Abrasive fluid control valve with plastic seat

A valve to control abrasive fluids under high pressure has a plastic seat. A circular ridge peripherally formed on the valve cartridge sealingly engages the seat. A means is provided within the valve cartridge to support the seat axially and radially. The diameter and taper of the poppet match those of a mating recess in the seat.

BACKGROUND OF THE INVENTION 
The present invention relates to a valve for use in abrasive fluid handling 
applications, which employs a plastic valve seat. 
Machines and systems which are designed to carry fluids usually incorporate 
valves of various types to control the flow and pressure of fluids in the 
system. For example, spring-biased check valves are used to regulate the 
flow of fluid into a pump thereby maintaining the desired fluid flow, 
volume, or pressure within the pump. Similar valves are used to control 
the flow of fluids out of the pump. 
The use of abrasive fluids under high pressure poses particular problems 
for the internal components of the fluid control valves. Latex paint can 
cause rapid wear of the valve seats in pumps used in airless paint spray 
systems, and of seats in valves used to control paint flow out of the 
spray gun. To minimize the resultant wear, tungsten carbide valve seats 
and poppets have been used. Tungsten carbide is, however, an expensive 
material. Also, its relative hardness means that the seat must be machined 
to very close tolerances so that it can be press-fit into the valve 
cartridge. Otherwise, it must be braised in place using heat. Also, a hard 
material such as tungsten carbide does not give as tight a seal as do 
softer materials which can deform to compensate for wear. 
Valve seats made of plastic are well known and preferred because of their 
low cost and resilient sealing properties. In high pressure, abrasive 
environments such as that presented by an airless paint pump and spray 
gun, ultra-high molecular weight (UHMW) polyethylene is an ideal material, 
because it is both slick and long wearing, like tungsten carbide, while 
being much less expensive. Prior attempts at using UHMW polyethylene in 
paint control valves have not been truly successful, because of wear and 
extrusion problems. These problems have been primarily the result of valve 
designs that did not adequately support the seat, as UHMW polyethylene is 
not a structural material. The present invention solves these problems 
through a unique combination of design features which minimize the 
extrusion pressure on the seat and which transmit loads to surrounding 
structural components. 
SUMMARY OF THE INVENTION 
In the present invention a spring-biased fluid check valve is connected at 
one end to a source of fluid to be pumped, such as paint, and on the other 
to a pumping chamber. Suction created in the pumping chamber causes the 
valve to open and permits the flow of fluid from the source into the 
pumping chamber. The paint is pumped through a hose into a spray gun 
activated by a paint control valve having a plastic seat with means for 
radially and axially supporting the seat while under pressure. 
The check valve includes a valve cartridge in which a valve stem and poppet 
are slideably mounted in the bore of a plastic bearing which has radiating 
fins engaging the inlet bore of the valve cartridge. The poppet seats on a 
plastic valve seat which fits into the inlet or high-pressure end of the 
valve cartridge. The valve seat covers the entire high-pressure end 
surface of the cartridge, eliminating the need for a separate washer. The 
high-pressure end cartridge surface is formed with a circular ridge around 
its outside edge to partially engage the valve seat, thereby minimizing 
the area of the seat susceptible to extreme deformation and improving its 
sealing ability. 
The central portion of the valve seat which receives the poppet is recessed 
and extends downward into a corresponding recess in the valve cartridge. 
The walls of the seat which contact and receive the poppet are tapered 
inward and down to match the corresponding top to bottom inward taper of 
the poppet. Thus, when the poppet is forced into the seat under high 
pressure, the axial and radial forces are effectively transmitted to both 
the valve cartridge and poppet. 
The paint control valve is provided with a brass ring cartridge insert to 
provide radial support for the seat and a steel back-up washer to provide 
axial support. 
An object of the present invention, then, is to provide a fluid control 
valve which is inexpensive and long wearing even in the presence of 
abrasive liquids under high pressure. 
A further object of the present invention is to provide a plastic valve 
seat which is subject to a minimum of wear and deformation from axial and 
radial forces. 
A further object of the present invention is to provide a valve which does 
not require the use of close tolerance, press-fit valve seats. 
Another object of the present invention is to provide a valve seat which 
affords an effective and long lasting seal against fluid leaks.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As best seen in FIG. 1, an assembled check valve 1 is located within block 
2 of a pump of an airless spray paint system. As typically used, low 
pressure-end 3 of valve 1 is connected to a paint source, and high 
pressure port 4 discharges into pumping chamber 5. 
Circular valve cartridge 6, preferably made of brass, steel or other 
similar material, is provided with external threads for securing valve 1 
inside block 2. The lower section 7 of the cartridge 6 is machined to 
accept a standard socket-type wrench so that the valve can be quickly 
installed or removed from its low pressure-end. 
Extending longitudinally through the center of cartridge 6 is circular bore 
8. Said bore 8 is of uniform diameter except where it narrows at seat 
support ledge 9 and then widens slightly above said ledge. Centrally and 
slidably mounted within bore 8 is valve stem 10. A plastic bearing 11 
surrounds a portion of valve stem 10 inside bore 8 and has radiating fins 
11a which contact the interior surface of cartridge 6 and the lower 
surface of ledge 9. 
A coil spring 12 surrounds bearing 11 and contacts the lower edges of fins 
11a. The lower portion of spring 12 surrounds plastic spring support 13 
which is press fit on the lower end of valve stem 10. Spring support 13 is 
secured to valve stem 10 by split washer 14 that press fits into slot 15 
on valve stem 10. 
Circular valve poppet 16, preferably made of steel, ceramic, or other 
structural material, is cemented on valve stem 10 against integral stem 
lip 17. Poppet 16 is tapered inward and down such that its maximum and 
minimum diameters are identical to the maximum and minimum diameters of 
bore 8 respectively. 
Valve seat 18, preferably made of ultra-high molecular weight polyethylene, 
is generally circular in shape with a valve poppet seat section 19 which 
loosely engages the top surface of seat support ledge 9 and interior walls 
of the upper portion of bore 8. The inner walls 20 of cylindrical section 
19, rather than being vertically oriented like the exterior walls, are 
tapered inward and down to match and receive the taper of valve poppet 16. 
Valve seat 18 covers the entire horizontal surface of the high-pressure end 
of valve cartridge 6, initially and primarily contacting circular ridge 21 
which is integral to the top surface of cartridge 6. This eliminates the 
need for a press-fit valve seat with corresponding close tolerances and 
the need for a separate sealing washer. When check valve 1 is assembled, 
little resistance is felt against the wrench while the cartridge is 
initially being torqued down. When the lower surface of valve seat 18 
engages ridge 21, a sudden increase in required torque is perceived, and 
the assembler then knows that the proper depth of cartridge 6 within block 
2 has been achieved. Circular ridge 21 is preferably approximately 
one-half the thickness of valve seat 18 so that ridge 21 can penetrate but 
not pierce seat 18. This provides an excellent seal against leaks under 
high pressure. It also focuses the forces exerted by poppet 16 while under 
pressure along the outside edge of seat 18, thereby minimizing the 
possibility of extrusion of seat 18 overall. 
Spring 12 biases valve 1 in the normally closed position, forcing valve 
stem 10 and poppet 16 into and against seat 18. Under pressure, cartridge 
6, particularly ledge 9, block 2, and poppet 16 provide both radial and 
axial support for seat 18, reducing wear and effectively transmitting 
extrusion forces to poppet 16, cartridge 6, and block 2. 
As shown on FIGS. 6 and 7, paint control valve 22 employs slightly 
different means for providing the unique radial and axial support for 
valve seat 23. Fluid filter-diffuser 38, which receives and supports the 
low-pressure side of seat 23, has a bore 24 which is larger in diameter 
than preferred for seat 23. Back-up washer 28, made of a structural 
material such as steel, effectively reduces that diameter and provides 
axial support for seat 23. Sealing washer 33, made of a resilient 
material, forms a seal between filter-diffuser 38 and back-up washer 28. 
Seat 23 is mounted between valve cartridge 26 and back-up washer 28. 
Circular ridge 30 is formed around the outside edge of cartridge 26 to 
sealingly engage seat 23. Seat support ring 25, made of brass or similar 
material, is placed inside the high-pressure end of cartridge 26 to 
radially receive and support cylindrical section 31 of seat 23. 
The interior walls of seat 23 are tapered to receive and match the taper of 
poppet 32. Valve needle stem 34 extends centrally through the bore of 
cartridge 26 and into poppet 32. Retainer 36 surrounds stem 34 and 
transmits the forces of spring 37 to seal 35. Seal 35 is made of a 
resilient material which expands to prevent fluid leakage past stem 34 and 
out of cartridge 26. 
When the spray gun operator wishes to commence paint flow, needle stem 34 
is actuated, moving poppet 32 away from seat 23. Paint under high pressure 
can then enter port 39 and flow into fluid filter-diffuser 38.