Power and Efficiency of Hydraulic Pumps

Power and Efficiency

The power loss of hydraulic pump. The power loss of hydraulic pump has two parts: volume loss and mechanical loss:

1. Volume loss. Volume loss refers to the loss of hydraulic pump flow, the actual output flow of the hydraulic pump is always less than its theoretical flow, the main reason is due to the leakage of the internal high-pressure cavity of the hydraulic pump, the compression of the oil and in the suction process due to the suction resistance is too large, the oil viscosity and high speed of the hydraulic pump causes the oil can not be fully filled with sealed working chamber. The volume loss of the hydraulic pump is expressed by the volumetric efficiency, which is equal to the ratio of the actual output flow q of the hydraulic pump to its theoretical flow qi. Therefore, the actual output flow q of the hydraulic pump is: q=qiηv=Vnηv(3-4); where: V is the displacement of the hydraulic pump (m3/r); n is the speed of the hydraulic pump (r/s).

The volumetric efficiency of hydraulic pump decreases as the working pressure of hydraulic pump increases, and varies with the structure type of hydraulic pump, but is less than 1.

2. Mechanical loss. Mechanical loss refers to the loss of hydraulic pump in the torque. The actual input torque T0 of the hydraulic pump is always greater than the theoretical required torque Ti, which is mainly due to the loss of friction torque caused by mechanical friction between the relative moving parts in the hydraulic pump and the loss of friction caused by the viscosity of the liquid. The mechanical loss of the hydraulic pump is expressed by the mechanical efficiency, which is equal to the ratio of the theoretical torque Ti to the actual input torque T0 of the hydraulic pump, and the torque loss is set as ΔT.

Power of Hydraulic Pump

1. input power Pi. the input power of the hydraulic pump is the mechanical power acting on the main shaft of the hydraulic pump, when the input torque is T0 and the angular velocity is ω, there are: pi=Toω (3-6)

The output power of the hydraulic pump is the product of the actual differential pressure Δp between the suction and pressure ports and the output flow rate q during the operation of the hydraulic pump, i.e.: p=Δpq (3-7)

Where: Δp is the pressure difference between the suction and pressure ports of the hydraulic pump (N/m2); q is the actual output flow rate of the hydraulic pump (m3/s); p is the output power of the hydraulic pump (N・m/s or W).

In the actual calculation, if the tank through the atmosphere, the hydraulic pump suction, pressure difference between the oil often used in the hydraulic pump outlet pressure p substitute.

3. The total efficiency of the hydraulic pump. The total efficiency of the hydraulic pump is the actual output power of the hydraulic pump and its input power ratio, where Δpqi / ω is the theoretical input torque Ti.

Commonly Used Hydraulic Pumps

Gear pumps are available in two structural forms: external gear pumps and internal gear pumps. External gear pumps have simple structure, low cost, good dirt resistance and self-priming, so they are widely used in low pressure systems.

Gear pump is a volumetric rotary pump. When the active gear in a pair of meshing gears is driven by the motor to rotate, the driven gear rotates by meshing with the active gear. In the A cavity, the volume gradually increases due to the gear teeth continuously disengaging, forming a local vacuum and sucking oil from the oil tank, and as the gear rotates, the oil filled in the tooth groove is brought to the B cavity, and the volume gradually decreases in the B cavity due to the gear teeth continuously engaging, discharging the oil.

According to the different ways of working, the vane pump is divided into single-acting vane pump and double-acting vane pump two kinds. Single-acting vane pump is generally a variable pump, double-acting vane pump is generally a quantitative pump.

Double-acting vane pump working principle: when the rotor rotates, the vane in the centrifugal force and the action of the pressure oil, the tip of the stator tightly on the inner surface. In this way, the two vanes and the rotor and stator inner surface of the work volume, first from small to large oil suction, and then from large to small oil discharge, vane rotation a week, complete two suction and two oil discharge.

According to the different directions of the plunger arrangement, the piston pump is divided into two kinds of radial piston pumps and axial piston pumps. Due to the structural characteristics of the radial piston pump so that its application is limited, has been gradually replaced by the axial piston pump.

Axial piston pump is the use of the plunger parallel to the drive shaft in the plunger hole reciprocating movement generated by the volume change to work. The plunger pump consists of a cylinder and a plunger, the plunger in the cylinder for reciprocating motion, in the work volume increases when the oil suction, in the work volume decreases when the oil discharge.

There are two main types of screw pumps: rotor type positive displacement pumps and rotary type positive displacement pumps. According to the number of different screws, there are single screw pump, double screw pump and three screw pump.