Safety valve assembly

Details Safety valve assembly Safety valve assembly

2000-02-15

2001-04-24

Shaver, Kevin (Department: 3754)

Valves and valve actuation

Fluid actuated or retarded

Pilot or servo type motor

C251S038000

Reexamination Certificate

active

06220565

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a pilot-operated safety valve assembly and more particularly to a safety valve assembly suitable for a hydraulic overload protector of a mechanical press.
2. Description of Prior Art
There is a conventional safety valve assembly which is recited in Japanese Patent Publication No. 54-23474 the present inventors previously proposed, as an example of the safety valve assembly of this type.
The conventional safety valve assembly comprises a cylindrical main valve member brought into butting contact with a pilot valve member urged by a pushing spring for setting a safety operation pressure. The butting portion of the main valve member constitutes a relief valve seat.
In order to immediately reduce an abnormally increased pressure of fluid, it is necessary to enlarge a maximum relief amount at the time of a safety operation.
However, the safety valve assembly of the conventional structure has only one relief valve seat. Therefore, a trial to enlarge the maximum relief amount increases a sectional area of a hole of the relief valve seat to result in enlarging a pressure receiving area which starts the pilot valve member opening. And fluid pressure acting on the pressure receiving area determines a pushing force of the pushing spring. Accordingly, it is required to adopt a strong and large one for the pushing spring, which results in enlarging the safety valve assembly.
SUMMARY OF THE INVENTION
The present invention has an object to provide a compact safety valve assembly that can quickly perform a safety operation.
In order to accomplish the above object, an invention of claim
1
has constructed a safety valve assembly in the following manner, for example, as shown in
FIGS. 1
to
3
,
FIG. 4
or FIG.
5
.
The safety valve assembly is adapted to open a main valve
5
by opening a pilot valve
6
. The main valve
5
comprises a first valve seat
11
provided between a pressure port (P) and a discharge port (R), a first closure member
14
which makes an opening and closing movement to the first valve seat
11
, and an urging means
21
for urging the first closure member
14
to the first valve seat
11
. The first closure member
14
has an interior area provided with a restricting passage
16
communicating with an interior area of the first valve seat
11
. The restricting passage
16
has an outlet communicating with an actuation chamber
17
for valve closing which pressurizes the first closure member
14
in a closing direction. Arranged in a radially outer space of the first valve seat
11
between the pressure port (P) and the discharge port (R) is a fitting wall
23
with which the first closure member
14
fits by a predetermined length at a final time of its closing movement. A fitting portion
24
of the fitting wall
23
defines an inner space which forms a valve-opening holding chamber
25
. When an inner pressure of a second valve seat
31
communicating with the actuation chamber
17
for valve closing has exceeded a set pressure, the pilot valve
6
is arranged to separate a second closure member
34
from the second valve seat
31
against a pushing means
37
to discharge fluid within the second vale seat
31
to an exterior area. A sealing sectional area (S) of the second valve seat
31
, a sealing sectional area (T) of the first valve seat
11
, a pressurizing sectional area (U) of the actuation chamber
17
for valve closing and a pressurizing sectional area (V) of the valve-opening holding chamber
25
are set to values enlarging one after the other in the mentioned order.
The invention of claim
1
operates in the following manner, for example, as shown in FIGS.
2
(
a
) and
2
(
b
) as well as in FIGS.
3
(
a
) and
3
(
b
).
As shown in FIG.
2
(
a
), in a state of a normal pressure (Po) where the pressure port (P) has a pressure lower than a set pressure for a safety operation, the pushing means
37
has a valve closing force which overcomes a valve opening force produced by pressurized fluid within the second valve seat
31
to bring the second closure member
34
into closing contact with the second valve seat
31
. At the same time, a valve opening force that pressurized fluid within the first valve seat
11
produces is overcome by a force resultant from a valve closing force produced by pressurized fluid within the actuation chamber
17
for valve closing and a valve closing force of the urging means
21
to bring the first closure member
14
into closing contact with the first valve seat
11
.
As shown in FIG.
2
(
b
), when pressurized fluid within the pressure port (P) has increased to have an abnormal pressure (P
1
), the second closure member
34
separates from the second valve seat
31
to discharge the pressurized fluid within the pressure port (P) to the discharge port (R) through the restricting passage
16
and the second valve seat
31
. Then the actuation chamber
17
for valve closing has an inner pressure rapidly decreased due to flow resistance of the pressurized fluid passing through the restricting passage
16
. Thus the valve opening force produced by the pressurized fluid within the first valve seat
11
becomes larger than the force resultant from the valve closing force produced by the pressurized fluid within the actuation chamber
17
and the valve closing force of the urging means
21
.
The above differential force separates the first closure member
14
from the first valve seat
11
as shown in FIG.
3
(
a
) to rapidly discharge the pressurized fluid within the first valve seat
11
to the discharge port (R) through the valve-opening holding chamber
25
.
The discharge of the pressurized fluid quickly reduces the inner pressure of the pressure port (P). This also decreases the inner pressure of the second valve seat
31
. Then, first the second closure member
34
is brought into closing contact with the second valve seat
31
through a pushing force of the pushing means
37
to enhance the inner pressure of the actuation chamber
17
to a value near that of the inner pressure of the first valve seat
11
. Therefore, the first closure member
14
is pushed in the closing direction through the valve closing force of the pressurized fluid within the actuation chamber
17
.
However, as shown in FIG.
3
(
b
), just before a leading end of the first closure member
14
starts fitting with a front end of the fitting wall
23
, limitation is put on the discharge of the pressurized fluid from the valve-opening holding chamber
25
to the discharge port (R). Consequently, the valve-opening holding chamber
25
has its pressure increased to a value near that of the inner pressure of the first valve seat
11
. This retains the first closure member
14
separated from the first valve seat
11
through the thus increased inner pressurizing force of the valve-opening holding chamber
25
.
And the pressurized fluid within the pressure port (P) is discharged to the discharge port (R) via the interior area of the first valve seat
11
, the holding chamber
25
and the separating gap in order. When the pressure port (P) has almost lost its pressure, an urging force of the urging means
21
brings the first closure member
14
into closing contact with the first valve seat
11
.
The invention as set forth in claim
1
produces the following effects since it is constructed and functions as mentioned above.
When the safety valve assembly performs the safety operation, it is possible to discharge a large amount of fluid from the first valve seat having a large sectional area. Accordingly, there is no need for enlarging the sectional area of the second valve seat so as to increase a maximum relief amount. This reduces a pressure receiving area for starting the valve opening of the second closure member to be brought into closing contact with the second valve seat. As a result, it is possible to downsize the pushing means for the second closure member and therefore make the safety valve assembly compact.
Besides, the actuation chamber for valve closing reduces its pres

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