Note: Descriptions are shown in the official language in which they were submitted.
CA 022~2874 l998-l0-29
W O97/41496 PCT~US97/00944
PrLOT-OPE~ ED S~FEl~Y ~ ~,T,n~ V~L~E ~ ~ MnR~.y
~ Field of the Invention
This invention pertains to a safety relief valve assembly and method
and, more particularly, to such an assembly and method in which a pilot valve
5 operates a safety relief valve, and a regulator is provided which cooperates
with the pilot valve for modlllAtin~ the degree of opening of the safety relief
valve.
Ba~ ul.d of the Invention
Pressurized vessels and conduits are comm--nly fitted with pressure
10 relief valves to prevent the pressure of fluid inside the vessels and conduits
from exceeding a prescribed limit beyond which the vessel, conduit, or
equipment corlnected thereto, could rupture or be damaged.
A typical pressure relief valve has an inlet in fluid communication with
the main fluid line and an outlet connected to an exhaust line. A piston, or
15 valve meçh~ni.cm, is provided which is normally m~int~ined in a closed
position by a compressed spring. The compression of the spring is adjusted to
keep the piston in its closed position until the fluid on the inlet side ~tt~in.~ a
predetermined pressure. When this occurs, the piston moves to an open
position, fluid flows into the inlet, through the valve housing, and out through20 the outlet, thereby relieving the pressure. Once the pressure is reduced to apoint below the predetermined pressure, the spring moves the piston back to
its closed position, and normal fluid flow through the line resumes.
Safety relief valves of this type must maintain a sealed closure of the
vessel or conduit under normal service con~lition.~, and must achieve minim~l
25 "blowdown", i.e. the difference between the opening pressure and the closing
pressure. To ~ccomp~ h this, and to achieve increased pelru~ ance in other
respects, safety relief valve assemblies have evolved which are controlled by a
piloting device which senses the pressure of the fluid in the vessel or conduit
and actuates the valve as a function of this pressure almost instantaneously
30 to achieve rapid an.d complete openingA and closures with relatively small
blowdown.
Present day pilot-operated safety relief valves are generally of the "pop"
type which includes a pilot relief valve which opens at a predetermined
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- pressure, thus causing the safety relief valve to open. In a typical
arrangement of this type, the dome pressure (i.e., the pressure which holds
the main valve closed) is reduced to atmospheric pressure, and the piston thus
moves to a full open position, almost inst~nt~neously. However, this causes
several proble_s. For ~ mple, extremely large qllAntities of fluid are
discharged from the safety relief valve in response to the quick opening of the
piston. Also, the extremely quick opening and closing of the piston causes an
inordinate amount of wear and stress on the piston and its associated
components as well as the associated flow conduits. Further, under cel~
resonant conditions, the piston will "chatter~, that is, open and close at a very
rapid rate which renders it dysfunctional and subject to prPm~hlre failure.
Still further, these type of pressure relief valves and associated pilot valves
are relatively complicated and expensive.
Therefore, what is needed is a pilot-operated safety relief valve in which
the amount of fluid discharge from the valve is modulated, and wear and
stress on the valve components and the associated flow conduits are
minimi7:ed. Also needed is a valve of the above type that does not chatter and
is relatively inexpensive and simple in construction and operation.
Sllmm~ry of the Invention
The present invention, accordingly, provides an assembly and method in
which a pilot valve is provided which controls the operation of the safety relief
valve, and a regulator modulates the operation of the pilot valve, and
thwe~le the opening and clo~ing of the safety relief valve. To this end, an
operating fluid is provided in a chamber which provides a pressure that
normally biases the piston of the safety relief valve to a closed position. The
pilot valve is connected to the safety relief valve in a m~nner to vent the
operating fluid from the chamber and thus enable the piston to open. The
regulator is connected to the pilot valve in a mAnnÇr to control the tli.~r.h~rge
of the operating fluid so that the safety relief valve gradually opens.
Thus, major advantages are achieved with the assembly method of the
present invention since the amount of fluid discharged from the safety relief
valve is reduced, and wear and stress on the valve components and the
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- associated flow conduits are minimi7ed. Also, the safety relief valve does notchatter and is relatively in~Xp~n~cive and simple in construction and operation.Brief De~cription of the Drawin~
Figure 1 is a partial sectinnAl-partial s- h~m~t.ic view of the safety relief
5 valve assembly of the present invention.
Figure 2 is an enlarged sectional view of the pilot valve and the
regulator of figure 1, showing the pilot valve and the regulator their closed
positions.
Figure 3 is a view, simil~r to figure 2 but depicting the pilot valve and
10 the regulator in their open positions.
De~l;u~ion of the Preferred Embodiment
ReferIing to figure 1 of the drawings, the lefelellce numeral 10 refers,
in general to a safety relief valve including a housing 12 having an inlet
passage 12a formed through one wall thereof for receiving a conduit 14
15 cont~ining a fluid under pressure. An outlet passage 12b i9 also provided in
the housing 12 which ~xten~l.c at right angles to the inlet passage 12a for
exhausting the fluid under conditions to be described.
A movable piston 16 is provided in the housing and, in its closed
position, rests against a seat bushing 18 disposed in the housing 12 in
20 ~lignment with the inlet passage 12a. The piston 16 moves up and down in
the housing 12 as viewed in figure 1, and a cylindrical g~ude member 20 is
disposed in the housing above the bushing 16 for guiding this movement. A
cover 22 extends over the upper portion of the housing 12 to define a chamber
24 between the upper portion of the piston 16 and the cover. A control fluid is
25 contained in the chamber 24 for bi~.cinF the piston 16 to its closed positionresting against the seat bushing 18, as shown in figure 1. In this contQxt., theupper end portion of the valve 16 is curved to define a larger surface area
than that of the lower end of the valve. Since the pressure of the control fluidin the chamber 24 is essentially the same as the pressure of the ~y~lelll fluid
30 in the inlet passage 12a, as will be ~.x~ ined further, the force exerted on the
upper portion of the piston 16 by the control fluid is greater than the force
exerted on the lower end of the piston by the system fluid due to the
differences in these areas. A spring 26 is also disposed in the chamber 24
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,
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- which adds to the downwardly-directed forces acting on the upper end portion
~f the piston 16.
A port 22a is provided through the cover 22 and cnmmllnicates with the
chamber 24. The port 22a is connected, via a conduit 28, to a pilot valve 30,
shown schematically in figure 1, for controlling the fluid pressure in the
chamber 24 in a m~nn~r to be described. A port 12c is provided through a
wall of the housing 12 in comm-ln~ tion with the inlet passage 12a, and is
conn~cted, via a conduit 32, to the pilot valve 30. A branch conduit 32a also
connects the conduit 32, and therefore the port 12a, to a regulator 34, also
shown sch~m~tically. The regulator 34 regulates the operation of the pilot
valve 30 in a m~nn~r to be described, and to this end, a conduit 36 connects
an outlet of the pilot valve 30 to an inlet of the regulator 34, and a conduit 37
connects the outlet of the regulator to the outlet passage 12b of the safety
relief valve 10. These various connections between the safety relief valve 10,
the pilot valve 30, and the regulator 34 will be described in detail.
A~s stated above, the forces caused by the pressure of the control fluid
and the spring 26 in the chamber 24 acting against the upper end of the
piston 16 normally bias the latter member to its closed position shown in
figure 1. However, when the pressure of the control fluid in the chamber 24 is
relieved by the valve assembly of the present invention, the piston 16 is forcedupwardly away from the seat bushing 18 and the pressurized fluid in the inlet
passage 12a is relieved and some of the fluid flows through the inlet passage
12a, the housing 12 and exits the housing through the outlet passage 12b.
Since the safety relief valve 10, per se, does not form a part of the present
invention, the more specific details of same, including the provision of seals,
and the like, associated with the valve have been omitted. In the latter
cont~rt. a full, detailed disclosure and description of the safety relief valve 10
is cont~inerl in U.S. patent No. 4,917,144, ~ igned to the ~ ignee of the
present invention, the disclosure of which is incorporated by ~ er~ ce.
Figure 2 depicts the details of the pilot valve 30 and the regulator 34.
The pilot valve 30 includes a housing 40 having an inlet passage 40a
connected to the conduit 32 for receiving the system fluid from the safety
relief valve 10 (figure 1). A passage 40b is also provided in the housing 40
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- which is connected to the conduit 28 ~xtqn-ling from the chamber 24 (figure 1)of the safety reliefvalve 10, and an outlet passage 40c is connected to the
conduit 36 extenl1ing to the regulator 34.
A centrally-located bore 40d ~tan~.q though the length of the housing
40 and commllnicates the passages 40a-40c. The upper portion of the bore
40d is enlarged and receives a piston 42. Reciprocal movement of the piston
42 in the housing 40 is permitted by an ~nmll~r diaphragm 44 e~t~nrling
across the enlarged portion of the bore 40d and secured between the upper
end of the housing 40 and a cover 46 ~ten~ing over the latter end. The cover
46 is secured to the housing 40 by a threaded bolt 48 ~ten~ling through
corresponding threaded openings in the cover and the housing.
The piston 42 has a stepped outer diameter defining four portions with
vary~ng diameters including an upper stem 42a having a reduced di~meter.
The stem 42a extends through aligned central openings in the diaphragm 44
and a center plate 50 extenrling over the exposed portion of the diaphragm 44.
An intermediate portion 42b of the piston 42 extends immediately below the
diaphragm 44 and a nut 52 is in threaded engagement with the stem 42a to
secure the center plate 50 and the diaphragm 44 between it and the shoulder
defined between the stem 42a and the piston portion 42b.
The piston portion 42b ~rten(ls into the bore 40d, a necked-down
portion 40c of the piston 42 extends immediately below the portion 42b, and a
control stem 42d extends below the necked down portion. When the piston 42
is in its closed position shown in figure 2, the lower end of the piston portion42b abuts an internal flange 40e ~rtenrling inwardly from the bore 40d. The
flange 40e has a seal ring 52 mounted to its inner surface which, in the closed
position of the piston 42, ~ ounds the necked-down piston portion 42c with a
clearance therebetween. An annular groove 40e' is formed in the upper
surface of the flange 40e to provide for fluid c- mmllniÇ~tion from the passage
40a, through the groove 40e' and the bore 40d, and including the space
between the flange 40e and the necked-down piston portion 42c, and to the
passage 40b. This equalizes the fluid pressure in the passage 40b, and
therefore the chamber 24 of the pressure relief valve 10 to that of the system
pressure in the cha_ber 40a, for reasons to be described.
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- A sleeve 54 is mounted in the bore 40d of the housing 40 and ~srt~n~lq
below the flange 40e in a spaced relationship thereto. The sleeve 64 is sized
so as to fit snugly within the bore 40d, and a seal ring 54a ~t~n(l.~ between
the outer surface of the sleeve 54 and the corresponding surface of the housing
40 d~fining the bore 40d. A seal ring 54b is mounted on the inner surface of
the sleeve 54 and, in the closed position of the piston 42 shown in figure 2,
engages the outer surface of the lower end portion of the stem 42d to block
flow commlmication between the passages 40b and 40c through the bore 40d.
A spring 56 is applied to the upper stem 42a of the piston 42 to urge
the piston downwardly as viewed in figure 2. Since the spring 56 is of a
conv~ntionz.l design, it is not shown in detail and its associated components
are not shown, in the interest of clarity. The downwardly-directed force
exerted by the spring on the piston 42 is opposed by an upwardly-directed
force exerted against the diaphragm 44, and therefore the piston 42, by the
pressure of the system fluid from the conduit 32 that enters the inlet passage
40a of the housing 40. The design is such that, if the pressure of the system
fluid stays within normal limits, the force of the spring 56 acting on the piston
42 will exceed the upwardly-directed force applied by the fluid pressure acting
on the diaphragm 44, and mz~in~in the piston 42 in its closed position of
figure 2. However, if the force of the system fluid acting against the lower
end of the diaphragm 44 is greater than the force of the spring 56 acting
against the piston 42, the central portion of the diaphragm, and the1ero~e the
piston 42, will move upwardly. This causes the stem 42d of the piston 42 to
clear, or rise, above the seal ring 54b and attain the position shown in figure
3. This commllni~tes the passage 40b and 40c through the bore 40d and thus
permits the control fluid from the chamber 24 (figure 1) of the safety relief
valve 10 to flow through the conduit 28, the housing bore 40d, and to the
outlet conduit 40c for passage to the regulator 34. Also, in the open position
of the piston 42 shown in figure 3, the upper portion of the stem 42d of the
piston 42 engages the seal ring 52 to prevent fluid communication between
the passages 40a and 40b. The signifi~nce of this will be described later.
A blowdown adjustment plug 58 is mounted in the lower portion of the
bore 40d. The upper end portion of the plug 58 has a reduced diameter and
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- nestles within the sleeve 54 in threaded engagement therewith. The plug 58
has a central passage 68a connected to the passage 40b and a radial passage
58b connected to the central passage to permit the above-mentioned flow from
the passage 40b, through the bore 40d and to the passage 40c. The lower end
6 portion of the plug 58 and the corresponding internal surface of the housingdefinin~ the bore 40d are threaded and in engagement so that the axial
position of the plug, and therefore the sleeve 54, can be adjusted relat*e to
the housing 40 by rotating the plug. A seal ring 54a extends between the
corresponding surfaces of the plug 58 and the latter housing surface to
prevent fluid leakage therebetween. This axial rotation of the plug 58 sets the
position of the sleeve 54 relative to the 42d of the piston 42, and thus çn~llesthe blowdown of the assembly to be adjusted, as will be discussed.
The regulator 34 consists of a housing 60 having an inlet passage 60a
which is connected to a branch conduit 32a ~xtentling from the conduit 32 and
therefore receives the system fluid from the safety relief valve 10 (figure 1). A
second inlet passage 60b and an outlet, or vent passage 60c are provided in
the housing 60, and a central bore 60d is provided through the housing that
connects the passages 60a, 60b, and 60c.
A valve assembly 62 is disposed in the bore 60d of the housing 60 and
includes a piston 64 and a sleeve 66 exten~ing below the piston and in
engagement therewith. A center plate 68 is provided in a counterbore
provided in the sleeve 66 and engages a seal ring 70 provided in a groove
formed in the inner surface of the seal ring defining the counterbore. A bolt
72 ~tenf1.~ through threaded, aligned, central openings formed through the
piston 64 and the sleeve 66 and through the center opening in the center plate
68, to connect the center plate 68 and the sleeve 66 to the piston 64. Two seal
rings 74a and 74b are respectively located in two axially spaced grooves
formed in the outer surface of the sleeve 66 and engages the corresponding
surface of the housing d~fining the bore 60d.
The lower end portion of the bore 60d is enlarged and the inner wall
portion of the housing 60 d~fining this lower end portion is threaded. A plug
76 is mounted in the lower end portion of the bore 60d and has a bore that
defines the inlet passage 60b. The plug 76 has an externally threaded outer
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surface portion in threaded engagement with the threaded inner wall portion
of the housing 60. An annular, upwardly-~xten-lin~ flange 76a ~ n~l.q from
the upper end of the plug 76 and, in the closed position of the valve assembly
shown in figure 2, the outer surface of the flange 76 engage the seal ring 70 ofthe valve assembly 62.
The pressure of the system fluid from the branch conduit 32a thus acts
on the upper end of the valve ~qcemhly 62 to urge it to its closed position in
which the seal ring 70 engages the flange 76a of the plug 76. However, when
fluid is passed from the outlet passage 40c of the housing 40 to the conduit 36
10 under conditions to be described, the pressure of the fluid in the conduit 36acts against the lower end of the valve assembly 62. The area of the lower
surface of the valve assembly 62 is greater that the area of its upper surface,
and since the respective pressures of the control fluid and the system are the
same for the reasons discussed above, the control fluid pressure acting on the
15 lower end of the valve assembly 62 creates a force that is greater than the
force caused by the system pressure acting on the upper end of the valve
assembly. As a result7 the valve assembly 62 will move ullw~udly in the bore
60d to its open position and thus permit the fluid in the conduit 36 to pass
from the passage 60b, through a portion of the bore 60d and to the outlet
20 passage 60c. The fluid then exits the regulator 34 and passes through the
conduit 37 to the outlet passage 12b of the safety relief valve 10 (figure 1). It
is noted that the ulJwal d movement of the valve a.qs~mhly 62 is limited by the
engagement of corresponding shoulders formed on the sleeve 66 and the
housing 60 as shown in figure 3.
In operation, when the system fluid pressure is within a predetermined
limit, the pistons 16 and 42 of the safety relief valve 10 and the pilot valve 30,
respectively, as well as the valve assembly 62 of the regulator 34, stay in
their rlorrn~l, closed position shown in figure 2. As a result, the pressure of
the control fluid in the conduit 28 is equalized to the pressure of the system
30 fluid in the conduit 32 through the pilot valve housing 30 and, more
particularly, through the inlet passage 40a, the groove 40e', the space between
the necked-down piston portion 40c and the seal ring 52, the bore 40d, and
the passage 40b. Also, the flow of the system fluid through the safety relief
- 8 -
. _. ....
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- valve 10, and the flow of the control fluid from the chamber 24 of the safety
~elief valve 10 through the conduit 28 and to the pilot valve 30, are prevented.However, when the system fluid pressure exceeds the predetermined
limit, the corresponding force acting on the lower surface of the diaphragm 44
5 by the system fluid in the passage 40a of the pilot valve 30 forces the piston42 upwardly to the position shown in figure 3. In this position, the upper
portion of the stem 42d of the piston 42 engages the seal 52 and thus blocks
commllnication between the passages 40a and 40b; while the lower end of the
stem 42d is above the seal ring 54b to permit flow of the control fluid from thechamber 24 of the safety relief valve 10, through the conduit 28, and to the
pilot valve 30. The control fluid thus passes through the bore 40d of the pilot
valve 30 and, via the conduit 36, to the inlet passage 60b of the regulator 34.
Immediately after the opening of the piston 42 of the pilot valve 30 in
the above m~nner the pressure of the control fluid passing from the chamber
15 24, through the pilot valve and to the regulator 34 is substantially the sameas the system pressure. Therefore, the pressure of the control fluid in the
passage 60b acting against the lower end of the valve assembly 62 of the
regulator 34 forces the valve assembly upwardly to its open position against
the force applied to the upper end of the latter assembly by the system fluid
20 pressure. The control fluid thus passes from the passage 60b, through the
lower portion of the open bore 60d, and to the outlet passage 60c for passage,
via the conduit 37, to the outlet passage 12b of the safety relief valve 10 for
disposal. After a portion of the control fluid evacuates the cha_ber 24 of the
safety relief valve 10 and passes through the pilot valve 30 and the regulator
25 34 as described above, the pressure of the control fluid lowers to the extentthat the resulting upwardly-directed force acting on the lower end of the valve
~.qs~mhly 62 becomes apprr-~nm~t~ly equal to, or just less than, the force
caused by the system pressure acting on the upper end of the valve assembly.
When this occurs the valve assembly 62 moves back to its closed position of
30 figure 2.
The design is such that the valve ~.~semhly 62 will move back to its
- closed position when a predetermined percentage of the control fluid evacuates
the chamber 24 in the foregoing m~nn~r. This is achieved by fabric~ting the
g
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- valve assembly 62 in a m~nn~r so that the surface area of its upper end is a
predetermined percentage of the surface area of its lower end, which
percentage corresponds to the percentage of the control fluid that evacuates
the chamber 24. More particularly, and by way of ~x~mple only, the design of
the valve assembly 62 is such that the surface area of the upper end of the
valve assembly 62 is al-ll.,xi~ tely 73% ofthe surface area of its lower end.
Therefore, after opening in the above-described m?~nn~r, the valve assembly 62
will close back when the pressure of the control fluid in the chamber 24
reaches approximPtely 73% of the pressure of the system fluid, which results
in minim~l blowdown.
In the meantime, the piston 16 of the safety relief valve 10 responds to
the increased system fluid pressure and to the control fluid pressure reduction
in the chamber 24 by moving to its open position to relieve the fluid pressure
in its inlet passage 12a to its outlet passage 12b. Since the fluid pressure
16 reduction in the chamber 24 is apprn~im~t~ly 27%, the design of the safety
relief valve 10 can be such that the piston 16 will open when the fluid
pressure reduction is slightly less than this value, for ~mple, appro~im~tely
24%. ACCOLdi11g to a main feature of the present invention, the remAining
fluid pressure in the chamber, in effect, resists the upward, opening
movement of the piston 24 and thus insures that the opening movement of the
piston is modulated and that it will thus open gradually. During this time,
the piston 42 of the pilot valve 30 remz~in.~ in its upper, closed position thusisnl~ting the system pressure in the conduit 32 from the control fluid in the
conduit 28 and therefore the chamber 24 of the safety relief valve 10.
When the system fluid pressure is reduced to a predetermined value as
result of the opening of the safety relief valve 10 in the foregoing m~nn~r, thepistons 16 add 42 move to their closed positions shown in figures 1 and 2,
respectively. As a result, flow of the control fluid from the chamber 24 of the
safety relief valve, through the pilot valve 30 and to the regulator in the
above-described manner is terminated, and the pressure of the control fluid
eql7~ with the ~y~leln fluid pressure through the passages 40a, the pilot
- valve 30 and the passage 40b as described above.
- 10 -
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- As a result of all of the foregoing, the opening of the piston 16 of thesafety relief valve is modulated and thus prevented from opening too quickly.
Thus, the almost inst~nt~neous opening of the piston of the prior art safety
relief valves, as described above, is ~.limin~ted. As a result, the amount of
5 fluid discharged from the safety relief valve 10 of the present invention is
reduced and the wear and stress on the valve components and the associated
flow conduits is ..~ ed. Also, the pistons 16 and 42 of the safety relief
valve 10 and the pilot valve 30, respectively, as well as the valve assembly 62
of the regulator do not "~h~t,t~r" Further, the ~.qs~mhly of the present
10 invention is relatively inexpensive and simple in construction and operation.It is understood that several variations may be made in the foregoing
without departing from the scope of the invention. li',x~n~ples of these
variations are as follows:
1. The branch conduit 32a of the conduit 32 can be elimin~ted to
15 ~limin~te the application of the system fluid pressure on the upper portion of
the valve assembly 62 of the regulator 34, and a spring or the like can be used
to apply the latter force.
2. The diaphragm 44 can be replaced by another type of fluid
pressure responshe device such as a bellows, or the like.
3. One or more of the conduits 28, 32, 36, and 37 can be ~limin~ted
and the regulator 34 can be mounted directly on the pilot valve 30 and/or the
pilot valve can be mounted on the safety relief valve.
Other modific~tion.q, changes and substitutions are also intended and,
in some instances, some features of the invention will be employed without a
corresponding use of other features. Accordingly, it is appropriate that the
appended claims be construed broadly and in a manner conqi.qtent with the
scope of the invention.
