30-01-2013, 04:39 PM
PISTON PUMP
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A Piston pump is a type of positive displacement pump where the high-pressure seal resiprocates with the piston.
As per geometrical and physical arrangement of pistons they may be classified in three groups:
1. In-line crank shaft driven pump
2. Axial piston pump
3. Radial piston pump
AXIAL PISTON PUMP
An axial piston pump is a positive displacement pump that has a number of pistons in a circular array within a cylinder block. All axial piston pumps may be classified as:
1. In-line axial pumps
2. Bent axis pumps
Axial pumps are also classified as:
1. Swash plate axial piston pumps
2. Wobble plate axial piston pumps
In-line Axial Piston Pump
In In-line piston pump the piston pumps are arranged axially parallel to each other around circumferential periphery of the cylinder block. The pistons are driven to and fro inside a number of bores in the cylinder barrel. In such pumps either the cylinder barrel or a plate (swash plate) is rotated which makes the pistons to have to and fro motion. The flow rate can vary if the speed of rotation of the prime mover is altered or the angle between the axis of the plate and the barrel is varied.
In-line piston pumps are available either as a
1. fixed cam or swash palte or as
2. rotating swash palte
In swash plate stationery pump, the cylinder body containing the axially placed pistons, is made to rotate against a cam palte. The cam plate or swash palte being kept fixed and positioned at an angle with the axis of the cylinder block. As the cylinder barrel is rotated, the piston shoe follows the surface of the swash palte. Since the swash plate is at an angle, the piston has to reciprocate within the cylinder bore and thus oil is sucked during one half of the circle of rotation and during the other half of rotation, the oil is forced to the outlet port. While the pistons react inside the cylinder bores and the cylinder block passes over the kidney shaped inlet port in the valve plate, the fluid is forced into the cylinder bore through the valve opening. Further rotation causes the pistons to force out the oil.