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Commonly used formulas for vacuum calculations 1. Boyle's law Volume V, pressure P, P·V = constant (for a certain mass of gas, when the temperature remains constant, the pressure of the gas is inversely proportional to the volume of the gas. That is, P1/P2=V2/V1) 2. Gay-Lussac's law: When the pressure P remains unchanged, the volume V of a certain mass of gas is proportional to the absolute temperature T.: (V1/V2=T1/T2=constant) When the pressure remains unchanged, for a certain mass of gas, every time the temperature increases (or P decreases) by 1°C, its volume will increase (or decrease) by 1/273 compared to the original volume. 3. Charles's Law: When the volume V of the gas remains constant, the pressure P of a certain mass of gas is proportional to other absolute temperatures T, that is: P1/P2=T1/T2 Under a certain volume and a certain mass of gas, for every 1°C increase (or decrease) in temperature, its pressure will increase (or decrease) by 1/273 compared to the original value. 4. Mean free path: λ＝(5×10-3)/P (cm)5. Pumping speed: S=dv/dt (liter/second) or S=Q/PQ=flow rate (torr·liter/second) P=pressure (torr) V=volume (liter) t=time (second) 6. Conductance: C＝Q/(P2-P1) (L/sec) 7. Vacuum pumping time: For calculation of pumping time from atmospheric pressure to 1 Torr: t=8V/S (empirical formula) (V is the volume, S is the pumping rate, usually t is selected within 5 to 10 minutes. ) 8. Maintain pump selection: S dimension=S front/109, diffusion pump pumping speed estimation: S＝3D2 (D＝diameter cm) 10. Front stage pumping speed of Roots pump: S=(0.1~0.2)S Luo (l/s) 11. Leakage rate: Q leakage = V (P2-P1)/(t2-t1) Q leakage - system leakage rate (mmHg·l/s) V - system volume (l) P1 - pressure in the system when the vacuum pump stops (mmHg) P2 - pressure reached in the vacuum chamber after time t (mmHg) t - time elapsed when the pressure rises from P1 to P2 (s) 12. Pumping speed selection of rough pump: S=Q1/P preset (l/s) S=2.3V·lg (Pa/P preset)/tS - Effective pumping speed of mechanical pump Q1 - Vacuum system leakage rate (Torr·L/sec) Ppre - The required prevacuum degree (Torr) V - Vacuum system volume (liter) t - The time required to reach P preset Pa - Atmospheric pressure value (Torr) 13. Pumping speed selection of the backing pump: Transmission pumps whose exhaust port pressure is lower than one atmosphere, such as diffusion pumps, oil booster pumps, Roots pumps, turbomolecular pumps, etc., require a backing pump to maintain their backing pressure below the critical value. The selected backing pump must be able to discharge the maximum gas volume of the main pump. According to the principle of equal flow in each section of the pipeline,: PnSg≥PgS or Sg≥Pgs/PnSg - the effective pumping speed of the backing pump (l/s) Pn - the critical backing pressure of the main pump (maximum exhaust pressure) (l/s) Pg - the highest working pressure of the vacuum chamber (Torr) S - the effective pumping speed of the main pump at Pg when working. (l/s) 14. Diffusion pump pumping speed calculation formula: S＝Q/P＝(K·n)/(P·t)(L/sec) where: S - Pumping rate of the pump under test (l/s) n - Number of grids of oil column rising in the dropper (grids) t - Time required for the oil column to rise n grids (seconds) P - Pressure measured near the pump port (Torr) K - Dropper coefficient (Torr·L/sec) K＝V0·(L/n)·(Υ0/Υm)+Pa△Vt where V0-original volume of the dropper and vacuum hose (liters) L - the length of the graduated part of the dropper (mm) n - the number of grids in the graduated part of the dropper (grids) Υ0 - the specific gravity of oil (g/cm3) Υm - the specific gravity of mercury (g/cm3) Pa - local atmospheric pressure (Torr) △Vt - the corresponding volume of one grid on the scale of the dropper (liters/grid) 15. The geometric pumping speed calculation formula of the rotary vane vacuum pump: S＝πZnLKv(D2-d2)/(24×104) (l/s) where: Z is the number of rotors, n is the rotation speed (rev/min), L is the length of the pump chamber, D is the diameter of the pump chamber, d is the diameter of the rotor (cm), and Kv is the volume utilization coefficient (usually 95%). 16. The depth of the O-type rubber groove B = 0.7DD is the rubber diameter, the groove width C = 1.6B17. The depth of the square rubber groove B = 0.8A1. Boyle's law volume V, pressure P, P·V = constant (for a certain mass of gas, when the temperature remains unchanged, the pressure of the gas is inversely proportional to the volume of the gas. That is, P1/P2=V2/V1) 2. Gay-Lussac's law: When the pressure P remains unchanged, the volume V of a certain mass of gas is proportional to the absolute temperature T.: (V1/V2=T1/T2=constant) When the pressure remains unchanged, for a certain mass of gas, every time the temperature increases (or P decreases) by 1°C, its volume will increase (or decrease) by 1/273 compared to the original volume. 3. Charles's Law: When the volume V of the gas remains constant, the pressure P of a certain mass of gas is proportional to other absolute temperatures T, that is: P1/P2=T1/T2 Under a certain volume and a certain mass of gas, for every 1°C increase (or decrease) in temperature, its pressure will increase (or decrease) by 1/273 compared to the original value. 4. Mean free path: λ＝(5×10-3)/P (cm)5. Pumping speed: S=dv/dt (liter/second) or S=Q/PQ=flow rate (torr·liter/second) P=pressure (torr) V=volume (liter) t=time (second) 6. Conductance: C＝Q/(P2-P1) (L/sec) 7. Vacuum pumping time: For calculation of pumping time from atmospheric pressure to 1 Torr: t=8V/S (empirical formula) (V is the volume, S is the pumping rate, usually t is selected within 5 to 10 minutes. ) 8. Maintain pump selection: S dimension=S front/109, diffusion pump pumping speed estimation: S＝3D2 (D＝diameter cm) 10. Front stage pumping speed of Roots pump: S=(0.1~0.2)S Luo (l/s) 11. Leakage rate: Q leakage = V (P2-P1)/(t2-t1) Q leakage - system leakage rate (mmHg·l/s) V - system volume (l) P1 - pressure in the system when the vacuum pump stops (mmHg) P2 - pressure reached in the vacuum chamber after time t (mmHg) t - time elapsed when the pressure rises from P1 to P2 (s) 12. Pumping speed selection of rough pump: S=Q1/P preset (l/s) S=2.3V·lg (Pa/P preset)/tS - Effective pumping speed of mechanical pump Q1 - Vacuum system leakage rate (Torr·L/sec) Ppre - The required prevacuum degree (Torr) V - Vacuum system volume (liter) t - The time required to reach P preset Pa - Atmospheric pressure value (Torr) 13. Pumping speed selection of the backing pump: Transmission pumps whose exhaust port pressure is lower than one atmosphere, such as diffusion pumps, oil booster pumps, Roots pumps, turbomolecular pumps, etc., require a backing pump to maintain their backing pressure below the critical value. The selected backing pump must be able to discharge the maximum gas volume of the main pump. According to the principle of equal flow in each section of the pipeline,: PnSg≥PgS or Sg≥Pgs/PnSg - the effective pumping speed of the backing pump (l/s) Pn - the critical backing pressure of the main pump (maximum exhaust pressure) (l/s) Pg - the highest working pressure of the vacuum chamber (Torr) S - the effective pumping speed of the main pump at Pg when working. (l/s) 14. Diffusion pump pumping speed calculation formula: S＝Q/P＝(K·n)/(P·t)(L/sec) where: S - Pumping rate of the pump under test (l/s) n - Number of grids of oil column rising in the dropper (grids) t - Time required for the oil column to rise n grids (seconds) P - Pressure measured near the pump port (Torr) K - Dropper coefficient (Torr·L/sec) K＝V0·(L/n)·(Υ0/Υm)+Pa△Vt where V0-original volume of the dropper and vacuum hose (liters) L - the length of the graduated part of the dropper (mm) n - the number of grids in the graduated part of the dropper (grids) Υ0 - the specific gravity of oil (g/cm3) Υm - the specific gravity of mercury (g/cm3) Pa - local atmospheric pressure (Torr) △Vt - the corresponding volume of one grid on the scale of the dropper (liters/grid) 15. The geometric pumping speed calculation formula of the rotary vane vacuum pump: S＝πZnLKv(D2-d2)/(24×104) (l/s) where: Z is the number of rotors, n is the rotation speed (rev/min), L is the length of the pump chamber, D is the diameter of the pump chamber, d is the diameter of the rotor (cm), and Kv is the volume utilization coefficient (usually 95%). 16. O-shaped rubber groove depth B = 0.7DD is the rubber diameter, groove width C = 1.6B 17. Square rubber groove depth B = 0.8A