Safety relief valve

A safety relief valve having a disc carrier with a downwardly extending flange which overlaps an adjusting ring located on a valve seat member for providing a quicker full rated lift and shorter blowdown. The downwardly extending flange has a beveled end to form an orifice between the outer peripheral surface of the adjusting ring member for flowing media.

FIELD OF INVENTION 
This invention relates to a valve for relieving excess pressure, and more 
particularly to a safety relief valve that achieves full lift at a 
pressure slightly above a set pressure and closes fully at a pressure 
slightly below the set pressure for the safety relief valve. 
BACKGROUND OF THE INVENTION 
There are a variety of applications for safety relief valves in the 
commercial as well as residential environment. To insure safety, the 
American Society of Mechanical Engineers (ASME) has prepared a code of 
minimum requirements for broad classifications of uses for pressure relief 
valves. Because of the great damage that can result from a faulty safety 
relief valve on a power boiler, the ASME Code Section I is the most 
stringent. It requires that a safety relief valve for a power boiler: 1) 
close at a closing pressure no lower than 96% of the set pressure for that 
valve; and 2) have the valve attain a full rated lift at a pressure no 
higher than 103% of the set pressure. In contrast, for an unfired pressure 
vessel, the ASME Code Section VIII requires a pressure relief valve have a 
closing pressure not lower than 93% of the set pressure, and a full rated 
lift at a pressure not to exceed the set pressure by more than 10%. 
Optimally, a valve should open when the system pressure exceeds a 
predetermined set point for pressure and quickly reach a full open or 
"full lift" position without excessive overpressure buildup. Also, the 
valve should close as soon as it has vented the excess volume that is 
sufficient to return the system pressure below the set pressure and 
provide a rapid closing or "blowdown" to prevent an excessive loss of 
fluid from the system. 
Attempts have been made at providing a pressure relief valve that will meet 
the demanding standards of ASME Code Section I. Stewart et al, U.S. Pat. 
No. 4,130,130 disclosed a safety relief valve that included a nozzle ring 
and a curved inwardly facing surface formed on a shroud portion of the 
valve head to define an annular secondary flow orifice. This orifice was 
too large to provide any restriction to flow and therefore failed to 
assist in the lifting force on the valve to achieve full opening and flow. 
Scallan U.S. Pat. No. 4,708,164 addressed the problem of valve "chatter". 
The Scallan patent disclosed a safety relief valve having an adjusting 
ring and a valve carrier with a downwardly projecting peripheral flange. 
The ring included an axially projecting annular portion that extended 
towards the valve carrier to form an orifice to control the closing or 
"blowdown" of the valve. The outer peripheral surface of the ring formed a 
second orifice with the flange to aid in the lifting of the valve to a 
full open position. Though this invention provided stability in opening 
and closing of the valve, the closure of this valve did not meet the 
minimum required standard for a power boiler as dictated by ASME Code 
Section I. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide full and rapid opening of a 
safety relief valve at a pressure slightly above a set pressure level, as 
well as full and rapid closing of the valve at a pressure slightly below 
the set pressure level. 
It is a feature of the invention to include an adjusting ring located on 
the valve seat member that cooperates with the valve carrier member to 
create a pair of orifices to aid in the rapid opening and rapid closing of 
the safety relief valve. 
It is a feature of the invention to include a disc carrier having a radial 
chamber peripherally defined by a bevel surface and a downwardly extending 
flange with an inwardly facing beveled end to provide a rapid closure of a 
disc against a valve seat. 
A safety relief valve in accordance with the present invention includes a 
valve body with a fluid inlet, fluid outlet, and valve seat encircling the 
inlet. The valve body houses a disc member movable toward and away from 
the seat and a disc carrier with a cavity for the disc, a first chamber 
radially adjacent the cavity and a downwardly projecting skirt flange with 
an inwardly facing beveled end for forming a second chamber and an annular 
surface within the disc carrier. A ring member is movably located on the 
valve seat and adjacent the disc carrier. The ring member has an axial 
projecting annular portion that extends toward the disc carrier to form a 
radial orifice and an outer peripheral surface forming a peripheral 
orifice with the beveled end of the flange. An adjustable spring assembly 
biases the disc into sealing engagement with the valve seat and the disc 
carrier into cooperation with the ring member. In accordance with an 
important aspect of the invention, the bevel surface of the first chamber 
and the bevel end of the extending flange allow pressure within the safety 
relief valve to reduce at a faster rate as pressure in the fluid inlet 
reduces, thereby providing a quicker closing or a shorter "blowdown". 
Other objects, features and advantages of the invention will be apparent in 
the following description and claims in which the invention is described, 
together with details to enable persons skilled in the art to practice the 
invention, all in connection with the best mode presently contemplated for 
the invention.

DETAILED DESCRIPTION OF THE INVENTION 
The preferred embodiment of the present invention is illustrated by way of 
example in FIGS. 1-4. With specific reference to FIG. 1, a safety relief 
valve 10 includes a hollow valve body 12 having an inlet passage 14 and an 
outlet passage 16 for incompressible or compressible fluid flow. 
As shown in greater detail in FIGS. 3 and 4, a valve seat member 18 is 
mounted within inlet 14 of valve 10. The valve seat member 18 has an 
annular valve seat 20 forming the upper end and a series of threads 22 
along the exterior of the upper portion of valve seat member 18 and below 
valve seat 20 to receive an interiorly threaded ring member 24. 
A disc carrier 26 having a cavity 27 into which a disc 28 is secured, is 
positioned directly over valve seat 20. The disc 28 is constructed and 
arranged for sealing engagement with annular valve seat 20 and preferably 
has a diameter at least equal to the diameter of the annular valve seat 
20. The disc carrier 26 has adjacent to cavity 27, a radial chamber 30 
having its perimeter defined by a bevel surface 32. Bevel surface 32 is 
preferably at a 45.degree. angle relative to the axis of inlet 14. 
Additionally, the disc carrier 26 has a downwardly projecting skirt flange 
34 which forms an outer chamber 36 having an interior surface 
perpendicular to an annular surface 38 within disc carrier 26. On the free 
end of skirt flange 34 is an inwardly facing bevel 40, preferably at a 
45.degree. angle, which is in close proximity to the peripheral surface 42 
of ring 24. 
The disc carrier 26 is coupled to a spring assembly 44 through a valve 
actuating rod 46. The spring assembly 44 exerts a downward force on the 
disc carrier 26, biasing the disc member 28 into sealing engagement with 
valve seat 20 to define a closed position of the valve 10 as shown in FIG. 
2. An adjusting mechanism 48 is located at the top portion of valve 10 to 
calibrate the force exerted by the spring assembly 44 and thereby provide 
the set pressure of the safety relief valve 10. 
The ring member 24 may be adjusted by rotating on threads 22 toward or away 
from disc carrier 26. A locking member 50 is provided through valve body 
12 into engaging slots 52 formed in lower end of ring 24 to prevent 
inadvertent movement of ring 24. 
Ring 24 includes an upper end portion 54 that axially projects toward bevel 
surface 32 of disc carrier 26. This end portion 54 may be adjusted to a 
position that is in close proximity to surface 32 when valve 10 is in the 
closed position as shown in FIG. 2. This position forms a radial orifice 
56 with surface 32. The ring 24 also includes an enlarged diameter portion 
58 forming the outer peripheral surface 42 which preferably has an upper 
radiused edge 60 to form a peripheral orifice 62 with flange 34 on carrier 
26. Preferably the rounded edge 60 cooperates with the beveled end 40 of 
flange 34 to vary the area of peripheral orifice 62 as the carrier 26 
moves upwardly during the opening of valve 10. 
The operation of the safety relief valve 10 requires that the spring 
assembly 44 be set to exert a proper loading or biasing force on disc 
carrier 26 and disc 28, equal to the set pressure of the valve. The 
compressor force required on the disc 28 to initially open or "crack" the 
valve is of a predetermined value slightly lower than the set pressure of 
the valve. When the inlet pressure is equal to the set pressure, some 
media flows past the seating surface 20 and into radial chamber 30. As a 
result of the restriction of flow in radial orifice 56, pressure 
accumulates in chamber 30 to help lift disc member 28 higher off of valve 
seat 20. Because the inlet pressure can now act over a larger area (area 
of disc 28 and chamber 30), a greater force is available to overcome the 
force of spring 44. By adjusting ring member 24, the opening in the radial 
orifice 56 can be altered, thus controlling pressure accumulation in 
radial chamber 30 to overcome the spring force and displacement of disc 
28. 
As the safety valve 10 opens wider (see FIG. 3), an instantaneous flow of 
media enters outer chamber 36. Because of the restriction to flow through 
peripheral orifice 62 formed between the beveled end 40 of skirt flange 34 
and the outside peripheral surface 42 of ring member 24, an additional 
force acts against surface 38 in outer chamber 36 to cause the disc member 
28 to lift substantially to the full open position shown in FIG. 4. 
At the full open position, the fluid flow is restricted by the valve seat 
area rather than by the radial or peripheral orifices 56, 62. 
As the inlet pressure drops, both disc carrier 26 and disc member 28 start 
to move toward valve seat 20 under the force of spring assembly 44. The 
disc member 28 will seat against valve seat 20 when the inlet pressure 
reaches a closing pressure which is slightly below the set pressure. This 
difference between set pressure and closing pressure of the valve is 
divided by the set pressure and expressed as "blowdown". "Blowdown" is 
caused by the result of the spring force not being able to overcome the 
summation of the forces under disc member 28, radial chamber 30 and outer 
chamber 36 until the inlet pressure drops below the set pressure. 
As shown in FIG. 3, both the beveled surface 32 and the beveled end 40 of 
skirt flange 34 allow the pressure to reduce at a faster rate as the inlet 
pressure reduces, thus giving the valve a shorter blowdown which reduces 
the pressure within radial chamber 30 and outer chamber 36. The beveled 
end 40 of skirt flange 34 forms a larger peripheral orifice 62 with edge 
60 to allow media to flow unrestricted and thereby diminishing the lifting 
force within outer chamber 36. Likewise, bevel surface 32 forms a large 
radial orifice 56 with upper end portion 54 to reduce the lifting force in 
radial chamber 30 and allow media to flow less restricted than the prior 
art. The "blowdown" can be decreased by adjusting ring member 24 away from 
disc carrier 26 and creating larger orifices. 
The safety relief valve 10 of this application can be adjusted to provide a 
full rated lift with less accumulated pressure and a shorter "blowdown" to 
meet the ASME Code Section I requirements for power boilers. This 
invention provides a design to convert a standard valve certified for the 
ASME Code Section VIII to meet the more stringent Section I requirements. 
It is to be understood that the terminology as employed in the description 
and claims incorporated herein is used by way of description and not by 
way of limitation, to facilitate understanding of the structure, function 
and operation of the combination of elements which constitute the present 
invention. Moreover, while the foregoing description and drawings 
illustrate in detail one successful working embodiment of the invention, 
to those skilled in the art to which the present invention relates, the 
present disclosure will suggest many modifications in the construction, as 
well as widely differing embodiments in applications without thereby 
departing from the spirit and scope of the invention. The present 
invention, therefore, is intended to be limited only by the scope of the 
appended claims and applicable prior art.