GB2108728A - A temperature responsive valve assembly - Google Patents

Abstract

A temperature responsive valve assembly includes a 3-way valve (10) Fig 1, not shown operated by a servo- motor (32, 34) of the double acting piston type, and a wax-filled temperature sensitive element (40) having a linearly movable plunger connected with a transducer (38) which converts linear movement of the plunger into a pressure signal proportional thereto. The transducer (38) comprises a flapper (24) controlling the pressure to a valve (60, 58) which provide the separating signal to the servo-motor control valve (30) at (118). The flapper (74) is moved by rod (76, 80), can (82), adjustable lever 86, lever 94 and spring 96. Fluid pressure feed back is provided at 98. <IMAGE>

Description

SPECIFICATION A temperature responsive valve assembly This invention relates to temperature responsive fluid flow control valve assemblies for use, for example, for controlling and maintaining a substantially constant temperature of a coolant or lubricant leaving an engine such as a marine diesel engine.

British Patent Specification No. 1,200,244 discloses a temperature responsive fluid flow control valve assembly comprising a 3-way valve of the type wherein three ports in the valve housing are controlled by a rotor such that the flow rate through one of the three ports is equal to the sum of the flow rates through the other two ports which themselves vary in dependence upon the position of the rotor, a single-acting piston type servo-motor which controls the position of the rotor and is operated by a servo fluid, a pressure controller for regulating the pressure of the servo fluid, and a wax-filled temperature sensitive element having a plunger connected to the pressure controller. This arrangement suffers from the disadvantage that the valve rotor often tends to hunt.This is due, in the first place, to the fact that the single-acting piston, which is springreturned, of the servo-motor does not exhibit an adequately quick response to the pressure variations in the servo fluid and, in the second place, to the fact that a valve element of the pressure controller tends to travel from its fully closed position to its wide open position, and vice versa, with a narrow range of temperature change of the temperature sensitive element. In addition, the use of the single-acting, spring-returned piston as an actuator of the servo-motor requires the piston to move only by the spring force during its return stroke so that the value of limiting differential pressure of the valve, that is, the maximum pressure difference existing between the pressures in the two outlet ports of the valve at which the valve rotor is operable to rotate, is limited.Further, if the pressure controller arrangement as shown in Figure 5 of the British Patent 1,200,244 is employed for the purpose of providing a fail-safe function, the output servo fluid pressure of the pressure controller decreases as the coolant temperature increases, so that it will be most difficult to achieve accurate valve control at a high temperature range in which temperature control of the coolant is most important, thereby resulting in the overrun of the rotor and hunting of the valve.

There is also known in the prior art a temperature responsive 3-way valve of the type described above and provided with a servo-motor of the type including a double-acting piston serving as an actuator of the servo-motor and a piston positioner as a control valve for the actuator. The piston positioner is connected to an aneroid type temperature sensitive element or bellows structure which senses the temperature of the coolant from the power plant and expands to generate pressure variations in the pressure signal which is fed to an input chamber of the piston positioner. The piston positioner has a sliding spool which displaces in response to the pressure signal applied to the input chamber to control a serparate servo fluid to flow into the cylinder at either side of the piston.By using the double-acting piston type servo-motor, this temperature sensitive valve assembly is free, to a considerable degree, from the aforementioned problems of hunting and low limiting differential pressure inherent in the single-acting piston type servo-motor. However, this valve assembly has a drawback in that the linear expansion of the bellows structure is very small so that the bellows structure must be arranged in a multiple stage configuration whereby the overall assembly becomes extremely complex.

According to the present invention, a temperature responsive fluid flow control valve assembly comprises a 3-way valve of the type having three ports controlled by a rotor such that the fluid flow rate through one of said ports is equal to the sum of the fluid flow rates through the other two ports for all positions of the rotor, the fluid flow rates through the other two ports being varied in dependence upon the position of the rotor, a servo-motor of the double-acting piston type connected to the rotor for regulating the position of the rotor in response to a fluid pressure signal applied to the servo-motor, and a wax-filled temperature sensitive element having a plunger which is linearly movable in response to the temperature of a fluid in which said element is immersed, wherein a transducer is connected between said plunger and said servo-motor, the transducer converting linear displacement of the plunger into a fluid pressure signal the magnitude of which is related to the displacement, and feeding said pressure signal to said servo-motor to cause the servo-motor to regulate the position of the rotor to control the relative proportions of the total fluid flow rate through the valve between the other two ports in dependence upon the temperature of the fluid in which said element is immersed.

Preferably, the transducer comprises a housing, a pressure signal line in said housing and having an inlet port adapted to be connected to a compressed air source and an outlet port connected to the servo-motor, a pilot operated flow control valve arranged in said pressure signal line for controlling the flow of compressed air passing therethrough, a nozzle and a flapper mechanism provided in said housing, means connected between the flapper of said nozzle and flapper mechanism and the plunger of said temperature sensitive element for transforming the translational movement of the plunger into a biassing force urging the flapper against the nozzle to increase the back pressure of the nozzle in proportion to the increase in the fluid temperature, and means connected to said nozzle of the nozzle and flapper mechanism and to said flow control valve for actuating the flow control valve to open in response to the rise in the back pressure of the nozzle to increase the pressure signal at the outlet port.

With this arrangement, even a small amount of linear displacement of the plunger due to a slight temperature change of the fluid is translated into a considerable degree of pressure variations in the pressure signal, and these pressure variations are substantially proportional to the temperature change. These are achieved in a quite simple manner, while retaining the full advantages of the double-acting piston type servo-motor.

Preferably, the tranducer is provided with a feedback mechanism for feeding the variations in the output pressure signal back to the flapper.

These and other features and advantages of the present invention will become apparent from the following detailed description in conjunction with the accompanying drawings in which: Figure 1 is a diagrammatic view of an embodiment of the temperature responsive valve assembly according to the present invention, showing the overall arrangement of various parts; Fig. 2 is a schematic perspective view, partly in cross-section, of the transducer assembled to the temperature sensitive element; Figs. 3A to 3C are cross-sectional views of the servo-motor with its spool in various positions; Figs. 4A and 4B are piping diagrams showing two examples of valve arrangement; Fig. 5 is a piping diagram of the experimental apparatus used in comparative experiments; and Fig. 6 is a graph showing the results obtained by the experiments.

Throughout several views, like reference numerals will be used to indicate like parts and members.

Referring to Figure 1, the temperature responsive valve assembly according to the invention includes a conventional rotary type 3way valve 10 known per se. The 3-way valve 10 comprises a cylindrical casing 12 having three ports 14, 16, and 18 angularly equally spaced apart from each other. The casing 12 closely receives a rotor 20 which comprises a pair of parallel, spaced side plates (one of which is shown at 22) extending perpendicularly to the axis of the casing and carrying a pair of arcuate closure members 24 and 26. The side plates are rigidly secured to a rotor spindle 28 mounted pivotably to a pair of end plates, not shown, of the valve.The closure members 24 and 26 are so sized that the total opening area of the ports 16 and 1 8 is constant for all positions of the rotor, so that the flow rate of a fluid flowing into or out of the valve through the port 14 is equal to the sum of the flow rates of the fluid flowing out of or into the valve through the other two ports 16 and 18.

By turning the rotor in one direction or the other, it is possible to vary the proportions between the flow rates through ports 16 and 18.

The position of the rotor 20 is controlled by a servo-motor including a piston positioner 30, serving as a control valve for the servo-motor, and a double-acting piston type cylinder 32, serving as an actuator for the servo-motor, which cylinder has an output rod 34 linked to a crank arm 36 secured to the rotor spindle 28. A pressure or pilot signal for the piston positioner or control valve 30 is supplied from a transducer 38 which is adapted to convert the translational movement of a plunger of a wax-filled temperature sensitive element 40 into a pressure or pilot signal having a pressure proportional to the temperature of a fluid in which the element 40 is placed.

Figure 2 shows the details of the transducer 38 shown in Fig. 1 as assembled to the temperature sensitive element 40. The transducer has a signal pressure line 42 provided in a housing (not shown) and extending from an inlet port 44, adapted to be connected to a suitable compressed air source, to an outlet port 46. The flow of air in the pressure signal line 42 is controlled by a pilot operated flow control valve 48 having a housing 50 which is suitably supported by the housing of the transducer 38.

The inside of the flow control valve housing 50 is divided into an inlet chamber 52 and an outlet chamber 54 by a partition 56 provided with a valve seat 58. A spring-biassed valve member 60 is resiliently received within the inlet chamber 52 for engagement with the valve seat 58 to control the flow of compressed air flowing out into the outlet chamber 54. The protruding end of the valve member 60 extends throughout the outlet chamber 54 and closely through a central opening of a diaphgram 62 into engagement with a second diaphragm 64 which.cooperates with the housing 50 to define a pilot chamber 66. The space between the diaphragms 62 and 64 is vented to the ambient atmosphere to ensure expanding movement of the diaphragm 64 in response to the pilot pressure in the chamber 66.

The pilot chamber 66 is communicated with the inlet chamber 52 by means of a passage provided with a restriction 68 so as to introduce a flow of compressed air therein. The pilot chamber 66 is also connected by a passage 70 to a nozzle 72 of a nozzle and flapper mechanism. The back pressure of the nozzle 72 is controlled by a flapper 74 and is reflected through the passage 70 into the pilot chamber 66.

Power inlet section of the transducer 38 includes a racked rod 76 mounted for sliding movement on the transducer housing in alignment with a plunger 78 of the wax-filled temperature sensitive element 40. The teeth of rod 76 is in mesh with a pinion 80 which is rotatably mounted on the transducer housing and is integral to a cam wheel 82 which in turn engages a cam follower 84 provided on a lever 86 pivoted to the transducer housing at 88. The lever 86 is provided with a toothed slot 90 for adjustably retaining therein an end of a span adjusting pin 92 which engages a second lever 94 pivoted at 95 to the housing. A tension spring 96 is mounted between the second lever 94 and the flapper 74.

The transducer 38 is also provided with a feedback mechanism including a feedback chamber 98 communicated by a passage 100 with the pressure signal line 42. The feedback mechanism has a diaphragm 102 defining a side of the chamber 98 and supporting the flapper 74 near the upper end thereof.

With this arrangement, the linear displacement of the plunger 78 of the temperature sensitive element 40 is translated into the angular movement of the lever 94 which is, in turn, translated into the spring bias built up in the spring 96. As the temperature of the fluid in which the element 40 is placed increases, the spring force of spring 96 increases to diminish the gap between the nozzle 72 and flapper 74 so that the nozzle back pressure increases accordingly.

The back pressure of the nozzle 72 is transmitted through passage 70 to the chamber 66 and acts as a pilot pressure exerting on the diaphragm 64 which expands toward the right as viewed in Fig.

2 to urge the valve member 60 away from its associating valve seat 58 against a spring bias to allow the compressed air to flow through the pressure signal line 42 out the outlet port 46.

Simultaneously, the signal pressure in line 42 is reflected via the passage 100 on the pressure in the feedback chamber 98 causing the diaphragm 102 to expand outwardly to counteract the spring bias of spring 96. Thus, the transducer converts a small amount of linear displacement of plunger into a large amount of pressure variations in the output pressure signal. In practical applications, the transducer as described and illustrated is capable of generating a pressure variation in the order of 0.1 kg/cm2 for each 1 mm linear displacement of the plunger, which displacement corresponds to a 1 OC change in the temperature of the fluid under control.

Referring to Figure 3A, the details of the servomotor are shown comprising the piston positioner or control valve 30 and the double-acting piston type pneumatic cylinder 32 as shown in Fig. 1.

Both the piston positioner 30 and cylinder 32 are of the conventional type. The piston positioner 30 is a spool valve of the pilot operated type with a feedback control mechanism and a nozzle and flapper mechanism. The piston positioner 30 has a pressure port 104 adapted to be connected to a compressed air source. The pressure port 104 communicates with a first chamber 106 defined by a diaphragm 108 connected to an end of a sliding spool 110. Port 104 is also connected via a restriction to a second chamber 112 defined by a diaphragm 114 having a larger pressure receptive area than that of the diaphragm 108.

The sliding spool 110 is provided with a nozzle 116 which is communicated with the chamber 112 and constitutes a part of the nozzle and flapper mechanism. A pressure signal or pilot pressure generated by the transducer 38 is supplied through an inlet port or pilot port 118 into a flexible annular input chamber 120 which carries a smaller diaphragm 122 and a larger diaphragm 124. The larger diaphragm 124 acts as a flapper of the nozzle and flapper mechanism.

As the pressure of signal from the transducer increases, the flapper or diaphragm 124 displaces toward the left to increase the back pressure of the nozzle 11 6 so that the spool 110 moves toward the left as shown in Figure 3B to permit the compressed air to flow into the left chamber of the cylinder 32 causing the piston to move to the right. The movement of the piston is transmitted by a link 126 to a feedback spring 1 28 connected to the smaller diaphragm 122, so that the piston continues to move until the nozzle pressure exerting on the diaphragm 124 becomes in equilibrium with the force of the feedback spring 128. To the contrary, if the pressure of pilot signal decreases, the spoo! of the piston positioner 30 moves to the right to move the piston to the left as shown in Fig. 3C.

Thus, the transducer 38 issues a pressure signal having a pressure which is proportional to the temperature of the fluid to be controlled, and the servo-motor rotates the rotor of the 3-way valve 10 through an angle which is proportional to the pressure signal.

Figures 4A and 4B illustrate representative examples of the manner in which the temperature responsive valve assembly according to the invention is employed. In the example of Fig. 4A, the coolant from a marine diesel engine 130 flows through a conduit 132 into a cooler 134 and returns therefrom through a conduit 136 back to the engine. The servo-controlled 3-way valve 138 controls the proportions between the flow from the cooler and the flow from the bypass 140 in response to the temperature of the coolant such that the temperature of the coolant leaving the engine becomes constant. In the example of Figure 4B, the flow of coolant is divided by the valve into a flow flowing into the cooler and a flow by-passing the cooler.

The inventor has conducted comparative experiments using the temperature responsive valve similar to that disclosed in British Patent 1,200,244 and the temperature responsive valve assembly according to the invention. The arrangement employed for these experiments is shown in Figure 5. Water in a reservoir 141 is heated by a boiler and is circulated by a pump 142 along a conduit 144. For simplicity of experiments, a cooler is not provided and the bypass 146 is simply controlled by valve assembly 148 with its temperature sensitive element 150 positioned between the reservoir and the 3-way valve. The results obtained are shown in the graph of Fig. 6. In the graph, the ordinate indicates the valve opening expressed in percentage, the abscissa indicates the temperature of the water.

For the valve assembly according to the invention, two assemblies were designed and tested, one having a value of limiting diffqrential pressure of 0.5 kg"cm2 and the other 1.5 kg/cm2. For the valve of the prior art, two valves having the value of limiting differential pressure of 0.5 and 1.2 kg/cm2 were tested. The results are plotted in the graph. As is apparent from the graph, the prior art valve opened from a fully closed position to a fully open position within a narrow range of temperature change of about 1 .50C and closed within a change of about 30C. The valve assembly according to the present invention began to open at about 360C, with its opening gradually increasing in response to the increase in temperature, and reached its fully open position at about 47.50C. As the temperature of water decreased, the opening of the valve according to the present invention decreased in proportion to the temperature drop, and the temperature change required for the valve to be fully closed was about 1 00C.

Claims (9)

Claims

1. A temperature responsive fluid flow control valve assembly comprising a 3-way valve of the type having three ports controlled by a rotor such that the fluid flow rate through one of said ports is equal to the sum of the fluid flow rates through the other two ports for all positions of the rotor, the fluid flow rates through the other two ports being varied in dependence upon the position of the rotor, a servo-motor of the double-acting piston-type conected to the rotor for regulating the position of the rotor in response to a fluid pressure signal applied to the servo-motor, and a wax-filled temperature sensitive element having a plunger which is linearly movable in response to the temperature of a fluid in which said element is immersed, wherein a transducer is connected between said plunger and said servo-motor, the transducer converting linear displacement of the plunger into a fluid pressure signal the magnitude of which is related to the displacement, and feeding said pressure signal to said servo-motor to cause the servo-motor to regulate the position of the rotor to control the relative proportions of the total fluid flow rate through the valve between the other two ports in dependence upon the temperature of the fluid in which said element is immersed.

2. A temperature responsive valve assembly according to Claim 1, wherein said transducer comprises a housing; a pressure signal line in said housing and having an inlet port adapted to be connected to a source of compressed air and an outlet port connected to said servo-motor; a pilot operated flow control valve arranged in said pressure signal line for controlling the flow of compressed air passing therethrough; a nozzle and flapper mechanism provided in said housing; means connected between said flapper of the nozzle and flapper mechanism and said plunger of the temperature sensitive element for transforming the translational movement of the plunger into a biassing force urging the flapper against the nozzle to increase the back pressure of the nozzle in proportion to the increase in the fluid temperature; and means connected to said nozzle of the nozzle and flapper mechanism and to said flow control valve for actuating the flow control valve to open in response to the rise in the back pressure of the nozzle to increase the pressure signal at the outlet port.

3. A temperature responsive valve assembly according to claim 2, wherein said means for transforming the translational movement of the plunger into a biassing force comprises: a racked rod connected to said plunger in alignment therewith and received by said housing for sliding movement thereto; a pinion mounted rotatably on the housing in meshing engagement with said rack; a cam wheel integral to said pinion and mounted rotatably on said housing; a lever mounted pivotably at its end to the housing and having a cam follower engaging said cam wheel for performing an angular movement in response to the translational movement of the plunger; and means associated with said lever for transmitting the angular movement thereof to the flapper of the nozzle and flapper mechanism.

4. A temperature responsive valve assembly according to claim 3, wherein said lever has an elongated longitudinal slot and wherein said means for transmitting the angular movement of the lever to the flapper comprises a span adjusting pin retained in said slot for sliding movement therealong, a second lever pivoted at an end thereof to the housing and engaging near the middle portion thereof with the other end of said span adjusting pin, and a tension spring connected at an end to the other end of said second lever and at the other end to said flapper for resiliently urging the flapper against the nozzle of said nozzle and flapper mechanism.

5. A temperature responsive valve assembly according to any one of claims 2 to 4, wherein said pilot operated flow control valve comprises a valve seat and a cooperating valve member, wherein said nozzle of the nozzle and flapper mechanism is in communication with said pressure signal line upstream of the flow control valve via a restriction, and wherein said means for actuating the flow control valve comprises a pilot pressure chamber communicating with said nozzle, said chamber being defined at a side thereof by a diaphragm engaging said valve member for moving the valve member away from its associating valve seat through a distance in proportion to the back pressure of the nozzle so that the pressure of the output pressure signal increases as the back pressure of the nozzle augments.

6. A temperature responsive valve assembly according to any one of claims 2 to 5, wherein said transducer further comprises feedback means associated with said flapper for feeding the variations in the output pressure signal back to the flapper.

7. A temperature sensitive valve assembly according to claim 6, wherein said feedback means is a diaphragm device having a working chamber communicating with said pressure signal line downstream of said flow control valve and a diaphragm defining a side of said working chamber, said diaphragm being connected to an end of the flapper opposite said nozzle such that an increase in the pressure signal reflected within said working chamber exerts a pressure on the diaphragm in a sense to counteract the biassing force that urges the flapper against the nozzle.

8. A temperature responsive valve assembly according to Claim 1, substantially as described with reference to Figures 1 to 3c of the accompanying drawings.

9. A marine diesel engine having a cooling water circuit the temperature of the water in which is controlled by a valve assembly in accordance with any one of the preceding Claims