Abstract:
Apparatus and method for releasing a stuck inlet check valve of a paint pump including a solenoid connected to the check valve with a pusher element which momentarily displaces a moveable element such as a ball in the check valve to break any adhesion between the movable element and a valve seat. A control provides a single pulse of energy to the solenoid each time power is applied to the pump. The control includes an SCR connected between a full wave rectifier and a coil of the solenoid, with gate current removed from the SCR to commutate the SCR after a predetermined time interval after power is applied.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to the field of paint pumps having an inlet check valve. In the past, such paint pumps have frequently experienced an inlet check valve stuck in the closed position, because of inadequate cleaning from a prior use. When paint remains in the inlet check valve, the movable element (typically a ball) is adhered to the seat, and inlet suction of the pump is often inadequate to break the adhesion. In the past, such a condition was evidenced by the pump failing to draw paint from a reservoir, and required disassembly of the inlet check valve to free the movable element from the seat, causing inconvenience and delay to the pump operator. 
   The present invention addresses and overcomes the problem of a stuck inlet valve by providing an automatic inlet check valve release, which operates to break any such adhesion between the movable element and the seat automatically each time the pump is readied for operation. 
   SUMMARY OF THE INVENTION 
   In one aspect the present invention is an automatic inlet check valve release which operates to release a movable element of the check valve from adhesion to a seat in the check valve each time electrical power is applied. 
   In another aspect, the present invention is a liquid tight assembly of a solenoid and inlet check valve to prevent contamination of the solenoid by paint. 
   In another aspect, the present invention is an electrical circuit that provides a pulse of energy to the solenoid each time electrical power is applied. 
   In yet another aspect, the present invention is the combination of the automatic inlet check valve release for paint pumps which has a liquid tight assembly of a solenoid and check valve and a control for the solenoid which momentarily energizes the solenoid each time electrical power is applied to the pump. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified block diagram of a pump system useful in the practice of the present invention. 
       FIG. 2  is a perspective view of an inlet check valve useful in the practice of the present invention. 
       FIG. 3  is a perspective view of a solenoid useful in the practice of the present invention. 
       FIG. 4  is a section view of an assembly including the inlet check valve of  FIG. 1  and the solenoid of  FIG. 2 . 
       FIG. 5  is an exploded view of the inlet check valve of  FIG. 1 . 
       FIG. 6  is an exploded view of the solenoid of  FIG. 2 . 
       FIG. 7  is an electrical schematic of a control for the solenoid. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the Figures, and most particularly, to  FIG. 1 , a system  2  for the present invention may be seen. System  2  includes a paint pump  4  having an ON-OFF switch  6  connected to electrical power via a plug  8 . A paint reservoir  3  provides a source of liquid coating material  7  (referred to herein as paint) via a suction tube or apparatus  5  to an inlet check valve  12  associated with and in fluid communication with the pump  4 . When the switch  6  is turned ON, the pump  4  is energized to deliver paint to a paint applicator or sprayer, such as a spray gun (not shown). However, if the inlet check valve is not properly cleaned, a movable element in the check valve may be adhered (by dried paint) to a valve seat, preventing paint from being suctioned by the pump. The present invention has a control  16  that momentarily activates a solenoid  14  (as indicated by pulse  15 ) to momentarily displace the movable element from the seat in the check valve  12 , to break such adhesion. 
   Referring now to  FIGS. 2 ,  3  and  4 , an apparatus  10  having an inlet check valve  12  and a solenoid  14  may be seen. Apparatus  10 , together with a suitable control, makes up an automatic inlet check valve release mechanism. One form of control is shown in  FIG. 7  and is described infra. 
   Referring now also to  FIGS. 4 and 5 , the check valve  12  of apparatus  10  includes an inlet fitting or housing  18 , a valve seat  20 , which may be made of carbide, and a movable element in the form of a ball  22 , it being understood that other movable elements may be used in the inlet check valve while remaining within the scope of the present invention. Ball  22  is retained in proximity to seat  20  by a cage  24  formed integrally with a retainer  26 . A suction set inlet fitting  28  may be threaded into housing  18  and sealed to the housing with an O-ring  30 . Suction set inlet fitting  28  is adapted to receive and secure a suction tube  5  or other suction apparatus such as an extended suction set (not shown). 
   A ball pusher stem  32  is retained to housing  18  by a solenoid inlet fitting  34 . A seal  36  is received on stem  32  to seal stem  32  to housing  18 . A large spring  38  and a small spring  40  are received on stem  32  and urge stem  32  away from ball  22  by reacting against a washer  42 . A nut  44  is loosely captured on inlet fitting  34  and has internal threads  46  to receive and mate with the solenoid  14 . Threads  46  may be conventional garden hose fitting threads. 
   Referring now most particularly to  FIGS. 4 and 6 , the solenoid  14  includes an assembly  50  having a coil  52  and a plunger  54 , with the plunger  54  free to move axially with respect to the coil  52 . An electrical power cord  56  has a pair of insulated conductors  58  connected to terminals  60  on assembly  50  to provide electrical power to coil  52  when desired. An enclosure  62 , together with a cover  66  surrounds assembly  50  and provides a liquid-tight container for assembly  50  and cord  56  by sealing with an O-ring  64  against solenoid enclosure cover  66 . Cover  66  has male threads  68  sized to mate with threads  46 , and an O-ring  70  provides a seal between cover  66  and housing  18  to complete the liquid tight arrangement for the combination of the solenoid  14  and check valve  12 . Threaded fasteners  72  secure cover  66  to enclosure  62 . Although not shown, a ground connection from cord  56  may be secured to a metal frame  74  of assembly  50 . 
   Referring now to  FIG. 7 , a circuit  80  of control  16  for solenoid  14  may be seen. Circuit  80  includes a full wave bridge  82  connected to terminals  84 ,  86  which receive 120VAC electrical power. A 20K ohm resistor  88  supplies DC power to a 9 volt zener diode  90  through a diode  92  which has a  22  microfarad filter capacitor  94  connected across it, along with a low pass filter  96  made up of a 470K ohm resistor  98  and a  10  microfarad capacitor  100 . A 1Meg ohm resistor  102  is connected across capacitor  100 , to discharge capacitor  100  when power is removed. A 1 K ohm resistor  104  provides base current to an NPN transistor  106 . A 10K ohm resistor  108  is connected between the 9 volt regulated supply of the zener diode  90  and the gate connection  110  of an SCR  112  which controls power to the coil  52  of the solenoid  14 . A back diode  114  is connected across coil  52 . Transistor  106  is preferably a type 2N3904 and SCR  112  is preferably a type EC103D. 
   Operation of the automated inlet pusher valve release is as follows. Each time power is applied to the pump to which apparatus  10  is connected, for example, when an ON-OFF switch (not shown) is turned from OFF to ON, circuit  80  will provide a pulse of energy sufficient to cause plunger  54  to move stem  32  forward, displacing ball  22  from seat  20 , after which pulse the plunger  54  and stem  32  will retract (because of springs  38  and  40 ), allowing the ball  22  to thereafter seat and unseat against seat  20  as the inlet check valve  12  operates to suction paint to the pump to which apparatus  10  is attached. Such momentary ball displacement serves to break any adhesion between ball  22  and seat  20  at the beginning of pump operation. 
   More particularly, when initially energized, circuit  80  provides gate current through resistor  108  via gate terminal  110 , momentarily turning on SCR  112  and energizing coil  52 . Once the low pass filter  96  times out, the transistor  106  will shunt gate current away from gate terminal  110 . Once gate current is removed from SCR  112 , the next time the unregulated DC available at terminals  60  falls toward zero, SCR  112  will shut off when the current through it falls below the holding current level sufficient to maintain conduction. Thereafter transistor  106  remains in a conducting state, keeping SCR  112  turned off for the duration of operation of the pump (not shown). Once power is removed from terminals  84 ,  86  (for example when the ON-OFF switch (not shown, but to be understood to be connected in series with one of terminals  84  or  86 ) is turned OFF, resistor  102  will “reset” the circuit  80  by discharging capacitor  100 , after which the circuit will be ready to supply a single pulse to momentarily displace the ball in check valve  12  again when power is reapplied. 
   This invention is not to be taken as limited to all of the details thereof modifications and variations thereof may be made without departing from the spirit of the invention. For example and not by way of limitation, other forms of control  16  may be utilized, such as a momentarily closed relay, while still remaining within the scope of the presently claimed invention.