H04- Hydraulic pumps and pumping theory

Pump is One of the important element in the hydraulic system which is also be called as heart of the hydraulic system. The main purpose of the pump in hydraulic system is generation of hydraulic power i.e. pump acts as power generating element.

What is pump?

The device which converts mechanical energy to hydraulic energy is called as pump. The pump which converts energy from one form to another form.

Here what happens is the pump is driven from a motor i.e. energy conversion takes place from electrical energy/muscle energy to mechanical energy in motor. As the pumping element inside the pump starts to move pressure/flow of the fluid is going to increases i.e conversion of energy from mechanical to hydraulic energy takes place.

How the pump will work?

When a hydraulic pump operates, it performs two functions. 1st mechanical action creates partial vacuum at pump inlet which allows the atmospheric pressure to force the liquid from reservoir into the pump inlet. 2nd the mechanical action delivers the liquid to the pump outlet and forces it into the hydraulic system.

A simple example is shown above figure which is a representation of simple reciprocating pump which is very easy to understand the pumping theory. The pump is fitted with two non return valve in which one is fitted to inlet and one is at outlet of the pump. The reservoir is open to atmosphere that means the atmospheric pressure is acting on the surface of liquid in reservoir. Here the cylinder is marked with two points namely A and B. When piston moves from A to B a partial vacuum is created inside the cylinder. Since the liquid is maintained at atmospheric pressure which is greater than vacuum pressure the suction of fluid inside the cylinder takes place inside the cylinder. As the piston moves from B to A the piston pushes liquid due to the non return valve at inlet closes the liquid forces at outlet of the pump.

A pump produces liquid movement or flow only. It does not generate pressure. It produces flow necessary for the development of the pressure which is a function of resistance to fluid flow in the system.

i.e. In a hydraulic system the pump outlet is not connected to any load OR the pipe which do not offer any resistance their will be no generation of pressure i.e. the liquid will simply flows away. When output is connected to some load the pressure will rise so that to overcome resistance of load.

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