A pump, which is the heart of a hydraulic system, converts mechanical energy into hydraulic energy. The mechanical energy is delivered to the pump via aprime mover such as an electric motor. Due to mechanical action, the pump creates a partial vacuum at its inlet. This permits atmospheric pressure to force the fluid throughthe inlet line and into the pump. The pump then pushes the fluid into the hydraulic system.
There are two broad classification of pump as identified by the fluid powerindustry.
1. Nonpositive displacement pumps: this type is generally used for low-pressure, high-volume flow applications. Because they are not capable of withstanding highpressure, they are of little use in the fluid power field. Normally their maximum pressure capacity is limited to 250-300 psi. This type of pump is primarily used fortransporting fluids from one location to another.
2. Positive displacement pumps: this type is universally used for fluid power systems. As the name implies, a positivedisplacement pump ejects a fixed amount of fluid into the hydraulic system per revolution of pump shaft rotation. Such a pump is capable of overcoming the pressure resulting fromthe mechanical loads on the system as well as the resistance to flow due to friction. These are two features that are desired of fluid power pump. These pumps have thefollowing advantages over nonpositive displacement pumps:
a. High-pressure capability (up to 10,000psi or higher)
b. Small, compact size
c. High volumetric efficiency
d.Small changes in efficiency throughout the design pressure range
e. Great flexibility of performance (can operate over a wide range of pressure requirements and speed ranges)