Patent Publication Number: US-2010126599-A1

Title: Pilot operated check valve

Description:
This invention relates to a pilot-operated check valve. More particularly, it relates to a pilot-operated check valve comprising a valve housing and a main slide, the main slide being movable between a first and a second position in the valve housing. The main slide communicates with at least two main ports in the valve housing. A movable valve body, which cooperates with a valve seat in the main slide, is arranged to block flow in a first direction between the main ports and to open to flow in the opposite direction between the ports. The valve body bears in an opening manner, possibly via intermediate components, against the valve housing when the main slide is in its second position in the valve housing. 
     Prior art pilot-operated check valves often include a valve body which bears in a biasing manner against a valve seat in a valve housing. Fluid pressure in a first direction has the effect of further increasing the closing force of the valve body against the valve seat. If it is desirable to open to flow in this first direction, the valve body is moved away from the valve seat by means of a normally fluid-operated actuator. 
     Fluid pressure in a second direction flows through the valve by the bias against the valve body being overcome and the valve body thereby being moved away from the valve seat. 
     Valves of this kind are well suited for applications in which the opening to flow through the valve in the first direction may be carried out by supplying the actuator with pressurized fluid with a good pressure margin, that is to say that the pressure supplied to the actuator is substantially higher than the pressure which is normally necessary for the check valve to be opened. 
     If it is necessary to be able to open the valve to flow in the first direction at a relatively accurate pilot pressure and mainly independently of what pressure is acting in a closing manner on the valve body, it has turned out to be difficult for prior art valves, in particular when there is a question of opening at a relatively high pilot pressure, to achieve satisfactory functional reliability. 
     The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art. 
     The object is achieved in accordance with the invention through the features, which are specified in the description below and in the claims that follow. 
     A pilot-operated check valve in accordance with the invention comprises a valve housing and a main slide, the main slide being movable between a first and a second position in the valve housing, and the main slide communicating with at least two main ports, a movable valve body, Cooperating with a valve seat in the main slide, being arranged to block flow in a first direction between the main ports, and to open to flow in the opposite direction between the main ports. The check valve is characterized by the valve body bearing in an opening manner, possibly via intermediate components, against the valve housing when the main slide is in its second position in the valve housing. 
     The valve body is typically in a longitudinal bore in the main slide, the valve body being moved in a biasing manner against the valve seat by means of a closing spring. 
     The length of movement of the main slide in the valve housing may be limited by a stop connected to the valve housing, the stop possibly projecting, for example, into an elongated groove in the main slide. 
     In a practical design a release element will extend between the valve body and the stop. 
     The main slide is biased in the direction of its first position in the valve housing by a main spring bearing against one end portion of the main slide. The main spring typically also braces against an adjustment screw in the valve housing. 
     At its opposite end portion relative to the main spring the main slide is provided with a piston surface. Fluid pressure against the piston surface results in a displacement force on the main slide in the direction of the second position of the main slide in the valve housing. By sufficient pressure on the piston surface the force of the main spring is overcome, whereby the main slide is moved from its first position in the valve housing into its second position in the valve housing. 
     By the fact that the length of movement of the main slide is relatively short and the necessary opening force against the valve housing is relatively small, a pilot-operated check valve according to the invention will open to flow in the first direction within a relatively small pilot pressure interval. 
    
    
     
       In what follows is described a non-limiting example of a preferred embodiment which is visualized in the accompanying drawings, in which: 
         FIG. 1  shows a section IIIa-IIIc of  FIG. 3  of a pilot-operated check valve according to the invention; 
         FIG. 2  shows a section IIIb-IIIb of  FIG. 3 ; 
         FIG. 3  shows a section I-I of  FIG. 1 ; and 
         FIG. 4  shows an alternative embodiment of the pilot part of the check valve. 
     
    
    
     In the drawings the reference numeral  1  indicates a pilot-operated check valve including a valve housing  2  and a main slide  4 , the main slide  4  being movably arranged in a main bore  6  in the valve housing  2 . 
     The main slide  4  is provided with encircling seal grooves  8 , in which are arranged, in a manner known per se, seals  10  to prevent unintentional fluid flow between the main slide  4  and the main bore  6 . 
     A main spring  12  extends in a biasing manner in a somewhat reamed portion of the main bore  6  between the main slide  4  and a control washer  14  resting on an adjustment screw  16 . The adjustment screw  16  is disposed in a threaded bore  18  in the valve housing  2 . The threaded bore  18  is arranged concentrically in the extension of the main bore  6 . 
     A first main port  20  and a second main port  22  open into the main bore  6  with interspacing along the main bore  6 , whereas a pilot port  24  opens into the bottom portion  26  of the main bore  6 . Additionally, the valve housing  2  is provided with necessary drain channels, not shown. 
     Transversally to its moving direction the main slide  4  is provided with an oval opening  28  extending through it. The largest diameter of the oval opening  28  coincides with the longitudinal direction of the main slide  4 . A stop  30  in the form of a cylindrical axle, which is connected to the valve housing, extends through the oval opening  28 . The length of movement of the main slide  4  in the main bore  6  is thereby limited by the stop  30 . 
     Through the main slide  4  extends a stepped concentric longitudinal slide bore  32  which is closed at its end portion n facing the main spring  12  by means of a first plug  34 , and is closed at its opposite end portion, at the pilot portion  36 , by means of a second plug  38 . 
     A shoulder  40  in the slide bore  32  forms a valve seat for a valve body  42 , here in the form of a ball. A support slide  44 , which is provided with a through channel  46 , is moved in a biasing manner by means of a closing spring  48  against the valve body  42 , whereby the valve body  42  bears in a biased manner against the valve seat  40 . The force of the closing spring  48  is insignificant in relation to the force of the main spring  12 . 
     The first main port  20  communicates via a first slide channel  50  with the slide bore  32  on the spring side of the support slide  44 . 
     In the slide bore  32 , between the stop  30  and the valve body  42 , is disposed a release element  52 . The second main port  22  communicates via a second slide channel  54  with the slide bore  32  on the release element side of the valve body  42 . 
     The main spring  12  moves the main slide  4  inwards within the main bore  6  until the oval opening  28  hits the stop  30 . The main slide  4  is now in its first position in the valve housing  2 , see  FIG. 1 . 
     Pressurized fluid seeking to flow in a first direction of flow from the first main port  20  to the second main port  22  is prevented from such flow by the valve body  42  bearing sealingly against the valve seat  40 , the pressurized fluid thereby causing the valve body  42  to be further braced against the valve seat  40 . 
     Pressurized fluid seeking to flow in a second direction from the second main port  22  to the first main port  20  overcomes the force of the closing spring  48  on the valve body  42 . The valve body  42  is thereby moved together with the support slide  44  in a direction away from the valve seat  40 . Thereby, fluid may flow from the second main port  22 , via the second slide channel  54 , slide bore  32 , valve seat  40 , channel  46  in the support slide  44  and the first slide channel  50  to the first main port  20 . 
     The end surface of the pilot portion  36  of the main slide  4  forms, together with the second plug  38 , a piston surface  56  for pressurized fluid entering the main bore  6  via the pilot port  24 . 
     When the pressure in the pilot port  24  increases sufficiently, the pressure forces on the piston surface  56  overcome the force of the main spring  12 , whereby the main slide  4  is moved in the direction towards the main spring  12  until the oval opening  28  hits the stop  30  on its opposite side, see  FIG. 2 . The main slide  4  is now in its second position in the valve housing  2 . The length of the release element  52  is adapted in such a way that just before the main slide reaches its second position, the release element  52  hits the valve body  42  and stop  30 . Thereby, the valve body  42  is moved out from the valve seat  40 . When the main slide  4  is in its second position in the valve housing  2 , fluid may flow in the first direction of flow from the first main port  20  via the first slide channel  50 , slide bore  32 , channel  46 , valve seat  40  and second slide channel  54  to the second main port  22 . 
     When the pressure in the pilot port  24  is relieved, the main spring  12  returns the main slide  4  into the first position in the valve housing  2 , whereby the valve body  42  closes to flow in the first direction of flow. 
     The check valve  1  is balanced in the sense that pressure from fluid in the main ports  20  and  22  only to a quite insignificant degree applies resulting axial forces to the main slide  4 . 
     When a check valve  1  is involved which is to open only at a relatively high pilot pressure, it is, for practical reasons, not convenient to use a main spring  12  having correspondingly great tension. 
     The piston surface  56  is therefore reduced to an annular area  58 , see  FIG. 4 , by stepping down the pilot portion  36 .