GB2042220A - Pressure regulator - Google Patents

Abstract

A pressure regulator for providing a control pressure varying in dependence upon temperature, said regulator comprising a control pressure determining valve having a valve closure member 5 carried by a diaphragm 25; a lever 10; an expansible temperature sensor 17 for varying the angular position of the lever in dependence upon temperature; and a plurality of springs 29, 30, 46, 71 acting together on said diaphragm to determine maximum, intermediate and minimum values for the control pressure, the lever and springs being arranged such that upon a sensed increase in temperature from a low value, the lever will act against the bias of a first spring 46 to permit the other springs to become operative in determining a value of the control pressure below the maximum value set by the first spring, wherein a second 29 and a third 71 of the springs set intermediate values for the control pressure, and wherein a fourth spring 30 acting between the first and third springs sets the minimum value for the control pressure. <IMAGE>

Description

SPECIFICATION Pressure regulator This invention relates to pressure regulators, and in particular to servo pressure regulators of the type described and claimed in our British Patent No.

1537220, and as used as part of the gas control valves such as described in German Offenlagungsschrift No. 2455569. In such gas control valves, the servo pressure regulator accurately maintains outlet gas pressure at a sensibly constant level regardless of fluctuations in inlet pressure; working gas is taken from the main gas inlet for use in the servo regulator and is used to adjust the position of the main valve according to demand. The servo pressure regulator is initially adjusted to maintain the pressure needed for correct main burner operation. Outlet pressure is sensed and controls the working gas pressure acting on the main valve positioning diaphragm, the main valve being adjusted until the correct gas pressure is sensed at the valve outlet.

According to the invention, there is provided a pressure regulator for providing a control pressure varying in dependence upon temperature, said regulator comprising a control pressure determining valve having a valve closure member carried by a diaphragm; a lever; an expansible temperature sensor for varying the angular position of the lever in dependence upon temperature; and a plurality of springs acting together on said diaphragm to determine maximum, intermediate and minimum values for the control pressure, the lever and springs being arranged such that upon a sensed increase in temperature from a low value, the level will act against the bias of a first spring to permit the other springs to become operative in determining a value of the control pressure below the maximum value set by the first spring, wherein a second and a third of the springs set intermediate values for the control pressure, and wherein a fourth spring acting between the first and third sets the minimum value for the control pressure.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which corresponding parts in these drawings and those of our Patent No. 1537220 are give the same reference numbers, and in which: Figure lisa longitudinal section through a servo pressure regulator according to the invention, and forming part of a gas control valve, the main valve of which is not show, and, Figure2 is a graph of the control pressure P provided by the regulator of Figure 1, plotted against temperature.

The servo regulator shown in Figure 1 would in use be mounted on the body of a gas control valve used for example to control the operation of a burner in for example a water central heating system. The gas contol valve (not shown) consists of a main valve for controlling the main flow of gas to the burner, the main valve having a closure member mounted on a diaphragm which is subjected to a spring force in a direction closing the main valve and to a servo gas pressure acting to open the main valve.

The servo gas pressure is generated in chamber 1 of the servo regulator. Chamber 1 is supplied with gas from the main gas flow via a throttling member (not shown). The pressure within chamber 1 is controlled by bleeding off gas from chamber 1 through valve seat 2 into chamber 3 which is in communication with the gas outlet of the control valve via conduit 4, the amount of gas bleeding off being determined by the position of a valve closure member 5 relative to the valve seat.

The servo pressure regulator consists essentially of three parts, a thermostat portion 6, a pressure regulator portion 7 and a maximum temperature limit portion 8, all three portions being in operative connection with a lever 10 pivotable about axis 9.

Thermostat portion 6 includes an extensible diaphragm capsule 17 located in a recess 12 and biased toward a minimum volume condition by a compression spring 19 acting between the bottom of recess 12 and a diaphragm plate 18 in contact with capsule 17. Expansion of the diaphragm is effected by a temperature sensor 16 connected to the interior of the diaphragm by means of capillary tube 14 and connector 15, and by a heat expansible liquid filling in parts 14 to 16. As the sensed temperature rises, the capsule 17 extends causing a pin 20 carried by plate 18 to move against the bias of spring 19 in a downward direction to depress the left hand end of lever 10.

Adjustment of the position of the capsule 17, and hence of the set-point temperature, can be effected by a sleeve 21 screw threadedly mounted in cover 11 of the recess 12 and adjustable relative to the cover by control knob 22, spring 19 maintaining connector 15 in contact with sleeve 21 during an adjustment operation.

Pressure regulator portion 7 includes a diaphragm 25 carrying valve closure member 5 and clamped at its periphery between a lower portion 27 of the regulator body and a connector plate 28 which defines valve seat 2. Fixed to portion 27 is a blade spring 30 acting in a downward direction toward diaphragm 25 and applying its bias to the diaphragm via a series connected C-shaped auxiliary spring 29; spring 29 may be a coil or a conical spring. The applied bias of spring 30 determines the minimum outlet pressure of the control valve and the bias can be adjusted by rotation of pin 32 screwthreadly mounted in cover 31.

Superimposed on spring 30 is a further blade spring 71 also fixed to housing portion 27. Spring 71 acts in a downward direction toward diaphragm 25 and engages upstanding projections 73 formed at the free end of spring 30. Pin 32 extends freely through an aperture 72 in spring 71.

The maximum outlet pressure is determined by the bias of a conical compression spring 46 acting in series on spring 71 via sleeve 38 and pin member 36; lever 10 is engageable with sleeve 38 which is guided for sliding movement only in bore 39 of upper housing portion 13. Adjustment of the bias spring 46 and hence of the maximum outlet pressure is effected by rotation in an appropriate direction of a sleeve 41 screwthreadly mounted in a housing recess 44 closed by cap 45.

To adjust the position of the proportional band along the temperature axis of the graph (M in Figure 2), member 36 is provided in the form of a screw screwthreadly mounted in sleeve 38 and has a lower end 35 which freely passes through a hole 37 in lever 10 and which engages spring 71; an upper end 40 of screw 36 projects through a central bore in sleeve 41 to permit adjustment of the screw when cap 45 is removed.

Maximum temperature limit portion 8 includes a normally closed snap-action switch 51 having a plunger 50 acted upon by the free end of a flat spring 49 secured to lever 10 by rivet 48; terminals 52 of the switch are electrically connected to external terminals 54 of the regulator by connection springs 53. In use, the switch 51 would be connected in series with a thermostat connected into the energising coil circuit of a solenoid valve which switches the servo system on. The solenoid valve is located between the above mentioned throttling member and chamber 1 and operates to cut-off gas supply to chamber 1 in the event either the limit temperature defined by switch 51 has been exceeded or the thermostat no longer calls for heat from the boiler.

The operation of the above described thermostatically controlled pressure regulator is as follows:- If the temperature measured by temperature sensor 16 is very low the diaphragm 17 is in a minimum volume condition. In this condition, lever 10 is not acted upon by pin 20 and therefore does not transmit a force to switch 51 or to sleeve 38. The adjustment screw 36 is pressed under the full tension of conical spring 46 in the direction of the auxiliary spring 29 and the diaphragm 25 so that the closure member 5 closes the valve seat 2. The servo control pressure therefore has its maximum value as it is shown in Figure 2 on the left side of the graph. This maximum pressure opens the main valve to its maximum permitted flow rate.As the temperature measured by temperature sensor 16 increases, so the heat expansible liquid expands causing the diaphragm capulse 17 to expand and pin 20 to move downwardly along with the left hand end of lever 10. As long as the right end of lever 10 does not engage with the bottom side of sleeve 38, the pending condition of maximum gas supply remains. During this movement, springs 71 and 30 are pressed together as shown in Figure 1. This in Figure 2 corresponds to the line left of point A. The combined spring force of springs 71 and 30 is less than that of spring 29.

At point A of the graph in Figure 2 lever 10 engages the bottom of sleeve 38, and the force generated by conical spring 46 and transmitted via threaded pin 36, spring 71, spring 30 and spring 29 to diaphragm 25 disappears since this force is taken up by lever 10. Spring 29 begins to expand against the force of spring combination 30,71 which engages end 35 of threaded pin 36. The outlet pressure P of the pressure regulator now changes along graph portion AF, and only the force of springs 71,30 and 29 determine the force acting upon diaphragm 25 and the end 35 of threaded pin 36 moves upwards further.

At point F of the graph, a condition of force balance is reached between the spring combination 71,30 on the one hand and the spring 29 on the other.

As the temperature increases further the spring combination 71,30 and the spring 29 are relieved in the same amount because threaded pin 36 moves further in upward direction. The less steep portion FB of the graph ensures that temperature changes generate smaller changes of the control pressure P and therewith generates smaller changes of the gas supply. Thus a generally uniform fuel supply can be achieved without hunting. Such a type of operation leads to more comfort and saves energy. It prevents overheating and avoids strong throttiing and subsequent reopening of the main valve. At point B of the graph, the force of spring 30 adjusted by means of adjusting screw 32, equals the force of spring 29. If the temperature increases further, threaded pin 36 disengages spring 71 so that now only the forces of springs 30 and 29 act upon diaphragm 25.Thus at point B, the beginning of the flat portion BC is reached whose value corresponds the minimum control pressure P and is predetermined by the position of adjusting screw 32. The minimum control pressure determines the minimum flow rate of the servo controlled gas valve. In this range, spring 71 has disengaged spring 30 in the area of end 35 of the adjusting pin 36.

Should the temperature T continue to increase in spite of the reduction of the gas supply to its minimum rate, the spring blade 49 fixed to the right lever arm of lever 10 will operate switch 51 at point C of the graph and thereby interrupt the current to the solenoid valve of the servo system, causing the main valve to close completely to shut off the gas supply to the main burner. This distance between points B and C can be changed by adjusting pin 36 within the internal thread of bushing 38.

Under normal conditions however, the temperature will not reach the limit according to point C, because either the heat radiation of the boiler just balances the heat supply at minimum flow rate or because the temperature decreases due to the reduced supply of heat. If the limit switch 51 had responded and if due to the cooling down of the water surrounding sensor 16, pin 20 moves upwards, switch 51 switches on the servo system after the switching differential S has been passed at point D. Thus the main burner is again ignited and in particular in the position of minimum gas flow rate.

If the temperature continues to decrease, transmission lever 10 turns in clockwise direction until threaded pin 36 under the force of the spring 46 moves the spring 71 against the projections 73 of the first adjusting spring 30. Now both springs 30 and 71 together generate a reset force on diaphragm 25.

Should the temperature continue to decrease, for instance, due to a heavy hot water demand or increased heating demand, spring blade 49 will tilt lever 10 further in clockwise direction until at point A of the curve it disengages from the bottom of sleeve 38 because this sleeve abuts with its collar 74 on the bottom of recess 44. Now again the full force of the second adjusting spring 46 is effective and the main valve is completely opened.

The control pressure P therefore moves between the maximum value and the minimum value dependent on the temperature T along a line as shown in Figure 2. The width of the modulating range M between points A and B is adjusted to the desired value by properly selecting the spring constants of springs 29 and 71. The same is true for the inclination of the two portions AF and FB. In some applications it might be desired to operate the pressure regulator with only one of the two slopes of the characteristic. This can be achieved in an easy manner in that for suppressing portion FB one adjusts the minimum pressure by means of adjusting screw 32 up to the value at F. Similarly, the portion AF may be suppressed by reducing the maximum value (by means of threaded piece 41) to the value at F. In all applications and types of adjustment, spring 29 determines the width of the modulating range.

Claims (5)

1. A pressure regulator for providing a control pressure varying in dependence upon temperature, said regulator comprising a control pressure determining valve having a valve closure member carried by a diaphragm; a lever; an expansible temperature sensor for varying the angular position of the lever in dependence upon temperature; and a plurality of springs acting together on said diaphragm to determine maximum, intermediate and minimum values for the control pressure, the lever and springs being arranged such that upon a sensed increase in temperature from a low value, the lever will act against the bias of a first spring to permit the other springs to become operative in determining a value of the control pressure below the maximum value set by the first spring, wherein a second and a third of the springs set intermediate values for the control pressure, and wherein a fourth spring acting between the first and third springs sets the minimum value forthe control pressure.

2. The pressure regulator of Claim 1, wherein said third and fourth springs are provided by two superimposed blade springs clamped at one end to a housing of the regulator and acting in a direction toward said diaphragm.

3. The pressure regulator of Claim 2, wherein the second spring is a C-shaped spring, coil or conical spring located between the diaphragm and the blade springs.

4. The pressure regulator of Claim 1, 2 or 3, wherein the first spring acts on a sleeve slidably mounted in a housing of the regulator, the sleeve carrying a member passing through a hole in the lever to engage one of said third and fourth springs, and wherein the lever is engageable with the sleeve to reduce the effect of the bias of the first spring on the remaining springs.

5. The pressure regulator of Claim 1,2,3 or 4, including means for adjusting the bias provided by the springs setting said maximum and minimum values.