Note: Descriptions are shown in the official language in which they were submitted.
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OW PRESSI~RE HIGH TEMPERATURE SAFETY ~AL~IE
Technical Field
1. The technical field to which the invention relates
comprises the art of fluid handling.
Background of the Invention
Standard safety valves for industrial applications are
commonly constructed in a manner disclosed generally, for
example, in U.S. patent 2,628,632. In such arrangements,
the valve typically includes a flow passage extending from
an inlet to an outlet on an axis offset with respect to the
inlet. At an intermediate location of the passage, a
closure disc cooperates with an annular seat to open and
close the valve to fluid flow. Urging the disc toward a
closed position by imposing a predetermined loading force
against the topside of the disc is usually achieved by means
of a compressed coil spring acting in opposition to the
fluid force of the system being monitored that tends to urge
the disc on its underside toward the open position. The
magnitude of force imposed by the compressed spring is
generally preadjusted to a customer's specification for the
set point at which a value of fluid pressure to be relieved
can initiate movement of the disc toward the open valve
position.
Valves of the foregoing type are typically utilized
25 for relief of fluid pressures on the order of 50 to 2000
psig and at temperatures usually less than about 1000F.
Under such conditions, set point operation of the valve is
reliably predictable pursuant to the government codes
regulating performance of these valves. However, under
operating conditions of relatively low pressure, on the
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order of less than about 50 psig, and high fluid temperature,
on the order of 1000F and above, thermal conductivlty from
the fluid median within the valve body tends to introduce
physical property changes in the coil spring which in turn
alters the spring load previously set. These load changes
that are attributed to spring force variations caused by
thermal expansion and modulus of elasticity changes of the
spring materials as a function of temperature, have been
found to cause operational instability of the valve by
adversely affecting the intended set point previously
established.
Prior but unsuccessful attempts to resolve
the foregoing have largely centered around modified spring
designs or inverted mountings to remove intrinsic component
weight effects. However, despite recognition of the problem,
a more satisfactory solution therefor has not heretofore
been known.
This invention relates to industrial type
safety valves for relief of overpressure from a fluid system
and more specifically to such valves operative under fluid
relief conditions of low pressure and high temperature at
which previous constructions have generally operated unsatis-
factorily.
The present invention therefore resides in
a safety valve for relieving overpressure of a fluid at
temperatures of about at least 1000F including a body defining
a fluid passage extending between an inlet and an outlet,
an annular se~surrounding the passage at an intermediate
location thereof and a disc displacably movable from between
an urged first position engaging the seat to prevent fluid
flow therepast towards a second position removed from the
seat which permits fluid flow to the outlet in response
to a fluid overpressure. In the present invention, there
is provided an arrangement for imposing the set point load
force against the disc, this including an elongated spindle
operably connected to the disc for displacement therewith
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and a mass of predetermined weight capable of imposing at
least eighty-five percent of the force sought to be imposed
against the disc for urging the disc towards the closed
position, the mass being of a stainless steel composition
characterized by a relatively high mass per unit volume
affording a relatively high order of thermal stability with
a thermal conductivity substantially in the range of 6.85-
21.4 Btu/h/ft2/F/ft and including a central bore through
which to receive the spindle. Support means is provided
to support the mass at a location physically displaced from
the disc but in force imposing relation thereagainst, the
support means including means providing an engagement inter-
ference in a weighted direction between the mass and the
spindle. A coil spring is operably positioned in a series
load relatio~ with the mass for imposing the remaining load
force sought to be imposed against the disc. The spring
is positioned for relative temperature stability at a mass
surface location further removed from the fluid passage
in the body in relative thermal isolation from the temperature
of the fluid passage as compared to the disc. Adjustment
means is provided to adjust the load imposed by the spring
to calibrate the combined loading for the intended set point
setting of the valve.
It is therefore an object of the invention
to provide a safety valve construction affording reliably
predictable
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set point operation for fluid monitoring conditions of
relatively low pressure and relatively high temperature.
It is a further object of the invention to effect the
foregoing object in a highly novel and economical manner.
Brief Description of the Drawing
Fig. 1 is a sectional elevation through a safety valve
incorporating the inventlon hereof.
Referring now to the drawing, there is basically
disclosed a safety valve of a type commercially available
as a CONSOLIDATED(R) type 1900 series safety valve. Briefly,
the valve is comprised of a body or base 10 defining a flow
passage 12 extending from an inlet 14 through nozzle 16 to
an outlet 18 surrounded by flange 20. At the downstream
end face of nozzle 16 there is provided an annular seat 22
with which a displaceable closure disc 24 is adapted to
cooperate for opening and closing fluid flow through passage
12 from inlet 14 to outlet 18.
Bolted to the top portion of the body is an internally
open bonnet 26 which with a hollow cap 28 encloses a slide-
able spindle 30. The spindle is secured at its lower endin a disc holder 32 adapted for upward displacement within
tubular guide 34 and on which disc 24 is mounted. For
imposing the set point loading of the valve there would
normally be provided a compressed coil spring (not shown)
adjustable by means of an adjustment screw 36. The adjust-
ment screw is threadedly displaceable in bonnet threads 38
for vertical positioning of spring washer 40. A screw nut
42 is utilized to secure the position of screw 36 after all
adjustments have been completed.
For effecting set point loading for low pressure high
temperature conditions in accordance with the invention, the
conventional coil spring supra has been eliminated, and
instead is imposed by a combination of a cylindrical mass 44
in combination with a relatively small spring 46 operable
in a manner as will be explained. To accommodate massweight 44 in this arrangement, the weight includes a central
axial bore 48 through which to loosely receive spindle 30
and is of outside diameter sufficiently smaller than the
internal diameter of bonnet 26 thereat as to enable upward
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displacement of the weight free of sidewall interference.
To effect loading for purposes hereof, mass
44 is intended to provide at least eighty-five percent and
preferably at least ninety to ninety-five percent of the
set point load force so as to minimize the remaining load
assumed by spring 46, it being the purpose of the spring
to enable fine tune adjustment of set point via adjustment
screw 36. Mass 44 for these purposes should preferably
be of a high density, high mass per unit volume composition
and typically is a metal alloy. A preferred alloy is a
stainless steel to also minimize and avoid potential corrosion
that could otherwise occur. Stainless steel has a thermal
conductivity that is substantially in the range of 6.85-
21.4 Btu/h/ft2/F/ft. With the loading participation con-
tributed by spring 46 being limited to on the order of less
than ten percent, and being located above mass 44 furthest
removed from body 10, any thermal effects imposed on mass
44 will have minimal, if any, effect on spring 46, and an
inconsequential, if any, effect on the set point operation
of the valve.
By the above description there is disclosed
a novel construction which readily adapts an otherwise standard
safety valve for reliably predictable operation when monitoring
high temperature fluid at relatively low pressure set points.
Since variations in thermal effects imposed on mass 44
do not per se affect the loading, and any thermal effect thereof
is transmitted to spring 46 would be miniscule if at all,
operation under those conditions can be reliably ar.d pre-
dictably obtained by a modest structural substitution at
minimal, if any, increase in cost. The arrangement provides
maximum benefit for extremely high temperature relief devices
due to superior thermal stability of the resisting force,
while at the same time is more finely adjustable than conventional
designs in providing a constant resisting force regardless
of lift position. Consequently, a solution to a long standing
problem is resolved in accordance with the invention in
a highly satisfactory manner as compared to previous approaches
pursued therefor.
Since many changes could be made in the aboveconstruc-
tion and many apparently widely different embodiments of this
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invention could be made without departing from the scope
thereof, it is intended that all matter contained in the
drawing and specification shall be interpreted as illustra-
tive and not in a limiting sense.
