GB1576677A

GB1576677A - Gas valve assembly

Info

Publication number: GB1576677A
Application number: GB16967/78A
Authority: GB
Original assignee: Honeywell BV
Current assignee: Honeywell BV
Priority date: 1977-05-02
Filing date: 1978-04-28
Publication date: 1980-10-15
Also published as: FR2389818B1; FR2389818A1; DE2719523C3; DE2719523A1; IT7849142A0; NL7804623A; DE2719523B2; IT1102509B; JPS53137424A; NL178726C

Description

(54) GAS VALVE ASSEMBLY (71) We, HONEYWELL B.V. a Dutch Company of Rijswitjkstraat 175, Amsterdam, Netherlands, 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 invention relates to a gas valve assembly such as is used for instance, in the supply line to a gas burner to servo control the gas pressure thereto. In one type of valve assembly the pressure of the gas under control is employed to actuate the main valve connected in the gas path, which main valve is normally closed by spring force and is opened by a starting valve. The starting valve at actuation supplies gas under the inlet pressure via a servo feed orifice to one side of a diaphragm actuating the main valve.A servo valve controlled by the output gas pressure of the assembly vents said one side of the diaphragm when a predetermined output gas pressure is reached to close the main valve. In order to be able to use a main valve with a small stroke for a control as sensitive as possible, the servo feed orifice should be small in order that the gas supply to said one side of the diaphragm remains small and the venting by the servo valve is possible with a small movement of the valve. On the other hand there is a requirement that an output gas pressure sufficient for the ignition of a burner must be established within a predetermined time of, for instance, 2 or 3 seconds, that means, a pressure sufficient for the actuating of the main valve must be reached at said one side of the diaphragm in this time interval.However, the diaphragm chamber comprises a certain volume by reasons of the diaphragm diameter and stroke necesary for actuating of the main valve, and this diameter needs to be large when the gas valve in a Class A valve must overcome a strong spring acting upon the main valve.

It has now been proven that the above described type of assembly does not allow the establishment of the pressure necessary for the ignition within the predetermined time interval. The requirement for a small servo feed orifice and the requirement for the establishment of an actuating pressure within short time are difficult to reconcile.

It is an aim of the present invention to develop a gas valve assembly which satisfied both these requirements.

According to the invention, there is provided a gas valve assembly comprising a main valve for controlling the flow of gas through the assembly; a diaphragm which when pressure is applied to one side thereof causes the main valve to open against the action of a valve closing bias member and the action of gas inlet pressure; and means for directing gas from the inlet side of the valve assembly to said one side of the diaphragm, said means including a servo feed orifice, a second valve connected in parallel with the orifice and a starting valve located downstream of said orifice and said second valve and operable to stop or allow the flow of gas to said one side of the diaphragm, said second valve gradually closing in response to gradually rising gas pressure at said one side of the diaphragm.

Two embodiments of the invention will now be described by way of example with reference to the attached drawings in which: - Figure 1 is a section through a gas valve assembly according to the invention and Figure 2 shows in section a modified part of that assembly according to the invention.

According to figure 1, a main valve 1, 2 controls the gas flow from an inlet 10 to an outlet 17. A closure member 1 of the main valve is pressed by a relatively strong spring 3 against a valve seat 2. The spring 3 is so dimensioned that the valve is able to resist a back pressure of at least 1500 mm ws (water column) and so satisfy certain requirements for valves of class A.

A diaphragm 4 acts via a pusher member 31, a double lever system 5, 6 and a pusher member 30 on the member 1 of the main valve. A chamber 29 on a side of the diaphragm remote from member 31 can be connected via an electromagnetically actuated double seat starting valve 8, 7, 9 to the outlet 17 or to the inlet 10. The double seat valve comprises a closure member 7 and two valve seats 8 and 9, the member 7 when engaging the valve seats 8 or 9 being operable to close gas channels 33 and 34 respectively which are connected to the inlet 10 and to the outlet 17, resp. A further gas channel 32 connects the chamber 29 to the double seat valve 7, 8, 9. An orifice 11, called servo feed orifice, is arranged in the gas channel 33 between the inlet 10 and the valve 7, 8 of the double seat valve. A shunt gas channel 35 removes gas from the channel 33 downstream of the orifice 11.An orifice 16, called bypass orifice, and a valve 14, 15 are arranged in series connection in the shunt gas chamnel 35. Downstream of valve 14, 15 the shunt gas channel 35 ports into part of gas channel 33 downstream of orifice 11.

A closure member 14 of valve 14, 15 is secured to a diaphragm 12, and a spring 13 arranged at the other side of the diaphragm biases member 14 toward valve seat 15.

Spring 13 is arranged in a chamber 39 which is vented via a throttle 40 to the atmosphere. The force of the spring 13 is adjustable.

A gradual venting of chamber 29 is achieved by a servo valve 21, 22 working as a pressure controller. An outlet passage 36 in communication with chamber 29 forms a valve seat 22 co-operating with a closure member 21 secured to a diaphragm 19 which normally presses the member 21 against the valve seat 22 by means of a spring 20. On the other side of the diaphragm, the pressure at the outlet 17 acts over a gas channel 37 against spring 20. The outlet 17 communicates with the diaphragm 19 via an opening 18, a chamber 38 comprising the interconnected lever system 5, 6 and the gas channel 37.

According to figure 2 a modification is proposed in which a spring 26 presses via a diaphragm 25 a closure member 24 against a valve seat 23 in the shunt gas channel 35 and in which the spring 26 is arranged in a chamber 28 which is connected by a throttle 27 to a gas channel 32 leading to the chamber 29.

Operation of the valve assembly of Figure 1 will now be described. First it may be assumed that there is input pressure at the inlet 10 and the main valve 1, 2 is closed by the force of spring 3. The double seat starting valve 7, 8, 9 occupies the position shown in figure 1 in which the closing body 7 closes the gas channel 33 at the valve seat 8. The chamber 29 is vented into chamber 38 via the gas channel 32, the opened valve 7, 9 and the gas channel 34, whereby the pressure in chamber 29 assumes that prevailing at the outlet 17. Since the main valve 1, 2 has closed, the pressure at the outlet 17 substantially zero. The input pressure at the inlet 10 rises in the gas channel 33 and the shunt gas channel 35 over the servo feed orifice 11 and the bypass orifice 16. The input pressure prevailing at diaphragm 12 keeps valve 14, 15 closed against the force of the spring 13.

The servo valve 21, 22 also closes the outlet opening 36 of the chamber 29 because there is no outlet pressure on the diaphragm 19 and therefore no force is exerted counteracting that of spring 20.

If now a burner connected to the outlet 17 is to be supplied with gas, then the double seat starting valve 7, 8, 9 is electromagnetically actuated, whereby it takes a position opposite to the shown position in which the member 7 is in contact with the valve seat 9. The pressure in the gas channel 33; and in the shunt gas channel 35 downstream of the orifice 11, drops to the pressure in chamber 29. This pressure is practically zero. Therefore the spring 13 can move the diaphragm 12 and also the member 14 to open the valve 14, 15. In addition to the relatively small quantity of gas flowing through the servo feed orifice 11, a larger quantity of gas flows through the enlarged bypass nozzle 16 and the valve 14, 15 through the opened electromagnetic valve 7, 8 into chamber 29. Accordingly the chamber 29 is relatively quickly filled with gas from the inlet 10 so that the diaphragm 4 through the pusher members 30, 31 and the interconnected lever system 5, 6 moves the member 1 of the main valve against the force of the spring 3. A pressure is thereby built up at the outlet 17.

At the same time, the rising pressure in chamber 29 which acts on the diaphragm 12 causes closing of the valve 14, 15 at a certain pressure value adjusted in advance.

Now the servo feed orifice 11 alone is responsible for the supply of gas to the chamber 29. The rising pressure at the outlet 17 and in the chamber 38 acts on the other side of the diaphragm 4. Further this pressure at the outlet, via the gas channel 37, acts on the under-side of the diaphragm 19 so that at a certain level of output pressure adjusted in advance, the diaphragm 19 moves the member 21 away from the valve seat 22 against the force of the spring 20 whereupon the chamber 29 is gradually vented to the outlet. The pressure arising in the chamber 29 and at the outlet 17 therefore is determined by the force of the spring 20. The springs 13 and 20 acting on the diaphragms 12 and 19 are arranged in chambers which are vented via venting openings to atmosphere.The diameter of these venting openings is chosen such that in the event of diaphragm breakage, the gas leakage is not extraordinarily high. If the burner is to be disconnected from the gas supply the double seat starting valve 7,8,9 is de-energised whereupon the closure member again assumes the position shown in figure 1. The chamber 29 is thereby momentarily vented to the outlet 17 so that the spring 3 shuts the main valve 1,2. The higher pressure from the inlet 10 now prevailing at diaphragm 12 further keeps the valve 14,15 closed. The valve 14, 15 is only opened when double seat starting valve 7,8,9 is actuated and when low pressure is present in the chamber 29. The valve 14,15 may be regarded as performing a "derivative action" since it fully opens in response to initial opening of valve 7 (step function input) and gradually closes with increasing pressure in chamber 29.

According to the embodiment of figure 2, with valve 7,8,9 in the position shown, the pressure arising from the inlet 10 acts on the diaphragm 25 and moves the member 24 away from the valve 23 against the force of the spring 26. The air in chamber 28 is thereby vented via the throttle 27 into the gas channel 32. If now the starting valve 7,8,9 is energized, the pressure downstream of the servo feed orifice 11 momentarily drops; however the valve 23,24 is unable to close momentarily because the gas is allowed to flow only slowly into the chamber 28 via the throttle 27. Therefore, initially an additional gas flow is added via. the enlarged bypass nozzle 15 to the gas flow flowing through the servo feed orifice so that the chamber connected to the gas channel 32 is relatively quickly brought to a pressure sufficient for the actuating of the main valve.After a certain time delay, the valve 23,24 closes and the servo feed orifice 11 alone is responsible for the gas supply. In relation to the total gas flow the gradually closing valve 23,24 also has the function of a member with derivative action.

WHAT WE CLAIM IS: 1. A gas valve assembly comprising a main valve for controlling the flow of gas through the assembly; a diaphragm which when pressure is applied to one side thereof causes the main valve to open against the action of a valve closing bias member and the action of gas inlet pressure; and means for directing gas from the inlet side of the valve assembly to said one side of the diaphragm, said means including a servo feed orifice, a second valve connected in parallel with the orifice and a starting valve located downstream of said orifice and said second valve and operable to stop or allow the flow of gas to said one side of the diaphragm, said second valve gradually closing in response to gradually rising gas pressure at said one side of the diaphragm.

2. The assembly of claim 1, wherein the second valve is initially closed by the gas inlet pressure and is opened when the starting valve is actuated.

3. The assembly of claim 1, wherein the second valve is initially open by gas inlet pressure and is closed with a certain time delay after the starting valve is actuated.

4. The assembly of any one of the preceding claims including a bypass orifice in series with the second valve.

5. The assembly of claim 4, wherein the bypass orifice has a cross-sectional area larger than that of the servo feed orifice.

6. The assembly of claim 4 or 5 as appendant to claim 1, 2 or 3 wherein the bypass orifice is upstream of the second valve.

7. The assembly of claim 2, wherein the second valve is biased in an opening direction by a spring biased diaphragm, the spring side of the diaphragm being vented to atmosphere via a throttle.

8. The assembly of claim 3, wherein the second valve is biased in a closing direction by a spring biased diaphragm, the spring side of the diaphragm being connected to said one side of the first mentioned diaphragm via a throttle.

9. The assembly of any one of the preceding claims, comprising a double lever arrangement for providing an opening force to the main valve from the first mentioned diaphragm.

10. The assembly of any one of the preceding claims, including a servo valve for venting said one side of the first mentioned diaphragm, said servo valve being controlled by gas pressure at the outlet of the assembly.

11. A gas valve assembly substantially as hereby described with reference to Figures 1 or 2 of the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. moves the member 21 away from the valve seat 22 against the force of the spring 20 whereupon the chamber 29 is gradually vented to the outlet. The pressure arising in the chamber 29 and at the outlet 17 therefore is determined by the force of the spring 20. The springs 13 and 20 acting on the diaphragms 12 and 19 are arranged in chambers which are vented via venting openings to atmosphere. The diameter of these venting openings is chosen such that in the event of diaphragm breakage, the gas leakage is not extraordinarily high. If the burner is to be disconnected from the gas supply the double seat starting valve 7,8,9 is de-energised whereupon the closure member again assumes the position shown in figure 1.The chamber 29 is thereby momentarily vented to the outlet 17 so that the spring 3 shuts the main valve 1,2. The higher pressure from the inlet 10 now prevailing at diaphragm 12 further keeps the valve 14,15 closed. The valve 14, 15 is only opened when double seat starting valve 7,8,9 is actuated and when low pressure is present in the chamber 29. The valve 14,15 may be regarded as performing a "derivative action" since it fully opens in response to initial opening of valve 7 (step function input) and gradually closes with increasing pressure in chamber 29. According to the embodiment of figure 2, with valve 7,8,9 in the position shown, the pressure arising from the inlet 10 acts on the diaphragm 25 and moves the member 24 away from the valve 23 against the force of the spring 26. The air in chamber 28 is thereby vented via the throttle 27 into the gas channel 32. If now the starting valve 7,8,9 is energized, the pressure downstream of the servo feed orifice 11 momentarily drops; however the valve 23,24 is unable to close momentarily because the gas is allowed to flow only slowly into the chamber 28 via the throttle 27. Therefore, initially an additional gas flow is added via. the enlarged bypass nozzle 15 to the gas flow flowing through the servo feed orifice so that the chamber connected to the gas channel 32 is relatively quickly brought to a pressure sufficient for the actuating of the main valve.After a certain time delay, the valve 23,24 closes and the servo feed orifice 11 alone is responsible for the gas supply. In relation to the total gas flow the gradually closing valve 23,24 also has the function of a member with derivative action. WHAT WE CLAIM IS:

1. A gas valve assembly comprising a main valve for controlling the flow of gas through the assembly; a diaphragm which when pressure is applied to one side thereof causes the main valve to open against the action of a valve closing bias member and the action of gas inlet pressure; and means for directing gas from the inlet side of the valve assembly to said one side of the diaphragm, said means including a servo feed orifice, a second valve connected in parallel with the orifice and a starting valve located downstream of said orifice and said second valve and operable to stop or allow the flow of gas to said one side of the diaphragm, said second valve gradually closing in response to gradually rising gas pressure at said one side of the diaphragm.