Roots vacuum pump adopts advanced vacuum technology, and many people will confuse it with the front stage pump. However, in fact, the front stage pump is only a part of the equipment, so there is a relative relationship between the pumping speed of the two. The following is to introduce the relationship between the two:
1. When starting under high pressure
(1) the pressure drops rapidly and reaches the required pressure. Although the allowable pressure difference is exceeded when starting, the motor with overload in a short time will not cause problems.
(2) when the inlet pressure is very low or the air ballast valve of the front stage pump is working, the double stage front stage pump is usually used, otherwise the required pressure of the front stage is difficult to reach. Under this pressure, the pumping speed of the front stage pump becomes too low, which will lead to high compression ratio and low volumetric efficiency.
2. As the pressure difference increases, the required power will increase. A special gas cooler is set in the outlet pipe, and the allowable pressure difference can be increased because the return flow of cooling gas can keep the temperature of rotor within the specified range.
3. In the vacuum and high vacuum range, the pumping speed ratio is usually 10:1. When the inlet pressure changes greatly or the pressure of the front stage decreases, the compression ratio decreases, so the pumping ratio is more than 5:1.
4. When the pump inlet pressure is within the range of rough vacuum
(1) the pumping speed ratio of Roots vacuum pump and front stage pump is 6:1 when the inlet pressure is 15hpa and 2:1 when the inlet pressure is 75hpa, which is an important factor for the pressure difference.
(2) in the rough vacuum range, the pumping speed ratio of roots pump and front stage pump should be determined separately for each case, generally speaking, it is relatively small. And the volume efficiency is quite good.
(3) the allowable pressure difference range is 40-100hpa. When the pressure range is higher than 150hpa, the allowable pressure difference is slightly higher, because the volume of air to be pumped changes the cooling of the rotor.
There is a certain relationship between the pumping speed of Roots vacuum pump and the front stage pump. The relationship between them mainly depends on the volumetric efficiency and the allowable pressure difference of vacuum pump. If the pressure difference exceeds, it will overheat and expand, resulting in the equipment stuck.