Pressure/vacuum relief valve assembly

A non-sticking, field replaceable valve seat and pallet assembly for use in a pressure vacuum relief valve. The valve seat is adapted for positioning within a valve orifice inside the valve housing. The valve seat has three guide vanes spaced around and radiating inwardly from an inner wall of the valve seat, the guide vanes each having a tip. The pallet includes a pallet disc for sealingly engaging the valve seat and a cylindrical guide stem, a lower portion of which extends below the pallet disc for riding between the tips of the guide vanes. Both the valve seat and the lower portion of the guide stem are located "inside" the process where they are less apt to freeze. The distance between adjacent guide vane tips is less than the diameter of the guide stem; thus, the guide stem is prevented from moving out from between the guide vanes. The design minimizes the area of surface contact between the guide stem and the tips of the guide vanes, thus reducing potential sticking locations, allowing for smooth valve stroke during operation and reducing valve wear and flutter.

BACKGROUND OF THE INVENTION 
1. Technical Field 
This invention relates generally to pressure vacuum relief valves, and, 
more specifically, to a non-sticking valve seat and pallet assembly for 
use in a pressure vacuum relief valve for low pressure applications. 
2. Background 
Pressure vacuum relief valves are installed on storage tanks and the like, 
particularly hydrocarbon storage tanks, to provide protection against 
positive or vacuum over-pressure and to prevent air intake, evaporative 
losses of product, and the release of odorous and potentially explosive 
vapors. They are sometimes called breather vents, tank vents, and pressure 
vacuum release vents. Pressure vacuum relief valves are designed and 
utilized for both vent to atmosphere and pipe away applications. 
Pressure vacuum relief valves used in the oil and gas industry generally 
include a valve seat, typically a ledge formed around a valve orifice as 
part of a cast valve housing, and a pallet or disc designed to sealingly 
engage the valve seat. The pallet maintains a seal until system pressure 
or vacuum exceeds the set pressure of the valve. When over-pressure occurs 
the pallet lifts, breaking the seal between the valve seat and pallet, 
allowing vapors to pass through the valve orifice and relieving the 
pressure or vacuum build-up. The valve reseals upon relief and remains 
sealed. 
Current systems use several upstanding guide pins spaced around the 
periphery of the pallet above the top surface of the pallet (above the 
process) to guide the pallet when it raises or lowers. A stem extending 
above the top surface of the pallet is received in a receptacle space cast 
into a valve housing lid and keeps the pallet from lifting too far off the 
valve seat. 
Sludge and condensate build-up, along with temperature extremes, can 
interfere with valve operation. One problem with current systems, 
especially prevalent in low pressure applications, is the sticking or 
freezing of the valve seat and pallet. The ledge on which the pallet comes 
to rest and the multiple points of contact between the periphery of the 
pallet and the tangential guide pins provide a significant surface area 
for sticking or freezing to occur. 
Another problem caused by contemporary design is valve wear and flutter. 
Movement of the pallet against the valve seat and guide pins eventually 
wears down the component elements of the valve and damages the integrity 
of the seal. Compounding this problem is the difficulty in replacing valve 
components in the field. If a valve seat is machined into the valve 
housing, the entire housing must be replaced after the seat becomes worn. 
It is thus the object of the present invention to provide a valve seat and 
pallet assembly for use in pressure vacuum release valves that resists 
sludge and condensate build-up and otherwise prevents valve sticking and 
freezing. 
It is another object that the valve seat and pallet assembly provide a 
smooth valve stroke during operation to reduce valve wear and flutter. 
It is a further object that the valve components be field replaceable 
without the requirement for special tools or complex procedures. 
SUMMARY OF THE INVENTION 
These and other objects are achieved in a pressure vacuum relief valve 
incorporating a non-sticking, field replaceable valve seat and pallet 
assembly. Rather than being molded or cast as part of a valve housing, the 
valve seat is a separate component adapted for positioning within a valve 
orifice inside the valve housing. The valve seat has three guide vanes 
spaced around and radiating inwardly from an inner wall of the valve seat, 
the guide vanes each having a tip. The pallet includes a pallet disc for 
sealingly engaging the valve seat and a cylindrical guide stem. A lower 
portion of the guide stem extends below the pallet disc for riding between 
the tips of the guide vanes. Both the valve seat and the lower portion of 
the guide stem are located "inside" the process where they are less apt to 
freeze. The distance between adjacent guide vane tips is less than the 
diameter of the guide stem; thus, the guide stem is prevented from moving 
out from between the guide vanes. This design minimizes the area of 
surface contact between the valve seat and pallet, thus reducing potential 
sticking locations, allowing for smooth valve stroke during operation and 
reducing valve wear and flutter. 
In accordance with another aspect of the invention, the tips of the guide 
vanes are radiused, or rounded-off, so as to reduce even more the area of 
surface contact between the guide stem and guide vanes. To help prevent 
sludge accumulation, the tips of the guide vanes may also be made to have 
a chisel point to provide a self-cleaning scraping action relative to the 
guide stem. In a related aspect, the upper surface of each guide vane is 
also radiused so as to achieve a self-draining and drip ring design. This 
minimizes the build-up of solid or liquid materials that might interfere 
with normal valve operation. 
In accordance with a further aspect of the invention, the guide vanes are 
each of an angular design having a width that narrows from the base of the 
guide vane toward its tip, whereby strength is imparted to the guide vane 
but a minimal area of surface contact between the guide stem and the tip 
of the guide vane is maintained. 
In accordance with yet another aspect of the invention, the valve seat and 
pallet are formed of a thermoplastic material, preferably 
polyphenylenesulfide, which provides superior resistance to corrosion, 
chemical attack, liquid or vapor adhesion, temperature extremes and 
sticking due to valve seat freeze. 
A better understanding of the invention and its objects and advantages will 
become apparent to those skilled in this art from the following detailed 
description, taken in conjunction with the attached drawings, wherein 
there is shown and described only the preferred embodiment of the 
invention, simply by way of illustration of the best mode contemplated for 
carrying out the invention. As will be realized, the invention is capable 
of modifications in various obvious respects, all without departing from 
the invention. Accordingly, the description should be regarded as 
illustrative in nature and not as restrictive.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring initially to FIG. 1, there is shown a pressure vacuum relief 
valve, generally indicated by the reference numeral 10, designed for pipe 
away applications. It should be noted that the present invention is useful 
in alternate designs for other applications, such as vent to atmosphere 
applications. Thus the invention as described in connection with FIG. 1 is 
for illustrative purposes and should not to be taken to limit the 
application of the invention in any respect. 
The pressure vacuum relief valve 10 comprises a valve housing consisting of 
an upper body 12 fastened to a lower body 14 by several bolts 16 (usually 
4-6). A gasket 18 lies between the upper body 12 and lower body 14. The 
upper body 12 has an internal chamber 20 for fluid communication with an 
outlet connection, such as a pipe (not shown). A flange 22 provides a 
mating surface for the outlet connection. The upper body 12 is capped by 
an upper body lid 24, whose fluid tight integrity is assured by an o-ring 
26. 
The lower body 14 of the valve housing includes a first internal chamber 28 
which communicates through an inlet connection with the interior of, for 
example, a storage tank (not shown). A first valve orifice 30 is formed at 
the point where the upper body 12 and lower body 14 are joined. A pressure 
relief valve assembly, generally indicated by the reference numeral 32, is 
positioned within the valve orifice 30 to control this fluid passageway. 
The lower body 14 of the valve housing further includes a second internal 
chamber 34 connected for fluid communication to the first internal chamber 
28. The second internal chamber 34 is capped by a lower body lid 36 and 
o-ring 38. The second internal chamber 34 sits above a valve orifice 40 
separating the second internal chamber 34 from the atmosphere. A vacuum 
relief valve assembly, generally indicated by the reference numeral 42, is 
positioned within the valve orifice 40 to control this fluid passageway. 
An extension screen 44, maintained in position by a retaining ring 46, 
lies below the vacuum relief valve assembly 42. 
The pressure relief valve assembly 32 and the vacuum relief valve assembly 
42 are the same in design, and reference should be made at this point to 
FIGS. 2-6 which illustrate these components in more detail. 
Both the pressure relief valve assembly 32 and vacuum relief valve assembly 
42 comprise a non-sticking valve seat and pallet assembly. The valve seat 
48 is preferably cylindrical and includes an outer wall 50 having a 
stepped lower portion 52 within which is a recessed area 54 containing an 
o-ring 56. The valve seats 48 as shown in FIG. 1 are snugly retained 
within the valve orifices 30, 40. With respect to the valve seat 48 
residing in valve orifice 30 (the pressure relief valve assembly 32), the 
stepped lower portion 52 of the outer wall 50 is retained between a lip of 
the valve housing upper body 12 and the mating surface of the lower body 
14. As for the valve seat 48 residing in valve orifice 40 (the vacuum 
relief valve assembly 42), the stepped lower portion 52 of the outer wall 
50 is retained between a lip of the valve housing lower body 14 and the 
extension screen 44. In both valve seats an o-ring 56 provides fluid tight 
integrity. 
Three guide vanes 58 are spaced around and radiate inwardly from an inner 
wall 60 of the valve seat 48. Each of the guide vanes 58 has a tip 62 that 
is preferably radiused, or rounded off, along the horizontal as best shown 
in FIG. 4. 
A pallet, generally indicated in FIG. 2 as element 64, includes a pallet 
disc 66 for sealingly engaging the valve seat 48 and an integrally formed 
cylindrical guide stem, generally indicated by the reference numeral 68. 
The guide stem 68 includes an upper portion 70 extending above the upper 
surface 72 of the pallet disc 66 and a lower portion 74 extending below 
the pallet disc 66. The lower surface 76 of the pallet disc 66 has a 
circumferential recessed area 78 designed to ride above the top surface 80 
of the valve seat 48. 
A pallet seal 82 lies adjacent to the lower surface 76 of the pallet disc 
66 and is held in place by a seal support 84. A retainer clip 86 maintains 
the position of the seal support 84, and, thus, the position of the pallet 
seal 82. 
The lower portion 74 of the guide stem 68 is designed for riding between 
the tips 62 of the guide vanes 58. The guide stem 68 is prevented from 
moving out from between the guide vanes 58 as the distance between 
adjacent guide vane tips 62 is less than the diameter of the guide stem 
68. There is only a minimal area of surface contact between the lower 
portion 74 of the guide stem 68 and the tips 62 of the guide vanes 58. 
This reduces potential sticking locations, allows for smooth valve stroke 
during operation and reduces valve wear and flutter. The upper portion 70 
of the guide stem 68 rides in a receiving area 88 in the valve housing lid 
24, 36. 
The valve seat and pallet assembly as illustrated provides protection 
against positive or vacuum over-pressure and prevents air intake, 
evaporative losses of product, and helps contain odorous and potentially 
explosive vapors. The pallet seal 82 maintains a tight seal against the 
top surface 80 of the valve seat 48 until system pressure or vacuum 
exceeds the set pressure of the assembly. When over-pressure occurs the 
pallet 64 lifts, breaking the seal between the valve seat 48 and the 
pallet disc 66, allowing vapors to pass through the valve orifice 30, 40 
and relieving the pressure or vacuum buildup. The assembly reseals upon 
relief and remains sealed. 
With respect to the illustration in FIG. 1, should a positive pressure 
build in a storage tank, such as might occur during warm weather, and a 
positive pressure is reached exceeding the set pressure of the pressure 
relief valve assembly 32, the pallet disc 66 would lift off of the valve 
seat 48 to allow the excess pressure to escape into the internal chamber 
20 of the upper body 12. Conversely, should a vacuum over-pressure occur 
in the storage tank exceeding the set pressure of the vacuum relief valve 
assembly 42, the pallet disc 66 would lift off of the valve seat 48 to 
allow atmospheric air to enter the second internal chamber 34 of the lower 
body 14 to prevent collapse of the storage vessel. 
The minimal area of surface contact between the lower portion 74 of guide 
stem 68 and the tips 62 of the guide vanes 58 reduces the risk of valve 
sticking and freezing in addition to reducing valve wear and flutter and 
allowing for smooth valve stroke during operation. As illustrated more 
particularly in FIG. 4, the tips 62 of the guide vanes 58 are preferably 
radiused so as to reduce even more the area of surface contact between the 
lower portion 74 of the guide stem 68 and the tips 62 of the guide vanes 
58. Similarly, the top surface 80 of each guide vane is radiused so as to 
minimize the buildup of solid or liquid material that might interfere with 
normal valve operation. FIG. 5 shows a crosssection a radiused guide vane 
58. To further reduce the risk of valve sticking or freezing, each of the 
tips 62 of the guide vanes 58 may also be provided with a chisel point to 
provide a self cleaning scraping action relative to the lower portion 74 
of the guide stem 68. The chisel point, best illustrated in FIG. 6, is 
formed by the parting line in the mold used to make the valve seat 48. The 
tip of the guide vane 58 has a first downward radius 90 and a second 
slightly steeper upward radius 92 creating a shoulder or ledge 94. The 
shoulder 94 provides a scraping action against the lower portion 74 of the 
guide stem 68. 
In the most preferred embodiment, each of the guide vanes 58 is of an 
angular design, such as is shown in FIG. 3, having a width that narrows 
from the base 96 of the guide vane 58 toward the tip 62 of the guide vane 
58. With this design strength is imparted to the guide vane 58 but a 
minimal area of surface contact between the lower portion 74 of the guide 
stem 68 and the tip 62 of the guide vane 58 is maintained. 
The valve seat 48 and pallet 64 are preferably formed of an engineering 
thermoplastic material such as polyphenylenesulfide. As the valve seat 48 
is not a cast component of the valve housing, the unit is field removable 
and replaceable. 
The present invention is particularly suited for low pressure applications. 
High strength castings provide added structural integrity and durability 
to the valve housing. Cast aluminum, ductile iron, stainless steel or 
vinyl ester FRP are the preferred valve housing materials of construction. 
The valve seat 48 and pallet 64 are preferably constructed of an advanced 
composite polyphenylenesulfide (PPS) such as is marketed by Phillips 
Petroleum Company under the trade name RYTON or by the Celanese 
Corporation under the trade name FORTRON. Optional materials of 
construction for the valve seat 48 and pallet 64 include alternative 
engineering thermoplastics such as polytetrafloralethalene (TEFLON), 
acetyl resins, polyetheretherketone, polysulfides, KYNAR or NYLON. The 
advanced composite thermoplastic materials provide superior resistance to 
corrosion, chemical attack, liquid or vapor adhesion, temperature extremes 
(-50 to 500.degree. F.) and sticking due to valve seat freeze. They also 
shed water and reduce sludge build up. The valve seat 48 and pallet 64, if 
desired, can also be made of stainless steel or other suitable materials. 
The preferred pallet seal 82 is an FEP TEFLON seal. Alternatively, nitrile, 
fluoroelastomer or other suitable seals can be used. The seal construction 
of the present invention exceeds the most stringent of industrial 
standards for allowable leakage (1 scfh @90% set point) and provides 
excellent set point accuracy (.+-.3%). 
Pallet weights are used to vary the set pressure of the valve seat and 
pallet assembly. Acceptable pallet weights include carbon steel, stainless 
steel, epoxy-coated carbon steel, resin coated carbon steel, lead or other 
weights. 
Internal gasketing can be made with nitrile, fluoroelastomer, TEFLON or 
other suitable gasket materials. 
Pressure vacuum relief valves constructed in accordance with the present 
invention can be sized and styled according to the required application 
dimensions. The valve seat 48 and pallet 64 are preferably injection 
molded to fit the valve orifice of the required housing. Other options 
include internal and external TEFLON or epoxy-coating of valve and other 
components and the addition of steam jackets and the like. 
The present invention thus provides a valve seat and pallet assembly for 
use in pressure vacuum release valves that resists sludge and condensate 
build up and otherwise prevents valve sticking and freezing. The present 
invention also provides a smooth valve stroke during operation to reduce 
valve wear and flutter and is field replaceable without the requirement 
for special tools or complex procedures. 
While the invention has been described with a certain degree of 
particularity, it is manifest that many changes may be made in the details 
of construction and the arrangement of components without departing from 
the spirit and scope of this disclosure. It is understood that the 
invention is not limited to the embodiments set forth herein for purposes 
of exemplification, but is to be limited only by the scope of the attached 
claim or claims, including the full range of equivalency to which each 
element thereof is entitled.