GB2140128A - Gas valve - Google Patents

Abstract

A gas valve 1 for a gas oven includes a conduit 8 for the passage of gas to the oven burner. The conduit 8 has a narrowing section defined by magnetic pole pieces 9 and 10, and a permanent magnet 11 is provided to generate a magnetic field across the gap between the pole pieces 9 and 10, constraining a ferrofluid 12 to prevent the passage of gas through conduit 8. To activate the valve 1, to permit passage of gas through the conduit 8, currents are passed through coils 13 and 14, which together urge the ferrofluid 12 out of the gap between pole pieces 9 and 10 and towards a pole piece 15. When the flow of currents in both coils 13 and 14 cease, the ferrofluid 12 returns to the gap between pole pieces 9 and 10. <IMAGE>

Description

SPECIFICATION Gas valve The present invention relates to a gas valve which can be controlled electrically, and particularly but not exclusively a gas valve for use in a gas appliance.

An existing gas valve which can be electrically controlled has a butyl rubber (or similar material) diaphragm able to close off an aperture. Such a construction requires accurate seating of the diaphragm and this can be difficult, particularly if the size of the valve itself is small. Moreover, this valve has only two modes, "off" and "on" mode. Also the valve may produce a clicking noise when switching between these modes.

Some objects of the present invention are to provide an electrically-controllable gas valve, of simple construction and low cost and with a low power requirement.

The present invention provides a gas valve comprising a chamber with a conduit for the passage of gas, a permanent magnet circuit arranged around a section of the conduit normally to hold ferromagnetic liquid in a first position within the valve, and magnetic means to maintain selectively the ferromagnetic liquid in a second position within the valve, whereby the ferromagnetic liquid, when in one of the positions, prevents the flow of gas through the valve and when in the other position permits the flow of gas therethrough.

Preferably, when in the first position, the ferromagnetic liquid prevents the flow of gas and when in the second position permits the flow of gas.

Preferably the magnetic means is a magnetic circuit formed of one or more electric coils arranged to interact with the magnetic effect of the permanent magnet circuit.

If the magnetic means opposes the permanent magnet circuit, then preferably the magnetic strength of the former exceeds the latter.

The valve may have a variable output rather than merely an "off" mode and an "on" mode. Preferably, the conduit is shaped, in the region occupied by the ferromagnetic liquid when in the "flow-prevention" position, to provide substantially linearly variable output-to-coil-current characteristics; this may be achieved by having, in that region, a trapezoi dal discharge orifice for the fluid.

Alternatively, the conduit may have a discharge orifice, in that region, having a rectangular section and a trapezoidal section; thus the valve can be provided with response characteristics which are linearly variable only at some values of applied coil current. This may be particularly advantageous for the control of certain appliances.

In one form of the invention, the valve includes a reservoir to accommodate the ferromagnetic liquid when in the "flow-permitting' 'position; this may contribute to overcoming any risk of loss of ferromagnetic liquid due to spitting.

A number of valves embodying the present invention may be arranged in parallel to control a burner in a gas appliance whereby the burner can be operated by feeding suitable digital logic signals to one or more of the valves.

Preferably, the ferromagnetic liquid is a ferrofluid formed of a colloid in which minute ferromagnetic particles are suspended in a liquid carrier.

In order that the invention may more readily be understood, a description is now given, by way of example only, reference being made to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a gas valve embodying the present invention; Figure 2 is a view in the direction of arrows Il-Il of Fig. 1; Figure 3 is a graph of the output flow against coil current characteristics for a gap profile as shown in Fig. 2; and Figure 4 is a cross-sectional view of another gas valve embodying the present invention.

A gas valve 1 for the oven of a gas cooker has a housing formed by three interconnected arms 2, 3 and 4 (of magnetic mild steel) interspersed with sections 5, 6 and 7 of nonmagnetic material. A conduit 8 extends through the valve 1 for the passage of gas to the oven burner. There is narrowing in one section of conduit 8 caused by broadening of the ends of arms 2 and 3 to form pole pieces 9 and 10. A permanent magnet 11 of barium ferrite is located equidistant from pole pieces 9 and 10 and between the arms 2 and 3.

Thus a magnetic field exists across the gap separating poles 9 and 10 to maintain there a quantity of ferrofluid 1 2 which thereby blocks off conduit 8 from the passage of gas.

To activate valve 1 to permit flow of gas to the oven burner, one current is passed through a coil 1 3 on arm 2 in a direction to produce a magnetic field in opposition to that of permanent magnet 11 and another current is passed through a coil 14 in arm 4 to augment the magnetic field there due to permanent magnet 11. Thus both of these currents contribute towards urging the ferrofluid 1 2 out of the gap between pole pieces 9 and 10 and towards a pole piece 1 5 on the end of arm 4. When the flow of currents in both coils 1 3 and 14 cease, the magnetic field due to permanent magnet 11 alone acts on ferrofluid 1 2 which thus returns to the gap between pole pieces 9 and 1 0.

As can be seen from Fig. 2, the gap between pole pieces 9 and 10 has a section with inclined major faces (which section procedures a linear relationship between gas output and coil current) and a section with parallel major faces (which section produces a nonlinear relationship). The characteristics curve of gas output against core current for such a gap profile is shown in Fig. 3. This form of control characteristic is particularly suited to a gas valve for an oven burner where it is preferred to have good adjustment control at low output levels while the overall range of levels desired is quite wide.

The characteristic curve shown in Fig. 3 of the gap is for a given constant gas pressure. If the gas pressure has a higher constant value, then the corresponding curve is of the same shape but shifted towards the y-axis.

Fig. 4 shows another gas valve 1 6 which is more compact than valve 1 and has a conduit 1 7 for the passage of gas with a gap 1 8 which is blocked by ferrofluid 1 9 when the valve is in the "flow-prevention" mode. A reservoir 20, leading off from conduit 1 7 at the gap 18, accommodates the ferrofluid 1 9 when the valve is in the "flow-permitted" mode. This reservoir 20 also communicates with conduit 1 7 further downstream, at point A. Thus, if during switching of the valve 1 6 between modes, some ferrofluid is urged by then gas flow down conduit 1 7 instead of directly into reservoir 20, the ferro-fluid falls back into reservoir 20 once it reaches point A.

Thus loss of ferrofluid due to spitting is avoided. Otherwise, valve 16 operates in the same way as valve 1 and has a corresponding permanent magnet 21 to maintain normally the ferrofluid in the ''flow-prevention'' mode and current coils 22 and 23 which are only operated when gas flow is intended.

Each of the constructions produces a gas valve of low cost with no solid moving parts resulting in no wear on components and silent operation; moreover each valve needs only low power for operation and can be controlled directly electrically (eg. by digitai logic signals).

Claims (11)

1. A gas valve comprising a chamber with a conduit for the passage of gas, a permanent magnet circuit arranged around a section of the conduit to hold ferromagnetic fluid in a first position within the valve, and selectively energisable magnetic means for urging the ferromagnetic fluid towards a second position within the valve, whereby the ferromagnetic fluid, when in one of the said positions, prevents the passage of gas through the valve and, when in the other of said positions, permits the passage of gas therethrough.

2. A gas valve as claimed in claim 1 wherein said ferromagnetic fluid prevents the passage of gas when in said first position and permits the passage of gas when in said second position.

3. A gas valve as claimed in Claim 1 or 2 wherein said magnetic means consists of a magnetic circuit including one or more electrical coils arranged to interact with the magnetic effect generated by said permanent magnetic circuit.

4. A gas valve as claimed in Claim 3 wherein said magnetic means opposes the magnetic effect generated by said permanent magnet circuit, the magnetic strength of said magnetic means exceeding the magnetic strength of said permanent magnet circuit.

5. A gas valve as claimed in any preceding claim wherein said conduit is shaped, in the region occupied by said ferromagnetic fluid when in said position for preventing the passage of gas, to provide a substantially linearly variable relationship between gas output and applied current through said magnetic means.

6. A gas valve as claimed in Claim 5 wherein said conduit is shaped in said region to provide a trapezoidal discharge orifice for said ferromagnetic fluid.

7. A gas valve as claimed in Claim 5 wherein said conduit is shaped in said region to provide a substantially rectangular section and a substantially trapezoidal section to provide said substantially linearly variable relationship at a limited number of values of said applied current.

8. A gas valve as claimed in any preceding claim and including a reservoir for accommodating said ferromagnetic fluid when in said position for permitting the passage of gas.

9. A gas valve as claimed in any preceding claim wherein said ferromagnetic fluid is a ferrofluid formed of a colloid comprising a liquid carrier having ferromagnetic particles suspended therein.

1 0. A gas valve substantially as herein described with reference to Figs. 1, 2 and 3 or Fig. 4 of the accompanying drawings.

11. A gas burner for a gas appliance incorporating one or more gas valves, as claimed in any preceding claim.