Abstract:
A valve apparatus comprising a housing, a piston mounted in the housing for movement between positions corresponding to open and closed conditions of the valve, a push rod movable by the piston and extending through an opening in the housing for actuating a device such as a micro-switch disposed externally of the housing, and a biasing spring arranged to transmit a biasing force between the piston and the push rod so as to mitigate movement of the push rod relative to the housing when the valve is in a predetermined operating condition. The valve apparatus preferably includes a debris shield arranged to close said opening around the push rod when the valve is in a predetermined operating condition.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a valve apparatus of the type having a housing, a piston mounted in the housing for movement between positions corresponding to open and closed conditions of the valve, and actuator means moveable by the piston and extending through an opening in the housing for actuating a device disposed externally of the housing.  
           [0002]    A valve apparatus of the above-mentioned type may, for example, be used as a pressure raising valve to ensure that general system pressure in a flow metering unit of an engine is maintained at a desired level by restricting flow through an orifice. The external device may, for example, be a microswitch device activatable by the actuator means, for signalling an electronic control unit that the valve is in a predetermined operating condition.  
           [0003]    A known valve apparatus of the above-mentioned type is shown in FIG. 4. In use, with the valve apparatus of FIG. 4 in an open condition, the actuator means, in the form of a pushrod  16 , tends to move together with a valve piston  2 . The piston  2  can move the pushrod towards the right in the orientation shown in FIG. 4 by abutment of the piston  2  against a laterally extending abutment  16 a of the actuator means, and the pushrod  16  is returnable towards the left in the orientation shown in FIG. 4 by a spring of an external microswitch device (not shown) connected to the pushrod externally of the valve, and a compression spring  8  acting between the piston  2  and its supporting housing  3 .  
           [0004]    It is known, as shown in FIG. 4, to provide a seal  20  between the pushrod  16  and the end wall  5  of the housing  3  within the opening  17  through which the push rod  16  extends to co-operate with the microswitch, the seal  20  preventing leakage of fuel from within the valve housing  3 . However, such seals can abrade in use, causing undesirable leakage of fuel from the valve housing.  
           [0005]    The applicant has identified that frequent reciprocation of the actuator means in use can be problematic. For example, it can be a significant factor in seal abrasion. Debris from within the housing, deposited in the opening in the area of the seal, is also thought to exacerbate abrasion of the seal material.  
           [0006]    An object of the invention is to reduce the frequency of reciprocation of the actuator means, in use.  
           [0007]    A further object of the invention is to prevent or reduce the egress of debris from the housing into the opening.  
         SUMMARY OF THE INVENTION  
         [0008]    In accordance with the invention, a valve apparatus is provided comprising a housing, a piston mounted in the housing for movement between positions corresponding to open and closed conditions of the valve, actuator means moveable by the piston and extending through an opening in the housing for actuating a device disposed externally of the housing, and biasing means arranged to transmit a biasing force between the piston and the actuator means so as to mitigate movement of the actuator means relative to the housing when the valve is in a predetermined operating condition.  
           [0009]    Preferably said actuator means has an abutment portion arranged so as to be biased by the biasing means into abutment with a portion of the housing in the predetermined operating condition of the valve.  
           [0010]    Desirably said abutment portion comprises a surface which abuts a surface of the housing around the opening in the predetermined operating condition of the valve, for closing said opening.  
           [0011]    Conveniently said biasing means allows a predetermined amount of lost motion between the actuator means and the piston.  
           [0012]    Preferably, the valve apparatus further comprises a debris shield arranged to close said opening around the actuator means when the valve is in a predetermined operating condition.  
           [0013]    Preferably said debris shield comprises a surface which abuts a surface of the housing around the opening in the predetermined operating condition of the valve, for closing said opening.  
           [0014]    In accordance with another aspect of the invention, a valve apparatus is provided comprising a housing, a piston mounted in the housing for movement between positions corresponding to open and closed conditions of the valve, actuator means movable by the piston and extending through an opening in the housing for actuating a device disposed externally of the housing, and a debris shield arranged to close said opening around the actuator means when the valve is in a predetermined operating condition.  
           [0015]    Preferably said debris shield comprises a surface which abuts a surface of the housing around the opening in the predetermined operating condition of the valve, for closing said opening.  
           [0016]    Conveniently the valve apparatus includes biasing means for biasing the debris shield into abutment with the housing.  
           [0017]    Desirably the debris shield is fixed for movement with the actuator means, and the biasing means is arranged to transmit a biasing force between the piston and the actuator means so as to mitigate movement of the actuator means relative to the housing when the debris shield abuts the housing.  
           [0018]    Desirably said biasing means allows a predetermined amount of lost motion between the actuator means and the piston.  
           [0019]    Preferably said housing further includes a boss extending internally of the housing from an internal face of the housing and around said opening, so as to provide support for the actuator means.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    In order that the invention may be better understood, two embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which:  
         [0021]    [0021]FIG. 1 is a schematic drawing showing a valve apparatus;  
         [0022]    [0022]FIG. 1 a  is a schematic drawing showing a modified valve apparatus;  
         [0023]    [0023]FIG. 2 is a schematic drawing showing an alternative valve apparatus;  
         [0024]    [0024]FIG. 3 is a schematic drawing showing an external device in the form of a microswitch operable by actuator means of the valve apparatus; and  
         [0025]    [0025]FIG. 4 shows a known valve apparatus. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    Referring to FIG. 1, a proportional control valve apparatus in the form of a pressure raising valve  1  comprises a piston  2  mounted in a valve housing  3 . The valve housing  3  comprises an axially extending generally tubular body portion  4  and an end closure  5 . The piston  2  comprises a substantially cylindrical piston body portion  6  defining an internal cavity in which a piston insert  7  is disposed. A primary spring  8  is disposed internally of the valve  1  between an internal face  9  of the closure  5  and a laterally extending portion  10  of the piston insert  7 . The primary spring  8  biases the piston insert against an internal face  11  of the piston body  6  and away from the internal face  9  of the closure  5 .  
         [0027]    The housing portion  4  is provided with an orifice  12  aligned with a flow passage  13 . In use, movement of the piston towards and away from the end face  9  so as to restrict the orifice  12  can be used to lower and raise the pressure of a fluid F flowing through a flow metering unit of which the flow passage  13  forms a part.  
         [0028]    A further orifice  15  is provided in the valve housing for supplying fluid under controlled pressure into the housing  3  to assist the primary spring  8 .  
         [0029]    Force tending to move the piston  2  towards the open condition (towards the right in the orientation shown in FIG. 1) is provided by the pressure of fluid F acting against an external face  14  of the piston  2 . Force tending to move the piston  2  towards the closed condition (towards the left in the orientation shown in FIG. 1) is provided by a combination of the biasing force exerted by the primary spring  8  away from the internal wall  9 , a force exerted by a device external to the valve (as will be described in further detail below), and pressurised fluid acting on the internal face  11  of the piston  2 .  
         [0030]    The valve apparatus  1  further comprises actuating means in the form of a rod  16  which extends through an opening  17  in the housing end closure  5 , for actuating the external device. Also, the insert  7  has a substantially cylindrical portion which extends in a direction axially away from the inner face  11  of the piston body  6  and is concentrically disposed about an end portion of the rod  16  (the left hand end in the orientation shown in FIG. 1).  
         [0031]    Biasing means in the form of a secondary spring  18  is provided in an annulus between the cylindrical portion of the piston insert  7  and the rod  16  for biasing the rod  16  away from the piston  2  towards the end closure  5 . The secondary spring  18  engages a radially inwardly extending abutment portion  7   a  of the piston insert  7  and a radially outwardly extending abutment portion  16   a  of the rod  16 . In use, force is transmitted from the piston  2  through the secondary spring  18  to the rod  16  for moving the rod  16  axially towards the end closure  5  (the open condition of the valve  1 ).  
         [0032]    To prevent fluid escaping from the housing  3  through the opening  17 , an annular seal  20  is disposed between the housing  3  and the rod  16  in an annular recess  21  within the opening  17  so as to slidingly seal the interface of the rod  16  and the opening  17 . A debris shield is provided in the form of a radially extending portion  22  of the rod  16  having a substantially planar surface  23 . The surface  23  is arranged to abut the internal surface  9  of the end closure  5  under the biasing force of the secondary spring  18  when the valve  1  is in the open condition, thereby shielding the opening  17 .  
         [0033]    The substantially planar surface  23  shown in FIG. 1 may be replaced by a surface  23  carrying a sealing member  23   a  as shown in FIG. 1 a  for engaging the internal face  9  to better ensure debris is excluded from the seal  20  within the opening  17 . The sealing member  23   a  is a substantially annular member housed in a correspondingly shaped groove in the planar surface  23  and may be bonded to the rod portion  22 .  
         [0034]    Retaining means in the form of a nut and washer  19  are provided at the inner end of the rod internally (to the left in the orientation shown in FIG. 1) of the piston insert abutment portion  7   a  for retaining the rod  16  in the piston insert  7 . Although a nut and washer are shown for this application, other means, such as a spring clip, could also be used. A small amount of free play is provided between the portion  7   a  and the rod  16  to provide alignment tolerance. The laterally extending abutment portion  16   a  of the rod  16  serves to facilitate alignment of the rod  16  within the valve  1  and to support and guide the rod  16  for axial movement relative to the piston insert  7 .  
         [0035]    The rod  16  is arranged to actuate an external device, which may be a microswitch device  25 , as shown in FIG. 3. In this manner, information can be passed to electronic control means regarding the condition of the valve  1 . The microswitch device  25  of FIG. 3 comprises a first contact  26 , and a second contact  27  biased by a spring  28  towards a switch closed position shown in broken lines in the lower portion of FIG. 3.  
         [0036]    When the valve  1  is in its closed condition, the piston  2  is disposed further to the left than shown in FIG. 1, closing the orifice  12  and preventing flow of fluid from the body portion  4  through the orifice  12  to the passage  13  is closed. In this condition the primary spring  8 , the secondary spring  18  and the microswitch spring  28  are relatively relaxed and the microswitch is closed. When the pressure of fluid F increases, the piston  2  starts to move towards the right in FIG. 1 against the resilient biasing force of the primary spring  8 , the microswitch spring  28  and the controlled force exerted by pressurized fluid inside the housing  3 . The position of the piston  2  for any given pressure of the fluid F can be controlled by controlling the pressure of fluid supplied into the housing  3  through orifice  15  to move the valve  1  in a desired direction.  
         [0037]    The secondary spring  18  is designed to provide relatively weak resistance in this condition, so as to give some lost motion between the piston  2  and the rod  16  as the valve starts to open. However, in the partially open condition of the valve, as shown in FIG. 1, the secondary spring  18  is stressed sufficiently to drive the rod  16  against the external microswitch spring  28 . As the rod  16  starts to move with the piston  2  towards the open condition of the valve  1 , the rod  16  moves the second contact  27  axially into the switch open position as shown in unbroken lines in FIG. 3.  
         [0038]    The piston  2  continues to drive the rod  16  to the right in the orientation shown in FIG. 1 carrying microswitch contact  27  with it until abutment surface  23  closes against end closure surface  9 , thereby closing the opening  17 . The piston  2  can be driven further to the right in the orientation shown in FIG. 1 against both primary and secondary springs  8 ,  18 , causing the secondary spring  18  to compress, thereby biasing the surface  23  with greater force against the surface  9 . The piston  2  can now reciprocate between various axial positions in the open condition of the valve  1  without moving the rod  16 , provided the secondary spring maintains the rod surface  23  in abutment with the housing surface  9 . The rod  16  thus remains in a substantially fixed position relative to the end closure  5 . This prevents reciprocation of the rod  16  causing wear to the seal  20 , and at the same time prevents debris entering the area of the seal  20 , when the valve is in the open condition.  
         [0039]    When the pressure of fluid F reduces, the forces of the primary and secondary springs  8 ,  18  and microswitch spring  28  combine with the force applied by the fluid supplied through orifice  15  to return the piston  2  towards the closed condition.  
         [0040]    If the valve  1  is used, for example, in a fuel supply system of an aircraft, the rod  16  will normally only need to move once per flight. This provides significant improvements in safety and reliability of the seal  20 . Furthermore, the debris shield  22  functions to mitigate the entrance of debris into the area of the seal  20  in-flight, further improving safety and reliability.  
         [0041]    Furthermore, in use with the valve fully open, a unidirectional load is applied to the valve components. In particular there is no frequent load reversal. This discourages particulate debris liberation which may be caused by fretting, for example between the rod  16  and abutment portion  7   a.    
         [0042]    [0042]FIG. 2 shows another pressure raising valve  1   a.  The construction and operation of the valve  1   a  is similar in many respects to that of the valve  1  described above. Items in valve  1   a  which perform a similar function to corresponding items in valve  1  are provided with identical reference numerals, and to avoid duplication of effort are not described again in detail. Also, the valve orifices  15  and  12  have been omitted from FIG. 2 for convenience.  
         [0043]    As seen in FIG. 2, a modified piston insert  37  is provided, and the secondary spring  18  is not housed within a cylindrical portion of the piston insert  37 , but instead abuts an end face  37   a  of the piston insert  37 . An opposite end of the secondary spring  18  abuts one axial side surface of a laterally extending abutment  22   a  of the rod  36 . An opposite side surface of the abutment  22   a  provides the surface  23  for closing the opening  17 .  
         [0044]    It can also be seen from FIG. 2 that the housing  3  includes a boss  39  which extends internally of the housing from the internal face  9  of the housing. The boss  39  also extends around the opening  17 , enabling the surface  23  to close the opening  17  by mating against an annular end surface  40  of the boss  39 .  
         [0045]    The boss  39  provides increased lateral support for the rod  36 , whilst providing a greater degree of lateral freedom for the laterally extending abutment  22   a  of the rod  36 , thereby facilitating the avoidance of snagging by the abutment  22   a  against the piston insert.