Hydraulic Pumps (Fluid in Motion)

Hydraulic pumps convert mechanical energy and motion into hydraulic fluid power. The basic idea is very simple: force that is applied at one position is transmitted to another position using an incompressible fluid, like oil, which cannot be compressed but rather is displaced when pressure is applied.

A reservoir, a hydraulic cylinder, and a pump make up the three main parts of a hydraulic pump. Pumping hydraulic fluid from the reservoir into the bottom cavity of the cylinder causes the piston rod to be pushed up, which pushes the fluid in the other cavity back into the reservoir. This procedure pressurizes the chamber and extends the piston to its full length. Pumping hydraulic fluid into the upper chamber of the cylinder pushes the piston rod down, pushing the oil in the other chamber back into the reservoir, completing the cycle.

Popular Hydraulic Pump Types

  • Vane pumps, piston pumps, and gear pumps are the foremost types of hydraulic pumps
  • Gear pumps – uses gears to pump fluid by displacement. Hydraulic gear pumps are one of the most common types of pumps. There are several advantages and disadvantages to gear pumps. The advantages are: high speed, high pressure, and quiet operation. The disadvantages are: the use of four bushings in the liquid area and fixed end clearances.
  • Rotary vane pumps – are positive-displacement. They include a ring mounted inside a cylindrical case. There are a number of radial slots in which sliding vanes are located. Mounted to the case is the ring and the vanes are designed to press against the inside wall of the case. Hydraulic pressure or spring force or centrifugal force as the ring is rotated will cause the vane to be forced against the wall.
  • Axial piston pumps – are positive displacement. There are several pistons in a circular arrangement in a cylinder block.
  • Radial piston pumps – a circular arrangement of hydraulic pistons, and valves which allow pressures greater than 650 Bar (~10,000 psi) to be built.
  • Screw pumps – positive displacement pumps. Have one or more screws that rotate to transfer high or low viscosity fluids along an axis.

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