Diaphragm valve

A diaphragm valve includes a single layer, metal diaphragm cooperating with a plastic valve seat. The surface area and volume of the valve seat is limited. Additionally, the central portion of the diaphragm is generally hemispherically offset and extends axially from a planar periphery. The actuating stroke of the valve is maintained less than the offset that is formed in the diaphragm. Lastly, the valve seat is secured in such a manner to insure repetitive long term shutoff under a variety of operating conditions and limit entrapment and outgassing of potential system contaminants.

BACKGROUND OF THE INVENTION 
This invention pertains to the valve art and more particularly to a 
diaphragm valve. The invention is particularly applicable to a fluid 
system requiring high purity, good fluid lead integrity, low internal 
volume and high reliability. However, it will be appreciated that the 
invention has broader applications and may be advantageously employed in 
other environments and applications. 
Certain sectors of the manufacturing industry have imposed increasingly 
stricter requirements on valve manufacturers, some of these standards 
being unthinkable only a few years ago. In addition to providing reliable 
open and closed positions to regulate fluid flow, the industry has become 
even more concerned with other characteristics of the valve, particularly 
cleanliness both before, during and after actuation. With more sensitive 
and accurate sensing equipment and the increased demand for purity in 
fluid systems, valve manufacturers are ever conscious of new and different 
arrangements that satisfy their customer's needs. 
As will be appreciated, plastic has been incorporated into valve designs 
due to the reliable sealing, durability, adaptability, and long cycle life 
attainable with selected plastics in the valve environment. Unfortunately, 
the use of plastic has come under increased scrutiny due to its ability to 
entrap and outgas fluids, i.e. release of fluid to the system at an 
undesired time, that could contaminate the system. 
In a related manner, use of plastic can also have a dramatic effect on the 
time required to clean or purge the system. Since the plastic can entrap 
fluid, longer cleaning times are necessary which results in increased 
down-time for the fluid system. Because of the tremendous cost to the 
manufacturer, decreasing down-time is always desirable and limiting the 
amount of plastic in the valve design is a key goal. 
Other valve designs incorporate greater amounts of plastic into the valve 
seat: either (i) by the method of containing the seat in the valve body, 
or (ii) by enclosing the seat in a movable valve member. The excessive 
surface area and volume of the plastic used in the valve seats of these 
designs contributes to fluid entrapment and subsequent potential system 
contamination. 
Many present day valves include multi-layer diaphragm constructions. This 
type of design has a primary drawback. That is, if one or more layers of 
the composite diaphragm fails, the operator may be unaware of its failure. 
This could cause a virtual leak between the diaphragm layers which would 
serve as an area for potential fluid entrapment. The fluid could be 
trapped between the diaphragm layers and released to the system at an 
undesired time. 
The number of diaphragms in the valve can also cause problems. Too few 
layers in a multi-layer design may not adequately address pressure 
containment concerns. On the other hand, too many layers makes the 
multi-layer diaphragm assembly too stiff and potentially unable to be 
moved to effect valve closure. Single layer diaphragm designs can also be 
subject to the inadvertent assembly of more than one diaphragm without 
operator awareness. 
Reliability of operation is always a primary concern with valves handling 
dangerous fluids. Under the general category of reliability, valve 
manufacturers have employed various arrangements to assure that the valve 
will open under all conditions. One arrangement is to structurally tie the 
actuating stem to the seat by forming an opening through a central portion 
of the diaphragm and directly fastening the stem and plastic valve seat 
together. This arrangement, where the plastic is secured to the diaphragm 
rather than the valve body, compromises the integrity of the diaphragm and 
defines yet another potential leak path that must be effectively addressed 
by the valve design. 
An alternate arrangement secures one face of the diaphragm to the actuating 
stem by welding or the like. Although the integrity of the diaphragm is 
maintained, this alternate arrangement has detrimental aspects of its own 
related to the welding operation. 
With some constructions it is even possible to deflect the diaphragm to a 
position where it can't be operated. For example, an overcenter position 
of the diaphragm may occur so that movement of the diaphragm from a first 
position toward a second position may be precluded even though the 
actuating stem is still operational. 
Still another aspect of reliability is effective sealing or closure of the 
valve. A metal seal would solve the entrapment problem but creates other 
problems. The force required to make a seal between a metal diaphragm and 
a metal valve seat is substantial. This is particularly a problem when an 
air actuated version of the valve is desired. That is, a manual actuator 
can easily supply a large closing force, but the closing force of the air 
operated version is dictated by the pressure source available to actuate 
the valve and also size constraints on the actuator itself. Even then, 
highly polished metal seal surfaces do not have the ability to conform to 
different operating conditions, in contrast to valves employing the 
plastic seats. Thus, the (i) metal-to metal and (ii) plastic valve seat 
designs are directed to entirely different structures that have their 
respective attributes and deficiencies. 
Another major concern with the air actuated version of the valve design is 
reducing the actuating force, and thus the actuating pressure, required to 
operate the valve, i.e., move the valve member toward open and closed 
positions. Multiple layers as in the composite diaphragm arrangement add 
to the stiffness of the diaphragm. This requires increased pressure to 
actuate the valve. Since the source of pressure is oftentimes located at 
remote locations relative to the valve, it becomes necessary to increase 
the actuating system pressure due to the pressure loss in delivering the 
gas to the point of use. This, in turn, encounters unnecessary expense. 
SUMMARY OF THE INVENTION 
The present invention contemplates a new and improved valve that overcomes 
all of the above-referenced problems and others, and provides a reliable 
valve structure incorporating a plastic valve seat. The subject diaphragm 
valve operates at low pressure and simultaneously effectively addresses 
the fluid system requirements. 
According to a more limited aspect of the invention, the diaphragm valve 
includes a body having inlet and outlet passages communicating with a 
valve chamber. A metal diaphragm is sealed along a peripheral planar edge 
to close the valve chamber and has a central portion that sealingly 
cooperates with the plastic valve seat. Both the surface area and volume 
of the valve seat are minimized. 
According to another aspect of the invention, the diaphragm is defined by a 
single layer. 
According to still another aspect of the invention, a generally 
hemispherical portion of the diaphragm extends axially outward from its 
planar edge a dimension greater than the stroke of the valve. 
According to yet another aspect of the invention, the valve seat is 
received in a groove so that only a portion thereof extends into the 
chamber. 
A principal advantage of the invention is providing a valve that satisfies 
fluid entrapment problems. 
Yet another advantage of the invention is found in reliable opening and 
closing of the valve. 
Another advantage of the invention is in maintaining leak integrity to the 
environment. 
Yet another advantage of the invention is realized by the low pressure 
required to actuate the valve. 
Still other advantages and benefits of the invention will become apparent 
to those skilled in the art upon a reading and understanding of the 
following detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings wherein the showings are for purposes of 
illustrating the preferred embodiment of the invention only and not for 
purposes of limiting same, the FIGS. show a diaphragm valve A having a 
body B, preferably of stainless steel construction, an actuating means c, 
a single layer, metal diaphragm D, a non-metallic or plastic button E, and 
plastic valve seat F. 
More particularly, and with reference to FIG. 1, inlet and outlet passages 
10, 12 communicate with a chamber 14 defined in the body. Each of the 
passages 10, 12 are connected to an external fluid system (not shown) via 
suitable connection means such as fittings 16, 18. Of course it will be 
understood that still other fittings can be used as alternatives to the 
illustrated arrangement. 
The chamber is closed on an upper side by bonnet 24 that is axially urged 
toward the body by retaining nut 26. Particularly, a lower portion of the 
bonnet extends through the nut and a radially extending shoulder 28 on the 
bonnet cooperates with a radially extending shoulder 30 of the nut. 
Threaded regions on the body and nut cooperate to axially advance the 
bonnet into clamping metal-to-metal sealing contact with a planar 
peripheral edge 32 of the diaphragm. Thus, the peripheral edge of the 
diaphragm is compressed between shoulder 28 of the bonnet and a 
projecting, integral lip 34 of the body. 
A through bore 40 of the bonnet receives a stem 42 of the actuating means 
C. More specifically, spaced grooves on a first or axially outer end 44 of 
the stem receive snap or retaining rings 46, 48, respectively, on opposite 
sides of actuating piston 50. The piston is sealed along a radially inner 
portion to the stem by a seal ring such as O-ring 52 and along a radially 
outer edge by O-ring 54. An upper end of the bonnet sealingly engages 
actuator housing 60 by means of O-ring 62, and the housing and bonnet are 
secured together by a snap ring 64. 
Generally concentrically received around the actuating stem 42, and 
entirely housed within the bonnet, is a means for biasing the actuating 
stem defined by spring 70. A first or upper end 72 of the spring 
cooperates with internal, radial shoulder 74 on the bonnet. Similarly, 
second or lower end 76 of the spring abuttingly engages shoulder 78 of the 
stem. As apparent, this arrangement continuously urges the actuating stem, 
and thus the diaphragm, toward a closed position (FIG. 4). Thus, FIGS. 1 
and 3 are representative of pressurized fluid entering through actuator 
inlet 90 to pressurize the actuating chamber 92, the underside of piston 
50, and overcome the spring biasing force thereby opening communication 
between the inlet and outlet passages 10, 12. It will also be noted that 
an opening 94 is provided through the actuator housing on the opposite 
side of the piston to permit venting. 
With additional reference to FIGS. 2-4, use of a resinous material or 
plastic button E is intended to limit galling or wear on the upper face of 
the diaphragm. By way of example only, one preferred material is TORLON, a 
registered trademark of Amoco Chemicals Corporation. The button is freely 
received in a recess 100 at the lower end of the actuating stem. 
Additionally, the button is not secured to the diaphragm, but merely 
abuttingly engages the upper face thereof. 
As clearly illustrated in FIG. 2, the diaphragm has a predetermined 
conformation that includes a planar peripheral edge 32 and a generally 
hemispherical central portion 102 that extends outward from the planar 
edge a predetermined axial dimension. It is important that the closing 
stroke, i.e., the extent of axial movement of the actuating stem, be less 
than the axial dimension of the diaphragm. Otherwise, the central portion 
of the diaphragm may deflect to an inverted position where it would extend 
axially from the planar edge toward the valve seat F. If such a condition 
occurred, there would be no manner of opening the valve due to the 
abutting engagement between the stem, button, and diaphragm. But in 
accordance with the dimensional relationships of the subject invention, 
the integrity of the diaphragm is retained and the valve operates in a 
reliable manner. 
The valve seat, as indicated above, is constructed from a plastic material. 
One preferred material of construction is KELF, a registered trademark of 
E.I. DuPont de Nemours. This material is desirable because of its 
compatibility with a wide variety of system fluids, its low permeability, 
strength, and a minimized tendency to entrap or absorb fluids in 
comparison to many other conventional materials. Of course still other 
materials incorporating some of these desired qualities may be used 
without departing from the scope and intent of the subject invention. 
The valve seat has a generally annular configuration in which a first or 
lower end 102 is received in a groove 104, preferably concentric with the 
inlet passage, where it merges with the chamber. It is important that the 
internal wall 106 of the groove covers a substantial portion of the seat 
ring to limit exposure of the plastic to the system fluid. Likewise, the 
external wall 108 substantially covers the valve seat to limit exposure to 
the system fluid. In this manner, the surface area exposed to system fluid 
is substantially reduced and fluid entrapment therein is substantially 
limited. 
As is also apparent from the drawings, the external wall 108 is deformed or 
crimped radially inward to hold the valve seat in place. It is preferable 
that the external wall be deformed, rather than the internal wall, so that 
the valve seat is placed under compressive forces rather than tensile 
forces. Imposing tensile forces on the plastic material forming the valve 
seat opens the pores in the material and aids in entrapment of fluid. On 
the other hand, if the valve seat is compressed, the pores decrease in 
size rather than increase, and entrapment becomes less of a problem. 
A second end 110 of the valve seat extends axially outward from the 
terminal ends of the internal and external walls. It is adapted for 
selective engagement with the bottom face of the diaphragm, i.e., opposite 
from the button E. The metal diaphragm cooperates with the plastic valve 
seat to provide an effective seal. 
Use of a single layer metal diaphragm is also advantageous from the 
standpoint that the air operated valve is designed to actuate at 
approximately 40 psi. If more than one diaphragm is inadvertently 
assembled into the valve, which could occur because of the thin nature of 
the diaphragm, the subject arrangement will not overcome the stiffness of 
the multi-layer assembly. It is then readily apparent in routine testing 
procedures that more than one diaphragm is present and the potential 
problem easily rectified before shipment to a customer. 
The combination of a single layer and low actuating pressure is also 
beneficial when compared to a multi-layer arrangement that requires 
greater pressure. Lower overall actuating pressure at the source, that 
already factors in the expected pressure drop from the fluid source to the 
end use, is always more desirable. 
Further, use of a single layer diaphragm eliminates any concern with 
virtual leaks. As previously discussed, one of the layers of the 
multi-layer diaphragm assemblies could fail and the remaining layers 
continue to function. Unfortunately, the failed layer of the diaphragm 
creates a dead space in which fluid can become entrapped. Obviously 
concerns with purity and entrapment make this undesirable. 
The failure of one of the layers in a multi-layer design causes concern 
from another aspect. That is, the remaining layers may not be designed to 
handle maximum system pressure. Thus, even though a pressure regulator is 
typically disposed downstream of the supply fluid cylinder and upstream of 
the diaphragm valve, a false sense of security is created. If the 
diaphragm is exposed to maximum supply pressure, and one of the layers has 
failed, the diaphragm may not be able to handle the pressure. 
The invention has been described with reference to the preferred 
embodiment. Obviously, modifications and alterations will occur to others 
upon a reading and understanding of the specification. It is intended to 
include all such modifications and alterations insofar as they come within 
the scope of the appended claims or the equivalents thereof.