Fluid handling – Systems – Multi-way valve unit
Reexamination Certificate
2000-05-26
2001-05-29
Lee, Kevin (Department: 3753)
Fluid handling
Systems
Multi-way valve unit
C137S487500
Reexamination Certificate
active
06237635
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of pressure control systems to control the exhaust pressure in exhausters or exhaust apparatus.
Description of the Prior Art
In oxidation, diffusion or CVD devices or similar devices, after various gases are supplied into the chamber for reaction, the gases which have passed through the reaction process are exhausted by the exhauster.
In this process, because a sudden change in the internal pressure of the chamber might bring an adverse effect on the reaction process in the chamber, a pressure control system is provided in the exhauster so that a constant exhaust gas pressure is maintained at any time, regardless of any change in the flow rate of the gas being exhausted and any change in the pressure in the downstream of the exhauster.
One example of this kind of exhauster pressure control system is the one defined in the U.S. Pat. No. 5,000,221. As shown in
FIG. 7
, in the pressure control system
100
according to that specification, a piston
300
is provided in the inside space of the main body in which an inlet port
220
and an outlet port
240
are formed; the piston
300
moves back and forth in the space according to variation in the pressure at the inlet port
220
and outlet port
240
to make the fluid pressure at the inlet port
220
constant.
Moreover, other examples of such pressure control systems are those defined in the unexamined Japanese Patent Publications Nos. 150938/92 and 317919/95. As shown in
FIG. 8
, the pressure control system
102
as defined there turns the valve disc
302
provided between the inlet port
222
and the outlet port
242
to open or close the fluid passage whose cross section is circular. By monitoring the pressure at the inlet port
222
and feeding back the output to the servo motor
400
, the valve disc
302
is turned so as to adjust its opening.
FIG. 9
shows the characteristic of the pressure control system
100
as shown in FIG.
7
. In this pressure control system
100
, which is not a system that detects the pressure at the inlet port
220
and feeds back the detected pressure to operate the piston
300
, the position of the piston
300
varies depending on the flow rate. Pressure variation caused by flow rate changes is considerable as shown in
FIG. 9
, resulting in poor stability. Even when stability is achieved, there remain problems relating to shift and hysteresis.
FIG. 10
shows the characteristic of the pressure control system as shown in FIG.
8
. In this pressure control system
102
, the pressure at the inlet port
222
as detected by the pressure sensor is fed back to the servo motor
400
to turn the valve disc
300
. The accuracy in the control pressure is comparatively high, but, as shown in
FIG. 10
, the magnitude of pressure variation caused by flow rate changes is considerable, resulting in poor stability.
BRIEF DESCRIPTION OF THE INVENTION
The problems of the prior art are solved according to the present invention which is characterized by an exhauster pressure control system comprising a main body in which an inlet and an outlet port are formed and a pilot chamber is provided, and a spool with a valve. A valve seat is formed on sliding surfaces connecting the inlet and outlet ports in said main body and said spool is held against said sliding surfaces by the force of a spring. The system includes a pressure sensor to detect the pressure at said inlet port, a control valve to supply regulating gas to said pilot chamber and a control circuit to drive said control valve according to the output of said pressure sensor.
Regulating gas is supplied to the pilot chamber according to the gas pressure at the inlet port and the pilot chamber internal pressure moves the spool axially to open or close the valve. Therefore, the gas pressure at the inlet port can be held constant only by adjusting the pressure of regulating gas, regardless of the gas pressure at the outlet port.
In addition, the gas pressure at the inlet port is detected by the pressure sensor and the output of the sensor is fed back, which results in improvement of the response to gas flow rate variation at the inlet port and improved accuracy and stability.
REFERENCES:
patent: 3548866 (1970-12-01), Kaiser et al.
patent: 4133511 (1979-01-01), Hartmann et al.
patent: 4212334 (1980-07-01), Dudar
patent: 4724864 (1988-02-01), Schwelm
patent: 5000221 (1991-03-01), Palmer
patent: 6065487 (2000-05-01), Watson
patent: 6073644 (2000-06-01), Friedmann et al.
patent: 4-150938 (1992-05-01), None
patent: 7-317919 (1995-12-01), None
Aera Japan Ltd.
Lee Kevin
Pearne & Gordon LLP
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