Posted by Hendrik on September 10, 2012 at 07:46:52 from (194.53.253.51):
Would like to learn about pressure control and (un)load control of displacement type pumps for liquids.
My sprayer piston pump has an adjustible pressure regulator, controlling the pressure at the hose and wand. What puzzles me is the following. Upon CLOSING the wand the pumped fluid is returned to the tank. Not simply through a pressure limit valve because the engine driving the pump labors LESS when the wand is closed and the liquid just flows, not squirts, back into the tank. The device seems to be called an unloader valve. How in the world does this valve operate? How does it know to increase the pressure the very moment I open the nearly pressureless wand? And, likewise, how does it reduce the pressure at the moment I close the wand? There must be a clever control mechanism, which I would like to master, because I hopefully can operate this pump safely. Functional description, pics, or pointers to books or web sites would be great.
(What I have is a 1950's Hardie sprayer with a 3-cylinder piston pump. To give you an idea of its capacity: 600 psi, 15 gallons per minute.)
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