Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an improvement in a
pressure relief device of the type generally used on
electrical power transformers.
device of the type under consideration is
disclosed in U.S. patent 3,217,082, issued on
November 9, 1965. This patent discloses two embodiments,
the first as shown and described with reference to
Figs. 1 to 8, the second as shown and described with
reference to Fig. 9. The difference between the two
embodiments is that the first utilizes two valve disks
41 and 51l while the latter utilizes a single valve disk
41a. In both embodiments, the valve disks are exposed
simultaneously to the action of compression springs 39
and 49, which results in a fixed rate of discharge and
~eclosing time for any pre-set maximum pressure within
the container on which the device is mounted.
The device of the present invention utilizes
two valve disks each of which is exposed to a separate
compression spring. In such manner, the rate of dis-
charge and reclosing time may be independently varied,
which satisfies installations wherein speed and volume
of discharge is of paramount importance, and in other
installations wherein rapid reclosing is important to
reduce loss of costly gases or liquids in the con-
tainer on which the device is mounted. jeans are also
provided in a second embodiment disclosed herein where
the compressive force of one of the springs may be
adjusted after the device is assembled, thereby affording
flexibility in establishment of operational character-
isles
The primary object of this invention is to pro-
vide an improvement in a pressure relief device wherein
opening and reclosing rate of valve means may be inde-
pendently regulated.
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A further object is to provide means in such a
device wherein the action of incorporated valve means
may be adjusted after the device has been assembled.
The present invention provides a pressure relief
device for mounting upon a container holding a pressuriz-
able medium, the device includes a base plate having a
central opening, a flat gasket mounted upon the base
plate and surrounding the opening, a first valve posi-
tioned in the opening and having a peripheral portion
seatable upon the gasket, a second valve positioned above
the first valve and concentric therewith, the second
valve has a peripheral portion seatable upon the gasket
sealing volume above first valve, a first helical spring
compressively positioned between the valves, a cover
secured to the base plate and having a fluid escape open-
ing, and a second helical spring compressively positioned
between the second valve and the cover, the springs being
further compressible upon attainment of a predetermined
medium pressure in the container whereby the valves are
unseated from the gasket. In another embodiment, the
second spring is of greater compressive strength than
the first spring.
These and further objects and features of the
invention will be realized from an understanding of the
following description.
In drawings which illustrate the embodiments
of the invention;
Fig. 1 is a sectional elevation view of a
pressure relief device of the invention shown in closed
condition and mounted upon a liquid containing enclosure.
Figs. 2 and 3 are partial sectional elevation
views of Fig. 1, showing parts of the device in various
operative positions;
Fig. 4 is a half sectional elevation view of a
second embodiment of the invention showing parts of the
devices in closed condition;
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Figs. 5 and 6 are half sectional elevation
views of Fig. 4, showing parts of the device in various
operative positions, and
Figs. 7, 8 and 9 are sectional elevation views
of three additional embodiments of the invention.
Referring now to Fig. l, numeral l identifies
a pressure regulating device incorporating an embodiment
; of the invention, which device is mounted atop a trans-
former tank 3, shown in fragmented section, and having
an opening 5 which exposes the contents of the tank,
liquid or gas, to the device. Device l includes a base
plate 7, preferably circular in cross-section, which is
af-Eixed by fastener means such as machine bolts 9, to
the top of the tank 3. A gasket 11 may be used to
provide a leak tight joint between the device and the
tank.
On the upper surface of the base plate a circum-
ferential groove 13 is provided for receipt ox a seat-
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ing means in the form of a flat circular gasket 15having a raised lip portion 17 extending about the inner
edge portion ox the gasket. A plurality of screw and
washer assemblies 19 retain the gasket 15 in seated
condition in the groove 13.
A first cup valve 21 is arranged to project into
an opening 23 formed in the base plate 7, the upper
periphery of the valve resting upon the raised lip
portion 17. A second cup valve 25, concentrically
arranged relative valve 21, is positioned above the first
cup valve 21 with the lower outer periphery of valve 25
seated upon the gasket 15. Compressively arranged
between the cup valves 21 and 25~ is a helical spring
27. A cover 29 encloses the second cup valve 25, the
lower end of the cover being affixed to an outer surace
of the base plate 7 by a plurality of screws 31 arranged
about the periphery of the base plate. The cover 29
has a plurality of openings 33 which provide for a flow
of liquid or gaseous medium from within the cover 290
Compressively arranged between the second cup valve 25
and the cover 29~ is a helical spring 35.
It will be noted that second cup valve 25 is
formed with a circular groove, or recess 37 which serves
to maintain the springs 27 and 35 in concentric align-
ment, while the top surface of the cover 29 is formedto stabilize the upper end of the spring 35 against
lateral movement.
Spring 35 must have a greater compressive force
than spring 27, so that it will maintain the valve 25
in seated condition upon the gasket 15 until pressure
relief action occurs. The discharge rate and volume
discharge of the tank liquid can be established by
proper selection of compressive force of spring 35.
Initial pressure value to unseat valve 21 is controlled
by the compressive force of spring 27. values of
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pressure release can be set for any desired figure,
a common range for use on power transformers being 4
to 20 pOs.i.g. which satisfies most operational re-
quirements on such equipment.
In operation the valve 21 is moved upwardly
and is unseated ~Fig.2~ when the pressure in the tank
3 attains predetermined value, allowing the gas or
liquid to flow into the region below the valve 25.
The pressure of the gas, or liquid involved, is exerted
upon the valve 25, which, together with the added lift-
ing rorce developed by the further compressed spring
27, causes the valve 25 to be unseated (Fig.3) from the
flat gasket 15 whereupon the pressurized medium will be
released to atmosphere by way of the opening 33 of the
cover 29. Once the pressure of the medium returns to
a predetermined value, the spring 35 will force the
valve 25 to be seated upon the flat gasket 15.
Simultaneously, the valve 21, will be reseated
upon the gasket lip 17 by action of the spring 27,
whereupon the device is returned to initial position
(Fig.l). The action of the device to provide a release
of gas pressure, is extremely rapid, such action being
more fully described in the operational theory set forth
in U.S. Patent No. 3,217,082 dated Nov.9, 1965 - King et al.
A second embodiment, illustrated in Figs. 4 to
6, incorporates certain modification in structure, over
that of the first embodiment described above. More
particularly, the second embodiment utilizes a disk-like
first valve plate 41 having a peripheral groove 43 in
which is seated a compression spring 45. The valve
plate 41 seats upon a valve seating means, namely, a
circular gasket 47 positioned in a base plate 49,
similar in structure and function to base plate 7 of the
first embodiment.
A valve seat 51 surrounds an upper portion of
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the base plate 49, and supports a circular gasket 53.
A second valve 55, which is a cup-like configuration,
and concentrically arranged relative to the valve 41,
engages the gasket 53 and has a peripheral shoulder 57
upon which a compression spring 59 is seated. The
upper end of the spring 45 abuts the inner surface of
the valve 55. A top plate 61 is axranged above the
valve 55, and has a circumferential recess 63 in which
the upper end of the spring 59 is seated. A plurality
of bolts 65 are arranged to positionally maintain the
spring 59, and allow adjustable compression thereof.
It will be seen that the amount of fluid pres-
sure in the transformer tank 7 to unseat the valve 41
will depend upon certain variables, such as relative
pressure sensitive areas of the valves 41 and 55, as
well as the compressive force of the springs 45 and 59.
In one pressure relief device made in accordance with
the invention, areas of valves 41 and 55 were 23 sq.
in. and 45.7 sq. in. respectively, and springs 45 and
59 had a compressive force of 65 lbs/sq.in. and 72
lbs/sq.in. respectively when compressed three inches.
Such design constants, allowed unseating of the valve
41, when the fluid pressure reached 8 p.s.i.g. + 1.
Fig. 4 illustrates the non-operative, or closed
condition of the device. Fig. 5 illustrates the
initial stage of operation when the valve 41 is forced
off the sealing gasket 47 by reason of fluid pressure
within the transformer tank 3 reaching preset unseating
pressure. Fig. 6 illustrates unseating of the valve
55, by reason of fluid passing valve 41, in which
condition the fluid is released to atmosphere, as
shown. Once the pressure in the tank 3 falls to a pre-
determined value, i.e., below preset value operational
value, the springs will function to return the valve
to the closed condition illustrated in Fig. 4.
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The embodiment illustrated in Fig. 7 incorpor-
ates a flat disc valve 69 arranged to seat upon a valve
seating means in the form o a circular gasket 71 posi-
tionea in a base plate 73~ which is mounted atop a
transformer tank in the rnanner of the predescribed
embodiments. A second valve 75 concentric with valve
69, is arranged to extend about the periphery of the
valve 69, an outer region 77 of the valve extending
downwardly and in sealing contact with a flexible seal
79 supported in the base plate 73. The flexible seal 79
is disclosed and claimed in my co-pending Canadian application
Serial No. 414,976, filed November 5, 1982. An inner
part 81 of valve 75 extends upwardly adjacent a helical
spring 83. The latter is compressively arranged between
the valve 75 and a cover 85 affixed to the base plate
73 by screws 87. One or more openings 89 are provided
ln the cover for release of pressure fluid, as will
later be described.
Affixed to the upper surface of the valve 69 is a
shield 91 which encircles a helical spring 93 compres-
sively arranged between the valve 69 and the cover 85.
Spring 93 is stronger compressively than spring 83.
Like the previous described embodiments, the
amount of fluid pressure in transformer tank 7 Jo unseat
the valve 69, will depend upon valve ratio variables
an`d spring rate variables, all of which can be arrived
at using well known design techniques.
It is to be noted that reseating action of the
valve 69 is maximized since the more powerful spring
93 is working against a smaller area, compared with the
total area of valves 69 and 75. During seating move-
ment the valves will be briefly separated. Fast closing
action of the valve 69 serves to reduce fluid e.g., oil,
loss in the transformer tank 7.
The embodiment of Fig. 8 is similar to that of
Fig. 7 except for minor design changes, such as a purge
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valve 95, which is used to allow escape of air in the
transformer tank during filling, and an access plate
97 arranged in an opening of a cover 99, and position-
ally maintained by a plurality of clip means 101. The
access plate provides access to the purge valve 95.
The embodlment of Fig. 9 is similar to that of
Figs. 7 and 8 except it incorporates a valve 103 which
is cup-shaped. A second valve 105 seats upon the valve
103, and is concentric therewith, while helical spring
83 is compressively arranged between the valve 105, and
a cover 107.
Spring 93 is compressively arranged between the
valve 103 and the shoulder of a sleeve 109. An adjus-
ting screw means 111 is arranged in the cover 109 to
seat upon the shoulder of the sleeve 109 whereby com-
pressive adjustment of the spring 93 can be achieved.
It is to be noted that the embodiment of Figs.
7, 8 and 9 have basic features in common, namely, both
valves used in each embodiment are in physical contact
prior to pressure release operation, and the compression
springs used in each will operate to reseat the primary,
or inner valve, before the outer valve is seated because
of area and spring pressure factors, as discussed above.
It is also to be noted that all five embodiments
disclosed herein, have a central operative theme in
common, namely the two valves in each move independently
during certain operation phases. In the Fig. 1 and 4
embodiments, the inner valve unseats prior to unseating
of the outer valve, while in the Fig. 7, 8 and 9 embodi-
ments, the inner valve seats prior to the seating of theouter valve. Such action is generated by the differing
compression factors of the springs bearing upon each
valve. As a result, more efficient operational results
are obtained with the pressure relief device of the sub-
ject invention as compared with such devices of the priorart.
