Abstract:
A valve connected into an ultra-high-pressure fluid circuit (20,000 to 60,000 psi) which, when the system pressure is exceeded to some preset level, vents the pumped fluid to atmosphere while reducing and maintaining a system pressure on the order of five percent (5%) of the original system value. Upon shutting down the system and restarting, system pressure will be restored.

Description:
PRIORITY CLAIM  
       [0001]    This application claims priority under U.S. Provisional Application No. 60/333,820 filed Nov. 16, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to over-pressure protection for any ultra-high-pressure circuit, and ideally for water jet cutting systems driven by the mechanical type, fixed-displacement pump.  
         BACKGROUND OF THE INVENTION  
         [0003]    A plugged orifice or defective valve in an ultra-high-pressure circuit could block normal fluid flow and result in a nearly instantaneous pressure surge which could damage or destroy the pump, blow out a line component or the line itself. The typically used device at present to prevent damage due to accidental over-pressurization is the rupture disc. This component is a metal diaphragm subjected to the system pressure, and designed to fail at some pre-calculated pressure value. But, because of variables in metallurgy and manufacturing accuracy, the burst-pressure varies substantially. The rupture is accompanied by a large bang and sometimes a shower, and afterward, the disc must be replaced.  
           [0004]    Use of the traditional spring-loaded poppet-seat arrangement widely used for pressure relief in hydraulic circuits is not practical for ultra-high-pressure application. Force required to seal the poppet at these high-pressure levels requires large pre-load springs accompanied by very high spring rates. When the spring is adjusted to maintain the poppet-seat seal at system pressure, cracking usually occurs at a substantially higher pressure. As the flow increases from cracking to full system flow, the stem is deflected away from the seat, further compressing the spring and because of the high spring rate increasing the poppet load and thus pressure on the water escaping from the seat. The resulting by-pass pressure could be as much as twice the original system pressure. This defeats the objective of pressure relief, and the sealing surfaces rapidly erode from the heat generated.  
           [0005]    The valve of this invention eliminates the poppet seat problems described above producing full by-pass flow at cracking pressure as little as five to ten percent (5% to 10%) above system pressure with minimal heat generation and erosion.  
         SUMMARY OF THE INVENTION  
         [0006]    The unloading valve of this invention is comprised of a main body threaded on the upper and lower ends. Within the body and extending below is the cylindrical seat, tapered in the lower end, compatible with any standard high pressure fitting. The through hole is blocked at the upper end by a conical poppet secured to the lower end of the spring-loaded stem. The lower end of the stem is slightly below the hole through the body wall which vents the diverted flow. As system pressure increases and unseats the poppet against the spring force acting in the stem, fluid flows into the body cavity below the lower end of the stem. Pressure builds in the cavity until the resulting pressure force on the lower surface of the stem lifts it slightly past the vent hole, and fluid begins to escape through the vent hole. Stem pressure is immediately reduced to the pressure drop across the orifice formed by the lower stem surface partially blocking the vent. The resulting pressure acting on the lower surface of the stem balances the downward spring force. When the pump is shut off, the pressure in the cavity decays allowing the poppet to seat and again hold against normal system pressure. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    Two figures are shown. FIG. 1 is a cross-section of the valve, fitting, and outlet hose. FIG. 2 shows the seat-poppet-vent area with the poppet deflected to full by-pass position. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]    The ultra-high-pressure unloading valve of the invention is designed to screw into a standard ultra-high-pressure fitting  10 , as shown in FIG. 1. The unloading valve includes a body  31 , having a lower threaded nipple  12  and an upper threaded nipple  34 . A seat  11  fits into a counterbore inside of the lower threaded nipple  12 , up to a shoulder  30  within the body. The seat is tapered at its lower end in compatibility with a counter sunk hole  35  in the high pressure fitting, and seals at the shoulder  30  above and in said counterbore  35  below when the lower threaded nipple is screwed and torqued into a threaded port  52  of the ultra-high-pressure fitting.  
         [0009]    The seat  11 , so located and sealed, provides high-pressure fluid communication between the ultra-high-pressure fitting  10  connected into a high-pressure circuit, and a poppet  17 , blocking said high-pressure flow. A spring set  22  provides the force to hold the poppet in sealing position, said force transferred from said spring set  22  through a spring guide  21  and a stem  20  to said poppet. Preferably the spring set is a belleville spring set. Spring force is adjustable by rotating the adjustment screw  24  within a spring housing  23  screwed on to the upper threaded nipple  34  of the body  31 . In an embodiment, the adjustment screw is rotated using a tee handle  25 . Other devices for rotating the adjustment screw are also contemplated, and considered to be within the scope of the invention. A short upwardly extending stem  33  from the top of the poppet  17  into the hole  18  in the lower surface of the stem  20 , the hole being slightly larger in diameter than said stem  20 , allows sufficient radial movement of the poppet to perfectly line up in said seat  11  while still maintaining squareness when the valve closes. This accommodates any misalignment of the internal features within the valve body  31 .  
         [0010]    A bushing  26  is pressed onto the end of the stem  20  providing a very close sliding fit inside of the upper bore of the body  31 . Preferably, the bushing is a bronze bushing, although other alloys or materials may also be used. The lower edge of the bushing is slightly below a vent hole  16  provided in the body when the poppet  17  is fully engaged in the seat  11 .  
         [0011]    The unloading valve is adjusted for overload protection at system pressure by relieving spring force on the poppet  17 . The adjustment screw  24  in the spring housing  23  is unscrewed, reducing the spring force until a slight weep shows at the exit of an outlet fitting  15 , then slightly re-tightened until weep stops. Pressure increase in the high-pressure circuit then slightly lifts the poppet  17  against the pre-load spring force creating leakage past the poppet, filling and pressurizing an interior cavity  13 . Pressure builds within the interior cavity until the pressure force on the lower area of the stem  20 , further exceeds the spring force and the poppet and stem move further away from the seat  11 , until the lower edge of the bushing  26  begins to uncover the vent hole  16 . This forms a small escape orifice area  27 , into the vent hole. The stem continues to move, further uncovering the vent hole and increasing the escape orifice area until the pressure drop across the equivalent escape orifice area, said pressure acting on the lower area of the stem, exactly balances the spring force acting on the stem and poppet at this deflection of said spring set  22 . High pressure fluid is prevented from leaking into the spring cavity  23  by O-ring  19  mounted in the stem above the vent hole. In an additional embodiment, the escape orifice area of the vent hole developed by the movement of the stem uncovering the vent hole can be duplicated by a drilled hole having that area, resulting in the same unloading function. Preferably, the vented fluid flows through the vent hole into the outlet fitting  15 , and flows further through an outlet hose  14  to prevent a sharp “pop” at opening. System pressure immediately decays to less than approximately ten percent (10%) of original system pressure and continues to dump until the system is shut down. After relieving the circuit obstruction, pump restart restores system pressure.