Calculate pump power

Power is work per unit of time, and work is force times distance.
Force, in turn, is mass times acceleration.

The basic parameters of mass, acceleration, time, and distance can be found within a pump. A fluid to be circulated naturally has a defined mass that is moved over a certain distance. This requires force. If you then add the factor of time, you arrive back at power.

What is the purpose of calculating pump power?

A pump performs two tasks in a hydraulic system:

• Generating operating pressure
  The higher the operating pressure, the greater the forces that can be produced. Operating pressure is independent of time. However, it defines the capacity of a hydraulic system in that it determines the work to be performed (force times distance).
• Generating a volume flow
  The volume flow ultimately indicates the speed of a hydraulic system. The faster the fluid flows in the system, the faster the connected actuators move.

Factors of pump performance

The performance of a pump depends on three factors:

1. Displacement volume of the pump unit
2. Rotational speed of the drive
3. Power of the drive

A drive can be designed to be as large as possible, but if the pump can only handle a small volume, then higher force or speed will not change anything. Conversely, a powerful pump can never reach its full potential if it is equipped with a drive that is too weak. Motor and pump must therefore be matched to one another in order to work as efficiently as possible.

Resistance to pumping work

In a hydraulic system, a pump always works against a certain resistance. Typical factors influencing this resistance are the viscosity of the hydraulic medium and the system’s own backpressure. Channels that are too narrow, incorrectly selected valves, or too many branches can significantly reduce the performance of a pump.

The hydraulic system and the performance of the pump with its drive must also be matched. In pump calculation, it is therefore preferable to work with the efficiency factor 510.

510 = 600 (conversion factor) * 0.85 (total efficiency of electric motor/pump)

Formulas for calculating a pump

The design of a pump unit for a hydraulic system takes place in three steps:

#1 Determination of the flow rate Q
The flow rate “Q” is the volume that the pump must move and is calculated using the pump displacement “Vg” and the number of revolutions “n”.

The formula is:
Flow rate “Q” equals displacement “Vg” times revolutions “n” divided by 1,000

Q = (Vg x n) / 1,000

#2 Determination of the drive power P
The power “P” of the connected motor is calculated using the pump pressure “p” and the efficiency “510” (also known as the pump constant).

The drive power “P” is equal to pump pressure “p” times flow rate “Q” divided by the efficiency “510”:

P = (p x Q) / 510

With these factors and these two formulas, every pump and its drive can be designed for the respective situation.

#3 Calculating pump power – using a practical example

A lifting platform requires a pump unit.
It requires a pressure of 100 bar and a flow rate of 10 l/min.

Calculation of motor power “P”:
P = (100 bar X 10 l/min) / 510 = 1.96 ≙ 2 kW

An electric motor with 2 kW of power and a speed of 1,000 rpm is sufficient in this case.

Now the pump is designed.
To do this, the formula for determining the flow rate “Q = (Vg x n) / 1,000” is rearranged for displacement “Vg”.

Vg = Q * 1,000 / n.

This results in:
Vg = 10 l/min x 1,000 / 1,000 rpm
Vg = 10 cm³/rev

A pump with a capacity of 10 cm³ / revolution is sufficient for this application.