Maybe we don’t understand why we need to cap the vacuum pump head sometimes? What’s the difference between adding a screw pump and not? Why add it?
It is a large volume pump in front of the screw pump. The compensation is due to the low vacuum degree of the front stage pump and the low pumping rate in the high vacuum area. Because of the characteristics of its use, the extracted gas can not be directly discharged into the atmosphere, so it needs to be matched with the corresponding front stage pump. As for the matching of what form of the front stage pump to see the specific use in what process. If it is used in vacuum distillation or dehydration and other condensable gas process, the best choice of water ring pump, such a configuration to avoid condensable gas is pumped into other mechanical pumps, resulting in emulsification of lubrication.
But no matter what kind of front stage pump is used, the smaller the compression ratio is, the better. In other words, if the main pump is a 600 roots pump and its pumping rate is 600L / L, the pumping speed of the corresponding front stage pump should not be lower than 150L / s. if the compression ratio is large, the roots pump will be overloaded. Another case is that the front stage pump of multi-stage Roots pump, because there is one or more roots pumps between roots pump and front stage pump, In this way, the front stage pump can be appropriately selected smaller. In another case, the former stage pump should be larger. Heartbroken to wait. The reciprocating vacuum pump can be made into a pump with high pumping speed, but its main disadvantage is complex structure. The water ring pump has simple structure and large vibration during operation. It can extract the gas with dust, condensable gas and gas-water mixture, with large volume and no need of lubrication in the pump. However, most people use water ring pump now. There is air in the liquid such as water. Because it can extract higher vacuum with other pumps, the vacuum produced must be lower and meet the requirements. But mechanical pump must be more complicated than water ring pump. In fact, you can understand from the structure that reciprocating pump is made by piston, and water ring pump is convenient.
In general, the compression ratio should be less than 4. That is to say, if the main pump is a 600 L / L pump and its pumping rate is 600L / L, then the pumping speed of the corresponding front stage pump should not be lower than 150L / s. if the compression ratio is large, the pump will be overloaded. There is also a case of multi-stage vacuum pump matching the front stage pump, because there is one or more pumps between the vacuum pump and the front stage pump, so the front stage pump can be appropriately selected smaller.
In another case, the front stage pump should be larger. If it is intermittent production, because the working area of the vacuum pump needs a certain degree of vacuum to start. Generally, it is necessary to pump the system pressure to – 0.093 or more. Therefore, if the pumping rate of the front stage pump is small, the whole working time will be prolonged.
To sum up, adding a screw pump to the vacuum pump can reduce the emulsification problem, reduce the overload and prolong the working time.