Calculation formula commonly used in vacuum

1, Boyier's law 2,Gay-Lussac's law 3,Charlie's law
4,Charlie's law 5,Pumping speed 6,Conduction
7,Vacuum pumping time 8,Selection of maintain pump 9,Diffusion pump’s pumping speed estimation
10,Backing pumping speed of Roots pump 11,Leakage rate 12,Choice of pumping speed of crude suction pump
13,Choice of pumping speed of the backing pump 14,Pumping speed calculation formula of diffusion pump 15,Geometric pumping speed calculation formula of rotary vane vacuum pump
16,O-type rubber groove depth 17,Square rubber groove depth Back to the home page

1,Boyier's law

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.


2,Gay-Lussac's Law

When the pressure P is constant, a certain quality of the gas, the volume of v is proportional to the absolute temperature T:


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℃.

3,Charlie's law

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:


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℃.

4,Mean free path:

λ=(5×10-3)/P (cm)

5,Pumping speed:

S=dv/dt (l / s) or S=Q/P
Q = flow (Torr.l/ second) P = intensity of pressure (Torr) V = volume (l) t = time (seconds)

6,Conduction: C=Q/(P2-P1) (L / s)

7,Vacuum pumping time:

Calculation formula from atmospheric pressure to 1 Torr pumping time:
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.

8,Selection of maintain pump:


9,Diffusion pump pumping speed estimation:

S=3D2 (D=diametercm)

10,Fore-stage pumping speed of Roots pump:

S=(0.1~0.2)SRoots (l/s)

11,Leakage rate:

Qleakage-leakage rate(mmHg·l/s)
V-system volume(l)
P1- system intensity of pressure when vacuum pump stops(mmHg)
P2-ntensity of pressure in the vacuum chamber after time t(mmHg)
t- time for the pressure increased from P1 to P2 (s)

12,Choice of pumping speed:

S=Q1/Ppre (l/s)
S-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)

13,Choice of the former pump pumping speed:

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:

PnSg≥PgS or
Sg-effective pumping speed (l/s) of backing pump
Pn-main pump critical fore-stage pressure (maximum exhaust pressure) (l/s)
Pg-maximum working pressure of vacuum chamber (Torr)
S-effective pumping speed of main pump at Pg (l/s)

14,Diffusion pump pumping speed calculation formula:

S=Q/P=(K·n)/(P·t)(l / sec)
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)
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)
Υ0-proportion of oil(g/cm3)
Υm-proportion of mercury(g/cm3)
Pa-local atmospheric pressure (Torr)
△Vt-The volume corresponded by each scale of dropper (l / grid)

15,Geometric pumping speed calculation formula of rotary vane vacuum pump:

S=πZnLKv(D2-d2)/(24×104) (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%).

16,O-type rubber groove deep B = 0.7D

D is rubber diameter, groove width C = 1.6B

17,Square rubber groove depth B = 0.8A

A is a square rubber side length, groove width C = 1.67B