It actuates via pilot valves at the top and the bottom of the stroke, which causes the unbalanced spool to shift and reciprocate the piston. This is a pilot-operated, unbalanced, lightweight spool, which directs drive pressure, first to the top of the drive piston, and then to the underside to reciprocate the piston (cycle). The pressure of hydraulic fluid on the down stroke closes the inlet check valve and acts against the spring to open the outlet check valve. They are spring-loaded and have a very low cracking pressure, allowing maximum opening on the induction stroke. These check valves control the flow of liquid through the hydraulic section. Fresh liquid is induced via the inlet check valve on the return stroke. On the down stroke, liquid in the hydraulic section is forced under compression through the outlet check valve. Outlet flow and pressure are determined by the area of the hydraulic piston head, its nominal ratio with the drive piston head, and drive pressure. The drive piston is linked and connected to the hydraulic plunger/piston in the hydraulic section. The piston is pre-lubricated during assembly and therefore no air line lubricator is necessary.
#Haskell pumps series#
Drive media forces the piston down on the compression stroke and raises it on the suction stroke (M series have a spring return). The piston, complete with “O” ring seal, operates in an epoxy filled,fiberglass wound barrel, the diameter of which is constant throughout a given series of pumps. The pump design is sensitive to very small pressure drops due to the low frictional resistance of the large diameter driveĪnatomy of a Pneumatic Driven Hydrostatic Test Pump when drive pressure x drive piston area equals outlet (stall) pressure The piston assembly then stalls when the forcesīalance, e.g. Stall pressure is achieved when the outlet pressure rises and offers more resistance to the reciprocating differential piston assembly. When a pressure drop downstream occurs, it will recycle as necessary in an It will cycle at a slower rate as the fluid meets resistance until it stalls at maximum output pressure. Initially, the pump will cycle at maximum speed acting as a transfer pump to pressurize downstream. The actual ratio is about 15% above nominal so that the pump continues to cycle when drive pressureĮquals nominal ratio.
The nominal ratio between piston sizes is indicated in the model coding and approximates to the maximum working pressure. Piston driven by relatively low pressure drive acts directly upon a smaller hydraulic piston. The hydrostatic pumps automatically reciprocate on a differential piston principle.
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