Thursday, December 22, 2011

Axial Piston/ Bent Axis Pump

This is a fixed volume multi-piston pump. The cylinder block and drive shaft rotate together, and because of the angle between the cylinder block and shaft axes, each piston moves into and out of its cylinder once each revolution.  The stationary valve block has two circumferential slots leading to the top of the cylinder block, which are connected to the fluid inlet and outlet ports, and are arranged so that the pistons draw fluid into the cylinders on the outward stroke, and expel fluid into the systems on the inward stroke.

In this pump the casing along with the cylinders are attached in an angle to the drive shaft and pistons.Due to this angle the volume of the chamber inside the cylinder and piston varies as it rotates. when the chamber volumes is increasing the Inlet port is opened to those pistons with increasing chamber. as the pistons start to go down inside the cylinder the fluid is pressed and pressured, as the piston moves to the lowest point inside the cylinder there its opened to the outlet port on the casing letting the trapped fluid to rush out creating a flow of fluid....

Wednesday, December 21, 2011

Gerotor Pump (Gear+Rotor )

The gerotor pump is a combination internal external gear pump. these pumps are having six tooth and Four tooth. The spur type drive gear is turned  by an accessory drive from the engine.  As it turns, it rotates the seven-tooth internal gear. 
In diagram the two marked teeth are meshed and the tooth of the spur gear almost completely fills the cavity in the rotor(Fig A).  As the drive gear rotates and pulls the driven gear round, the volume of the cavity increases until at (fig C) it is at its maximum.  During the rotation from (fig A) to (fig C) the expanding cavity is under the inlet port and fluid is drawn into the pump.

As the gears continue to rotate, the cavity formed by the marked teeth moves under the outlet port.  As the drive gear meshes with the cavity next to the marked cavity in the rotor, its volume decreases.  The fluid in this cavity is forced out of the pump through the outlet port.this process continues and provide a positive flow at the outlet.

Wednesday, December 14, 2011

Spur Gear Pump

The simple spur gear pump uses two meshing gears closely fitted into a housing.  One of the gears is driven by the engine accessory drive shaft, and this gear drives the other.  As the gears rotate into a direction , the space between the teeth on the inlet side becomes larger.  Fluid is sucked in at this stage, trapped between the teeth and the housing and carried around to the discharge side of the pump.
As the fluid comes to discharge the teeth of the two gears come into mesh, decreasing the volume, and force the fluid out the pump discharge.
A small amount of fluid is allowed to leak past the gears and around the shafts for lubrication and cooling(known as Case Lubrication of EDP).  This fluid drains into the hollow shafts of the gears and is picked up by the low pressure at the inlet side of the pump.  A weak relief valve holds the oil in the hollow shafts until it builds up to a pressure of about 3-6 psi.  This ‘Case’ pressure is maintained so that if the shaft or seal becomes scored, fluid will be forced out, rather than air being drawn into, the pump.  Air would otherwise displace the fluid needed for lubrication and the pump would be damaged due to less lubrication and overheating.

As the pump output pressure increases, there is a tendency for the case to distort and allow increased leakage.  To prevent this, some pumps have high-pressure oil from the discharge side of the pump fed through a check valve into a cavity behind the bushing flanges.  The bushings are forced tight against the sides of the gears, decreasing the side clearance and minimising leakage, also compensating for bushing wear.