Fluid handling – Processes – With control of flow by a condition or characteristic of a...
Reexamination Certificate
2000-10-11
2001-11-06
Hepperle, Stephen M. (Department: 3753)
Fluid handling
Processes
With control of flow by a condition or characteristic of a...
C137S271000, C137S517000, C137S843000, C138S046000
Reexamination Certificate
active
06311712
ABSTRACT:
The invention relates to fluid flow control valves. The invention relates more particularly to a method and system for producing fluid flow control valves each having an orifice defining a seat against which an elastomeric diaphragm is urged by pressure differential occurring across the diaphragm such that fluid flows through flow control passages defined between the diaphragm and the seat, and in which increasing pressure differential across the diaphragm causes the diaphragm to constrict the flow control passages through deflection of the diaphragm.
BACKGROUND OF THE INVENTION
Fluid flow control valves of the above-described type are particularly used for regulating fluid flow to a substantially constant flow rate over a range of pressure differentials, such as about 0.1 bar to 10 bars. In such valves, the diaphragm typically comprises a solid body of elastomeric material. When urged against the seat of the orifice, the diaphragm deforms, the degree of deformation increasing with increasing pressure differential across the diaphragm. As the deformation of the diaphragm increases, the flow control passages between the diaphragm and the seat become smaller. The valve is designed such that over the range of pressure differentials of interest, the changing flow area of the flow control passages offsets the changing pressure differential so as to maintain the flow rate substantially constant.
A common type of flow control valve employs a “torpedo” shaped diaphragm that has an outer peripheral surface of smaller diameter than the inner surface of the housing of the valve. In normal forward flow through the valve, fluid flows between the outer peripheral surface of the diaphragm and the inner surface of the housing and then is turned radially inwardly by the orifice and flows through the flow control passages between an end face of the diaphragm and the orifice seat.
Some manufacturers of constant-flow valves have machined various sculptured shapes into the seats of orifices and have assembled each different orifice with a common elastomeric diaphragm identical in shape from one valve to the next. The diaphragm hardness typically was specified as 68±5 Shore A durometer hardness. Because the allowable variation of ten counts of durometer hardness results in significant variations in flow rate for a given orifice, this manufacturing technique lead to a batch production process in which custom-designed orifices were produced for each production batch of elastomeric diaphragms, depending on the hardness of the batch of diaphragms.
The flow rate through the flow control passages between the diaphragm and orifice is proportional to the flow area of the passages multiplied by the square root of the pressure. Accordingly, the flow area of the flow control passages must change significantly from the lowest working pressure to the highest working pressure (e.g., from 0.1 bar to 10 bars) in order to maintain the flow rate substantially constant at all pressures. Various approaches have been taken to try to tailor the deflection of the diaphragm against the orifice seat so as to maintain approximately constant flow rate over the working pressure range. One prior approach employed a plurality of small projections of very small contact area on the orifice surface that engage the diaphragm in an attempt to increase the flow area at the low end of the pressure range. At low pressure differential, as the pressure differential increases the projections press into the diaphragm and locally deform it and the face of the diaphragm moves closer to the main surface of the orifice seat. A drawback of this approach is that the very small contact area of the projections causes a significant hysteresis effect. The valve also tends to have higher than desired flow in the pressure range where the diaphragm deflection makes a transition from local deformation to bending.
Another prior approach was to limit the deflection of the diaphragm to pure compression without bending, as shown in U.S. Pat. No. 3,189,125. This was accomplished by making the diaphragm of sufficient thickness and shaping the diaphragm to have its thickest section at the center so that substantially no bending would occur. This approach works well for differential pressures exceeding 1.0 bar. However, when the operating range is expanded to include pressure differentials below 1.0 bar, problems begin to arise.
SUMMARY OF THE INVENTION
The present invention addresses the aforementioned needs by providing a method and system for producing constant-flow valves having a plurality of different flow rates, wherein the number of different flow rates exceeds the number of different orifice configurations, and in which the durometer hardness of the diaphragms is used as a control parameter rather than being an uncontrolled manufacturing variable. To these ends, the system in a preferred embodiment of the invention includes a plurality of orifices each having a seat defining contoured flow control surfaces, the orifices having at least K different configurations of flow control surfaces, where K≧2, and a plurality of diaphragms of identical shape each formed of an elastomeric material having a defined Shore A durometer hardness, the diaphragms having at least M different Shore A durometer hardnesses, where M≧2, each diaphragm being configured to engage the flow control surfaces of the seat of each orifice so as to create flow control passages between the diaphragm and the flow control surfaces, the diaphragm being deflected by pressure differential across the diaphragm so as to constrict the flow control passages as the pressure differential increases. Thus, at least N valves having N=K·M different flow rates can be assembled by assembling at least one each of the K different orifices with one of each of the M different diaphragms, the configurations of the orifices and the hardnesses of the diaphragms being such that each different combination of orifice configuration and diaphragm hardness produces a unique flow rate over a predetermined range of pressure differentials, whereby N different flow rates are provided with only K different component configurations.
As an illustrative example, eight different orifice configurations can be combined with diaphragms of three different durometer hardness values so as to produce 24 different flow rates over a desired range of pressure differentials. This is made possible by careful design of the flow control surfaces of the orifices to achieve substantially constant flow rate from each orifice over the working pressure range. More particularly, the orifices preferably are designed to promote a supported beam-type bending of the diaphragm, which bending is readily modeled and predicted, thereby enabling the flow rates of the valves to be accurately tailored to the desired values. To promote such diaphragm bending, preferably each orifice seat has a main support surface defining a plurality of channels therein each converging in a downstream direction of the orifice including at least one relatively wide channel promoting localized bending of the diaphragm thereinto at a relatively low pressure differential range, and at least one relatively narrow channel promoting localized bending of the diaphragm thereinto at a relatively higher pressure differential range, each channel extending in a transverse direction of the orifice and the channels being circumferentially spaced from each other.
Preferably, each orifice further comprises a plurality of spaced protrusions formed on the orifice seat extending upstream of the main support surface thereof, the protrusions holding the diaphragm off the main support surface and having sufficient contact areas with the diaphragm to support bending forces that deflect the diaphragm in bending between the protrusions at differential pressures below a predetermined value. The diaphragm fully envelopes the protrusions when the pressure differential is increased above the predetermined value such that the protrusions cease to affect the flow rate through the val
Alston & Bird LLP
Hays Fluid Controls
Hepperle Stephen M.
LandOfFree
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