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Thursday, January 21, 2010

Variable Flow Control

Rather than by speed control (changes in the number of displacements in a given period of time), flow may be varied by changing the volume displace par stroke. Variable stroke are generally limited to small mattering or “controlled volume” pumps. Although large capacity variable strokes pumps have been built, the complexity of the mechanism involved and the development of other effective and economical means of flow control have precluded their use.

Changing Delivery to the System
Another means of capacity control is not to vary the pump capacity but to alter the amount of pumpage delivered to the system. There are two popular means of during thin.

Suction valve uploading:
Suction valve unloaders cause the displacement to the ineffective during the stroke for which the unloaders are activated. They command either full or zero delivery while the pump is kept running. Thus, current inrush problem from frequent motor starts are avoided. Because discharge pressure is not developed when suction valve are unloaded, energy consumption is held to a minimum.

A pump valve is unloaded by mechanically preventing the valve plate from returning to its sent. If the suction valve is held away from its sent, liquid will ebb and flow through the valve from suction header to pump cylinder and from cylinder to header during the stroking of the plunger or piston.

The unloader mechanism does not move the valve. The valve is lifted off its seat by the pressure differential created by normal pump operation. In synchronically unloading the suction valve spring that had already been compressed and moves away from the valve while the spring are still compressed. This permit the valve to close when the plunger begin its discharge stroke.

For smooth transition between full to zero, the unloading and loading are accomplished in an immediate and identical pumping order of the plunger. It is the function of the synchronized suction valve unloader distributor to control unloading event in that proper and immediate sequence. Similarly can be drawn in the gasoline engine distributor in its function of ensuring the proper and immediate sequence of firing of the spark plug.

The distributor driven directly by the crankshaft on its position is positively indexed in the stroking of the plungers. It provided an electrical signal to a solenoid valve, which admit motive fluid pressure to the unloader chamber when the suction valve to the particular cylinder has been opened. Then in sequence, each of the remaining suction valve is retained so, in the first revolution of the pump after a control signals the distributor to initiate so, in the first revolution of the pump after a control signals the distributor to initiate unloading, all suction valves are unloaded and the pump capacity is reduced to zero. When the control against to signal for capacity, such suction valve is released, in sequence during a single revolution of the crank.