In actual use, some non oil vacuum pump users will find no oil vacuum pump for airtight container pumping, found that the actual pumping rate and pump specifications of the pumping rate differences, and even greater differences. In principle, as one of the volume pumps, the pumping rate of the micro vacuum pump is determined only by the pump itself. In the case of pump failure and leakage of the container, the reasons are mostly from the gas extraction pipeline.
The extraction rate of a closed vessel is the rate at which the extracted gas moves away from the closed vessel, and the influencing factors are:
1. The amount of external air leaking into the confined space. Although some confined spaces can be operated with very low air leakage, almost none of them can be completely airtight. The amount of air leakage must be taken into account. The greater the pressure difference, the greater the leakage and leakage.
2. Condensable steam in confined space. For a confined space with gas-liquid two-phase, the condensable vapor on the liquid surface will also be evacuated when the vacuum is evacuated, so the amount of condensable steam must be considered.
3, the amount of gas released during the production process.
The relationship between the pumping rate of vacuum pump and the actual pumping rate of airtight container is as follows.
The vacuum pump and the airtight container are generally connected by pipes. The pipeline has a resistance to gas flow and a pressure drop is formed.
P1 is the pressure in confined space;
P2 is the inlet pressure of the vacuum pump;
Q1, Q2 is the pumping volume of confined space and vacuum pump, mmHg / m3/h;
S1 and S2 are the pumping rate of confined space and vacuum pump, respectively, m3/h.
Among them, S1=Q1/P1, S2=Q2/P2.
When stable, Q1=Q2, so S1 x P1=S2 x P2, knowable, S2=S1 x (P1/P2).
In any operation, the pressure in the confined space must be greater than the pressure at the inlet of the air pump, P1>P2, (P1/P2) >1, so S2>S1.
The pipeline fluid resistance (W) or the fluid conductivity (U) are defined as W= (P1-P2) /Q, U=1/W, and the S2=S1/ (1-S1/U) =S1/ (1-WS1) is introduced when the pumping rate is S1 in the enclosed space. The smaller the pressure loss of the suction pipe, the smaller the difference between S1 and S2. The pumping rate of vacuum pump is equal to the pumping rate in confined space only when the pipeline resistance is infinite or the fluid conduction capacity is infinite.
The resistance rate of gas pumping exhaust pipe affect the actual use can not be ignored. The pumping rate of various types of micro vacuum pumps was tested by technicians. When the gas pipeline with 11m length was connected, the pumping rate would even drop to 50-60% when connecting 1m long suction pipe. The pumping rate of the performance specifications of vacuum pumps is carried out under the standard experimental conditions, while the actual conditions of users are varied. In order to ensure the pumping speed, customers should shorten the length of the gas extraction pipeline, increase the caliber of the pipeline, reduce the elbow, valve and other resistance components. In the selection of oil-free vacuum pump, if the suction pipe resistance is larger, the larger flow type should be selected.