Valves and valve actuation – Fluid actuated or retarded – Pilot or servo type motor
Patent
1996-11-26
1998-03-31
Walton, George L.
Valves and valve actuation
Fluid actuated or retarded
Pilot or servo type motor
138 42, 251 38, 251 45, 251126, F16K 31385, F16K 3140
Patent
active
057329290
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to improvements in fluid flow-control devices of the type commonly known as pilot operated valves, the improvements causing a reduction in water hammer.
BACKGROUND ART
Valves are used to control flows of fluids, liquids and gases in piping systems and machinery. Many various types of valves are used for various applications. One of these is the fluid valve known as a pilot operated valve which is used in many industries such as the irrigation, petroleum and the white goods industry. Within the white goods industries in particular these valves may be used for washing machines, dishwashers and refrigerators.
These valves are in general controlled by, although not limited to, an electromagnetic means, typically solenoid and servo actuated. The controller, such as a solenoid, is not used to directly control the flow path of the fluid but rather acts upon a diaphragm which controls the water flow by sealing a suitable seat within the main flow path. In its simplest principle, the solenoid is used to control the pressure difference and thus the total force acting on both sides of the diaphragm causing it to experience a net force and move within its movement range. The diaphragm is constructed with an inlet bleed port allowing fluid to flow from an inlet chamber through the diaphragm into a closed chamber. To open the valve and allow the fluid to flow from the inlet chamber to an outlet chamber the diaphragm must be moved off the seat. This is achieved by actuating the solenoid to reveal an outlet bleed port, usually also constructed in the diaphragm, which bleeds fluid from the closed chamber into the outlet chamber. The outlet bleed port is designed to allow fluid to flow from the closed chamber at a rate that is faster than that of the fluid flow into the closed chamber through the inlet bleed port. This causes a pressure difference on the opposite sides of the diaphragm since the pressure in the closed chamber is now less than that in the inlet chamber. Depending on the total force experienced by the diaphragm (which is pressure times area) the diaphragm moves off the seat allowing fluid to flow from the inlet chamber directly into the outlet chamber. Conversely, to close the valve the solenoid is activated to seal the outlet bleed port thus increasing the pressure in the closed chamber since fluid still flows into the closed chamber through the inlet bleed port changing the net force exerted on the diaphragm and thus causing the diaphragm to move onto the seat closing off the main flow.
The drawback to this type of an arrangement is the fact that the solenoids, being electromagnetically controlled, are relatively fast acting and in conjunction with the servo actuator principle, open and close the outlet bleed port very quickly thus causing the valve to open and close very quickly. The closure of the main fluid flow path in so short a time causes an abrupt change of the fluid flow.
An abrupt change of fluid flow in a closed conduit system produces pressure changes or surges. This is commonly known as water hammer, aptly labelled due to the audible and mechanical slamming of the valves and conduit system. For fluids other than water, such as in the petroleum industry, the term used is surge.
The fundamental physical theorem describing water hammer is irrespective of the fluid used in the conduit, and can be equally well applied to petrol, oil or water and involves the physical characteristics of the fluid and conduit system only. Water hammer pressures are direct functions of the abrupt change in the fluid velocity and the surge-wave velocity in the system which are independent of the length of the conduit. The surge-wave velocity of the system is equivalent to the velocity of sound within that system and depends upon the diameter, thickness, and elasticity of the conduit and the compressibility and specific gravity of the fluid. The classic elastic-wave theory of water hammer has been well documented and will not be discussed here in further detail.
In the white goo
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Luppino Cosmo
Summerton Gregory
Technical Components Pty. Ltd.
Walton George L.
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