1. Field of the Invention
This invention relates to a three way sliding poppet valve for switching high pressure, high temperature fluids under low pressure control and, in particular, this invention relates to a low internal volume three way valve for high speed switching of high pressure, high temperature fluids without volume change for precision laboratory measurements such as is encountered in permeameter tests with corrosive fluids involving core samples.
2. Description of the Prior Art
In permeameter tests, high temperature (such as 280 degrees Fahrenheit) and high pressure (such as 10,000 psi) corrosive fluids (such as brine, oil, and gas) are injected into core samples to measure relative or specific permeability of the core sample. A computer operated permeameter requires a multi-port, three way valve capable of zero volume change and having low internal volume as well as a rapid response time. One prior art approach used VALCO rotary valves such as those manufactured by Valco Instruments, Inc., P.O. Box 55603, Houston, Tex. 77255. These rotary valves, however, have small flow paths and a slow response time such as 0.5-2.0 seconds.
Prior to the filing of the present invention, a patentability search was conducted resulting in the following patents:
______________________________________ Inventor Patent No. Date ______________________________________ C. M. Carlson 3,002,532 10-03-61 N. C. Hunt 3,016,917 01-16-62 Maurice F. Franz 3,570,541 03-16-71 Gerald Sorenson 3,587,156 06-28-71 Gerald Sorenson 3,762,443 10-02-73 Stoll et al. 3,794,075 02-26-74 Brake et al. 3,902,526 09-02-75 Charles Perkins 4,027,700 06-07-77 Erich Ruchser 4,067,357 01-10-78 Paul Arvin 4,103,711 08-01-78 Clifford Peters 4,209,040 06-24-80 Clifford Peters 4,217,934 08-19-80 Coppola et al. 4,567,914 02-04-86 ______________________________________
The 1971 and 1973 patents to Sorenson pertain to the method of manufacturing a pressurized fluid control valve utilizing a valve spool centrally located in a valve body. The embodiment shown in FIG. 17 of Sorenson shows a multi-passage valve utilizing a symmetrically shaped spool wherein the spool has an incline surface that seats against a sharp circular edge formed in the body. The Sorenson spool or valve body is constructed of deformable resilient materials such as polyurethane, neoprene, polyethylene, or rubber. Deformability of the valve spool or body of Sorenson is critical since in the manufacturing of the valve, the spool or body must deform in order to be inserted into the body. After the insertion, the deformed part recovers to its original condition. In such an embodiment, the forces of deformation are much greater than the forces experienced by the valve in operation. As such, it is believed that the valve of Sorenson would not be suitable to the high temperature, high pressure environments for which the valve of the present invention is ideally suited. Furthermore, Sorenson requires fluid exhaust ports. The present invention has no exhaust ports since it is applied to the flow of high pressure, high temperature fluids which must be completely contained within the valve. Sorenson relies on multiple annular rings providing simultaneous multiple seals caused by moving the spool. The current invention requires only one sealing surface to contact the spool at a time. Sorenson valves are commonly known as 4-way valves, whereas the present valve is specifically a 3-way valve. Finally, the present valve provides means of applying very large forces to a sealing line formed by the poppet (or spool) contacting the sealing surface in the body, namely the large diameter pistons.
The 1974 patent to Stoil U.S. Pat. No. (3,794,075) sets forth a multi-way valve having a switching time of six milliseconds and exhibiting short physical valve travel. The Stoll invention makes use of disc plane seals located on a symmetrical center spool. The spool is driven by the snap action of opposing diaphragms which are hydraulically activated. The rubber diaphragms comprising the spool end seals and snap action diaphragms make this valve unsuitable for high pressure applications. High internal pressures would collapse these parts causing the valve to fail. The central O-ring seal of the spool is not constrained so that back pressure on the seal would unseal the O-ring causing leakage. This is not the case in the present invention. Because of flexure of the rubber parts some internal volume change must occur in the Stoll valve after the seals make initial contact. This volume change will compress the fluid in one part of the valve causing a pressure change. This problem does not exist in the present invention. Under high differential pressure the unsupported elastomeric seals used by Stoll may experience extrusion. The problem is accentuated at high temperature. The present valve uses metallic sealing surfaces to eliminate the problem.
The 1962 patent issued to Hunt (U.S. Pat. No. 3,016,917) sets forth a valve for controlling high pressure fluid. The valve plunger of Hunt has an enlarged central body portion terminating in an angled seating surface on an enlargement of the valve which selectively abuts against a corresponding angled seat in the cavity. Hunt utilizes a metal to metal engagement between the valve enlargement and the seat to provide a seal against leakage of fluid pressure. The valve is held in the closed position by means of a solenoid and is returned to the opened condition by means of a spring. In this embodiment the central valve spool is not hydrostatically balanced.
The 1971 patent to Franz (U.S. Pat. No. 3,570,541) sets forth a three way directional control valve having a formed poppet member located internally to a body wherein the body has internally disposed conically shaped seats for selective engagement with the poppet member to open and close the three way valve. The poppet member and seat incorporate an elastomeric material. The Franz valve is designed to operate at 100 psi with an activating piston driven valve control operating at 70 psi.
The 1986 patent to Coppola (U.S. Pat. No. 4,567,914) relates to a two-stage hydraulic solenoid valve having a centrally disposed poppet member having incline surfaces that selectively seat with conical seats. The Coppola invention is designed for steam turbine control systems.
The 1978 patent to Ruchser (U.S. Pat. No. 4,067,357) relates to a sliding/spool direction control valve wherein the spool is of symmetrical construction and is driven by two opposing control pistons. The Ruchser embodiment provides a novel seating arrangement that selectively seals despite loss of tolerances due to wear, manufacturing, or use.
The remaining patents uncovered in the search are not as pertinent to the present invention as those discussed above.