Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
PILOT CONTROLLED ELECTROMAGNETIC VALVE WITH AUXILIARY PISTON
Document Type and Number:
WIPO Patent Application WO/2019/115828
Kind Code:
A1
Abstract:
An electromagnetic valve (4) for a fluid, comprises a body (18) with a fluid inlet (22), a fluid outlet (24); a shut-off device comprising a main seat (20) in the passage; a main closure element (12) mobile in longitudinal direction, with a front face (12.1) cooperating with the main seat (20) and with a channel (12.3) fluidly interconnecting the front face (12.1) and an opposed rear face; a pilot closure element (14) cooperating with a pilot seat (26) on the main closure element (12); and a piston (44) at the centre of the front face (12.1), configured for cooperating with the main seat (20) so as to form with the front face (12.1) in contact with the main seat (20) a cavity (48) fluidly connected to the channel (12.3), a building up of an inlet fluid pressure in said cavity (48) biasing the main closure element (12) away from the main seat (20).

Inventors:
SELLEN, Stephan (Zum Sägewerk 1, Wehingen, 66693, DE)
SCHMITZ, Philippe (18 rue des Etangs, 7303 Steinsel, 7303 Steinsel, 7303, LU)
Application Number:
EP2018/085277
Publication Date:
June 20, 2019
Filing Date:
December 17, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
LUXEMBOURG PATENT COMPANY S.A. (24 route de Diekirch, 7440 Lintgen, 7440 Lintgen, 7440, LU)
International Classes:
F02M21/02; F16K31/06; F16K39/02
Domestic Patent References:
WO2016180737A12016-11-17
WO2015149039A22015-10-01
WO2012003953A12012-01-12
WO2016180737A12016-11-17
Foreign References:
DE102007002432B32008-06-19
US20140042352A12014-02-13
US20140166915A12014-06-19
Attorney, Agent or Firm:
LECOMTE & PARTNERS (76-78, rue de Merl, 2146 Luxembourg, 1016, LU)
Download PDF:
Claims:
Claims

1. Electromagnetic valve (2, 4) for a fluid, comprising:

- a body (18) with a fluid inlet (22), a fluid outlet (24), and a passage fluidly interconnecting said inlet and said outlet;

- a shut-off device comprising

o a main seat (20) in the passage;

o a main closure element (12) mobile in longitudinal direction, with a front face (12.1) cooperating with the main seat (20) and with a channel (12.3) fluidly interconnecting the front face (12.1) and an opposed rear face;

o a pilot closure element (14) cooperating with a pilot seat (26) on the rear face of the main closure element (12);

- an electromagnet (10) configured for actuating the pilot closure element (14) relative to the pilot seat (26);

characterized in that the shut-off device further comprises

- a piston (44) at the centre of the front face (12.1), configured for cooperating with the main seat (20) so as to form with the front face (12.1) in contact with the main seat (20) a cavity (48) fluidly connected to the channel (12.3), a building up of an inlet fluid pressure in said cavity (48) biasing the main closure element (12) away from the main seat (20).

2. Electromagnetic valve (2, 4) according to claim 1 , wherein the main closure element (12) comprises a gasket (12.2) on the front face (12.1), said gasket being designed for sealingly cooperating with the main seat (20) when said front face (12.1) is in contact with said seat (20).

3. Electromagnetic valve (2, 4) according to claim 2, wherein the gasket (12.2) is distant from the piston (44) along the front face (12.1).

4. Electromagnetic valve (2, 4) according to one of claims 2 and 3, wherein the front face (12.1) of the main closure element (12) and the main seat (20) show a tapered profile, the gasket (12.2) being located on said profile of said front face (12.1) where the diameter is maximum.

5. Electromagnetic valve (2, 4) according to any one of claims 1 to 4, wherein the piston (44) is slidable with a limited stroke relative to the main closure element (12).

6. Electromagnetic valve (2, 4) according to claim 5, wherein the main closure element (12) has a stroke that is larger than the limited stroke of the piston (44).

7. Electromagnetic valve (2, 4) according to any one of claims 5 and 6, wherein the piston (44) is anchored to the main closure element (12) by a pin (46) extending transversally through said main closure element (12) and an oblong hole in said piston (44).

8. Electromagnetic valve (2, 4) according to any one of claims 1 to 4 and according to claim 7, wherein the gasket (12.2) is housed and vulcanised in a gas tight manner in a circular groove on the main closure element (12), the pin (46) being housed in two radially opposed holes formed in a bottom of said groove.

9. Electromagnetic valve (2, 4) according to any one of claims 1 to 8, wherein the piston (44) comprises a through hole (44.3) fluidly interconnecting a front face and a rear face of said piston (44).

10. Electromagnetic valve (2, 4) according to any one of claims 1 to 9, wherein the piston (44) comprises a front portion (44.1 ) configured for cooperating with the main seat (20) and an elongate portion (44.2) extending from the front portion (44.1 ) into a bore formed in the main closure element (12).

1 1. Electromagnetic valve (2, 4) according to any one of claims 1 to 10, wherein the pilot seat (26) is formed in an element (26) that is inserted into a bore formed in the rear face of the main closure element (12).

12. Electromagnetic valve (2, 4) according to claim 1 1 , wherein the main closure element (12) is made of metallic material, the element (26) forming the pilot seat being made of a material that is softer than the material of the main closure element (12).

13. Electromagnetic valve (2, 4) according to one of claims 11 and 12, wherein the element (26) forming the pilot seat shows a conical front face and a generally cylindrical outer surface with at least one circular lip.

14. Electromagnetic valve (2, 4) according to any one of claims 11 to 13, wherein the element (26) forming the pilot seat shows a rear face (26.1) with a through hole (26.2) and a conical surface (26.3) around said hole and for contacting, in operation, the pilot closure element (14).

15. Electromagnetic valve (2, 4) according to claim 9 and according to any one of claims 11 to 14, wherein the element (26) forming the pilot seat provides a through hole (26.2) with a minimum cross-section that is larger than the maximum cross-section of the through-hole (44.3) of the piston (44).

16. Electromagnetic valve (2, 4) according to any one of claims 1 to 15, wherein the pilot closure element (14) is housed in the main closure element (12) and mechanically to a sleeve-shaped electromagnetic core (16) surrounding the main closure element (12).

17. Electromagnetic valve (2, 4) according to claim 16, wherein the pilot closure element (14) is linked to the electromagnetic core (16) by means of a pin (32) extending radially through holes the core (16), oblong openings in the main closure element (12) and a hole in the pilot closure element (14).

18. Electromagnetic valve (2, 4) according to one of claims 16 and 17, wherein the electromagnetic core (16) comprises a front portion (16.1) axially overlapping a ring portion (20) of the body (18) forming the main seat (20).

19. Electromagnetic valve (2, 4) according to any one of claims 16 to 18, further comprising an electromagnetic counter-core (30) attached to the main closure element (12) and forming a first air gap (28) with the core (16).

20. Electromagnetic valve (2, 4) according to claim 19, wherein the core (16) is located axially between the main seat (20) and the counter-core (30).

21. Electromagnetic valve (2, 4) according to one of claims 19 and 20, further comprising an electromagnetic armature (8.2, 34, 42) with a bottom (34) forming a second air gap (40) with the counter-core (30).

22. Electromagnetic valve (2, 4) according to claim 21 , wherein the bottom (34) of the armature (8.2, 34, 42) and the counter-core (30) are shaped so as to engage each other in the presence of the second air-gap (40).

23. Electromagnetic valve (2, 4) according to claim 22, wherein one of the bottom (34) of the armature (8.2, 34, 42) and of the counter-core (30) comprises a circular protrusion (30.2) engaging a corresponding groove or shoulder portion on the other one of said bottom and counter-bore.

24. Electromagnetic valve (2, 4) according to any one of claims 16 to 23, further comprising a sleeve (8.1 ) slidably housing the core (16) and counter-core (30) and fixedly housing the bottom (34) of the armature (8.2, 34, 42).

25. Electromagnetic valve (2, 4) according to any one of claims 1 to 24, further comprising a spring (38) resiliently urging the pilot closure element (14) against the pilot seat (20).

26. Electromagnetic valve (2, 4) according to any one of claims 19-22 and according to claim 25, wherein the spring (38) is a first spring resting on the main closure element (12), the valve comprising a second spring (36) resting on the bottom (34) of the armature (8.2, 34, 42) and on the counter-core (30) and resiliently urging the main closure element (12) towards the main seat (20).

Description:
Description

PILOT CONTROLLED ELECTROMAGNETIC VALVE WITH AUXILIARY PISTON

Technical field

[0001] The invention is directed to the field of valves, more specifically the field of valves for compressed gas and the field of electromagnetic valves. More specifically, the invention is directed to a pilot operated electromagnetic valve for high pressure gases, e.g. compressed natural gas (CNG) and compressed hydrogen gas at pressures of up to 70 MPa.

Background art

[0002] Prior art patent document published WO 2016/180737 A1 discloses an electromagnetic valve for high pressure gases like compressed natural gas (CNG) and compressed hydrogen where the valve is operated by a pilot. The valve comprises a main valve member with a front face cooperating with a main seat, and with a pilot passage for the gas extending between the front face of said member and a pilot seat on a rear face thereof. The pilot valve member cooperates with the pilot seat on the rear face of the main valve member so as to close the pilot passage. The pilot valve member comprises a core that forms an air-gap with a counter-core rigidly fixed with the main valve member. Upon energization of a solenoid, the core is magnetically attracted towards the counter-core and the pilot valve member moves away from the pilot seat so as to open the pilot passage. The inlet pressure of the gas builds up on at the outlet so that the main valve member can move away from the seat so as to open the valve.

[0003] Upon opening of the pilot passage, under certain circumstances the main valve member can remain stuck to the main seat despite the building up of pressure at the outlet side and despite the magnetic attractive force generated by the energized coil, leading to non-opening or a late-opening of the valve.

[0004] Prior art patent document published US 2014/0042352 A1 discloses an electromagnetic valve for high pressure gases like compressed natural gas (CNG) and compressed hydrogen. The valve comprises also a main valve member cooperating with a main seat. The valve comprises also a pilot valve member that is however slidably anchored to the main valve member so that upon energization of the coil, the pilot valve member opens a pilot passage through the main valve member and once the pressure at the inlet of the valve has built-up at the outlet, the magnetic force exerted on the pilot valve member is sufficient for moving the main valve member away from the main seat so as to open the valve.

[0005] Prior art patent document published US 2014/0166915 A1 discloses an electromagnetic valve for high pressure gases like compressed natural gas (CNG) and compressed hydrogen, similar to the preceding valve. The valve comprises a main valve member with a pilot passage and a pilot valve member that is slidably anchored to the main valve member. Upon energization of the coil, the pilot valve member opens the pilot passage through the main valve member and once the pressure at the inlet of the valve has built-up at the outlet, the magnetic force exerted on the pilot valve member is sufficient for moving the main valve member away from the main seat so as to open the valve.

[0006] Similarly to the above first prior art teaching, upon opening of the pilot passage, under certain circumstances, the main valve member can remain stuck to the main seat leading to non-opening or late-opening of the valve. To avoid that, the solenoid can be dimensioned such as to create a higher magnetic field. This leads however to an increase of the power consumption, of the weight of the valve and of the manufacturing costs.

Summary of invention

Technical Problem

[0007] The invention has for technical problem to provide a pilot operated electromagnetic valve, in particular for compressed gas like compressed natural gas (CNG) and compressed hydrogen, that overcomes at least one of the drawbacks of the above cited prior art. More specifically, the invention has for technical problem to provide a pilot operated electromagnetic valve that avoids the main valve member to remain stuck on the main seat, i.e. which provides a higher security with regard to opening while requiring a limited electrical power consumption.

Technical solution [0008] The invention is directed to an electromagnetic valve for a fluid, comprising: a body with a fluid inlet, a fluid outlet, and a passage fluidly interconnecting said inlet and said outlet; a shut-off device comprising a main seat in the passage; a main closure element mobile in longitudinal direction, with a front face cooperating with the main seat and with a channel fluidly interconnecting the front face and an opposed rear face; a pilot closure element cooperating with a pilot seat on the rear face of the main closure element; an electromagnet configured for actuating the pilot closure element relative to the pilot seat; wherein the shut-off device further comprises a piston at the centre of the front face, configured for cooperating with the main seat so as to form with the front face in contact with the main seat a cavity fluidly connected to the channel, a building up of an inlet fluid pressure in said cavity biasing the main closure element away from the main seat.

[0009] According to a preferred embodiment, the main closure element comprises a gasket on the front face, said gasket being designed for sealingly cooperating with the main seat when said front face is in contact with said seat.

[0010] According to a preferred embodiment, the gasket is distant from the piston along the front face. The cavity spans along that distance.

[0011] According to a preferred embodiment, the front face of the main closure element and the main seat show a tapered profile, the gasket being located on said profile of said front face where the diameter is maximum.

[0012] According to a preferred embodiment, the piston is slidable with a limited stroke relative to the main closure element.

[0013] According to a preferred embodiment, the main closure element has a stroke that is larger than the limited stroke of the piston. The limited stroke of the piston relative to the main closure element is less than 50%, preferably less than 30%, of the stroke of the main closure element.

[0014] According to a preferred embodiment, the piston is anchored to the main closure element by a pin extending transversally through said main closure element and an oblong hole in said piston.

[0015] According to a preferred embodiment, the gasket in housed and vulcanised in a gas tight manner in a circular groove on the main closure element, the pin being housed in two radially opposed holes formed in a bottom of the said groove.

[0016] According to a preferred embodiment, the piston comprises a through hole fluidly interconnecting a front face and a rear face of said piston.

[0017] According to a preferred embodiment, the piston comprises a front portion configured for cooperating with the main seat and an elongate portion extending from the front portion into a bore formed in the main closure element.

[0018] According to a preferred embodiment, the pilot seat is formed in an element that is inserted into a bore formed in the rear face of the main closure element.

[0019] According to a preferred embodiment, the main closure element is made of metallic material, the element forming the pilot seat being made of a material that is softer than the material of the main closure element. The material of the element forming the pilot seat is advantageously not metallic.

[0020] According to a preferred embodiment, the element forming the pilot seat shows a conical front face and a generally cylindrical outer surface with at least one circular lip.

[0021] According to a preferred embodiment, the element forming the pilot seat shows a rear face with a through hole and a conical surface around said hole and for contacting, in operation, the pilot closure element.

[0022] According to a preferred embodiment, the element forming the pilot seat provides a through-hole with a minimum cross-section that is larger than the maximum cross-section of the through-hole of the piston. Advantageously, the through-hole of the element forming the pilot seat and the through-hole of the piston are circular and the through-hole of the element shows a minimum diameter that is larger than the maximum diameter of the through- hole of the piston, preferably larger than 120% of the maximum diameter of the through-hole of the piston.

[0023] According to a preferred embodiment, the pilot closure element is housed in the main closure element and mechanically to a sleeve-shaped electromagnetic core surrounding the main closure element. [0024] According to a preferred embodiment, the pilot closure element is linked to the electromagnetic core by means of a pin extending radially through holes the core, oblong openings in the main closure element and a hole in the pilot closure element.

[0025] According to a preferred embodiment, the electromagnetic core comprises a front portion axially overlapping a ring portion of the body forming the main seat.

[0026] According to a preferred embodiment, the electromagnetic valve further comprises an electromagnetic counter-core attached to the main closure element and forming a first air gap with the core.

[0027] According to a preferred embodiment, the core is located axially between the main seat and the counter-core.

[0028] According to a preferred embodiment, the electromagnetic valve further comprises an electromagnetic armature with a bottom forming a second air gap with the counter-core.

[0029] According to a preferred embodiment, the bottom of the armature and the counter-core are shaped so as to engage each other in the presence of the second air-gap. The engagement is present along the whole stroke of the main closure element.

[0030] According to a preferred embodiment, one of the bottom of the armature and of the counter-core comprises a circular protrusion engaging a corresponding groove or shoulder portion on the other one of said bottom and counter-bore.

[0031] According to a preferred embodiment, the electromagnetic valve further comprises a sleeve slidably housing the core and counter-core and fixedly housing the bottom of the armature.

[0032] According to a preferred embodiment, the electromagnetic valve further comprises a spring resiliently urging the pilot closure element against the pilot seat.

[0033] According to a preferred embodiment, the spring is a first spring resting on the main closure element, the valve comprising a second spring resting on the bottom of the armature and on the counter-core and resiliently urging the main closure element towards the main seat. Advantages of the invention

[0034] The invention is particularly interesting in that it facilitates the opening of the valve. Indeed, for application with high pressures such as above 50 MPa and even up to 70 MPa, the forces resulting from the gas pressure on the movable elements of a valve become high. In these circumstances, in the closed position, the main closure element can become stuck on the main seat. In addition, when the pilot closure element opens, the pressure at the outlet does not necessary build up immediately, leading to an important pressure difference between the inlet and outlet faces of the closure element. The presence of the piston according to the invention is particularly interesting because it specifically provides a counter force precisely at the beginning of the opening process, thereby alleviating the above drawbacks.

Brief description of the drawings

[0035] Figure 1 is a sectional view of an electromagnetic valve according to the invention.

[0036] Figure 2 is a sectional view of the operating part of the valve of figure 1 , the valve being in a closed position.

[0037] Figure 3 is a sectional view of the operating part of the valve of figure 2, similar to figure 1 , in an intermediate position before opening.

[0038] Figure 4 is a sectional view of the operating part of the valve of figure 1 , similar to figures 2 and 3, in a fully opening position.

Description of an embodiment

[0039] Figure 1 depicts with a sectional view an electromagnetic valve according to the invention. The valve 2 comprises an operating part 4 and a connector 6 attached thereto. The operating part 4 comprises essentially a sleeve- shaped body 8 receiving a coil or solenoid 10 and housing a main closure element 12, a pilot valve element 14 and magnetic core 16 attached to the pilot valve member 14.

[0040] Figure 2 to 4 illustrate the operating part 4 of the valve 2 in three different states, namely in the closed state (figure 2), in an intermediate state before opening (figure 3) and in a fully opened state (figure 4). [0041] With reference to figure 2, the valve body 8 comprises a first sleeve 8.1 and a second sleeve 8.2 mounted there over. The first sleeve 8.1 comprises a shoulder portion 8.1.1 and the second sleeve 8.2 comprises a first portion

8.2.1 also with a shoulder that abuts against the shoulder portion 8.1.1 of the first sleeve when the second sleeve 8.2 is slid over the first sleeve 8.1. The second sleeve 8.2 comprises a second portion 8.2.2 that forms with the first sleeve 8.1 an annular cavity that extends longitudinally, said cavity housing the coil 10. The second sleeve 8.2 can comprise on its outer surface, advantageously at the level of the first potion 8.2.1 , an outer thread 8.2.3 for engaging with an inner thread of body 18 on which the valve is mounted. The portions 8.1.1 and 8.2.1 are configured such that the second sleeve retains axially the first sleeve in contact with the body 18.

[0042] The inner sleeve 8.1 can comprise a front groove 8.1.2 housing a gasket that cooperates in a gas tight manner with a corresponding front surface of the body 18 onto which the valve is mounted.

[0043] The second sleeve 8.2 is made of ferromagnetic material whereas the first sleeve 8.1 can be made of non-ferromagnetic material and show an external groove filled with a ring of ferromagnetic material 8.1.3. The groove is such that it leaves a thin wall 8.1.4 of material unitary with the rest of the sleeve 8.1. The groove and the corresponding ring of ferromagnetic material 8.1.3 is advantageously located longitudinally at the level of the shoulder portion

8.2.1 of the second sleeve 8.2. Thanks to this construction, the first sleeve

8.1 can be made of stainless steel, e.g. austenitic stainless steel, that is particularly resistant to embrittlement in the presence of hydrogen under high pressure while still allowing the magnetic field produced by the coil to reach the inner cavity delimited by said sleeve. More specifically, the presence of the ferromagnetic ring 8.1.3 guides the magnetic field radially through the sleeve 8.1 until the thin wall 8.1.4 of non-ferromagnetic material. The low permeability of the material of that thin wall 8.1.4 is of a limited effect on the building up of the magnetic field so that said field can reach the inner cavity of the first sleeve 8.1 while said sleeve shows a perfect and continuous integrity and gas tightness to the high pressure in said cavity. The groove in the first sleeve 8.1. can be formed by machining and the ring of ferromagnetic material 8.1.3 can be applied by welding so as to restore, at least partially, the initial stability and rigidity of the sleeve.

[0044] The shut-off device of the valve, housed in the inner cavity of the first sleeve 8.1 will be described here.

[0045] The shut-off device comprises the main closure element 12 which is axially slidable in the inner cavity of the sleeve 8.1. More specifically, the main closure element 12 is generally elongate with a front conical face 12.1 engaging with a corresponding main seat 20 that is for instance formed in the body 18. The main closure element 12 comprises also a gasket 12.2 on the front face 12.1 , said gasket cooperating in a gas tight manner with the main seat 20. The gas tight cooperation of the main closure element 12 with the main seat 20 shuts-off the gas passage between a gas inlet 22 and a gas outlet 24.

[0046] The shut-off device further comprises the pilot closure element 14 that is slidable relative to the main closure element 12 so as to selectively close and open the channel 12.3 through the main closure element 12, interconnecting the inlet 22 with the outlet 24. More specifically, the pilot closure element 14 cooperates with a pilot seat that is advantageously formed on an element 26 that is inserted into a bore formed in the rear face of the main closure element 12. That element 26 is advantageously made of a material that is softer than the material of the main closure element. It can show a rear face 26.1 with a through-hole 26.2 which both cooperate with a conical tip of the pilot closure element. The element 26 can also show a conical front face 26.3 and a generally cylindrical outer surface 26.4 with circular lips.

[0047] The pilot closure element 14 can show a conical tip that engages with a corresponding conical surface of the pilot seat 26.

[0048] The pilot closure element 14 is rigidly fixed to a magnetic core 16 that forms an airgap with a counter-core 30 rigidly attached to the main closure element 12. For instance, the core 16 is cylindrical and surrounds the main closure element 12. It is attached to the pilot closure element 14 by means of a pin 32 extending radially through the core 16 and the pilot closure element 14. As is apparent figure 2, the pilot closure element 14 is slidably housed in a bore formed in the main closure element 12 and said element comprises two oblong holes through which the pin 32 extends. The core 16 forms with the counter-core 30 a first air-gap 28.

[0049] Still with reference to figure 2, the counter-core 30 is housed directly in the inner bore of the sleeve 8.1 , like the core 16. The bore of the sleeve 8.1 is closed in a gas tight manner by a plug 34 made of ferromagnetic material, said plug forming the bottom of the cavity. The plug 34 can be attached to the sleeve 8.1 by a threaded engagement as visible in figure 2. For instance, the plug 34 can be generally cylindrical with an external thread 34.1 engaging with a corresponding internal thread formed in the sleeve 8.1. The plug 34 can also show a projecting portion 34.2 housed in the sleeve 8.1. More specifically, the internal thread of the sleeve 8.1 can be formed in an end portion 8.1.5 of said sleeve 8.1 that forms a bore of a larger diameter. The projecting portion 34.2 of the plug 34 shows then a reduced diameter compared with the portion of the external thread and mates with the nominal bore of said sleeve. The projecting portion 34.2 can have an external groove 34.3 housing a gasket for a gas tight cooperation with the sleeve 8.1. The plug 34 can also feature a cavity, for instance a bore 36, that receives an end of a spring 36 whose other end engages with the counter-core 30. The compression spring 36 urges the main closure element 12, which is rigidly attached to the counter-core 30, against the main seat 20.

[0050] The main closure element 12 comprises a spring 38, for instance a compression spring, that urges the pilot closure element 14 against the pilot seat 26. More specifically, the main closure element 12 can comprises at its end opposite to the tip engaging with the pilot seat 26 an external thread that engages with an internal thread in a bore 30.1 formed in the counter- core 30, so as to provide a rigid attachment. The spring 38 rests then on one side against the bottom of the bore in the counter-core 30 and on the other side on the pilot closure element 14. In particular, the pilot closure element 14 can comprise an elongated end with a shoulder, the spring 38 being then slip on said elongated end and resting on said shoulder.

[0051] Still with reference to figure 2, the counter-bore 30 forms with the plug 34 a second air-gap 40. That second air-gap 40 is advantageously axially longer than the first one 28. More specifically, the counter-core 30 can show a circular protrusion 30.2 that extends axially in the second air-gap 40 where said protrusion engages around and along the projection portion 34.2 of the plug 34.

[0052] The main closure element 12 comprises a piston 44 at the centre of the front face 12.1 of said element, configured for cooperating with the main seat 20. The piston 44 can comprise a head portion 44.1 and an elongate portion 44.2, said elongate portion being housed in a bore formed in the main closure element 12. The head or main portion of the piston 44 shows front face that contacts the main seat 20 so as to form a cavity 48 fluidly connected to the channel 12.3 through the main closure element 12, interconnecting the inlet 22 with the outlet 24. A building up of an inlet fluid pressure in the cavity 48 biases the main closure element 12 away from the main seat 20.

[0053] The piston 44 advantageously comprises a through-hole 44.3 fluidly interconnecting a front face and a rear face of said piston. This hole allows a counter pressure to build up at the outlet 24 once the pilot closure element 14 releases the pilot seat 26 while keeping a pressure in the cavity 48 that is higher than the counter pressure at the outlet 24.

[0054] The elongate portion 44.2 of the piston 44 can comprise an oblong hole through which an anchoring pin 46 extends. Said pin extends diametrically through the main closure element 12, advantageously through a circular external groove of the main closure element 12 housing the gasket 12.2 on the front face 12.1 of said element. The pin 46 extends diametrically at each end until the bottom of the groove housing the gasket 12.2. The latter is advantageously vulcanised in said the groove so as to ensure a gas tightness between the inlet 22 and the channel 12.3 in the main closure element 12.

[0055] In figure 2, the valve is in a closed state, i.e. the fluid passage between the inlet 22 and the outlet 24 is shut-off. The spring 36 urges the main closure element 12 against the main seat 20 and the spring 38 urges the pilot closure element 14 against the pilot seat 26. The pressure at the inlet 22 is higher than the pressure at the outlet 24 so that both main and pilot closure elements 12 and 14 are further urged against their respective seats 20 and 26 by the difference between the inlet and outlet.

[0056] Upon energisation of the coil 10, a magnetic field is produced around said coil. More specifically, the coil 10 is generally ring-shaped and wound around the axis of the ring. The magnetic field produced therefore naturally encircles the coil 10. In fact, the magnetic field extends axially along the second outer sleeve 8.2 and forms a loop at the axial ends of the coil 8. Starting from the left end of the coil 10, the magnetic field develops in the portion of the second sleeve 8.2 located at the left side of the coil 10, in the ring of ferromagnetic material 8.1.3 as well as in the core 16, the counter- core 30 and then loops back at the right end of the coil 10 in the back plate 42 (figure 1) made also of ferromagnetic material. The low permeability of the non-ferromagnetic material of the thin wall 8.1.4 is of a limited effect on the building up of the magnetic field in view of its reduced thickness. The same applies to the first air-gap 28. The negative influence of the second air-gap 40 on the development of magnetic field inside the sleeve 8.1 can be reduced by providing the engagement of the circular protrusion 30.2 with the plug 34, as detailed above.

[0057] With reference now to figure 3, in the presence of a magnetic field in the core 16 and the counter-core 30, at the level of the first air-gap 28, a magnetic attracting force develops, tending to reduce said air-gap and bring the core 16 and the counter-core 30 into a mutual contact. In that sense, the core 16 is attracted towards the counter-core 30 so as to cancel the air-gap 28. By that movement of the core 16, the pilot valve element 14 is moved away from the pilot seat 26 against the resilient force of the spring 38. The gas under pressure at the inlet 22 flows through the channel 12.3 towards the piston 44, more precisely towards the through-hole 44.3 and the cavity 48. Upon development of a counter-pressure in the cavity 48, an opening force is exerted on the main closure element 12 against the closing force resulting from the gas pressure at the inlet against the main closure element 12 and also against the resilient force of the spring 36. This opening force resulting from the pressure in the cavity 48 adds to the magnetic force between the counter-bore 30 and the plug 34 at the second air-gap 40. The maximum cross-section of the through-hole 44.3 is advantageously smaller than the minimum cross-section of the through-hole 26.2 of the element 26, so as to promote the development of a counter-pressure in the cavity 48.

[0058] In other words, the piston 44 allows the building-up of a counter-pressure on a portion of the front face of the main closure element 12, facilitating the opening movement of the main closure element. The cavity 48 is active over a limited portion of the stroke of the main closure element 12, i.e. from the closed position (as illustrated in figure 2) in the opening direction as long as the gasket 12.2 is in tight contact with the seat 20 (as illustrated in figure 3).

[0059] The slidable attachment of the piston 44 to the main closure element 12 is configured so as to stop the relative movement between the piston and the main closure element once or shorty after that the gasket 12.2 does to cooperate anymore with the seat 20 in a gas tight manner. In figure 3, we can see that the attachment pin 46 is close to the end of the oblong holes in the elongate portion 44.2 of the piston.

[0060] With reference to figure 4, once the gasket 12.2 leaves the seat 20, the gas can flow directly from the inlet 22 to the outlet 24 between the seat 20 and the front face 12.1 of the main closure element 12. The cavity formed with the main seat 20, between the piston 44 and the gasket 12.2 does not exist anymore. Also the inlet pressure is present on both sides of the main closure element 12, so that essentially only the resilient force of the spring needs to be counter-acted by the magnetic force in the second air-gap 40 until said air-gap is cancelled and the counter-core 30 contacts the plug 34. During that movement, the main closure element 12 is moved away from the main seat 20 and the piston 44 is driven away by the main closure element 12.

[0061] Upon interruption of energization of the coil 10, the magnetic forces between the core 16 and counter-core 30 as well as between said counter-counter core 30 and the bottom 34 of the cavity disappears and the resilient forces of both springs 36 and 38 is not counter-acted anymore. As a consequence, the pilot closure element 14 is moved towards the pilot seat 26 and the main closure element 12 is moved towards the main seat 20, so that the gas passage between the inlet and the outlet is totally shut-off. [0062] The electromagnetic core 16 can comprise a front portion 16.1 axially overlapping a ring portion 20 of the body 18 forming the main seat 20. This overlapping is advantageously also when the valve is in a fully open position as illustrated in figure 4. The section for the fluid flowing between the outer surface of the ring portion 20 and the inner surface of the front portion 16.1 is less than the section of the passage between the front portion 12.1 of the main closure element 12 and the seat 20. This provides a protection of the gasket 12.2 in that the fluid is accelerated and then decelerated towards the bottom of the chamber 16.2 formed by the front portion 16.1. The chamber 16.2 forms than a stabilizing chamber that is beneficial for the gasket 12.2 and possible other sensible parts in the gas passage. The front potion 16.1 , the inner surface therefore and the outer surface of the ring portion 20 are advantageously generally cylindrical.