Select vacuum pump according to pumping speed

How many kinds of vacuum pump do you know?

Vacuum pump pumping speed as one of the important parameters of vacuum equipment selection, usually contact, but do we really understand the vacuum pump pumping speed?

The full pumping speed of the vacuum pump is called the pumping rate, also known as the volume flow rate. According to the definition, it refers to the ratio of the gas flow through the test cover and the balance pressure measured at the specified position on the test cover when the pump is equipped with a standard test cover and works under specified conditions. More generally, the speed of the vacuum pump refers to the volume of gas per unit time at the pump inlet, usually in liters per second (L/S).

Select vacuum pump according to pumping speed

But in practical application, we contact the meaning of pumping speed actually contains a variety of, let’s have a look at the following several pumping speed!

1. Nominal pumping speed

The nominal pumping speed is the label pumping speed of vacuum pump, which is one of the equipment parameters given by the vacuum pump manufacturer. The pumping speed we normally contact is actually the nominal pumping speed of the vacuum pump.

2. Geometric pumping speed, namely the theoretical pumping speed

Geometric pumping speed is the geometric volume of gas that can be discharged per unit time under a certain speed of the vacuum pump. It is related to the suction cavity volume of the vacuum pump, rotor speed, and the number of suction and exhaust of the rotor rotating once. When the vacuum pump geometry and the number of revolution is certain, its geometry speed is also determined.

But in fact, the vacuum pump in the use of reflux, leakage and inlet channel resistance, will lead to the loss of efficiency. The geometric pumping speed of vacuum pump is only the theoretical pumping speed, but it is difficult to realize. Therefore, it is greater than the nominal pumping speed of the product.

3. Actual pumping speed

The actual pumping speed is the effective pumping speed actually measured by the vacuum pump, or understood as the volume of gas that the vacuum system can remove from the pumped container per unit time under the pressure at the outlet of the container. In different pressure range, the pumping efficiency of the vacuum pump is variable: when the inlet pressure of the pump exceeds a certain pressure, its actual pumping speed will start to decline; When the working pressure of vacuum pump is close to its limit pressure, its actual pumping speed is close to zero. Therefore, the actual pumping speed is definitely less than the theoretical pumping speed, but it should be noted that in general, we will choose to work within the optimal pumping speed range of the vacuum pump, while in the stable pumping speed section, the actual pumping speed is greater than the nominal pumping speed.

At the same time, the flow conductivity of vacuum system pipeline also limits the pumping speed of vacuum pump.

pumping speed

The nominal pumping speed, geometric pumping speed and the actual pumping speed can be simply understood as: geometric pumping speed > actual pumping speed > nominal pumping speed.

In addition, the speed of the vacuum pump is also related to the type of gas. A given pumping rate represents only the pumping rate for a given gas. If there is no special mark, it refers to pumping air.

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