Abstract:
A surge suppression apparatus including a chamber divided into first and second sub-chambers by a diaphragm, a diaphragm follower maintained in contact with the diaphragm and, in use, following the movement of the diaphragm in response to a pressure differential between the first and second sub-chambers, the position of the diaphragm follower relative to the chamber wall determining the existence or otherwise of a communication pathway between the second sub-chamber and a gas inlet and the second sub-chamber and a gas outlet.

Description:
TECHNICAL FIELD 
     This invention relates to a surge suppression apparatus incorporating a pressure regulation assembly. More particularly, but not exclusively, the invention relates to a surge suppression apparatus having means for regulating the pressure of a pressurised gas therein. 
     BACKGROUND FIELD 
     It is known to use a reciprocating pump for the pumping of a liquid in a delivery system. Such reciprocating pumps do not have a smooth output and a pressure drop occurs in the liquid during the reversal of the pump stroke. Surge suppression. apparatus is used to negate the drop in pressure and thereby improve the constancy of the liquid output pressure. 
     A known surge suppression apparatus comprises a passive surge bottle which is basically a captive (static) gas volume acting as a pressure reservoir. A passive surge bottle inevitably loses pressure in use and thus there is a necessity for the periodic recharging of the bottle with compressed gas and the subsequent, associated recalibration of the system utilising the bottle. European Patent Application No. EP 0 707 173 A1 discloses a surge suppression apparatus incorporating an active pressure regulation arrangement which recharges the gas pressure therein automatically. Such an active pressure regulation arrangement in a surge suppressor removes the necessity for the periodic recharging of a passive surge bottle, but the apparatus disclosed in EP 0 707 173 A1 tends to be bulky and inconvenient in use. It is an object of the present invention to provide a surge suppression apparatus in an improved and simplified form. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention there is provided a surge suppression apparatus including a chamber divided into first and second sub-chambers by a diaphragm, a diaphragm follower in use following the movement of the diaphragm in response to a pressure differential between the first and second sub-chambers, the diaphragm follower being movable relative to the chamber wall and being the movable element of a first valve for determining the existence or otherwise of a communication pathway between the second sub-chamber and a gas inlet and being the movable element of a second valve for determining the existence or otherwise of a communication pathway between the second sub-chamber and a gas outlet. 
     The diaphragm follower is biased to contact the diaphragm at all times by a loading derived from gas pressure in the second sub-chamber. 
     Conveniently as an alternative or in addition, the diaphragm follower is coupled to the diaphragm. 
     Desirably said second valve includes a bleed path which opens prior to full opening of the second valve so as to effect a controlled release of pressure through said gas outlet. 
     Conveniently said chamber wall is part of a housing assembly which defines static parts of said first and second valves. 
     Preferably said first and second valves are so arranged that there is a range of movement of the diaphragm on opposite side of a central equilibrium position in which neither valve is operated so as to define a “dead band” in the operation of the apparatus. 
     Conveniently said diaphragm follower includes a disc of larger diameter than the shaft and smaller diameter than the diaphragm engaging the diaphragm and controlling flexure thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
     FIG. 1 a sectional view of a surge suppressor incorporating a pressure regulation apparatus according to the present invention; and 
     FIG. 2 is a sectional view of a surge suppression apparatus according to the present invention in an equilibrium configuration; 
     FIG.  3  and FIG. 4 are sectional views of the apparatus of FIG. 2 in alternative non-equilibrium configurations; and 
     FIG. 5 is across sectional view illustrating a desirable modification. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A surge suppression apparatus  10  includes a circular housing  12 , a circular cylindrical sleeve  14 , a follower shaft  16 , in the form of a sleeve, a centre feed shaft  18  and a flexible diaphragm  20 . 
     In the embodiment shown in the Figures the housing  12  is an integral part of a surge suppressor body  22  and the diaphragm  20  divides a chamber  24  thereof into first and second sub-chambers  26 ,  28 . 
     The housing  12  comprises a substantially cylindrical hollow body part  30  and a substantially annular cap  32 . 
     A wall  34  of the body part  30  is of differing thickness about its circumference such that the longitudinal axis of a cavity  36 , defined by the wall  34 , is not coincident with the longitudinal axis of the body part  30 . The internal surface of the wall  34  has an outwardly extending ledge  38  at the upper end thereof. A passageway  40  extends through the thickest part of the wall  34  from the second sub-chamber  28 , communicating with the cavity  36  above the ledge  38 . A passageway  41  extends through the narrowest part of the wall  34  near to the surge suppressor body  22 . A top surface  44  of the body part  30  engages an annular base  46  of the cap  32 , a ring seal  52  being seated therebetween. 
     A small chamfered annular projection  54  depends from the base  46  of the cap  32  and the cap  32  has a central longitudinal bore  49  therethrough, the bore  49  having a step  56  therein, the lower portion of the bore  49  being wider than the upper portion thereof. 
     The cylindrical sleeve  14  has an outer surface  58  and an inner surface  60 . A lip  62  projects radially from the outer surface  58  at a level near the upper endt of the sleeve  14 . A series of passageways  63  extend radially between the inner and outer surfaces  60 ,  58  of the sleeve  14  above the level of the lip  62 . The outer surface  58  has a first circumferentially extending groove  64  which is slightly below the level of the lip  62  and accommodates a first annular ring seal  66  and a second circumferentially extending groove  68  near to the bottom of the sleeve which accommodates a second annular ring seal  70 . An axial elongate gallery  72  is formed on the outer surface  58  extending substantially between the first and second grooves  64 ,  68 . A plurality of circumferentially spaced passages  74  extend radially through the sleeve  14  from near the base of the gallery  72 . A third circumferentially extending groove  76  is formed in the inner surface  60  of the sleeve  14  at a level between the passages  74  and the second groove  68  so as to accommodate a first radial lip seal  78 . 
     The follower shaft  16  has a head portion  80  and a body portion  82 , the body portion  82  having a smaller diameter than the head portion  80 . The head portion  80  has a first circumferentially extending groove  86  in the outer surface thereof provided so as to accommodate a second radial lip seal  88 . A second circumferentially extending groove  90  in the inner surface of the follower shaft  16 , slightly below the first groove  86 , accommodates a third radial lip seal  92 . Immediately below the head portion  80  there is a shallow annular recess  94  in the body portion  80 . A third circumferentially extending groove  96  is formed in the inner surface of the follower shaft  16  immediately below the recess  94  to accommodate a fourth radial lip seal  98 . A radially extending bore  100  is provided towards the lower end of the body portion  82 . 
     The centre feed shaft  18  has an circumferential groove  102  near the lower end thereof, a cross-drilling  104  which communicates with said groove  102  and a central longitudinal bore  106  extending from the top of the centre feed shaft  18 , intersecting the drilling  104 . 
     In use, the cylindrical sleeve  14  is fixed inside the housing  12  coaxial therewith, the underside of the lip  62  engaging the upper surface of the ledge  38 . The centre feed shaft  18  is fixed in the cap  32  such that the upper end of the centre feed shaft  18  abuts the step  56  and the bore  49  and the drilling  104  are coaxial. The lower end of the centre feed shaft  18  is aligned with the lower end of the sleeve  14  by the step  54  locating on the inner surface  60 . 
     The follower shaft  16  is slidably received by the inner wall  60  of the sleeve  14  and in turn slidably receives the centre feed shaft  18 . The lower end of the follower shaft  16  rests on the diaphragm  20  such that shaft  16  moves with the diaphragm relative to the sleeve  14  and the feed shaft  18 , in response to flexure of the diaphragm  20 . 
     The passageway  40  and the passageways  63  provide communication between the second sub-chamber  28  and a chamber  108  defined between the head portion  80  of the follower shaft  16  and the projection  54  so as to maintain an equal pressure therein. As the pressures in the second sub-chamber  28  and the chamber  108  are equal the vertical forces exerted on the head portion  80  and body portion  82  of the follower shaft  16  are determined by their effective areas. As the head portion  80  has a larger diameter than the body portion  82  the head portion  80  presents a larger effective area than the body portion  82 . Thus there is a net downward force exerted upon the follower shaft  16  maintaining it in contact with the diaphragm  20 . 
     In use, compressed air is supplied to the centre feed shaft  18  via the longitudinal bore  49  through the cap  32  at a pressure in excess of the pressure of the liquid medium present in the sub-chamber  26  in use. 
     FIG. 2, shows the surge suppression apparatus  10  in an equilibrium configuration, the pressure in the first sub-chamber  26  being approximately equal to that in the second sub-chamber  28 . In this configuration the first radial lip seal  78  is in engagement with the follower shaft  16  below the annular recess  94 , the second radial lip seal  88  correspondingly engages the sleeve  14  above the recess  94 , thereby preventing the venting of air from the second sub-chamber  28  to atmosphere via the passageway  41 . The third and fourth radial lip seals  92 ,  98  respectively engage the centre feed shaft  18  above and below the recess  102  (and cross drilling  104 ), thereby preventing the ingress of the compressed air into the second sub-chamber  28 . 
     FIG. 3, shows the surge suppression apparatus  10  in a configuration corresponding to a greater pressure in the first sub-chamber  26  than in the second sub-chamber  28 . In this configuration the follower shaft  16  is displaced upwards by the flexure of the diaphragm  20 , causing the fourth radial lip seal  98  to move above the level of the annular groove  102 . Compressed air supplied at the cap  32  can flow through the bore  106 , the drilling  104 , a clearance  110  defined between the follower shaft  16  and the centre feed shaft  18 , into the second sub-chamber  28  through the bore  100  thereby increasing the pressure in the second sub-chamber  28 . 
     As the pressure in the second sub-chamber  28  increases the pressure difference between the first and second sub-chambers  26 ,  28  is reduced thus restoring the equilibrium condition, the diaphragm  20  flexing downwardly. The follower shaft  16  follows this flexure, causing the fourth radial lip seal  98  to return to a position below the annular groove  102 , thereby preventing further ingress of air into the second sub-chamber  28 . 
     FIG. 4, shows the surge suppression apparatus  10  in a configuration in which there is a lesser pressure in the first sub-chamber  26  than in the second sub-chamber  28 . In this configuration the follower shaft  16  follows the downward flexure of the diaphragm  20 . 
     The downward displacement of the follower shaft  16  results in the lower end of the recess  94  passing below the level of the first radial lip seal  78 . The second chamber  28  and the passageway  41  are placed in communication with each other via the passages  74  and the gallery  72  allowing excess gas to be vented to atmosphere via the passageway  41 . In order to provide a low volume bleed to the exhaust passageway  41  immediately prior to recess  94  passing the seal  78  the shoulder of the recess at the end of the recess closest to the diaphragm, is provided with one or more narrow V-section grooves  94   a  which, when aligned with the seal  78 , allow a bleed of pressure past the seal to the passage  74 . The groove  102  is bounded above and below by the third and fourth radial lip seals  92 ,  98  respectively thus preventing the ingress of compressed gas into the second sub-chamber  28 . 
     As the pressure in the second sub-chamber  28  decreases the pressure difference between the first and second sub-chambers  26 ,  28  is reduced restoring the equilibrium condition, the diaphragm  20  flexing upwardly. The follower shaft  16  follows this flexure, causing the first radial lip seal  78  to return to a position below the recess  94 , thereby preventing communication between the second sub-chamber  28  and the passageway  41  and further venting of air from the second sub-chamber  28 . Once the pressures in sub-chambers  26  and  28  are in equilibrium (the FIG. 2 condition), small flexures of the diaphragm are accommodated without adding or exhausting compressed air to or from the sub-chamber  28  by providing a small range of movement of the shaft  16  (referred to as the “dead band”) in which the operative positions of the recesses and the seals does not change. The “dead band” avoids continual pressure adjustments, generally restricting adjustment of the pressure in the sub-chamber  28  to those conditions where there is a significant change in the fluid pressure in the sub-chamber  26 . 
     In the majority of applications the shaft  16  accurately follows the movement of the diaphragm by being biased against the diaphragm. However in addition to the biasing of the follower shaft  16  into contact with the diaphragm  20  it may be desirable in some circumstances to link the shaft  16  physically to the diaphragm so that it will follow the diaphragm movement irrespective of the biasing. In such circumstances it would be possible to dispense with the biasing of the shaft  16  against the diaphragm. 
     FIG. 5 illustrates a modification which desirably will be incorporated in the embodiment disclosed in FIGS. 1 to  4 . The shaft  16  engages the diaphragm  20  through the intermediary of a disc  110  the diameter of which is between the diameter of the diaphragm and that of the shaft. The disc thus increases the area of contact of the shaft with the diaphragm and in supports the diaphragm controlling the shape which the diaphragm assumes when subject to a pressure differential. The disc has a hollow, externally screw threaded spigot  112  received in threaded engagement in the end of the shaft  16  to secure the disc to the shaft, and there is a cross drilling  114  whereby the interior of the shaft  16  communicates with the sub-chamber  28 . In FIG. 5 the shaft is shown as two concentric components, the inner component simply being a sleeve used to hold the seal  98  in place in the shaft  16 . It will be understood that in those circumstances where connection of the shaft  16  to the diaphragm is preferred the disc  110  can still be provided and if desired a second similar disc can be provided at the opposite side of the diaphragm, linked to the disc  110  by a component extending through the diaphragm in sealing engagement therewith. 
     The arrangements described above will be used, inter alia, to eliminate pressure changes in the supply of liquid or fluid paint from a reciprocating supply pump to one or more paint spraying stations, the sub-chamber  26  communicating with the supply line from the pump. Pressure “spikes” to be eliminated by the above described suppressor can occur in the supply line as a result, for example, of the reciprocating pump changing stroke direction and one or more spray guns becoming inoperative.