# What is volumetric efficiency and mechanical efficiency

## pump

Differentiation pumps

The hydraulic pumps have the task of pushing liquid (mostly oil) into the working circuit. The main criteria for selecting a pump are:
- Necessary operating pressure
- Flow rate at nominal speed
- Constant or adjustable, possibly with two conveying directions
The hydraulic pump - a central element in the hydraulic system. Your job to make a selection!
Hydraulic pumps can be roughly classified into:

Performance assessment

Pumps usually convert electrical energy into hydraulic energy. Of course, energy conversion never takes place without loss.

Theoretical volume flow Qth
The design features of the piston diameter, piston stroke and number of pistons determine the theoretical delivery volume V.th fixed at one turn. The calculated volume flow Qth a pump determined as a parameter. Qth = n * Vth
 Part of the volume flow Qth flows inside the pump through the existing piston clearance, as squeeze oil through the tooth gaps of a gear pump back into the suction chamber.

This loss is referred to as leakage oil flow QL. depends on the play of the pump and increases with increasing pressure in the system. A large play of fit causes less friction, but the leakage losses are greater.

 One defines thevolumetric efficiency:ηVol = QeWith Qe = Qth - QL.V.th = theoretical delivery volume with one pump revolutionQe = effective volume flowQL. = internal leakage oil flow of the pumpQth = calculated (theoretical) volume flowηVol = volumetric efficiency
 Since a pump is a mechanical component, mechanical friction losses also occur. Therefore, the torque actually required must be correspondingly greater than the theoretically calculated torque to drive the hydraulic pump:M.to = Mth + MV.
 You define onemechanical-hydraulic efficiency:ηmh = MthM.to = Torque of the drive torque in Nm M.toM.th = calculated torque in Nm M.V.= Torque loss due to friction in Nm
 The pump is driven by an (electric) drive motor. Due to the leakage losses and the mechanical losses of the pump, the output (useful output) Pn be less.
P. to = (M to * n) asP.e = Qe * pe
9550                                                600
P.to = power supplied by the drive motor in kW
Pe = useful power transferred to the system in kW (index `e` for` effective`)
P.V. = Power loss of the pump in kW
M = torque in Nm
n = speed in min -1
Qe = effective flow rate in l / min
pe = Delivery pressure in bar
 This results in the overall efficiency ηtthe pumpη t = P e Ratio of output to outputor as a product of the individual degrees of efficiency:η t = η mh * η vol(Index t stands for `total`)
 The different degrees of efficiency of a pump can be combined in one Efficiency characteristic field represent. The volumetric efficiency η is shownVol, the mechanical-hydraulic efficiency ηmh and the overall efficiency ηtdepending on different operating pressures:
The Power flow diagram (Sankey diagram) illustrates the losses in a hydraulic system as follows: