Multi-stage vacuum pump ratio

Vacuum units generally include Roots water ring vacuum units, Roots screw vacuum units, etc.

The combination methods are all clear; but how should the specific model parameters of the pre-pump and the first and second stage Roots pumps be matched under high vacuum conditions?

The last edit to this post was made by mfsjpsq on 2020-7-11 at 10:13. Thinking in reverse, it can be approached as follows: 1) Regardless of the type of vacuum pump used, the mass flow rate during evacuation remains constant; any condensate liquid produced by an intermediate condenser must be taken into account, while gases supplied by devices such as water ring pumps or ejectors need to be added to the process gas； 2) The actual gas flow rate at each pump inlet and outlet, as well as within the volume, can be calculated using PV/T ； In a container, there are generally no changes in pressure or temperature, and the corresponding volumetric flow rate is calculated from the mass flow rate ； Due to changes in pressure and temperature before and after various pumps, the corresponding volumetric flow rate also changes; the pump connected to the next stage must be capable of handling the flow rate discharged by the pump in the previous stage ； 3) In a rough configuration, rotary vane pumps are paired with screw pumps, water ring pumps, steam ejectors, and so on. Generally, it is recommended that S (the flow rate of the next stage pump) = (1/2~1/10)S (the flow rate of the previous stage rotary vane pump). That is, after pressurization by the rotary vane pump, taking into account temperature rises and the proportionate changes in gas flow rate, a good configuration requires repeated calculations based on the individual performance characteristics of each pump as well as process data in order to determine the optimal pairing ； 4) Pumps manufactured by reputable manufacturers come equipped with software for calculations; each type of pump does not rely on a simple standard performance curve alone, such as the performance curve of rotary vane pumps or the curve showing the maximum compression ratio at zero flow rate ； The standard performance curves for water ring pumps, as well as the correction factor curves for different working fluid temperatures and pumping temperatures, etc., eliminate the need for manual calculations; the process remains the same in all cases.

Choose how many pumps and what size of pumps to use based on the ultimate pressure and pumping speed required in your actual application； The person on the 4th floor explained it in great detail

I mainly want to figure out how to calculate the model matching between different levels of pumps

The simplest principle is to start counting from the inlet of the vacuum pump: the pumping speed of the first pump is twice that of the second pump, the second pump’s speed is twice that of the third pump, and so on. However, this ratio ensures that your vacuum system will function, but it is not necessarily the most efficient or energy-saving option.

The screw vacuum pump has very little vibration; a coin placed on it won’t fall over.

To understand the mixing ratios, it is first necessary to know the characteristics of rotary vane pumps. You should pay attention to several parameters such as the compression ratio at zero flow rate, the maximum pressure difference, the pumping speed curve of the rotary vane pump, and the volumetric efficiency. Once these are understood, one will know how to assemble a Roots pump. The general selection principle is to determine the maximum pumping capacity by calculating the process conditions, and then configure the Roots pump and the pre-pump based on the characteristics of the pump.