Fluid handling – Line condition change responsive valves – Direct response valves
Reexamination Certificate
2000-02-24
2001-09-18
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Line condition change responsive valves
Direct response valves
C137S522000, C137S540000
Reexamination Certificate
active
06289927
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressure control valve for keeping the interior of a pressure circuit at a specified setting pressure.
2. Description of the Related Art
As a pressure control valve for keeping the interior of a pressure circuit at a specified setting pressure, a direct-operated relief valve
2
, for example, is known which is illustrated in FIG.
6
.
The direct-operated relief valve
2
keeps a relief port
3
, which is open to the pressure circuit, closed with a valve plug
6
which is pressed by a pressure adjusting spring
4
against the relief port
3
. When the pressure in the pressure circuit rises above a specified setting pressure, the valve plug
6
is pushed up and the relief port
3
communicates with the pressure circuit and part of the fluid flows out of the pressure circuit into the drain port, so that the pressure circuit can be held at a specified setting pressure. Note that the setting pressure is adjusted by changing the pressure of the spring by turning the adjust screw
8
.
In the direct-operated relief valve
2
, the pressure adjusting spring
4
also presses the valve plug
6
and therefore it is necessary to use a strong spring for the pressure adjusting spring
4
when the direct-operated relief valve
2
is used in a pressure circuit at high pressure. However, the use of a large, strong spring makes the relief valve itself large and there is a limit to the strength of the spring used. For this reason, normally, a pilot-operated relief valve
10
shown in
FIG. 7
is adopted in pressure circuits for high pressures.
The pilot-operated relief valve
10
is structured such that the relief port
3
communicates through a throttle
12
with an upper chamber
14
a
of a main valve
14
and also with a direct-operated relief valve
18
that constitutes a pilot section as illustrated in FIG.
7
. When the pressure of the pressure circuit rises above a specified setting pressure and surpasses the pressure of the spring
18
b
, the valve plug
18
a
goes down and the direct-operated relief valve
18
opens. Consequently, the upper chamber
14
a
communicates with the drain port
5
, the pressure of the upper chamber
14
a
decreases, with the result that the main valve
14
opens and the fluid of the pressure circuit flows to the side of the drain port
5
. Thus, the pressure circuit at high pressure can be kept at the specified setting pressure.
For use as an alternate pilot section to replace the direct-operated relief valve
18
of the pilot-operated relief valve
10
shown in
FIG. 7
, if a proportional electromagnetic pressure control section for controlling the pressure of the upper chamber
14
a
by an electric pilot signal is incorporated, it is possible to implement automatic control of the setting pressure of the pressure circuit within a specified range.
However, if the proportional electromagnetic pressure control section mentioned above is used, there is a possibility that the resultant pressure control valve is a type of a complicated internal structure, which increases production cost and poses a problem of safety, such as a fire caused by the use of electricity.
The present invention has been made with the above problem in mind and has as its object to provide a pressure control valve capable of stepless automatic control of the setting value of a pressure circuit, which is made possible by the adoption of a pilot-operated simple-structure without use of electric signals.
SUMMARY OF THE INVENTION
The pressure control valve of the present invention comprises a valve plug placed against a valve seat at a relief port connected to a pressure circuit; and a spring for the valve plug to press the valve plug against the valve seat, the pressure control valve being capable of keeping the interior of the pressure circuit at a specified setting pressure by discharging part of the fluid when the fluid pressure in the pressure circuit surpasses the force of the spring for the valve plug, wherein the force of the spring for the valve plug is increased or decreased by the movement of a pilot piston according to an increase or decrease in the pressure of a pilot liquid, the pilot piston freely movable in the direction of expansion and compression of the spring for the valve plug being disposed at one end of the spring for the valve plug away from the valve plug, the pilot piston being provided with an adjusting spring at the other end of the pilot piston opposite the one end where there is the spring for the valve plug, and the pilot piston being so structured as to move in a direction of going away from the valve plug when the pilot piston receives a pilot fluid at a specified pressure.
According to the pressure control valve when there is no influx of the pilot fluid, the valve plug is being pressed against the valve seat by the spring for the valve plug and the adjusting spring and therefore the interior of the pressure circuit is held at a specified setting pressure. When the pressure of the pressure circuit rises above the setting pressure and surmounts the force of the spring for the valve plug, the valve plug recedes to open the relief port and allow the fluid from the pressure circuit to enter and flow out of the drain port. And, when the pressure of the pressure circuit goes down and reaches the setting pressure, the valve plug is brought into contact with the valve seat at the relief port by the force of the spring for the valve plug and the interior of the pressure circuit is held at the setting pressure.
Because, when the pilot fluid flows in, the pilot piston moves in the direction of going away from the valve plug, the spring for the valve plug is increased in length and the pressure of the spring is decreased. As the pressure of the spring for the valve plug is decreased, the force pressing the valve plug against the valve seat decreases, and thus the pressure control valve works as a pressure control valve with a lower setting pressure.
The pressure control valve further comprises a first piston movement limiting means for preventing the pilot piston, which has moved to a position closer to the valve plug, from moving the pilot piston beyond the above-mentioned closer position on the side of the valve plug even if the pressing force of the adjusting spring is increased. The pilot piston does not move in the direction of going away from the valve plug before the pressure of the pilot fluid rises to a specified value and a fixed large spring force presses the valve plug against the valve seat. Therefore, this pressure control valve can be used as a pressure control valve with an upper limit of setting pressure.
The pressure control valve furthermore comprises a second piston movement limiting means for preventing the pilot piston, which has moved to a position remote from the valve plug, from moving to a remoter position beyond the above-mentioned remote position even if the pressing force of the adjusting spring is decreased. When the pressure of the pilot fluid rises above a specified value, a fixed small spring force of the spring for the valve plug presses the valve plug against the valve seat. Therefore, this pressure control valve can be used as a pressure control valve with a lower limit of setting pressure.
REFERENCES:
patent: 2742054 (1956-04-01), Poundstone
patent: 2944564 (1960-07-01), Pettey
patent: 3713295 (1973-01-01), Haak et al.
patent: 3923075 (1975-12-01), Farrell
patent: 4463929 (1984-08-01), Dantlgraber et al.
patent: 5234028 (1993-08-01), Takano et al.
patent: 2184814A (1987-07-01), None
Furukawa Co., Ltd.
Michalsky Gerald A.
Young & Basile P.C.
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