Abstract:
A check valve is installed in the pressure flow line of an abrasive blaster of the type having a pop-up valve which opens under pressure and closes when depressurized to a predetermined level. The check valve is upstream of the pop-up valve and includes a having a valve chamber in communication with the pressure system for seating a valve mechanism adapted for opening and closing the valve chamber in response to the pressure level in the pressure system for closing the pressure system to back flow when the pressure in the system reaches a predetermined level.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of application Ser. No. 12/011,339, filed on Jan. 26, 2008 and claims priorty based thereon. application Ser. No. 12/011,339 is fully incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention is generally related to abrasive blaster system and is specifically directed to a balancing system for controlling backflow of abrasive into the pressure system during blow down operations. 
         [0004]    2. Discussion of the Prior Art 
         [0005]    Abrasive blaster systems are well known. Typical abrasive blaster include the 1.5, 3.5, 6.5, 8, 10 and 20 cubic feet abrasive blasters manufactured and sold by Axxiom Manufacturing, Inc., Fresno, Tex., USA and sold under the brand name SCHMIDT. These systems include a pressure vessel or tank having two chambers, a pressure chamber and an abrasive chamber. In order for the system to operate properly, the pressure chamber and the abrasive chamber must be balanced. A pop-up valve in the pressure inlet pipe permits the system to automatically react to pressure changes by opening and closing a passageway between the abrasive chamber and the pressure chamber. 
         [0006]    During blow down, when the system is depressurized, the pop-up valve closes the pressure inlet. This is primarily to prevent stray abrasive particles for flowing back into the pressure system. However, it has been determined that this is an inefficient method for closing the pressure system to back flow of some of the particles. Therefore, there is a need to further reduce the potential back flow of particles into the pressurization system during blow down and depressurization of the pressure chamber. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is directed to the check valve assembly which is located in the pressure line for the pressure chamber of an abrasive blaster upstream of the mushroom pop-up valve. The check valve is positioned in the pressure system upstream of the pop-up valve and comprises a valve body having a valve chamber in communication with the pressure system for seating a valve mechanism and a valve mechanism seated in the valve chamber and adapted for opening and closing the valve chamber in response to the differential pressure level in the pressure system for closing the pressure system to back flow when the pressure in the system reaches a predetermined level. 
         [0008]    In the preferred embodiment the check valve includes a bleed hole in the valve body which is always open. The valve mechanism is a ball check valve and the valve body includes a ball seat. A biasing system may be incorporated in the valve for normally biasing the ball valve into closing engagement with the ball seat. 
         [0009]    The check valve assembly includes a body for housing the check valve mechanism, an outlet coupler and an inlet coupler. When the system is pressurized, the check valve opens and the pressurized fluid flows through the check valve permitting the mushroom pop-up to lift into the chamber. When the pressure is relieved, gravity permits the mushroom valve to retract. 
         [0010]    The check valve of the subject invention substantially reduces the likelihood of back flow into the external system. 
         [0011]    When the system is pressured up, the ball is lifted in the seat for permitting pressurized flow in normal fashion, lifting the mushroom pop-up valve. As the system blows down, and pressure drops, the ball drops into the seat and closes off the pressure system as soon as pressure is low enough to permit the ball to drop. 
         [0012]    This is also the time when migrant abrasive particles tend to back flow into the system. The ball check valve prevents this occurrence. 
         [0013]    In the preferred embodiment the bleed hole is provided in the valve body for balancing the system during low pressure conditions. This provides a balancing feedback function. Typically, the bleed hole is much smaller than the main valve bore. 
         [0014]    The ball valve may be biased toward the seat by gravity or by other biasing means such as a compression spring or the like. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a cutaway view of a pressure vessel incorporating the check valve system of the subject invention. 
           [0016]      FIG. 2  is a view of the pop-up valve in the down position, with the check valve at the lower end thereof. 
           [0017]      FIG. 3  is a view looking in the same direction as  FIG. 2 , with the pop-up valve in the up position. 
           [0018]      FIG. 4  illustrates the pop-up valve, check valve and pipe assembly. 
           [0019]      FIG. 5  is an exploded sectional view of the check valve assembly. 
           [0020]      FIG. 6  is an exploded perspective view of the check valve assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    The check valve system  10  of the subject invention is adapted to be used in combination with the pressure vessel of an abrasive blaster system. As shown in  FIG. 1 , the pressure vessel  11  may be stationary or portable. When portable, the vessel  11  is mounted on a frame  12  having wheels  14 , a load skid  16  by which the vessel may be stowed in a horizontal orientation, and a handle  18  for facilitating movement of the pressure vessel. 
         [0022]    The pressure vessel  11  is subdivided into a plurality of chambers, and as here shown includes the upper chamber or pot  19  for holding the abrasive. The lower chamber  20  is the pressurized chamber. A source of pressurized fluid, typically air, is introduced into the vessel  11  and the pressure chamber  19  through an inlet pipe  22 . The inlet pipe  22  is typically connected to piping and valves coupled to a source of pressurized air (not shown). The abrasive chamber  19  includes a lower inlet  24  through which the pressurized fluid flows to mix with the abrasive and force through a suitable outlet (not shown). Typically a lid  26  is provided for covering the abrasive chamber. However, the lid is not required for operation. Also, a screen  27  may be provided where desired. As the pressurized air enters the chamber via inlet  22  it drives the abrasive flow through outlet  23  to a metering valve (not shown) which is coupled to the outlet  23 . 
         [0023]    A blowdown or depressurizing outlet  25  is provided for depressurizing the entire system when off or as required for maintenance. 
         [0024]    In most configurations a handway assembly  30  is provided and includes a sealing gasket  32 . The handway assembly may be manually opened and closed for access to the pressure chamber  20  for cleaning and maintenance. 
         [0025]    Pressurized fluid is introduced into the vessel through pipe  22 . A mushroom pop-up valve  34  is located in the vertically oriented open end  37  of the inlet pipe. Typically, the mushroom head is made of a heavy, durable material such as, by way of example, polyurethane. The inlet  24  in the upper abrasive chamber  19  is adapted to mate with head  34  and is provided with a gasket  36  for substantially sealing the pressure chamber  20  from the abrasive chamber  19  when the system is fully pressurized. Specifically, as the pressurized fluid flows into the chamber  19  through the pipe  22 , it lifts the pop-up valve upward and into closing contact with the gasket  36 . 
         [0026]    As is well known to those who are skilled in the art, the pressurized fluid flow introduced into the pipe  22  is also introduced into a control valve system (not shown) for controlling the release an abrasive and fluid mix through an application valve (also not shown). 
         [0027]    The present invention is directed to the check valve assembly  10  which is located in line in the pipe  22 , and positioned in a vertical orientation just below the lower most position  40  of the stem  38  of the mushroom pop-up valve  34 , see  FIGS. 2 ,  3  and  4 . As shown specifically shown in  FIG. 2 , the check valve assembly is located between the vertically oriented end  44  of inlet pipe  22  and the lower end  46  of outlet portion  37  of the pipe assembly. The check valve assembly includes a body  50  for housing the check valve mechanism, an outlet coupler  52  and an inlet coupler  54 . In the illustrated embodiment the couplers are adapted to be mated with complementary ends in the pipes  22  and  37 . However, it should be understood that any suitable coupling mechanism could be used, such as, by way of example, welding. 
         [0028]    In operation, when the pipe  22  is pressurized, the check valve  10  opens and the pressurized fluid flows through the check valve and into the pipe  37 . This lifts the mushroom pop-up valve  34  into engagement with the mushroom gasket  36  for closing off the abrasive chamber  19  from the pressure  20  (see  FIGS. 1 and 3 ). When the pressure in pipe  22  is relieved, gravity permits the mushroom valve to retract into the pipe  37 , with the mushroom head substantially closing off the upper end of pipe (see  FIGS. 1 ,  3  and  4 ). 
         [0029]    However, during the blow down period small amounts of abrasive may enter into the pipe  37  and as the system is depressurized abrasive material can backflow into the system outside of the tank  11 , causing malfunction or damage. The check valve  10  substantially reduces the likelihood of back flow from pipes  37  and  20  into the external system. As specifically shown in  FIGS. 5 and 6 , the check valve assembly includes a body  50  with connector or coupler nipples  52  and  54 . The body  50  includes a ball seat  56  for receiving the ball  58 . Through flow through the valve body is provided by the central bore  60  in the inlet nipple  54 , bore  62  in the body  50  and in communication with the ball seat  56 . A retainer disc  66  is adapted to be received in the outlet end of the body  56  and secured in place for holding the ball  58  in the body  50 . The retainer disc  66  includes one or more through holes  64 . 
         [0030]    When the system is pressured up, the ball  58  is lifted in the seat  56 , opening the bore  62  and permitting the pressurized fluid to flow through pipe  22  and pipe  37  in normal fashion, lifting the mushroom pop-up valve  34 , as previously described. As the system blows down, and pressure drops, the ball  58  drops into seat  54  and close off the bore  62  as soon as pressure is low enough to permit the ball to drop. This is also the time when migrant abrasive particles tend to back flow into the system. The ball check valve  10  prevents this occurrence. 
         [0031]    In the preferred embodiment a bleed hole  68  is provided in the valve body  50  for balancing the system during low pressure conditions. This provides a balancing feedback function. Typically, the bleed hole  68  is much smaller than the main valve bore  62 . It has been determined that a bleed hole having 1/100 the flow of the main bore  62  is sufficient to provide proper balancing feedback. 
         [0032]    The ball valve  58  may be biased toward the seat  56  by gravity or, as shown in  FIGS. 5 and 6 , by a compression spring  70  which is also held in place by the retainer disc  66 . 
         [0033]    The incorporation of the check valve assembly  10  into the pressure circuit of the blaster system has reduced backflow of the abrasive into the system and reduced both maintenance and incidence of failure of the system. While certain embodiments and features of the invention have been shown and described in detail herein, it should be understood that the invention includes all modifications and enhancements within the scope and spirit of the following claims.