Note: Descriptions are shown in the official language in which they were submitted.
~ 27~
This invention relates to a hydraulic relief valve
responsive to sense and relieve excessive pressure in a
pressurized chamber.
This hydraulic relief valve has a particular but not
exclusive application to relieving an overload in mechanical
presses. Mechanical presses are commonly used for forming objects
between dies. In these presses, the upper die is carried
repeatedly by a reciprocating ram into and out of co-operative
relation with the lower die in t.he forming operation,
overload can occur during the operation of such a
mechanical press due to obstruction or to misalignment of the
dies. This can cause serious damage to the press an~ to the dies
and it is important to sense and relieve overload quickly and then
stop power input to the ram.
Hydraulic systems have been developed which are capable
of sensing and relieving overload quickly and which are capable of
then stopping power input to the ram. In the use of these systems
a hydraulic overload chamber is provided within the ram, This
chamber is pressurized with a hydraulic Eluid from a pressure
controlled source. ~s the ram descends, pressure in the hydraulic
overload chamber is increased due to die action. These systems
sense the fluid pressure in the overload chamber and act to
relieve an undue increase in pressure by venting the pressurized
overload chamber to atmosphere or a lower pressure chamber. When
so vented, the overload chamber collapses and relieves the
overload. It also sets a control apparatus into motion that
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HAS(l) - 46181
disengages the drive to the ram of the press
To properly protect the mechanical press, the relief
system should preferably be able to vent the overload chamber in
the ram and permit its collapse in approximately a couple of
millisecondsA This requires a low inertia relief valve element
that can be accelerated to its open position by the full force o
the overload pressure acting on the relief valve element's area
exposed to the overload chamber. The more simple hydraulic relief
systems of the prior art have been inadeguate because they are
slow. Low inertia valve assemblies have been developed but for
one reason or another they have not been reliable in use.
United States Patent ~,015,620 to LoUis E. Carrieri
discloses a valve assembly having a light weight low inertia
single spool valve element that is designed to accelerate its
opening under the full force produced by the overload pressure
acting on spool's area exposed to the overload chamber and vent an
abnormally high pressure in the overload chamber. It is effective
in some conditions of operation, but, like other rellef valves, it
is insensitive to low flow rates. Since the motion of the ram in
a mechanical press is sinusiodal, its velocity approaches and
reaches zero as the ram approaches and reaches its bottom dead
centre position. Also, most overloads in mechanical presses will
occur in this reyion of low ram velocity due to improper die
setting practices or simply because many press users purposely
bottom out a die to give the formed part its final set. Overloads
of this nature, occurring only several thousands of an inch above
HAS(l) - 46181 ~278~
bottom dead centrel must only displace a small volume of fluid
from the overload chamber within the ram to relieve the excessive
pressure build up, which is occurring at a relatively slow rate.
Carrieri's valve, which requires by design a short cylindrical
sealing surface between the relief valve spool and its housing to
seal the overload chamber from the relief valve's vent, possesses
an inherently poor seal with a leak rate that can exceed the Elow
rate from the overload chamber, making it ineffective under the
common conditions described above. ~ow flow rates from the
overload chamber within the ram can also be encountered higher up
in the press stroke on presses equipped with slow inch drives used
for die tryout. If an overload of this type cannot be detected
because of leakage by the overload valve, a multi-point press
could be seriously damaged if the overload occurred under only one
point as its overload chamber could completely collapse and cause
the press ram to twist.
In addition to the drawbacks described above, leakage
past the overload valve from the overload chamber within the ram
can cause the overload system to malfunction at pressures
encountered below the overload pressure. Since most overload
relief valves rely on an area differential across the relief valve
spool to bias the valve closed, it becomes necessary that the
pressure build-up within the overload chamber exceed the initial
pump pressure used to preload the overload chamber. Any leakage
that occurs past the overload valve from the overload chamber at
these higher pressures cannot be replenished by the pump. AS a
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result the overload chamber will collapse by the amount of this
leakage and cause complete loss of overload chamber pressure as
soon as the press ram passes through bottom dead centre. Since
a certain amount of overload chamber pressure is required for
proper cycling of the press, pressure sensing devices are
normally present and will stop the press if the overload chamber
pressure is lost, as it would be abve.
This invention overcomes the di f f iculties of Carrieri
and other prior art by providing two leak proof low inertia
valve elements, a trigger valve element and a relief valve
element, both of which are designed to accelerate their
sequential opening under -the full force produced by the overload
pressure acting on each element's area exposed to the overload
chamber.
According to this invention, there is provided a fast
response relief valve comprising: a housing having a pressure
setting chamber and a pressure sensing chamber; a trigger valve
seat; a low inertia trigger valve element extending between said
pressure setting chamber and said pressure sensing chamber and
reciprocable along a path between said pressure sensing chamber
and said pressure setting chamber between an open and a closed
position on said trigger valve seat such that said trigger valve
element is responsive to the differential in force between said
pressure sensing chamber and said pressure setting chamber; a
relief valve element seat; a low inertia relief valve element
extending between said pressure setting chamber and said
pressure sensing chamber and reciprocable along a path between
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said pressure sensing chamber and said pressure setting chamber
between an open and a closed position on said relief valve seat
such that said relief valve element is responsive to the
differential in force between said pressure sensing chamber and
said pressure setting chamber; said trigger valve element seat
and said relief valve element seat each being a positive stop
for their respective valves; a pressure relief passage, said
trigger valve element when seated on its seat being adapted to
seal said pressure setting chamber and said pressure sensing
chamber from said pressure relief passage and when open adapted
to permit communication between said pressure set-ting chamber
and said pressure relief passage, while still maintaining said
seal between said sensing chamber and said relief passage; said
relief valve element when closed being adapted to seal said
pressure setting chamber and said pressure sensing chamber from
said pressure relief passage and when open being adapted to
permit communication between said pressure sensing chamber and
said pressure reIief passage, while still maintaining said seal
between said setting chamber and said relief passage, said
trigger valve element and said relief valve element being
reciprocable as aforesaid independently of each other.
In another aspect there is provided a fast response
relief valve comprising: a housing having a pressure setting
chamber, a pressure sensing chamber, and a pressure relief
passage intermediate said pressure setti.ng chamber and the said
pressure sensing chamber; a relief valve element seat between
said pressure sensing chamber and said pressure relief passage;
lZ78~39
a relief valve element extending axially between said pressure
sensing chamber and said pressure setting chamber and
reciprocable along its axis between an open and a closed
position on said relief valve seat; a trigger valve seat between
said pressure settiny chamber and said pressure relief passage;
a trigger valve element extending axially between said pressure
sensing chamber and said pressure setting chamber and
reciprocable along its axis between an open and closed position
on said trigger valve seat; a trigger valve element seal
between said pressure sensing chamber and said pressure relief
passage; a relief valve seal between said pressure sensing and
said pressure relief passage; whereby said trigger valve element
is responsive to the differential in force between said pressure
sensing chamber and said pressure setting chamber and when
seated on its seat, saaling said pressure setting chamber and
said pressure sensing chamber from said pressure relief passage
and when unseated from its seat permitting communication between
said pressure setting chamber and said pressure relief passage
while maintaining said seal between said pressure sensing
chamber and said pressure relief passage and said relief valve
element is responsive to the differential in force between ~aid
pressure sensing chamber and said pressure setting chamber and
when seated on its seat, sealing said pressure setting chamber
and said pressure sensing chamber from said pressure relief
passage and when unseated from its seat permitting communication
between said pressure sensing chamber and said pressure relief
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~27~ 8~
passage, while maintaining said seal between said pressure
setting chamber and said pressure relief passage.
By design, the area ratio across the trigger valve
element upon which the setting and sensing fluid pressures act is
preferably made substantially less than the area ratio across the
relief valve element upon which the same setting and sensing fluid
pressures act. This difference in area ratios across the two
valve elements ensures that the trigger valve element will always
respond first to an overload pressure, shifting axially while
still maintaining a leak proof seal with respect to the overload
chamber within the ram. This feature ensures that -the valve
remains sensitive to low flow rates as the total volume of high
pressure fluid forced out of the overload chamber by an overload
is available to shift the trigger valve element to an open
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HAS(l) - 46181
position with respect to the setting pressure end of the trigger
valve element and a venting chamber. The metal to metal contact
seat at this juncture permits the loss of setting pressure fluid
for any incremental shift of the trigger valve element which in
turn completely unbalances both the trigger and relieve valve
elements and causes them to accelerate to their fully open
positions under the full pressure of the overload fluid. In the
case when the overload chamber pressure produces a force that
approaches or equals the force produced by the setting pressure
holding the trigger valve element closed, the trigger valve
element may shift only slightly~ but not enough to vent sufficient
setting pressure to unbalance the trigger valve element. Under
these conditions, no loss of fluid is experienced by the overload
chamber within the ram as the trigger valve element remains leak
proof at this juncture for any amount of axial movement and the
larger area ratio across the relief valve element ensures that it
remains leak proof at its overload chamber juncture. AS soon as
the press ram begins its upstroke, the setting pressure will
reseat the trigger valve element and force the incrementa:L amount
of fluid from the overload chamber used to shift the trigger valve
element slightly back into the overload chamber, preventing any
loss oE overload chamber pressure at that instant.
The invention will be clearly understood after reference
to the following detailed specification read in conjunction with
the drawings. In the drawings:
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HAS(l) - 46181
Figure 1 is a schematic illustration of a relief valve
according to the invention mounted on the overload housing within
a ram of a press;
Figure 2 is a sectional illustration through the relief
valve showing the valve elements seated against their respective
seats as they would be seated in use and connected to a
schematically illusteated overload chamber and schematically
illustrated pressure setting assembly;
Figure 3 is a cross-sectional illustration o~ the relief
valve, similar to that shown in Figure 2, unpressurized and
s~ow~g t~ ~e~ ye e~ement in a 10ating and unseated
position and showing the trigger valve element spring biased to a
closed position; and
Figure 4 is a view along the line 4-4 of Figure 2 showing
the disposition of the mounting hub for the alignment pin of the
trigger valve element.
rrhe relief valve is generally indicated by the numeral
10. It has a tubular housing 12 closed at one end by a plate 14
and at its other end by a plate 16. Four bolts 18 extend through
the housing and mount the valve on the press that contains the
ovérload chamber to be monitored.
In this latter respect it will be noted that, as
illustrated in Figure 2, the plate 16 is formed with a pressure
sensing chamber 17 which communicates with a passage 19 that in
turn communicates with the overload chamber 20 of the ram 22 of a
press It is the pressure in the overload chamber 20 that is to
HAS(1) - 46181
be monitored. The bolts 18 thread into threaded openings in the
side of the overload housing 23. It will be apparent as the bolts
are tightened that the plates 14 and 16 are secured to the tubular
body portion 12 to form the assembly.
Numerals 24 and 26 refer to seals that ensure a tight
hydraulic Eit. A light weight low inertia relieE valve element
28, annular in cross~section, is reciprocable within a bore 30 of
the housing. Relief valve element 28 has a seating surface that
seats on a valve seat 32 of the end plate 16 in use.
In use, as will be referred to later, relief valve
element 28 is normally biased to the right, as shown in FigUre 2,
under the action of the pressure in the pressure setting chamber
33, to seat against valve seat 32 of end plate 16 and seal the
pressure sensing chamber 17 from the pressure relief passage 54.
The assembly includes a light weight low inertia trigger
valve element 36 which is reciprocable in a bore 38 of the relief
valve element 28. The trigger valve element 36 has an alignment
pin 40 extending therefrom that freely enters into a bore 42 of
the hub 46 of the wheel generally indicated by the numeral 48. It
will be noted that the wheel, generally indicated by the numeral
48, has openings 50 radially spaced thereabout so that the setting
pressure communicated to the interior of the setting chamber 33
through openlng 52 extends throughout the setting chamber 33 and
against trigger valve element 36.
The trigger valve element 36 and the relief valve element
28 each slide in bores as explained. They have circumferentially
extending grooves therearound to provide a good sliding fit in
HAS~ 46181 ~Z7~8~
accordance to standard practice. The length of the sliding
contact of each valve element in its respective bore is
sufficiently long to achieve a good seal and at the same time an
easy fit under conditions of the designed pressure differential
between the pressure sensing chamber 17 and the pressure setting
chamker 33. It will be apparent by lengthening the contact one
can improve the seal and it is significant that the design of the
assembly is such that length can be increased to achieve these
objectives.
A vent chamber 54~ annular in cross-section, communicates
with the interior of the sleeve-like relief valve element through
openings 56. The vent chamber 54 communicates with atmosphere
through a radially extending duct indicated by the numeral 58. A
spring 60 is compressed between the hub 46 and a shoulder on the
trigger valve element 36 to urge the trigger valve element 36
against its seat 35 on the relief valve element under
non-operating conditions. This is a relatively light spring and
its purpose is to achieve the seating of the trigger valve element
when the valve assembly resets itself after an overload condition
in use.
In use, the operation of the spring 60 permits the
trigger valve element 36 to close first after the valve assembly
has been operated to vent the overload chamber 2n and each of the
valve elements 28 and 36 has been moved to the open position.
Spring 60 has a strength that will close the trigger valve element
36 against its seat 35 on the relief valve element 28 whereby to
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HAS(l) - 46181
seal the setting chamber 33 from the pressure relief passage 56,
Fluid entering the setting chamber 33 will again build up pressure
in this chamber and force the relief valve element 28 against its
seat 32 which resets the valve by sealing the sensing chamber 17
from the pressure relief passage 54,
As indicated above, this valve assembly has a practical
use in the sensing of overload in the operation of a mechanical
press, It is known to provide an overload chamber 20 for the ram
of a mechanical press, The overload chamber is filled with
hydraulic fluid at a predetermined pressureO AS the ram bears
downwardly to perform its pressing operation, the overload chamber
is subjected to the reaction of the die elements, ThiS valve
assembly vents the overload chamber to atmosphere and permits its
collapse if the pressure in the overload chamber due to die
element reaction exceeds a predetermined amount,
In the simplified schematic illustration of a such an
arrangement in Figure 2 of the drawings the numeral 22 refers to
the ram of the press and the numeral 64 refers to an element that
is connected to a die of the press, A hydraulic fluid under
pressure is contained in the overload chamber 20, It will be
apparent that as the ram comes down and the dies engage, pressure
in the overload chamber 20 will build up, The present invention
is designed to sense the pressure in the overload chamber 20 and
to relieve the pressure if it exceeds a predetermined amount,
In use, the relief valve 10 is bolted by means of bolts
1~ to the overload housing 23 so that the pressure sensing chamber
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HAS(l) - 461~1
17 in the end plate 16 of the relief valve housing communicates
with the overload chamber 20 through passage 19. The bolts are
secured sufficiently to achieve a good seal at the seals 24, 26.
Numeral 65 refers to a reservoir for hydraulic ~luid and pump 66
pumps f].uid from the reservoir 65 through the check valve 68 into
the overload chamber 20. check valve 68 permits flow only into
the chamber 20. Numeral 70 is a pump relief valve set to drain
output of the pump 66 over and above a predetermined pressure back
into the reservoir 65. ThUS, by an appropriate setting of the
reservoir relief valve 70, one can set the pressure in the
overload chamber 20.
Numeral 72 re~ers to a pump for pressurizing the setting
chamber 33 of the housing 10~ It likewise has a check valve 74 in
its line which will permit the flow of hydraulic fluid only in a
direction into the chamber 33 of the casing. It also has a
reservoir relief valve 76 that is set to achieve a predetermined
pressure in the chamber of the casing in a similar manner to the
relief valve 70. Varying the pressure setting of relief valve 76
will vary the pressure at which the overload valve will sense a
press overload.
Thus by operation of the rel.ief valves 70 and 76, one can
set the pressures within the overload chamber 20 and the pressure
setting chamber 33. The pressure sensing chamber 17 is at the
same pressure as the overload chamber 20.
In the operation of the overload relief valve as
connected hydraulical].y in Figure 2, pump 72 and valve 76 are
operated to raise the pressure in the setting chamber 33 on the
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HAS(l) - 46181
inside of the relief valve element 28 to the overload response
pressure desired which is somewhat below the pressure that will
build up in the overload chamber under die operation as the dies
are moved into normal co-operative relation with its mating die
because of the area differential across both trigger and relief
valve elements. The pump 66 and valve 70 are operated to set the
normal pressure in chamber 20 which is normally, but not
necessarily, substantially below the pressure in setting chamber
33.
Figure 2 shows schematically the position of the trigger
valve element and relief valve element when the pressure setting
chamber is pressurized to close the trigger valve element 36 and
relief valve element 28 against their respective seats and
maintain them closed against the normal pressure in the overload
chamber 20 and the pressure sensing chamber 17 as maintained by
pump 66.
The area ratios across both the trigger valve element and
relief valve elements in their directions of closure are such
that, at the operating pressures chosen, both valve elements are
biased against their respective seats when pressurization is
achieved.
Under normal conditions of press operation the pressure
in the overload chamber 20 of the ram and in the pressure sensing
chamber 17 will increase and decrease cyclically as the dies go
into and out of operative relation. The force differential
existing across both valve elements between the setting chamber 33
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HAS(l) - ~6181
and the sensi.ng chamber 17 is such that the trigger valve element
36 and relief valve element 28 will not open~
If, however, the dies should become obstructed or the
like and becorne subjected to unduly high forces as they move
towards each other, the pressure in the overload and sensing
chambers, 20 and 17 respectively, will increase above a predefined
limit. When this maximum allowable pressure is exceeded, it will
produce a force on the end of the trigger valve element exposed to
sensing chamber 17 that exceeds the Eorce maintained on its
opposite end by pump 72 and spring 60 forcing the trigger to shift
to the left and open its metal to metal seal at seat 35 as seen in
Figure 2. At this instant, due to the larger area ratio across
the relief valve element 28, the force produced by pump 72 on the
area of the relief valve element exposed to the setting chamber 33
still exceeds the force produced by the overload pressure acting
on its other end in sensing chamber 17 and the seal at seat 32 of
the relief valve element is maintained, preventing any loss of
fluid from the overload chamber 20 during this incremental period
of time This important feature allows the valve to remain stable
when operating at or near overload pressures as any minor pressure
spikes will not cause any loss of fluid from the overload
chamber. If, or as, the overload continues, the trigger valve
element wil]. be forced further off of its seat 35 allowing the
pressure setting chamber 33 to be communicated to atmosphere
through the vent passages 56 and vent chamber 54 and duct 58 and
back to the reservoir ~5. The rapid depressurizing of the
H~S(l) 46181
pressure setting chamber in this manner causes an enormous
increase in net force available to force the trigger valve element
36 fully open and simultaneously causes the relief valve element
28 to become comple~ely unbalanced and shift to the left from its
seat 32 under the full force produced by the overload pressure as
viewed in Figure 2. As the relief valve element 28 shifts, the
sensing chamber 17 and overload chamber 2~ vent through vent
chamber 54, duct 58 and back to reservoir 65. This immediately
depressurizes the overload chamber 20 and permits the collapse
axially of the ram 22 to prevent further buildup of dangerous
forces at the dies.
The collapse of the chamber 2Q sets into motion circuitry
to cut o~ power to the ram.
Thus, the fast depressurizing of the overload chamber 20
prevents immediate danger of destruction to the dies and operates
a switch to turn off the power to the ram.
The closure of the valve elements and repressurizing of
the overload chamber 20 has been indicated above. once the
chamber of the valve assembly 10 has been depressurized, spring 60
closes the trigger valve element 36. Relief valve element 28
floats in the open position at this stage. closure oE the trigger
valve permits build-up of pressure in the pressure setting chamber
33 under the continuous operation of pump 72 and relie~ valve 76.
~s pressure is built up in the pressure setting chamber 33, the
relief valve element 28 moves to the right and seats on its seat.
Once seated, the pump 66 and relief valve 70 build up the normal
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HAS(l) - ~6181
set pressure in the overload chamber 20.
It will be apparent that the operation of the trigger
valve element 36 and the relief valve element 28 is a function o~
the pressures on each side of their respective seats and their
areas on each side of their respective seats that are subjected to
the pressures.
Spring 60 is also a minor factor in the forces acting on
the trigger valve element. It is, however~ a relatively weak
spring and its principal ~unction is to reset the trigger valve
element 36 after operation.
In operation it is the difference in force on the two
ends of the valve elements that is responsible for operation and,
with the two pump arrangemen~ illustrated, it is a more practical
design for the valve elements to have a relatively high pressure
in the setting chamber 33 of relief valve housin~ and a lower
pressure in the sensing and overload chambers, 17 and 20. By
having a lower normal pressure in the overload chamber 20,
retention of ram 22 in its housing when pressuri2ed but under no
external load due to die operation is easier and permits a
simplified joint design. It should be noted that the valve will
function equally well with equal initial pressures on both ends o~
the valve elements
While two pumps have been illustrated to achieve the dual
pressures in the setting chamber 33 and the overload chamber 20
and sensing chamber 17, it will be apparent to those skilled in
the art that similar dual pressures could be achieved with a
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HAS(l) - 46181
single pump and a pressure reducing valve arrangement.
In a typical mechanical press operation, one might want
to limit the pressure build-up in the overload chamber and
pressure sensing chamber to about 2500 p.s i. ~he relief valve of
this invention as illustrated in the hydraulic hook-up of Figure 2
can protect against pressures of this order by operating with a
pressure that is somewhat less than 2500 p.s.i. in the setting
chamber 33 due to the area ratios across the valve elements, and a
pressure of about 500 p.s.i. in the overload and sensing chambers
20 and 17. This is an advantage oE the double pump operation. If
the device were operated from a simple single pump operation, it
would be necessary to have equal pressures on each side of the
valve members under conditions of normal operation.
It will be understood that in devices of this kind, the
area differential across the ends of the valve elements is a
factor in their operation and by selection of appropriate areas,
the setting pressure is lower than the sensing pressure at the
point where the forces on the trigger valve element are balanced
just prior to operation of the trigger valve by an overloacl.
It is significant that the inertia of the trigger valve
element 36 is absorbed by the relief valve element and the impact
force adds to the hydraulic force acting on the relief valve
element to make the embodiment of the invention illustrated in the
drawings more responsive.
Numeral 66 refers to a snubbing nose on the hub of wheel
48 which enters a fluid filled cavity on the plate 14 to
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HAS(l) - 46181
decelerate both valve elements and prevent damage to them in
operation.
The embodiment of the invention illustrated is by way of
example only. It is not contemplated that the trigger valve be
only within the pressure relieE valve as shown. A valve wherein
the trigger valve and relief valve were mounted for movement on
spaced apart axis is thought to be within the scope of the
invention.
The figures used in these examples are used for
illustrative purposes only. It is not intended that the scope of
protection be restricted to the single embodiment herein described
but that it extend to cover the invention as a whole as claimed in
the appended claims.
