Calculation Formula of
Vacuum in common use
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Calculation Formula of
Vacuum in common use
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Volume express by V，Pressure by P，P·V＝constant Definite amount of air，while the same temperature,the relation of the air pressure and volume is reverse proportion. It is: P1/P2＝V2/V1 While the pressure isn't changed, the relation of the definite amount of air's volume and absolute temperature is reverse proportion： V1/V2＝T1/T2＝constant While the same pressure to the definite amount of air, its volume would increase (or decrease)1/273 of its initial volume if the temperature was improved (or reduce)1℃. To the definite amount of air, while the air keeps its volume not to change, the relation of its pressure intensity and temperature is reverse proportion： P1/P2＝T1/T2 To the definite quatity air, while the same volume, the temperature increases (or decreases)1℃，its pressure intensity would improve (or reduce )1/273 of the initial volume. λ＝(5×10-3)/P (cm) S＝dv/dt (L/s)或 S＝Q/PQ＝Flow volume(Torr·L/s) P＝Pressure Intensity(Torr) V＝Volume(L) t＝Time(s) 6、Communication Conductor： C＝Q/(P2-P1) (L/s) The calculation formula of the pumping time from ATM to 1Torr：t＝8V/S (experience formula) V represents the volume，S reprensents the suction capacity，the "t" is usally selected during the 5~10 minutes. S Maintain＝S Fore/10 9、Eltimation suction capacity of the diffusion pump： S＝3D2 (D＝Diameter cm）10、Suction capacity of the fore pump of Roots pump： S＝(0.1~0.2)S Roots (l/s)QLeakage＝V(P2-P1)/(t2-t1) Qleakage－system leakage rate(mmHg·l/s) V－system volume(l) P1－the system pressure intensity when stop the vacuum pump(mmHg) P2－the pressure intensity of the vacuum pump after passing the time "t"(mmHg) t－the pressure expends the time(s) from 1L to 2L 12、Rough vacuum pump's suction capacity selection： S＝Q1/P Pre (l/s)S=2.3V·lg(Pa/P Pre)/t S－the efficient suction capacity of the chemical pump Q1－the vacuum system leakage rate(Torr·L/s) P Pre－need reach to the preparation vacuum (Torr) V－vacuum system volume(L) t－the expending time to reach at the preparation pressure Pa－ATM(Torr） 13、Fore pump suction capacity selection： The convery pump that exhaust port pressure is lower than the ATM such as Diffusion pump,oil add-pressure pump,the Roots, molecule pump etc. They need the fore pump to keep the preparation pressure is lower than the critical date.The selected fore pump must discharge the suction capacity of the main pump.According to the pipe path, every cross flow volume is equal by bellow condition： PnSg≥PgS orSg≥Pgs/Pn Sg－the efficient suction capacity of the fore pump(l/s) Pn－the main pump's critical pressure intensity (the max suction capacity)(l/s) Pg－the highest working pressure of vacuum(Torr) S－the efficient suction capacity of the main pump at Pg.(l/s) 14、Suction capacity calculation formula of the diffusion pump： S＝Q/P＝(K·n)/(P·t)(L/s)in equation：S－experiment pump's suction capacity(l/s) n－the oil post in the burette increase scale t－the expending time to increase n scale for the oil post(s) P－the measure pressure intensity near the casing mouth(Torr) K－the burette coefficient(Torr·L/s) K＝V0·(L/n)·(Υ0/Υm)+Pa△Vt thereinto V0－initial volume of the burette and vacuum rub pipe(L) L－the length of the burette scale part(mm) n－the scale number of the buretter scale part Υ0－specific gravity of oil(g/cm3) Υm－the specific gravity of Hydrargyrum(g/cm3) Pa－the local ATM(Torr) △Vt－one scale of the burette is corresponding volume (L/Scale) 15、Geometry calcutaltion formula of the Rotary pump's suction capaity： S＝πZnLKv(D2-d2)/(24×104) (l/s)in formula：Z is the vane number，n is the rotated speed(rpm)，L is the casing cavity length,D is the diameter of casing cavity，d is the Rotor diameter(cm)，Kv is the volume using coefficient(usally is 95％)。 16、O ring rubber groove depth B＝0.7D D is the diameter of the rubber，the groove wide C＝1.6BA is the side length of the square shape rubber，the groove wide C＝1.67B |