Pump throughput Q is equal to Pressure X Pumping Speed (Q = PS)
It is normally specified in mbar · l /s.
Here P is the pressure on the intake
side of the pump. If P and V are constant at the intake side of the pump, the throughput of this pump can be expressed with the simple equation: Q = P.S where S is the pumping speed of the pump at intake pressure of P.
The concept of pump throughput is of major significance in practice and should not be confused with the pumping speed. The pump throughput is the quantity of gas moved by the pump over a unit of time, expressed in mbar.l/s; the pumping speed is the “transportation capacity” which the pump makes available within a specific unit of time, measured in m³/h or l/s or cfm.
The throughput value is important in determining the size of the backing pump in relationship to the size of a high vacuum pump with which it is connected in series in order to ensure that the backing pump will be able to “take off” the gas moved by the high vacuum pump.