GB2121925A - Improvements relating to piloted solenoid valves - Google Patents

Abstract

A piloted solenoid valve has a main valve seat (14) and a differential piston (10) closing the same, the back of the piston bounding a chamber (36) communicating with a valve entry (2) by way of small gap cross-sections. A pilot valve is axially aligned with the differential piston (10) and seals off the chamber (36) behind the piston (10) from a lower-pressure chamber (37). A pull rod (28) is rigidly secured to a plug (23) of the pilot valve and acts on the differential piston (10) in an opening direction after a partial movement of the pilot valve and, upon the differential piston (10) making an independent opening movement, extends thereinto without impeding its movement. For positional indication, an axially guided rod (35) is rigidly connected to the pilot valve spindle (22) and extends by way of the solenoid to a position indicator (8) disposed thereafter. <IMAGE>

Description

SPECIFICATION Improvements relating to piloted solenoid valves The invention relates to piloted solenoid valves.

Such valves may comprise a main valve having a valve seat and a differential piston closing the same, the back of the piston bounding a chamber communicating with the valve entry by way of small gap cross-sections. A pilot valve disposed after the differential piston in axial extension thereof seals off the chamber at the back of the differential piston from a lower-pressure chamber.

Valves of this kind are used as control valves in piping. A preferred sphere of activities is as control valves for controlled valves or the like. Since elements of this kind are often safety devices and must have high standards of operating reliability, similar considerations apply to their control valves.

A risk with piloted solenoid valves is that the pilot valve and the main valve may operate alternately and thus produce oscillations downstream of the valves. The mass flow through the valve therefore pulsates and operation of the main valve required to control this flow becomes uncertain. A piloted solenoid valve must therefore be designed to be substantially free from this interaction.

A requirement for safety facilitates, and therefore the associated control valves, is to have substantial reserves of actuating force, to ensure satisfactory operation notwithstanding the friction and wear associated with a prolonged period of operation. bn the other hand, the solenoid valve is required to have a very modest consumption and to need very little magnetic force, so that power supply can be reliable and cheap and the magnet needed can be small.

In plants which have to be monitored, for instance, in nuclear and fossil fuel power stations and pressure vessel plants, inspections are made at regular intervals of the operating reliability of safety facilities. It must therefore be possible for valves to be checked by simple means without any disturbance of operation and a requirement in this connection is reliable positional indication.

It is an object of the invention to provide a piloted solenoid valve which alleviates the disadvantages of the known constructions, such that: the initial position of the pilot valve does not alter during operation of the valve; the forces needed to operate the pilot valve are small; direct indication of pilot valve position and indirect indication of the main valve can be provided by simple means; and the elements for transmitting the actuating forces to the pilot valve are such that no mass forces of the magnet are transferred to the pilot valve in the opening operation.

According to the invention, this invention provides a piloted solenoid valve comprising a main valve having a valve seat and a differential piston closing the same, the back of the piston bounding a chamber communicating with the valve entry by way of small gap cross-sections, a pilot valve which is disposed after the differential piston in axial extension thereof and seals off the chamber at the back of the differential piston from a lower-pressure chamber, an entraining member being rigidly secured to the plug of the pilot valve so as to act operatively on the differential piston in the sense of an opening movement after a partial movement of the pilot valve, and extending into the piston so as not to impede movement thereof, when differential piston makes an independent opening movement.

According to a preferred feature of the invention, the entraining member is a pull rod having a head at its end and is guided in a recess in an end cap of a pull tube rigidly attached to the back of the differential piston, the pull tube extending into the differential piston.

The solenoid may be so positioned that its operating force keeps the pilot valve closed against the pressure of the working medium in the chamber at the back of the differential piston. In this case the pilot valve opens in response to an interruption of its power supply, for instance, at a changeover or in the event of a power failure, as a result of the pressure of the working medium which, more particularly at low pressures, may be boosted by the force of a helical compression spring. This valve is thus a self-closing or servoclosing device.

In another construction, the force of a spring disposed in the solenoid casing is effective to close the pilot valve and keep it closed against the pressure of the working medium in the chamber at the back of the differential piston. In this case the pilot valve opens in response to energization of the solenoid, whose magnetic force reduces the force of the lattter spring, as a result of the pressure of the working medium, which, more particularly at low pressures, is boosted by the force of a helical compression spring. This valve is thus an assisted closing device.

According to another preferred feature of the invention, there is only pressure contact between the pilot valve spindle and an actuating element of the solenoid. This feature ensures that mass forces of the magnet and of the part moving with it cannot be transmitted to the pilot valve during opening.

The differential piston is preferably guided in a cylinder to which the valve seat element is rigidly attached, that element being screwed to the valve casing below the valve seat and, advantageously, at a distance therefrom of approximately twice the valve seat diameter.

In order to provide a direct indication of pilot valve position, an axially guided rod may be rigidly attached to the plug or spindle of the pilot valve and to extend by way of the solenoid to a, for instance, electrical or mechanical position indicator disposed after the solenoid.

A large area on which the pressure of the working medium can act can be provided by a dished widening formed on the pilot valve plug above the sealing surface. After the pilot has opened the opening movement is boosted by the forces of the working medium which are operative on the dished widening.

The invention may be performed in various ways and one preferred embodiment thereof will now be described with reference to the drawings, in which: Figure 1 is a view in partial axial section of an embodiment of a piloted solenoid valve according to the invention; and Figure 2 is an enlarged view of a portion of the valve shown in Figure 1.

A casing 1 of the valve has a side entry passageway 2 and a bottom exit passage 3.

Operating elements of the main valve are disposed in a cylindrical inner chamber 4 of the casing 1, which is closed at the top by a cover 5 which also receives parts of the pilot valve. A lantern 6 is secured to the free end face of the cover 5 by screwed connections and carries a casing 7 of a solenoid magnet. Secured to the casing 7 is another casing 8 containing means for positional indication.

The operating elements of the main valve include a seat element 9, a differential piston 10 and a helical compression spring 11. The seat element 9 comprises a cylindrical top part 1 2 and a bottom part 1 3 which carries the actual valve seat 14 and which extends into the bore of the top part 12. The element 9 is introduced downwardly into the chamber 4 and rests on a collar 1 5. A screwthreaded extension 1 6 extends downwardly through the collar 1 5 and a seat nut 17 is screwed onto the extension 1 6 from the exit end. This single securing at a place far away from the valve seat 14 obviates the transmission of external forces through the casing 1 to the cylindrical top part 12 and the piston 10.

The cylindrical top part 12 is formed at the level of the entry passageway 2 with two radial bores 1 8 of greater diameter than the diameter of the entry passageway 2. One bore 1 8 extends towards the entry passageway 2. The medium can therefore enter the cylindrical inner chamber 4 unimpeded. The gap between the casing 1 and the seat element 9 above the entry passageway 2 is substantially sealed, for instance by a piston ring.

The piston 10 moves in the cylindrical top part 12 with close guidance in order to limit the leakage flow between the piston and the cylinder.

The piston 10 has on its underside a sealing surface 1 9 which corresponds to the valve seat 14, engages thereon with the valve closed and forms the isolation between the valve entry passageway 2 and valve exit passage 3.

The back of the piston 10 is formed with a recess 20 receiving the spring 11, which is prestressed, and bears on the cover 5 so as to keep the piston 10 closed.

The pilot valve comprises a seal element 21 fashioned in the cover 5, a spindle 22 with a plug 23, a bellows 24, a helical compression spring 25 and a closure or isolating cover 26 screwed to the cover 5. The bellows 24 disposed in the bore of the cover 26 serves to seal off the inner chambers of the valve completely from the environment.

The seat element 21 and the plug 23 provide a sealing-tight closure of the inner chamber 36 at the back of the piston 10. The spindle 22 has, immediately above the plug 23, a dished abutment 27 which, with the pilot valve open, engages the bottom end face of the cover 26 and thus limits valve movement. A pull rod 28, having a terminal head member 29, extends from the plug 23 and through a recess in an end cap 30 of a pull tube 31 which is integral with the piston 10.

The clearance between the member 29 and the cap 30 is such that the pilot valve has to make a predetermined idle movement before the pull rod 28 acts on the tube 31 and therefore in the sense of an opening of the piston 10. Also, the axial clearance between the member 29 and the piston 10 is such that an independent opening movement thereof is not impaired.

The spindle 22 extends from the top part of the cover 26. A two-element closure member 32 engages positively about a thickened part 22a at the end of the spindle 22, has a conical outer wall, and engages by way thereof in a matching bore in a spring cup 33 on which the spring 25 bears. The free end of an actuating rod 34, connected to the solenoid, rests freely on the member 32 of spindle 22 and so can only apply pressure thereto, thus avoiding the application of unwanted pulls to the pilot valve.

The spring 25 between the spring cup 33 and the cover 26 is operative in the opening direction and keeps the pilot valve open in the absence of a closing force applied by way of the rod 34 to overcome the force of the spring 25. When the valve is pressureless or pressure in it is low, the spring 25 can open the main valve piston 10.

A rod 35 extends axially from the outer end of the spindle 22 and through the solenoid casing 7 into the casing 8 where it acts on means to indicate the position of the pilot valve. Since the spindle 22 is connected to the piston 10 by way of the rod 28 after an appropriate idle travel of the pilot valve, the rod 35 can provide information about the opening of the main valve.

Operation of the piloted solenoid valve will now be desirable. The piloted solenoid valve is normally in the closed state. The internal chamber 36 is at the pressure of the working medium. The pressure thereof and the force of the spring 11 keep the main valve piston 10 closed while the solenoid, acting by way of the rod 34, keeps the pilot valve plug 23 closed against the pressure of the working medium and the force of the spring 25. During self-closing the force of the solenoid acts directly on the plug 23 whereas in the case of assisted closing the closing force is produced by a spring whose action on the rod 34 is cancelled or reduced after the solenoid has picked up.

Movement of the solenoid is triggered, for instance, by a signal given by a pressure switch.

The closing force applied by the rod 34 to the pilot valve plug 23 disappears and the pressure of the working medium opens the plug 23 far enough to allow the chamber 36 to communicate with a chamber 37 and lower the pressure in the chamber 36 at the back of the main valve piston 10, since the inflow cross-sections are considerably smaller than the outflow crosssections. The operative surface of the back of the piston 10 is considerably larger than the actuation area on the other face of the piston 10 so that, after pressure has dropped sufficiently, the pressure acting on the difference surface between the differential piston 10 and the valve seat opens the piston 10. The plug 23 opens further, boosted by the deflection of the stream by means of the dished abutment 27 disposed above the plug 23 and by the force of the spring 25.The pilot valve remains open even though the piston 10 moves rapidly, since pilot valve movement is independent of the main valve movement.

If, at low pressures, the pressure drop on the back of the piston 10 fails to open the same or if the unit is pressureless, the spring 25 acts by way of the rod 28 to open the piston 10 after the idle movement has been taken up.

When the solenoid picks up again, the force applied to the rod 34 returns the plug 23 to its closed position. Because of the relatively narrow inflow cross-sections between the valve entry passsageway 2 and the chamber 36 at the back of the piston 10, the pressure in the latter chamber rises to the pressure of the working medium, the piston 10 therefore being forced back into the closed position. The closing force is boosted by the spring 11 associated with the piston 10, although the force of the spring 11 is less than the force of the pilot valve spring 25.

Claims (9)

1. A piloted solenoid valve comprising a-main valve having a valve seat and a differential piston closing the same, the back of the piston bounding a chamber communicating with the valve entry by way of small gap cross-sections, a pilot valve which is disposed after the differential piston in axial extension thereof and seals off the chamber at the back of the differential piston from a lowerpressure chamber, an entraining member being rigidly secured to the plug of the pilot valve so as to act operatively on the differential piston in the sense of an opening movement after a partial movement of the pilot valve, and extending into the piston so as not to impede movement thereof, when differential piston makes an independent opening movement.

2. A solenoid valve according to claim 1, wherein the entraining member is a pull rod having a head at its end, and is guided in a recess in an end cap of a pull tube rigidly attached to the back of the differential piston, the pull tube extending into the differential piston.

3. A solenoid valve according to claim 1 or claim 2, wherein the solenoid is so positioned that its operating force keeps the pilot valve closed against the pressure of the working medium in the chamber at the back of the differential piston.

4. A solenoid valve according to claim 1 or claim 2, wherein a spring stressed by the solenoid is effective to keep the pilot valve closed against the pressure of the working medium in the chamber at the back of the differential piston.

5. A solenoid valve according to any one of claims 1 to 4, wherein pressure contact is possible only between the pilot valve spindle and an actuating rod of the solenoid.

6. A solenoid valve according to any of claims 1 to 5, wherein the differential piston is guided in a cylinder to which the valve seat element is rigidly attached, that element being screwed to the valve casing below the valve seat and at a distance therefrom of approximately twice the valve seat diameter.

7. A solenoid valve according to any one of claims 1 to 6, wherein an axially guided rod is rigidly attached to the pilot valve spindle and extends by way of the solenoid to a position indicator disposed thereafter.

8. A solenoid valve according to any one of claims 1 to 7, wherein a dished abutment is provided on the pilot valve plug above the sealing surface.

9. A piloted solenoid valve substantially as herein described with reference to the accompanying drawings.