid inlet/outlet opening and a flexible wall which enables the volume of the pressure relief chamber to increase as fluid enters and which is biased by a gas under a predetermined pressure to return fluid to the circuit on reduction of the pressure therein, said flexible wall being a shaped disc of gas impermeable synthetic plastics material with at least one corrugation whereof the concave surface is directed inwardly of said pressure relief chamber.

2. A thermostat as claimed in claim 1, wherein said shaped disc has a flat central area, a rim trapped between a fixed wall of the pressure relief chamber and a containing wall of a chamber for the pressurized gas, and an intermediate corrugation of annular form.

3. A thermostat as claimed in claim 2, wherein the fixed wall of the pressure relief chamber and the shaped disc are of com plementary shape and the disc in its rest position bears against said fixed wall.

4. A fluid pressure operated thermostat substantially as herein described with reference to and as illustrated in the accompanying drawings.