Fluid handling – Processes – Involving pressure control
Reexamination Certificate
2002-03-15
2004-08-17
Krishnamurthy, Ramesh (Department: 3753)
Fluid handling
Processes
Involving pressure control
C137S487500, C251S029000, C251S129060
Reexamination Certificate
active
06776180
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a water distribution system pressure control method and apparatus.
One of the applicant's prior patents, European Patent No. 574241, the teaching of which is incorporated herein by reference, describes a low power control apparatus for controlling the pressure at the outlet of a valve in a water distribution system by applying a variable pressure signal to one chamber of a dual diaphragm pilot valve. The pilot valve in turn controls the main valve. The variable pressure signal is varied by the operation of a pair of low power solenoid valves, one of which is connected to a source of high pressure and the other of which is vented to atmospheric pressure.
The design concentrates in minimizing power consumption from its battery supply by keeping the pulsed operation of the solenoid valves to a minimum, and trapping a volume of water at a controlled pressure in the second chamber of a dual chamber pilot. The design is inherently low power for it has no requirement for operating solenoid valves when the required pressure is reached and demand (flow) conditions remain the same.
The solenoid valves used in this device are required to be small so that the energy required to operate is kept to a minimum. However, the smaller the solenoid valve, the smaller the orifice size, and the finer the filtration required to prevent solids from interfering with the solenoid valve operation. Using too fine filtering causes frequent blocking of filter and hence loss of operation in most water quality conditions encountered in potable water distribution systems. This compromise between orifice size, energy level and filtration requirement limits the reliability of the system.
Another aspect of the apparatus of EP574241 is to “trap” a volume of water at a given pressure (control pressure) within the control chamber of the valve pilot. Due to the incompressibility of the water and the fact that the pilot stem needs to be free to move to control its outlet pressure, the apparatus relies on the elasticity of the pipe work and the flexibility of the diaphragm (which can change shape to keep the trapped volume constant but allows movement of the stem). In certain conditions where the stability of the valve remains affected, compressibility of the control volume may be provided by an additional reservoir.
A control system for a gas distribution system is disclosed in U.S. Pat. No. 5,047,965 (Zlokovitz).
Adjustment of a gas regulator valve having a spring based diaphragm control pilot valve is effected by supplying or augmenting pressure to the spring side of the diaphragm from a supply of pressurized gas via an electrically adjustable regulator valve under the control of a local microprocessor. This apparatus could not be used with a water pressure control system as water is incompressible and therefore could not be used in one of the chambers of the spring based diaphragm controlled pilot valve.
SUMMARY OF THE INVENTION
The present invention aims to provide a control apparatus and method which mitigates some of the above problems.
Accordingly, in a first aspect the present invention provides control apparatus for controlling the pressure of a water distribution system, the apparatus including:
variable gas pressure output means for connection to a suitable control means of the water distribution system, and
a relatively high gas pressure source and a relatively low gas pressure source, each being selectively connectable to the variable gas pressure output means in order to vary the pressure of the variable gas pressure output means.
In this way, a low power control apparatus may be provided without using solenoid valves to control the variable pressure output means.
Preferably the apparatus includes at least one, and most preferably two, piezo valves. Such valves are disclosed in the following patents: U.S. Pat. No. 4,567,394 (EP0191011), U.S. Pat. No. 4,625,139 (EP0191011), EPO565510, U.S. Pat. No. 5,318,271 (EP0547022) and U.S. Pat. No. 5,343,894 (EP0538236), the disclosures of which are incorporated herein by reference.
The principle of a piezo valve is that an element of piezo electric material is moveable on application of a voltage. The movement of the element is used to open/close a small valve orifice. The advantage of this type of valve for this application is that because of the capacitor-like operation of the valve it consumes very little power—a typical power consumption of a piezo valve is a few micro watts whereas a typical power consumption of a solenoid valve is around 1 watt. Typically, the movement of the element is relatively small and so a piezo valve usually has only a small orifice and is therefore suitable for gas as a medium. For this reason, the invention is particularly suitable for use with a pilot valve in which the change in control pressure can be “amplified” to produce a larger change in the pressure of the valve being controlled—see for example, the dual chamber pilot valve described below with reference to FIG.
9
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As an alternative to using one or more piezo valves, the present invention may instead employ any alternative type of valve which operates at a suitably low power. In this context, low power operation preferably means a power consumption of less than one milii watt, more preferably less than 100 micro watts and most preferably less than 10 micro watts.
Preferably one piezo electric effect valve connects the relatively high gas pressure source to the variable gas pressure output means and a second piezo electric effect valve connects the relatively low gas pressure source to the variable gas pressure output means. By suitable operation of the two piezo valves (e.g. using a controller such as a microprocessor) the pressure of the variable gas pressure output means may be altered. As the piezo valves are effectively “zero power”, this provides a very low power way to control the pressure of the water distribution system.
Preferably, the relatively low gas pressure source is atmospheric pressure i.e. the second piezo valve is simply connected between a pipe connected to the atmosphere and the variable gas pressure output means (e.g. an outlet pipe).
Preferably the relatively high gas pressure source is a gas reservoir and the gas may be air. In one embodiment, the pressure in the reservoir is controlled by feeding air into the reservoir from an air pump or other air pressure means via a check valve or other control means. The pressure in the reservoir is preferably monitored using a pressure sensor such as a pressure transducer and, upon receipt of a suitable signal from the pressure sensor, the controller operates the air pump to “top up” the pressure in the reservoir. In this way, the pump need only be operated sporadically and assuming negligible leakage in any pipework between the pump and the first (inlet) piezo valve, the pressure in the reservoir remains substantially constant until air usage takes place by operation of the piezo valve. This also helps provide a low power control apparatus.
By comparison with the pressure control apparatus described in EP 574241, a low power operation is achieved by reducing the power needed to control the valves by replacing the solenoid valves with piezo valves and only energizing the pump where a supply has been utilized for control. Effectively the burden of power consumption is transferred from the solenoid valve operation to the pump operation.
Preferably the first (inlet) piezo valve is of the type which is normally closed when unpowered and the second (outlet) piezo valve is of the type which is normally open when unpowered. This arrangement means that, in the absence of power, the pressure of the variable pressure output means is maintained at atmospheric pressure. Since the pressure of the reservoir may be selected by suitable operation of the pump or other pressure generation means, the variable outlet pressure may be suitably controlled. This, together with operation of the piezo valves, permits full control of the pressure of the water supply system and
Head Johnson & Kachigian
Krishnamurthy Ramesh
Technolog Limited
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