Pfeiffer Vacuum A Passion for Perfection

2.6.2 Calculations

Power requirements of a Roots vacuum pump

A Roots vacuum pump is a pure positive-displacement pump without internal pre-compression. Consequently, its power input P, as well as the pressure differential Δp between inlet side connection and pressure side connection S0, are proportional.

Formula 2-8:

Roots pump power input

S0=pumping speed of a Roots vacuum pump without counter-pressure, in m3 / s
Δp=pressure differential between inlet-side connection and pressure-side connection, in Pa
ηmech=mechanical efficiency of the pump (approximately 0.85 for Roots vacuum pumps)
P=power requirement or motor rating, in W

Although the mechanical losses are low, it is advisable to use contactors in the control cabinet for heavy-duty start-up. After power-up, the power requirement in the medium vacuum range is low.

All further calculations relating to the pumping speeds of pumping stations and pump-down times are provided in Chapter 7: Configuration.

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