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# Calculation formula commonly used in vacuum

Volume V, pressure P, V * P = constant A certain quality of gas, when the temperature is constant, the pressure of the gas and the volume of the gas is inversely proportional.
P When the pressure P is constant, a certain quality of the gas, the volume of v is proportional to the absolute temperature T:
V When the pressure is constant, a certain quality of gas, its volume increases (or decreases) 1/273 of the original, if the temperature increases (or decreases) 1℃. When the volume of the gas V remains constant, a certain mass of gas, the pressure T is proportional to its absolute temperature P, namely:
P Under a certain volume, a certain quality of gas, its intensity of pressure increases (or decreases) 1/273 of the original, if the temperature increase (or decrease) per 1℃.
λ＝(5×10 _{v}/d_{t} (l / s) or S＝Q/PQ = flow (Torr.l/ second) P = intensity of pressure (Torr) V = volume (l) t = time (seconds)
t＝8V/S (empirical formula) V for the volume, S for the pumping rate; usually it is chosen in the range of 5~10 minutes. S _{dimension}＝S_{before}/10
^{2} (D＝diametercm）
_{Roots} (l/s)Q _{leakage}＝V(P_{2}-P_{1})/(t_{2}-t_{1})Q _{leakage}－leakage rate(mmHg·l/s)V－system volume(l) P _{1}－ system intensity of pressure when vacuum pump stops(mmHg)P _{2}－ntensity of pressure in the vacuum chamber after time t(mmHg)t- time for the pressure increased from P1 to P2 (s) S＝Q _{1}/P_{pre} (l/s)S=2.3V·lg(P _{a}/P_{pre})/tS－effective pumping speed of mechanical pump Q1 - air leakage rate of vacuum system (Torr*l / s) P pre - pre vacuum degree needs to achieve (Torr) V- vacuum system volume (l) t - the time required to reach Ppre Pa- atmospheric pressure values (up)
Outlet pressure below the atmospheric pressure transmission pump such as diffusion pump, oil booster pump, Roots pump and turbo molecular pump, they work need to backing pump to maintain the front pressure is lower than the critical value, the choice of first stage pump must be the main pump maximum amount of gas discharge, according to the tube, the principle of flow identity of each section are： P_{n}S_{g}≥P_{g}S orS _{g}≥P_{gs}/P_{n}S _{g}－effective pumping speed (l/s) of backing pumpP _{n}－main pump critical fore-stage pressure (maximum exhaust pressure) (l/s)P _{g}－maximum working pressure of vacuum chamber (Torr)S－effective pumping speed of main pump at Pg (l/s)
Where, S - pumping rate (l/s) of tested pump n- rising number of oil column in the dropper (grid) T - the time required by the oil column to rise n grids (second) P - pressure measured near the pump port (Torr) K -coefficient of the dropper(Torr. l / s) K＝V _{0}·(L/n)·(Υ_{0}/Υ_{m})+P_{a}△V_{t}Where, V0- original volume of dropper and vacuum hose (l) L- length of the dropper scale part (mm) n- the number of the dropper scale (grid) Υ _{0}－proportion of oil(g/cm^{3})Υ _{m}－proportion of mercury(g/cm^{3})P _{a}－local atmospheric pressure (Torr)△V _{t}－The volume corresponded by each scale of dropper (l / grid)
_{v}(D^{2}-d^{2})/(24×10^{4}) (l/s)Where: Z for the number of spin, n for speed (RPM / min), L for the pump cavity length, D for the pump cavity diameter, d for the rotor diameter (cm), Kv for the volume of the utilization factor (generally taking 95%).
A is a square rubber side length, groove width C = 1.67B |