U.S. patent number 3,865,132 [Application Number 05/389,139] was granted by the patent office on 1975-02-11 for pilot operated relief valve.
Invention is credited to Charles W. Wiegand.
United States Patent |
3,865,132 |
Wiegand |
February 11, 1975 |
Pilot operated relief valve
Abstract
An Assembly comprising of a piston/cylinder means adapted to a
spring loaded pressure relieving valve wherein the piston area by
being greater than the seat area of the valve will when the
cylinder is in fluid communication with vessel pressure will
operatively compress the valve spring from its maximum set pressure
allowed by pressure vessel and boiler codes to a higher setting for
greater seat loading as the pressure in the vessel on which the
valve is attached approaches the normal set pressure value. When
the pressure in the vessel reaches the normal set pressure value, a
pilot valve responsive to pressure and normally open to the flow of
vessel pressure to the cylinder will close the pressure to the
cylinder and concurrently exhaust the pressure therein thus
removing the force of the piston on the valve spring which now
returns to its normal setting and the opening of the main valve
without simmer. The piston by operatively engaging one end of the
spring insures "fail safe" opening of the main valve by the
resilience of the spring in the event the piston and/or pilot valve
should malfunction in as much as the valve stem does not engage the
piston. The stroke of the piston can be limited by a travel stop to
control the compressing of the valve spring from its normal set
pressure to a predetermined higher setting.
Inventors: |
Wiegand; Charles W. (New
Rochelle, NY) |
Family
ID: |
23536994 |
Appl.
No.: |
05/389,139 |
Filed: |
August 17, 1973 |
Current U.S.
Class: |
137/492.5;
137/489; 251/63.4; 251/63.6; 251/77 |
Current CPC
Class: |
F16K
17/105 (20130101); Y10T 137/777 (20150401); Y10T
137/7764 (20150401) |
Current International
Class: |
F16K
17/10 (20060101); F16K 17/04 (20060101); F16k
017/02 () |
Field of
Search: |
;137/488,489,492.5
;251/61.4,63.6,63.4,77 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Klinksiek; Henry T.
Claims
I claim:
1. In a valve assembly adapted to relieve excess pressure from a
pressure vessel, the assembly comprises a pressure relief valve, a
pressure responsive means and a pilot valve,
whereas said relief valve is held in a closed position by a
compression spring adapted to release pressure when a predetermined
pressure is reached,
whereas said pressure responsive means comprises a cylinder closed
on one end and a piston slidable therein, the open end of said
cylinder is mounted on the top of said relief valve so that said
piston can operatively engage the top end of said compression
spring when said cylinder is supplied pressure from said vessel
through a conduit to activate said piston which by having a larger
area than the seat area of said relief valve will urge said
compression spring beyond its initial preset position thereby
increasing the spring loading in said relief valve,
whereas said pilot valve being operable in response to pressure
from said vessel and normally open to the flow of pressure from
said vessel to said cylinder will activate said piston and at a
predetermined pressure said pilot valve being positioned in said
conduit will close the pressure to said cylinder and concurrently
exhaust the pressure therein whereas said piston being deactivated
will recede in said cylinder by the returning of said compression
spring to its initial preset position wherein said relief valve
will open at its initial set pressure.
2. In accordance to claim 1 wherein the stroke of said piston when
pressure activated can be predetermined by a travel stop positioned
to operatively limit said stroke and in turn limit the further
compressing of said compression spring beyond its initial preset
position by the force from said piston on said compression
spring.
3. In accordance with claim 1 wherein the disk of said relief valve
being biased by said compression spring in said relief valve means
providing a lost motion connection between said piston and said
relief valve to allow it to open to relieve excess pressure from
said vessel even though said piston should seize in said cylinder
or should said pilot valve fail to close the pressure from said
vessel to said cylinder and exhaust the pressure therein when a
predetermined pressure is reached in said vessel.
4. In accordance to claim 1 wherein the end of the stem in said
relief valve can rise in a space to permit discharging excess
pressure from said vessel should said piston seize in said cylinder
or should said pilot valve malfunction.
Description
The present invention relates to the conventional spring loaded
pressure relieving valve used to protect vessels from excessive
pressure. This tyoe of valve depends on seat tightness by the
differential of the set pressure of the valve and the operating
pressure in the vessel on which the valve is attached. The spring
is limited to 100 percent loading on the valve disk.
The operating pressure is usually a fixed value and to minimize
vessel cost, the Maximum Allowable Working Pressure (MAWP) is
usually selected relatively close to operating pressure leaving
little net spring force to differential remaining to be exerted on
the valve disk. Pressure vessel codes limit the set pressure of the
valve so as not to exceed the M.A.W.P. of the vessel. Currently in
order to increase the differential, the set pressure and the spring
loading must be higher which in turn increases the M.A.W.P. and the
cost of the vessel.
The spring loaded valve is inherently prone to simmer (a phase just
prior to opening) on gas and vapor service. The valve starts to
simmer 3 to 5 percent below the normal set pressure. This simmer
further reduces the differential or seat loading from the numerical
difference of the set pressure and operating pressure. Should the
vessel pressure reach the simmer phase but not to the set pressure
and then recede to the normal operating pressure, the valve will
continue to simmer.
This invention when operatively adapted to a conventional spring
loaded pressure relieving valve will provide the necessary force
from a piston when pressurized to compress the valve spring from
its normal setting to a higher setting resulting in a greater
differential and tighter valve than the conventional valve under
similar operating and set pressure conditions. It will also permit
the vessel operating pressure to be within 97 percent of the normal
set pressure and the M.A.W.P. of the vessel due to the higher
spring loading on the valve disk. Simmer is eliminated as the
spring loading is reduced to the initial loading by the fast action
of a pilot valve in exhausting of the pressure in the cylinder and
on the piston when the set pressure value is reached in the vessel.
There are valves that utilize the piston/cylinder means in which
the force of the piston is applied directly on either the valve
stem or on the valve disk. The pressure to the cylinder is
controlled by a pilot valve. The lading fluid in the vessel and/or
chemical treatment used on steam boilers may cause the piston to
seize and/or the small orifices in the pilot valve to plug shut. In
either case the main valve could be locked in a closed
position.
The piston/cylinder means of this invention comprises a closed end
cylinder axially affixed to the closed end of a bonnet on a main
valve. A piston operatively positioned in the cylinder bore to
engage the threaded end of a slidable shouldered rod which is
axially interposed between the piston and one end of a compression
spring encompassed by the bonnet. The shouldered rod is axially
guided by a bushing threaded into the closed end of the bonnet. The
lower annular surface of the bushing to engage the shoulder on the
rod to initially load the spring to its normal set pressure by
applying torque force to the bushing. The higher spring setting is
obtained when the vessel pressure in the cylinder is exerted on the
top of the piston and operatively on the spring as the vessel
pressure approaches the set pressure of the main valve and the
pilot valve. The free end of the valve stem is axially guided by a
bore in the shouldered rod.
The piston area must be greater than the seat area of the valve in
order for the piston force to further compress the spring from its
normal setting (set pressure) to a higher setting. The higher
setting of the spring is controlled by a nut threaded on the
shouldered rod which limits the stroke of the piston. The
adjustable gap between the nut and the top of the threaded bushing
predicates the increase in spring force and loading desired from
the piston force available.
A pressure responding pilot valve which is normally open to the
flow of vessel pressure to the cylinder thus energizing the piston
as the pressure approaches the set pressure of the main valve. The
pilot valve is set to close the pressure to the cylinder and
concurrently exhausting the presssure therein when the vessel
pressure reaches the normal set pressure value thus removing the
piston force on the main valve spring allowing it to return to its
normal set pressure and the opening of the main valve without
simmer.
A diaphragm or bellows can be used in place of the piston/cylinder
illustrated in as much as the axial movement is miminal.
The conventional type lifting lever is not applicable to a valve
using this invention. However a "Navy" type lever can be used, it
operatively engages the lower end of the valve spring.
FIG. 1 is an outline drawing of the main valve showing the location
of the piston/cylinder means on the main valve, the pilot valve and
the necessary conduit to interconnect vessel pressure to the pilot
valve and the cylinder.
FIG. 2 is partial sectioned view of the main valve bonnet, spring
and stem and full sectioned view of the piston/cylinder means and
the pressure responding pilot valve at normal or static spring
settings on both valves with no vessel pressure present.
FIG. 3 is the same as shown in FIG. 2 except that it shows the
piston at its maximum stroke when the cylinder is pressurized with
vessel pressure by the pilot valve and the main spring compressed
to its higher setting.
Referring to FIG. 1 the outline drawing shows the location of the
piston/cylinder means on the bonnet of a spring loaded main valve
and a pressure responding pilot valve with interconnecting
conduits. The dotted line 9 is the vessel nozzle to which valve
body 11 is attached, bonnet 12 is axially affixed to the valve body
11, one end of the cylinder 13 is closed by blind flange 14, tie
rods 15 axially secure the flange 14 and cylinder 13 to the closed
end of bonnet 12, conduit 28 connects pressure tap 10 to pilot
valve 26, conduit 29 connects control valve 26 to blind flange 14,
pilot valve 26 to exhaust the pressure in cylinder 13 through
conduit 30.
Referring to FIG. 2, Cylinder 13 and blind flange 14 are axially
held secure to the closed end of bonnet 12, by tie-rods 15, piston
16 is positioned in the bore of cylinder 13, valve stem 17 is
guided in bore 40 in shouldered rod 21, threaded bushing 20 is
axially engaging the closed end of bonnet 12 for initially loading
spring 18 by engaging the shoulder on rod 21 and spring washer 19,
bore in bushing 20 to axially guide rod 21, the top of end of rod
21 is threaded to accomodate nuts 22 and 23 which act as a limit
travel stop for piston 16 when cylinder 13 is subject to vessel
pressure, gap 36 between nut 22 and top of bushing 20 predetermines
the stroke of piston 16 and the compression of spring 18 from its
normal setting position 37 to its higher setting position 38.
(shown in FIG. 3).
Pressure responding pilot valve body 26 includes pipe taps for
conduits 28,29 and 30, valve disk 32 to contain vessel pressure in
cylinder 13, a spring 31 to load disk 32 up to the set pressure, a
back seat 33 to close vessel pressure to conduit 29 and cylinder 13
when vessel pressure reaches the set pressure and concurrently
discharge the pressure in cylinder 13 through conduits 29 and 30.
Spacer 34 between valve disks 32 and 33 to dislodge disk 33 from
its seat thus permitting disk 32 to reseat when the vessel pressure
drops from its set pressure to a predetermined blow-down or is
manually reset. Spring 35 to offset the weight of disk 33 and
spacer 34 so that disk 33 can act as a check valve when disk 32 is
in an open position, thus discharging pressure from cylinder 13 to
conduit 30 and concurrently the closing of vessel pressure to
conduit 29 by disk 33.
FIG. 3 shows the piston 16 under pressurized condition in which the
vessel pressure has stroked piston 16 toward spring 18 until limit
travel stop nut 22 engages the top of bushing 20 thereby
compressing spring 18 from its normal position 37 (shown in FIG. 2)
to position 38 which operatively increases the spring loading on
the main valve disk (not shown) as long as pilot valve 26 is in a
closed position to atmosphere as shown in FIG. 2. Spring position
38 returns to position 37 (shown in FIG. 2) when pilot valve 26 has
closed the flow of pressure to cylinder 13 and is concurrently
exhausting the vessel pressure from cylinder 13 through conduits 29
and 30.
FIGS. 2 and 3 shows valve stem 17 guided in bore 40 in rod 21, the
bore 40 to be of sufficient depth to permit the stem 17 and valve
disk (not shown) to lift its necessary distance for full discharge
capacity of the main valve in the event the pilot valve 26 and/or
piston 16 malfunction as a "fail safe" feature.
The spring loaded pressure relieving valve mentioned above to
include the common names of Safety, Safety-Relief and Relief
Valve.
In view of the foregoing, it should be apparent that by the
addition of a piston/cylinder means shown and described in the
present invention is an improvement to the conventional valve by
providing means whereby a given pressure design vessel M.A.W.P. can
operate closer to the set pressure without leaking, eliminate
simmer and provide "fail-safe" operation of the valve in the event
that the piston/cylinder and/or pilot valve should malfunction.
The pilot valve and/or the piston cylinder can be inspected and
replaced at intervals without shutting down the vessel in as much
as the valve spring furnishes 100 percent loading on the disk at
the normal set pressure.
It will be understood that this invention may be embodied otherwise
than shown and various changes in detail and construction and
arrangement of parts may be made without departing from the idea of
my invention within the scope of the appended claims.
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