(A), the type of water ring vacuum pump to determine the type of water ring vacuum pump mainly required by the work of gas, vacuum or exhaust pressure may be. Pump work, you need to pay attention to the following two aspects: 1. Whenever possible, in the high-performance area, that is, critical vacuum or critical exhaust pressure in the region. 2. Avoid operating near maximum vacuum or maximum exhaust pressure. Operating in this area is not only inefficient but also unstable and prone to vibration and noise. Cavitation occurs frequently in vacuum applications where the vacuum is high, and the obvious hallmark of this phenomenon is noise and vibration in the pump. Cavitation can cause damage to the pump body, impeller and other parts, so that the pump can not work. According to the above principle, when the pump required vacuum or gas pressure is not high, priority can be selected in the single-stage pump. If the vacuum or exhaust pressure is high, the single-stage pump often can not meet, or require the pump at higher vacuum conditions still have a larger amount of air, which requires the performance curve at a higher degree of vacuum is flatter, the choice of two Pump. If the degree of vacuum required in -710mmHg above, the optional water ring - air pump or water ring - Roots vacuum unit as a vacuum device. If only for the vacuum pump, the single-use pump is better. Because the single-action pump is simple in construction, easy to manufacture and maintain, and has good resistance to cavitation under high vacuum conditions. If only for larger compressor use, then the choice of double-acting pump more appropriate. Because the dual-acting pump has the advantages of large gas volume, small size and light weight, the radial force can be automatically balanced, the shaft is not prone to fatigue fracture, and the pump has a longer service life. (B), according to the amount of gas required for the system to select the vacuum pump After the initial selection of the type of water ring vacuum pump, but also for the vacuum pump, but also according to the amount of gas system to choose the pump model. About pumping speed selection and pumping time calculation can refer to: vacuum calculation formula. Vacuum formula: 1, Boyle's law of volume V, pressure P, P · V = constant constant mass of gas, when the temperature is constant, the gas pressure is inversely proportional to the volume of gas. That is, P1 / P2 = V2 / V1 2. Law of Guy Lussac When the pressure P is constant, a certain mass of gas whose volume V is proportional to the absolute temperature T: V1 / V2 = T1 / T2 = Variable, a certain mass of gas, the temperature increases (or P decreases) 1 ℃, then its volume than the original increase (or decrease) 1/273. 3, Charlie Law When the gas volume V remains unchanged, a certain mass of gas, pressure P and its absolute temperature T is proportional to, namely: P1 / P2 = T1 / T2 In a certain volume, a certain mass of gas, temperature per liter High (or lower) 1 ℃, its pressure increase (or decrease) than the original 1/273. 4. Average free path: λ = (5 × 10-3) / P (cm) 5. Pumping speed: S = dv / dt or S = Q / PQ = P = pressure (support) V = volume (liters) t = time (seconds) 6, conduction: C = Q / (P2-P1) Extraction time formula: t = 8V / S (empirical formula) V for the volume, S for the extraction rate, usually t within 5 to 10 minutes to choose. 8, to maintain the pump options: S-dimensional = S before / 10 9, diffusion pump pumping speed estimation: S = 3D2 (D = diameter cm) 10, Roots pumping pump speed: S = (l / s) 11 Leak rate: Q Leakage = V (P2-P1) / (t2-t1) Q Leakage - System Leakage Rate (mmHg · l / s) V- System Volume (l) System pressure (mmHg) P2-pressure reached in the vacuum chamber after time t (mmHg) t-pressure rise from P1 to P2 elapsed time (s) 12, roughing pump pumping speed selection: S = Q1 / P (l / s) S = 2.3V · lg (Pa / P pre) / t S-effective pump pumping speed Q1-vacuum system leak rate (T · L / Torque V- volume of vacuum system (liters) t-time required to reach P pre-Pa Pa-atmospheric pressure (Torque) 13, the choice of the pumping speed of the foreline pump: the transmission pump whose discharge port pressure is lower than one atmospheric pressure such as a diffusion pump , Oil booster pumps, Roots pumps, turbo molecular pumps, etc., they work before the need to maintain their pre-stage pump pressure below the critical value, the choice of the former stage pump must be able to discharge the maximum amount of the main pump gas, According to the pipeline, the flow of the cross-section of the principle of equality are: PnSg ≥ PgS or Sg ≥ Pg s / Pn Sg-effective pumping speed of foreline pump (l / s) Pn-main pump critical fore pressure (maximum discharge pressure) (l / s) Pg- maximum working pressure of vacuum chamber Effective pumping speed at Pg when working. (l / s) 14, diffusion pump pumping speed calculation formula: S = Q / P = (K · n) / (P · t) / s) n Number of rising columns of oil column in dropper (t) t- Time required for column to rise n (in seconds) P- Pressure measured in the vicinity of pump port K- Index of dropper Liter / sec K = V0 · (L / n) · (Y0 / Ym) + Pa · Vt where V0 - original volume of dropper and vacuum hose (liters) Length of L- The number of cells in the section of the eyedropper (cell) Υ0 - the specific gravity of the oil (g / cm3) Υm - the specific gravity of mercury (g / cm3) Pa- local atmospheric pressure Grid corresponding volume (L / s) 15, rotary vane vacuum pumping geometry calculation formula: S = πZnLKv (D2-d2) / (24 × 104) (l / s) Where: n is the speed (rpm), 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 volumetric utilization factor (typically 95%). 16, O-type rubber groove depth B = 0.7DD for rubber diameter, groove width C = 1.6B 17, square rubber groove depth B = 0.8AA square rubber side length, groove width C = 1.67B