Patent Application
20160169406
The present invention relates to a valve used in hazardous applications, and in particular to an electromechanical solenoid valve for mitigating the risk of flaming ingress from an explosion zone.
Solenoid valves are commonly used in hydraulic systems and they typically operate as pilot valves. An electromechanical solenoid valve is controlled by an electric current to a solenoid. The solenoid includes an electric coil arranged to operate an armature which can be actuated to open and close a flow channel.
The conditions in which solenoid valves operate may be broadly categorised as ‘hazardous’ or ‘non-hazardous’. A hazardous environment may include the possibility of the surrounding atmosphere being an explosive gas or dust mixture. In hazardous environments it is required that all electrical components are shielded from the explosive atmosphere to avoid the electrical components acting as an ignition source.
It is known in hazardous environments to locate electrical components such as solenoid valves within an explosion chamber. The valves are arranged such that the electrical components are located within the explosion chamber which acts to control and contain any spark or ignition source to prevent exposure to the external hazardous atmosphere.
In addition to preventing propagation of the initial combustion or spark source to the external hazardous environment, it is also critical that should any such explosion occur within the explosion chamber that combustion does not spread to the hydraulic fluid which would cause a serious incident in itself as well as risking external combustion release.
Containing the solenoid valve within the explosion chamber allows a lower specification part to be used, as external location of the solenoid valve requires the valve itself to include far more highly specified and toleranced components to avoid the valve presenting an ignition risk.
Where solenoid valves are connected to a manifold such that the solenoid and other electrical aspects of the valve are located within the explosion chamber a seal is provided at the point the solenoid connects to the manifold to provide a sealed barrier between the hydraulic process fluid and the explosion chamber. However, in higher pressure hydraulic systems the increased pressure increases the risk of primary seal failure. In the event of such failure high pressure hydraulic fluid may be released into the explosion chamber which would present a greatly increased explosion risk. It is therefore important, especially for higher pressure applications, that the risk of such leakage and pressure rise is mitigated.
It is therefore desirable to provide an improved solenoid valve assembly which addresses the above described problems and/or provides improvements generally.
According to the present invention there is provided a valve assembly as described in the accompanying claims. In addition there is provided a hydraulic actuator assembly as described in the accompanying claims.
In an embodiment of the invention there is provided a valve assembly comprising a valve including a valve body and a movable valve closure member; a manifold including a bore having a valve opening through which the valve is received into the bore, and at least one process fluid pathway defined within the manifold in fluid communication with the bore. The valve includes a proximal end section arranged to close the valve opening and an opposing distal end located within the bore inwardly of the proximal end, and the valve closure member is arranged to open and close the at least one fluid pathway. A primary seal is located between the valve body and the manifold to seal the valve opening and a secondary seal located inwardly of the primary seal along the bore relative to the valve opening arranged to create a seal between and the valve body and the bore to isolate the primary seal from the first fluid pathway. The valve assembly further includes a vent port in fluid communication with the bore located along the bore between the primary seal and the secondary seal.
The secondary seal seals and isolates the primary seal from the process fluid. As such, there is no process fluid pressure on the primary seal and a buffer chamber is defined between the primary and secondary seals, which is sealed from the process fluid. Therefore, in the event of primary seal failure the process fluid remains sealed from the explosion chamber and there is no fluid release into the chamber and no associated pressure rise thereby obviating the explosion risk. Furthermore, in the event of an explosion within the chamber a double seal barrier is provided between the explosion chamber and the hydraulic process fluid to mitigate the risk of combustion of the hydraulic process fluid.
The valve body and the manifold preferably include corresponding threads defining a threaded connection located between the primary seal and the secondary seal. The screw thread arrangement extends between the valve body and bore of the manifold along the buffer chamber. The low cross-sectional area and relatively long length of the thread acts as a damper to muffle any explosion that may pass the primary seal, thereby protecting the secondary seal in the event of an explosion. In the reverse direction, in eth event of secondary seal failure the fluid pressure at the primary seal is minimised by forcing the process fluid to flow through the thread.
The vent port is preferably located inwardly of at least a portion of the threaded connection along the length of the bore. In this way, the pressure of any explosion gases when they reach the vent port is minimised by the gases being forced through at least part of the thread before reaching the vent, thereby minimising the vent pressure. The vent port is spaced inwardly along the length of the bore from the threaded connection, thereby ensuring that the explosion is caused to travel the entire length of the thread before reaching the vent.
The threaded connection preferably includes at least five thread turns. The greater the number of thread turns the greater the dampening properties of the thread. However, typically within such valve assemblies space is at a premium and it has been found that five turns provides acceptable dampening while minimising thread length.
The valve assembly may include an explosion chamber in the form of a pressure vessel to which the manifold is secured such that the valve opening of the bore and the face of the manifold in which it is formed faces inwardly into the pressure vessel. The primary seal is arranged to provide a seal between the interior of the pressure vessel and valve bore of the manifold. The valve is preferably an electromechanical solenoid valve comprising an electrical coil and an armature configured to actuate the valve member, wherein the electrical coil is located at the proximal end of the valve body outwardly of the primary seal and within the pressure vessel. As such, the electrical components of the valve are contained within the pressure vessel and isolates by the primary and secondary seals from both the external hazardous environment and from the process fluid.
The valve body comprises a main body section having a bore which slidingly houses the armature, a head section secured to the main body section at least part of which is located inwardly of the main body section along the bore, and a spool slidingly received within a spool chamber in the head section to open and close an opening at the inner end of the head section, and a needle member movable by the armature to hold in the spool in the closed position in a first configuration, the needle and the spool defining the closure member; the manifold includes an inlet port and an outlet port and the valve includes a corresponding port located adjacent the inlet port which defines a fluid pathway between the inlet port and the outlet port via the spool chamber and the open end of the head; wherein a portion of the head section is received within a bore of in the main body section to secure the head to the body section and a third seal is provided between the outer surface of the head section and the bore of the main body section to prevent the flow of process fluid into the space between the primary and secondary seals.
The secondary seal is located outwardly along the bore of the inlet port and a fourth seal is provided inwardly along the bore of the inlet port to seal the inlet port along the length of the bore.
The primary and secondary seals may be annular resilient seals and are preferably o-ring seals.
In another aspect of the invention a hydraulic actuator assembly comprises a hydraulic actuator, a pump arranged to supply pressurised hydraulic to the actuator and a valve assembly as described arranged to control the supply of fluid to the actuator from the pump.
The present invention will now be described by way of example only with reference to the following illustrative figures in which:
Referring to
The manifold 12 is connected to a pressure vessel 14 that is configured as a flame resistant explosion chamber. The explosion chamber 14 is sealed from the external atmosphere and configured to contain and isolate any spark or ignition occurring within the chamber 14. The manifold 12 has an inner face which faces inwardly into the explosion chamber 14.
As shown in
A cylindrical valve head section 34 is located at the longitudinal inner end of the solenoid body. The terms ‘inner’ and ‘outer’ are relative and refer to the relative positions of the components in the longitudinal direction relative to the manifold with inward referring to the longitudinal inwardly directly into the manifold and outwardly being in the direction of the explosion chamber 14. The first end 36 of the head 34 is received within the inner end section 30 of the solenoid body. A threaded fastening section 38 secures the head 34 to the inner bore of the solenoid body 24. The head 34 includes an inner bore 40. A spool 42 is received within the inner bore 40 of the head 34, and is configured to slide within a section of the bore 40. A poppet or needle 44 is received within an inner bore 46 of the spool 42.
As shown in
An inlet port 60 is defined in the manifold and is arranged transverse to the longitudinal axis of the bore 20. The inner end of the bore 20 defines an outlet port 62. O-ring seals 64 and 66 are provided in corresponding annular grooves in the outer surface of the head 34 and are arranged longitudinally either side of the inlet port 60. A chamber 68 is defined between the spool 42 and the inner bore 36 of the head 34 at the inner end of the spool 42. A port 70 extending through the head connects the chamber 68 with the inlet port 60.
As shown in
A vent port 74 is defined in the manifold 12 and is located longitudinally along the bore 20 between the primary seal 72 and secondary seal 66. The vent port 74 is in fluid contact with the bore 20 and extends in a direction transverse to the longitudinal axis of the bore 20. The vent port 74 is located on the process side of the thread 32 between the solenoid body 24 and the bore 20 of the manifold 12 towards the secondary seal 66 at the longitudinal inward end of the thread 32 in fluid communication with the bore 20.
In use the needle 44 or spindle is biased to the closed position as shown in
When the solenoid coil is operated to actuate the armature 26 the needle 44 is retracted by the armature 26 moving the tip of the needle 44 out of the opening 52 and out of engagement with the spool 42. With the needle 44 disengaged the pressure within the chamber 68 acts on the shoulder 76 to slide the spool 42 away from engagement with the shoulder 58 to open a fluid pathway between the inner port 60 and outer port 62 via the mouth 40 of the head 34. The spool 42 continues to move longitudinally away from the shoulder 58 until it re-engages with the needle 44. The spool 42 is then held in this position by the hydraulic fluid pressure acting against it with this positioning defining the fully opened condition of the valve 22. To close the valve 22 the solenoid is de-activated which removes the retraction force of the armature 26 such that the spring force is able to overcome the hydraulic pressure force and return the spool 42 to the closed position thereby closing the valve 22.
Hydraulic fluid is prevented from passing to the primary seal 32 between the solenoid body 24 and the manifold 12 by the secondary seal 66. In arrangements of the prior art where only two seals are provided the primary seal is pressurised and contacted by the hydraulic fluid providing the sole barrier between the hydraulic fluid and the explosion chamber. As such, in the event of failure of the primary seal the hydraulic fluid is immediately dispersed into the explosion chamber which significantly increases the pressure in the explosion chamber and thereby dramatically raises the explosion risk. In the arrangement of the present invention the secondary seal 66 isolates the primary seal 72 from the process fluid to prevent this occurrence.
Once the valve 22 has opened and hydraulic fluid passes into the spool 34 there is the potential for hydraulic fluid to travel to the primary seal 72 via a pathway defined between the inner surface of the solenoid body 24 and the outer surface of the head and onwards past the inner end of the solenoid body into the buffer cavity 75 between the solenoid body 24 and the manifold 12. This is prevented by a fourth seal 78 which is provided between the outer surface of the head 34 and the inner surface of the bore of the solenoid body 24 on the process side of the threaded section 38 at its longitudinally inward end.
The vent port 74 is located with the buffer chamber 75 between the primary seal 72 and secondary seal 66. In the event of failure of the secondary seal 66 hydraulic fluid passing the seal 66 into the buffer chamber 75 between the head 34 and the manifold 12 would reach the vent port 74 before the primary seal 72. The pressurised fluid would be vented via the vent ports 74. As such, while it is possible that some hydraulic fluid may continue towards with the primary seal 72 the pressure at the primary seal 72 would be significantly less than process pressure due to the venting. Therefore, the risk of primary seal failure due to internal fluid pressure is mitigated. Furthermore, even if the primary seal 72 were also to the fluid would not be dispersed into the explosion chamber under high pressure and rather the high pressure hydraulic fluid would be vented via the vent port 74 with no significant pressure rise being experienced within the explosion chamber 14 or and any significant disbursement of hydraulic fluid occurring.
In the event of an explosion the primary seal 72 prevents propagation of the explosion into the bore 20. In the event of failure of the primary seal 72 during an explosion event the secondary seal 66 provides a further barrier between the explosion and the pressurised hydraulic process fluid. In a single seal arrangement of the prior art failure of the primary seal under explosion conditions would have resulted in instantaneous contact between the propagating explosion and the hydraulic fluid. In the present invention, in addition to the secondary seal 66 providing a secondary flame barrier between the explosion chamber 14 and the hydraulic fluid, the vent port 74 enables the high pressure from the explosion to be dissipated before it reaches the secondary seal 66 thereby avoiding the secondary seal 66 experiencing the full explosion pressure.
The vent 74 is located on the process side of the thread 32 between the solenoid body and the manifold 12. The thread 32 preferably includes at least five full thread turns. In the event of failure of the primary seal 72 the explosion would propagate down the bore 20 between the solenoid body 24 and the manifold 12 via the thread 32. The length and small cross-sectional area of the pathway defined by the thread 32 would rapidly dissipate the explosion pressure acting as a damper with any residual pressure then being dissipated via the vent 74 located on the process side of the thread 32. This assures that the vent 74 is not exposed to the full explosion pressure.
Therefore, the present invention provides hydraulic fluid containment separation through a double seal arrangement, with the primary seal providing the main interface and a secondary internal seal providing protection against primary seal failure. The chamber contained between the two seals is vented to provide further protection against fluid leakage and explosion propagation. The combination of the vent port 74 and the secondary seal 66 mitigate both the risk of high pressure fluid engaging and pressurising the primary seal internally in the event of failure of the secondary seal 66 also isolating and protecting the hydraulic fluid from flame contact in the event of an explosion. Furthermore, the location of the vent 74 on the process side of the thread 32 between the solenoid body 24 and the manifold 12 further mitigates the risk of hydraulic fluid combustion by enabling the explosion pressure to be dissipated via the thread 32 before then being vented by the vent port 74.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1313874.8 | Aug 2013 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2014/052324 | 7/29/2014 | WO | 00 |
