GB2234044A

GB2234044A - Fluid flow control device

Info

Publication number: GB2234044A
Application number: GB9015415A
Authority: GB
Inventors: David Mervin Jones; John Keith Maund
Original assignee: ADVENTEC Ltd
Current assignee: ADVENTEC Ltd
Priority date: 1989-07-14
Filing date: 1990-07-13
Publication date: 1991-01-23
Also published as: GB9015415D0; GB8916236D0

Abstract

A fluid flow control valve has a plurality of ports (6-9) disposed in a fluid flow path (4, 5) formed in a valve body (1) and two-state valves (10B-13B) associated respectively with the ports; solenoid or hydraulic control means (10-13) are operable to change the state of the valves selectively such that each valve is in either an open or closed position, whereby fluid flow along said path is determined by the respective states of the valves. <IMAGE>

Description

FLUID FLOW CONTROL DEVICE This invention relates to a fluid flow control device, primarily for controlling gas flow, such as the flow of a combustible gas to a heater burner.

In some conventional fluid flow control devices, flow control is achieved by varying the position of a valve element relative to a seat surrounding a port, so as to vary the effective size of the port and therefore the rate of fluid flow through the port. The increasing use of computers to control systems incorporating such valves necessitates the use of complex converters to enable a computer to control the valves, but this is an expensive and not wholly satisfactory expedient.

An object of the invention is to provide a fluid flow control device which can operate satisfactorily under the control of a computer without recourse to the aforesaid complexity.

According to the invention, a fluid flow control device comprises a plurality of ports disposed in a fluid flow path formed in a valve body, two-state valves associated respectively with said ports, and control means operable to change the state of said valves selectively such that each valve is in either an open or a closed condition, whereby fluid flow along said path is determined by the respective states of the valves.

Preferably, at least some of the valves, when open, admit respectively different proportions of the maximum flow rate along said path so that a stepped flow rate control is obtained by controlling the valves in a predetermined sequence.

The valves are preferably electrically operated and are typically two-position solenoid valves.

The invention will now be described, by way of example, with reference to the accompanying drawings in which:- Figure 1 is a longitudinal cross section of one form of the flow control device of the invention, Figure 1A illustrates a detail of Figure 1 to an enlarged scale; Figure 2 illustrates diagrammatically an alternative embodiment of the flow control device of the invention incorporated into a gas supply system feeding a burner, and Figure 3 is a graph illustrating the performance of the flow control device in the system of Figure 2.

Referring to Figure 1 of the drawings, this shows one practical example of the flow control device of the invention. The device has a body 1 with a gas inlet 2 at one end thereof and a gas outlet 3 at its other end, the body forming a flow path between the inlet and outlet.

The flow path consists of a pair of parallel conduits 4, 5, between which extend ports 6 to 9. Mounted on the body, conveniently externally as illustrated are four electrical solenoid valves 10 to 13, the armatures 10A to 13A of which carry respective generally conical valve heads lOB to 13B for engagement respectively with seats surrounding the ports, as will be described in more detail hereafter.

In this particular embodiment, the individual valve seats are formed on flanged cylindrical port elements 14 of which the outer cylindrical surfaces are threaded to enable the elements to be screwed into corresponding respective internal threads in the ports 6 to 9. This arrangement enables the port elements to be readily interchanged when different gas flow characteristics through the control device are required.

As will be seen more readily from Fig lA, the internal periphery of each flange 14A forms a valve seat 14B for engagement by the respective valve head lOB - 13B in order to close the associated port. Each port element 14 defines a port 14C, the size of which determines the fluid flow rate permitted by the port element when its associated valve head is in its open position. It will be seen that the provision of four independently operable valves permits sixteen possible combinations of flow orifices to be used by switching the valves on and off in different sequences. Appropriate choice of sizes for the ports 14C makes it is possible, by suitably sequencing the valve operation, to obtain a flow rate variable in known steps which can conveniently be arranged to approximate to proportional control.

Figure 2 shows a simpler form of the control device of the invention incorporated in a gas supply system feeding a gas burner. The flow control device is illustrated at 20 and is connected into a gas supply line through which gas is supplied via a pressure regulator 21 and the control device to a gas burner 22. In this case, the control device has three solenoid valves 20A, 20B, 20C, of which the valve port orifices are represented respectively at 21A, 21B, 21C. The sizes of these orifices are chosen so that, when open, they permit the passages respectively of 1/7, 2/7, and 4/7 of the maximum available gas flow.This permits eight different combinations of open and closed valves and the following table illustrates how these combinations may be used to obtain a regular stepped variation in the flow, the symbols 0 and 1 indicating respectively the on and the off position of each valve.

VALVE 20A VALVE 20B VALVE 20C TOTAL FLOW O 0 0 0 1 0 0 1/7 0 1 0 2/7 1 1 0 3/7 0 0 1 4/7 1 0 1 5/7 0 1 1 6/7 1 1 1 7/7 The flow control obtainable by operating the flow control device according to the table is illustrated in Figure 3 which relates the flow rate to the effective combined orifice sizes of the three valves. It will be seen that a regular stepped output is obtained which can readily be varied as desired by sequenced switching of the valves. Since the valves operate in a digital manner, they may readily be controlled by a computer, either according to a pre-set programme or in response to varying external parameters, such as ambient temperature in the case of the gas burner control system illustrated.

The armature of each valve would normally be urged towards one of its conditions, as for example by spring means, and be positively urged into its alternative condition against a return force. Whether the armature is urged into its open or closed position depends for example, upon the safety requirements for the particular system employed which govern whether fluid flow through the system should stop or continue when the motive power to the control device is switched off or fails. Although the valves are described as being actuated electrically, it would be possible to perform this in alternative ways, such as hydraulically for example. It will be understood that the control device may have any convenient number of valves and different combinations of orifice sizes depending upon the practical requirements. Two or more control devices may be connected together in series or in parallel to provide additional combinations of operational ports for different flow control requirements.

Claims

1. A fluid flow control device comprising a plurality of ports disposed in a fluid flow path formed in a valve body, two-state valves associated respectively with said ports, and control means operable to change the state of said valves selectively such that each valve is in either an open or closed condition, whereby fluid flow along said path is determined by the respective states of the valves.

2. A device according to Claim 1, wherein at least some of the valves, when open, admit respectively different proportions of the maximum flow rate along said path so that a stepped flow rate is obtained by controlling the valves in a predetermined sequence.

3. A device according to Claim 1 or Claim 2, wherein each valve admits a proportion of the maximum flow rate which is different from that admitted by each other valve.

4. A device according to any one of the preceding claims, wherein the valves are electrically operated.

5. A device according to any one of the preceding claims, wherein the two valves are two-position solenoid valves.

6. A device according to any one of the preceding claims, wherein the flow path includes a pair of parallel conduits in the body which communicate by way of a plurality of ports, the conduits communicating respectively with a fluid inlet and fluid outlet of the body.

7. A fluid control device, substantially as hereinbefore described with reference to Figures 1 and 2 or Figure 3 of the accompanying drawings.

8. A gas supply system incorporating a fluid flow control device according to any one of the preceding claims.

9. A system according to Claim 8, wherein three parallel flow paths are provided, each containing one of said valves and controlling gas flow between a gas supply and a gas burner.

10. A system according to Claim 9, wherein the valves provide respectively 1/7, 2/7 and 4/7 of the total flow path.

11. A gas supply system substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.