Fluid handling – Processes – With control of flow by a condition or characteristic of a...
Reexamination Certificate
2000-09-20
2001-11-13
Hepperle, Stephen M. (Department: 3753)
Fluid handling
Processes
With control of flow by a condition or characteristic of a...
C137S501000
Reexamination Certificate
active
06314980
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to devices for regulating fluid transmission. More particularly, the invention relates to pressure compensating devices that also control fluid flow.
2. Description of Related Art
One of the requirements associated with many fluid transmission tasks is the need to control fluid flow. A problem often encountered when controlling fluid flow, particularly at a constant rate, is the presence of pressure variations that can adversely affect the ability to control fluid flow at a constant rate. Fluid flow rates are proportional to both flow resistance and the differential pressure across the resistance. One way of solving the pressure problem is to maintain the differential pressure across a known resistance at a fixed value. By accomplishing this, flow rate remains constant.
Numerous control mechanisms have been devised to address the pressure variation problem. All such mechanisms achieve pressure control by utilizing two restrictions, the first one variable, e.g., a reducing valve, and the second one fixed, e.g., a reference restriction. During operation of such mechanisms, the reducing valve is modulated to maintain a constant pressure differential across the reference restriction. A sensor, e.g., a piston, diaphragm or electronic sensor, monitors the pressure drop across the reference restriction and produces a signal relative to the differential pressure. The signal, (physical displacement, voltage, current, etc.), produced is used to modulate the reducing valve. Modulation of the reducing valve in response to the pressure differential across the reference restriction maintains a constant differential pressure.
The reference restriction can be a fixed orifice, variable orifice or nozzle. Desired flow rate is achieved by sizing the reference restriction accordingly.
One of the main problems with conventional pressure compensating flow control devices (“PCFC”) is that they are not designed to handle low flow rates and pressures. Most PCFCs on the market today are designed to handle flow rates on the order of 0.5 to 5 gallons per minute and pressure in the 60 to 3,000 pounds per square inch (psi) range.
A further problem is sizing. Most PCFCs do not have assimilated components so their applications are limited. A yet further problem is the use of active controls to sense the pressure differentials and to electronically control the pressure-reducing valve.
Accordingly, it is an object of the present invention to eliminate the need for active controls for a PCFC. A further object is to combine the functions of multiple components into fewer components to reduce overall size for miniature applications. A yet further object is to provide a PCFC that is capable of handling low flow rates (0.0 to 0.017 gal/hr.) and low pressure rates (10-60 psi).
SUMMARY OF THE INVENTION
The PCFC invention described herein employs a novel needle valve/reducing valve assembly to streamline the PCFC for flow control applications that require minimum space utilization. The needle valve that acts as the reference restriction is situated to be in axial alignment with a piston/reducing valve assembly that modulates in response to the pressure differential across the needle valve. A spring is employed to maintain a fixed differential pressure across the needle valve.
The piston/reducing valve assembly has an axially extending internal fluid channel that eliminates the need for external connections to connect upstream fluid chambers with downstream fluid chambers in order to effectuate pressure differential control. This configuration results in the same upstream and downstream pressures acting on the reference restriction to also act on the reducing valve that modulates in response thereto to maintain the differential pressure constant. No outside power or control signals are needed for the PCFC to operate and perform the intended functions.
The PCFC of the present invention has the capability of maintaining flow rates of about 5 to about 60 cc/min. within 10% of setpoint with supply pressures fluctuating between 15 to 75 psig. These and other objects and features of the present invention will be apparent from a review of the drawings and a reading of the following detailed description of the invention.
REFERENCES:
patent: 353342 (1886-11-01), Wilder
patent: 3115892 (1963-12-01), Brewer
patent: 4471803 (1984-09-01), Ollivier
patent: 5913328 (1999-06-01), Taube et al.
patent: 939661 (1963-10-01), None
Conway, H.G., “Fluid Pressure Mechanisms”; London Sir Isaac Pitman & Sons, LTD, (1949).
Beswick Paul R.
Treadwell Gary
Hepperle Stephen M.
Kirkpatrick & Lockhart LLP.
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