Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
538-698
BACKGROUND AND SU~ARY OF THE INVENTION
.
This invention r01ates generally to pressure relief valves and
specifically to a device Eor securing the blowdown ring o:E the valve. Pres-
sure relief valves are required to be used on a large number of pressure ves-
sels. The :Eunction of these valves is to open when a certain pressure has
becll reached within the vessel. The opening of the valve exhausts the pres-
sure w:ithin the vessel. Conventionally, SUC}I valves include an outer hous-
ing into which a nozzle communicating with -the pressure vessel is inserted.
A disc is biased against the nozzle's opening to seal same. A large coil
spring, whose tension is adjustable, biases the disc into engagement with
the nozzle through a disc holder. Adjusting tension of the coil spring
alters the pressure at which the disc will unseat from the nozzle or "pop".
After the pressure has been exhausted from the vessel, the combination of
spring bias and blowdown ring setting will cause the disc to reseat or close
at a pressure below that at which the valve opened.
The nozzle has external threading and threaded thereto is a device
known as a blowdown ring. The threading on the nozzle and the blowdown ring
permit the blowdown ring to be axially adjusted with respect to the nozzle
as the blowdown ring is turned. The axial position of the blowdown ring
determines the efficiency of the huddling chamber which creates "pop" action
and the pressure at which the valve will blowdown or close. Thus, in such
valves, the opening pressure is adjusted by adjusting the tension of the
coil spring while the closing or reseat pressure is adjusted by adjusting
the position of the blowdown ring. The blowdown ring used in usual pressure
relief valves generally has a knurled or a gear-like outer surface with
radially extending teeth. The purpose of the teeth is to permit the blow-
down ring to be secured in
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place wi-th respect to the nozzle by means of an ex-ternal locking
device which ex-tends through the outer housing. However, the fact
that an opening must be made in the housing for the locking device,
seriously compromises the pressure integrity of -the housing and
the valve as a whole. The opening can provide an escape point
for the pressurized fluid. Any escape of pressurized fluid can be
dangerous, especially if the pressure vessel contains toxic or
poisonous gas or liquid. Leakage can be extremely dangerous in
cer-tain pe-troleum, chemical or nuclear applications and may result
in the release of hazardous materials. Where the pressure relief
valve design u-tilizes more than one blowdown or control ring,
additional openings are required in the valve housing to carry
the additional locking devices. It is desirable that the number
of points of potential leakage in safety relief valves be reduced
as much as possible.
Another problem exists with respect to the conventional
blowdown rina lockina devices. Because such devices are exter-
nally accessible, the possibility exists that these devices will
become damaged through inadvertant contact or be intentionally
tampered with. Damage or intentional tampering can cause the
locking device to be disengaged from the blowdown ring which
will permit the blowdown ring to become misadjusted. The radial
projection of this locking device is adjustable such that
accurate positioning of the locking device is possible to place
the locking portion precisely between the radially extending teeth
of the blowdown ring. The blowdown ring should be secured by the
locking device such that rotational movement of the ring once
adjusted is prevented but no rigid contact exists between the lock-
ing device and the blowdown ring~ (Misadjustment of the locking
device which results in external forces on the blowdown ring may
cause faulty valve performance such as leakage.) Furthermore,
damage or tampering may cause the external locking device to be
removed which will completely jeopardize the pressure securi-ty
of the valve. Even though safety codes, which govern the con-
struction of such valves, generally require the locking device
to be sealed, such seals can easily be broken and -thus provide
no real securi.ty for the locking device.
Generally speaking, -the inven-tion provides a safety
relief valve comprising: (a) a valve housing; (b) a nozzle
enclosed within sai.d housing, said noæzle having external
threading; (c) a blowdown ring threaded to said nozzle, said
blowdown ring including serrations; (d) means disposed about
the top of said nozzle to maintain said nozzle closed until a
predetermined pressure is reached within said nozzle and to open
said nozzle thereafter; (e) a collar disposed about said blow-
down ring and said nozzle and enclosed within said valve body,
said collar having a first section proximate said blowdown ring,
said collar having a second section proximate said nozzle; (f)
position securing means disposed at said first section of said
collar for being releasably disposed between the serrations of
said blowdown ring to prevent said blowdown ring from being
turned; and (g) fastening means disposed a-t said second section
of said collar for fixing said collar to said nozzle.
The position securing means and the fastening means
provide a locking device which preferably is not ex-ternally
accessible when installed in closed discharge systems so that
it in no way compromises the pressure integrity of the valve
and does not permit intentional or accidental misadjustment.
The locking device can be disengaged to permi-t adjustment of
the blowdown ring. The locking device permits the internal
use of a seal required by most safety codes so that it will
meet the code without the need for any amendments.
Other features of this invention will become
apparent upon reading of the detailed speciEication to follow.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, reEerence
is made to the following drawings as well` as to the de-tailed
description to follow, in which:
Figure 1 is a sectional view of a valve cons-tructed in
accordance wi-th the invention;
Figure 2 is an enlarged sectional view of the upper
portion of the nozzle; and
Figure 3 is a sectional view of the locking collar
constructed in accordance with the invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
The drawings illus-trate the improved pressure relieE
valve 10 ln accordance with the inven-tion. Valve 10 includes a
body 12 to which a bonnet 14 is joined by means of a stud 16
engaging a nut 18. Bonnet 14 and body 12 form the housing 20
of -the components of the valve 1~. Disposed between bonnet 14
and body 12 is a sleeve guide 22 having a bonnet gasket 24 a-t
the interface between itself and the bonnet and a bod~7 gasket 27
at the interface between i-tself and body 12. Threaded to
bonnet 14 at its upper portion is a cap 28. Bonnet 14 includes
an opening 30 sealed b~7 2 threaded pipe plug 32. The invention
has been illustrated in a conventional safety relief valve.
However, the invention is not limited thereto and may be used in
a large number of different valve configurations.
Threaded to the inlet opening 34 in lower portion of body
12 is a nozzle 36 having an opening 38 at its upper end. Disposed
above opening 38 of nozzle 36 is a disc 40 which has a semi-
spherical protuberance 42 extending from its upper portion. A
disc holder 44 engages disc 42 to hold same in contact with the
opening 38 in nozzle 36 to seal same against the passage of the
pressurized fluid. Disc holder 44 has an externally threaded
upwardly extending projectlon 46 which engages an internally
threaded opening 48 in a stem retainer 50. A lock screw 52
securely fastens disc holder 44 to stem retainer 50. Stem
retainer 50 is slidably disposed in a sleeve 54 which is joined
at its upper portion to an opening 56 in sleeve guide 22.
The upper portion of stem retainer 50 includes an opening
58 into which the lower portion 60 of stem 62 is inserted,
stem 62 is free to rotate without turning stem retainer 50. The
upper portion of stem 62 is slidably mounted within a spring adjustment
screw 64 which in turn is threaded to an opening 66 of bonnet 14. A lock
nut 68 is threaded to adjustment screw 64 and locks it in place. The adjust-
ment of screw 64 permits the adjustmeTIt of the opening or pop pOillt of the
valve as is describcd in greater detail below. Surrounding stem 62 within
bomlet 14 is a coil spring 70 disposed between an upper spring button 72
and a lower spring button 74. Upper spring button 72 rotatably engages the
underside of adjustment screw 64. Lower spring button 74 rotatably engages
a collar 75 on stem 62. The force of spring 70 is transmitted through disc
40 by means of disc holder 44, stem retainer 50 and stem 62.
As adjustment screw 64 is turned it will be moved upwardly or down-
wardly, expanding or compressing coil spring 70 as the lower portion of
screw 64 contacts and displaces upper spring button 72 while lower spring
button 74 remains stationary. As coil spring 70 is compressed, greater pres-
sure is exerted upon disc 40 from nozzle 36. Conversely, when spring 70 is
expanded by means of adjustment screw 64 a lesser force is exerted upon disc
40 and a lesser pressure is needed to unseat disc 40 from nozzle 36. When
disc 40 is displaced from nozzle 36, the pressurized fluid flows through noz-
zle 36 and thereafter is exhausted through exhaust opening 77 in body 12.
Fig. 2 illustrates in detail the upper portion of nozzle 36 and
its relationship to disc 40. The upper portion of nozzle 36 has external
threading 78 for engagement with the internal threading 80 disposed on a
blowdown ring 82. Thus, as blowdown ring 82 is turned with respect to noz-
zle 36, its axial position with respect to the opening 38 of nozzle 36 is
changed. The outer surface of blowdown ring 82 is knurled, serrated or has
radially extending gear teeth 84. As blowdown ring 82 is axially adjusted
by means of the threaded engagement with nozzle 36 the blowdown point or
point at which the disc 40 will reseat itself on nozzle 36 after the pres-
sure has been dissipated, may be adjusted.
In order to securely lock the axial position of blowdown ring 82
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with respect to nozzle 36, a blowdown ring collar 86 is provided. Collar 86
is generally annular in configurati.on having a cylindrical outer surface 88,
an upper portion 90, a lower portion 92 and an inward].y projecting inner rim
94. The inner wall 96 o:E the upper port;.on 92 is of a diameter that pro-
vides su:E:Eicient clearance so that blowdown ring 82 may be turned and
axially displaced between inner wall 92 and nozzle 36.
Upper portion 90 of collar 86 includes at least one threaded open-
ing 100 through which is inserted a threaded locking screw 102 which has a
conical projection 104 at its forward edge :Eor precise positioning between
the knurling, serrations or teeth 84 of blowdown ring 82. The end of lock
screw 102 distal to projection 104 includes a narrowed portion 106 having an
opening 108 for the insertion of a sealing wire and a slot 110 for insertion
of a tool such as a screw driver to turn lock screw 102 to thereby displace
same inwardly or outwardly with respect to blowdown ring 82. A jam nut 112
secures lock screw 102 to collar 86. The inner surface 98 of lower portion
92 of collar 86 has a diameter sufficient so as to fit abou-t section 109 of
nozzle 36 which has an enlarged diameter.
Lower portion 92 of collar 86 includes at least one opening 114
through which a threaded fastener 116 extends. Fastener 116 includes a
conical end 118 for engagement with a conical indentation 120 in section 109
of nozzle 36. The other end of fastener 116 secures collar 86 to nozzle 36
and lock screw 102 thereafter securely locks blowdown ring 82 against move-
ment with respect to collar 86 and thereby nozzle 36. Fastener 116 includes
an opening 124 through which a wire 126 which also is inserted through open-
ing 108 in lock screw 102. The appropriate wire seal 128 may then be
applied to the joined ends of wire 126.
A preerred embodiment of this invention includes two diametric-
ally opposed openings 100 in upper portion 90 of collar 86, and three open-
ings 114 at 120 intervals in lower portion 92 of collar 86. Thus, it is
seen that when the lock screw 102 is displaced out of engagement with blow-
down ring 82, turning and adjustment of blowdown ring 82 with respect to
nozzle 36 is permitted to thereby adjust the blowdown point of safety valve
10. When lock screw 102 is turned into engagement with blowdown ring 82 and
secured by jam nut 112, blowdown ring 82 will be secured against further
rotational movement and is accomplished without the need Eor any opening in
housing 20 W]liC}I would compromise the pressure integrity of valve lO.
Al-though the present invention has been described in conjunction
with preferred embodiments, it is to be understood that modifications and
variations may be resorted to without departing :Erom the spirit and scope of
the invention, as those skilled in the art will readily understand. Such
modifications and variations are considered to be within the purview and
scope of the invention and the appended claims.
