The function of the vacuum pump is to remove gas molecules from the vacuum chamber, reduce the gas pressure in the vacuum chamber, and make it reach the required vacuum degree. Generally speaking, there is a large range from the atmosphere to the extremely high vacuum, and so far no vacuum system can cover this range. Therefore, in order to achieve the process index of different products, work efficiency and equipment working life requirements, different vacuum sections need to choose different vacuum system configurations. In order to achieve the ideal configuration, the following points should be considered when selecting the vacuum system:

Determine the working vacuum range: ---- must first check to determine the vacuum degree required by each process. Because each process has its own suitable vacuum range, it must be carefully studied and determined.
Determining the ultimate vacuum degree
---- Check the ultimate vacuum degree of the vacuum pump system on the basis of determining the vacuum degree required by the process, because the ultimate vacuum degree of the system determines the ideal working vacuum degree of the system. Generally speaking, the ultimate vacuum degree of the system is 20% lower than the working vacuum degree of the system and 50% lower than the ultimate vacuum degree of the front pump.
The type of gas to be pumped and the amount of gas pumped
Check and determine the type and amount of extraction required by the process. Because if the gas species to be pumped reacts with the liquid in the pump, the pump system will be contaminated. At the same time, it must be considered to determine the appropriate exhaust time and the amount of gas generated during the extraction process.
Vacuum volume
Check the time required to reach the required vacuum, the flow resistance and leakage of the vacuum pipe.
Consider the pumping rate required to maintain vacuum under certain process requirements after reaching the required vacuum.

Selection and calculation of main vacuum pump
S=2.303V/tLog(P1/P2)
Among them:
S is the pumping rate of vacuum pump (L/s)
V is the vacuum chamber volume (L)
t is the time required to reach the required vacuum (s)
P1 is the initial vacuum (Torr)
P2 is the required vacuum (Torr)
For example:
V=500L
t=30s
P1=760Torr
P2=50Torr
则: S=2.303V/t Log(P1/P2)
       =2.303x500/30xLog(760/50)
       =35.4L/s
Of course, the above formula is only the result of theoretical calculation, and there are a number of variable factors that are not taken into account, such as pipe flow resistance, leakage, filter flow resistance, and the temperature of the pumped gas. In fact, the safety factor should also be taken into account.
At present, the most widely used in industry are water ring vacuum pumps and rotary vane vacuum pumps, etc.

The general requirements are:
1. Vacuum degree, vacuum volume, main medium, temperature, main volume equipment.
2. Vacuum inflow medium and flow rate, pressure, temperature and law.
3, pumping volume, pumping gas medium, temperature.
4. Covering area, automation degree and vacuum pipeline specifications of vacuum equipment

Matters needing attention when selecting vacuum pump:
The working pressure of the vacuum pump should meet the requirements of the ultimate vacuum and working pressure of the vacuum equipment. For example, vacuum coating requires a vacuum degree of 1 × 10-5mmHg, and the vacuum degree of the selected vacuum pump should be at least 5 × 10-6mmHg. Usually select the pump vacuum is higher than the vacuum equipment vacuum half to an order of magnitude.
Correctly select the working point of the vacuum pump. Each pump has a certain working pressure range, such as: diffusion pump is 10-3 ~ 10-7mmHg, in such a wide pressure range, the pumping speed of the pump varies with the pressure, and its stable working pressure range is 5 × 10-4~5 × 10-6mmHg. Therefore, the working point of the pump should be selected within this range, and it should not be allowed to work for a long time under 10-8mmHg. Another example is that the titanium distillation pump can work under 10-2mmHg, but its working pressure should be less than 1 × 10-5mmHg.
3. The vacuum pump should be able to discharge all the gas generated during the process of vacuum equipment under its working pressure.
4, the correct combination of vacuum pump. Because the vacuum pump has selective pumping, sometimes a pump can not meet the pumping requirements, and several pumps need to be combined to complement each other to meet the pumping requirements. Such as titanium submersion pump for hydrogen has a high pumping speed, but can not pump helium, and three-pole type sputtering ion pump, (or two-pole type asymmetric cathode sputtering ion pump) for argon has a certain pumping speed, the combination of the two, will make the vacuum device to get a better degree of vacuum. In addition, some vacuum pumps cannot work at atmospheric pressure and require pre-vacuum; some vacuum pumps have outlet pressures lower than atmospheric pressure and require pre-pumps, so they all need to be combined.
5. Requirements of vacuum equipment for oil pollution. If the equipment is strictly required to be oil-free, various oil-free pumps should be selected, such as water ring pump, molecular sieve adsorption pump, sputtering ion pump, cryogenic pump, etc. If the requirements are not strict, you can choose an oil pump, plus some anti-oil pollution measures, such as adding cold traps, baffles, oil traps, etc., can also meet the requirements of clean vacuum.
6. Understand the composition of the pumped gas, whether the gas contains condensable vapor, whether there is particulate dust, whether it is corrosive, etc. When selecting a vacuum pump, you need to know the gas composition and select the corresponding pump for the pumped gas. If the gas contains steam, particles, and corrosive gases, it should be considered to install auxiliary equipment on the inlet pipeline of the pump, such as condenser, dust collector, etc.
7. How does the oil vapor discharged from the vacuum pump affect the environment. If the environment does not allow pollution, you can choose an oil-free vacuum pump, or the oil vapor discharged to the outdoor.
8. Does the vibration generated by the vacuum pump affect the process and the environment. If the process is not allowed, should choose no vibration pump or take anti vibration measures.
9. The price, operation and maintenance cost of the vacuum pump.

This chemical manual has a formula, you can check it! S=QRT/(P*M)
S is the pumping rate and Q is the air leakage and deflation of the system. T is the temperature, P system pressure M is the molecular weight of the system gas!

Common formula for vacuum calculation
1. Boyle's Law
Volume V, pressure P,P • V = constant (a certain mass of gas, when the temperature is constant, the pressure of the gas is inversely proportional to the volume of the gas.
P1/P2 = V2/V1)
2. Guy Lussac's Law
When the pressure P is constant, the volume V of a certain mass of gas is proportional to the absolute temperature T:(V1/V2 = T1/T2 = constant)
When the pressure is constant, for a certain mass of gas, for every 1 ℃ increase in temperature (or P decrease), its volume increases (or decreases) by 1/273.
3 Charlie's Law
When the volume V of the gas remains unchanged, the pressure P of a certain mass of gas is proportional to other absolute temperature T, I .e. P1/P2 = T1/T2
Under a certain volume, a certain mass of gas, the temperature increases (or decreases) by 1 ℃, and its pressure increases (or decreases) by 1/273.
4. Average * * course:
Λ =(5 × 10-3)/p (CM)
5. Pumping speed:
S = dv/dt (l/s) or S = Q/P
Q = Flow (Torr • L/sec) P = Pressure (Torr) V = Volume (L) t = Time (sec)
6. Pass: C = Q/(P2-P1) (l/s)
7. Vacuum pumping time:
For the calculation of the pumping time from atmospheric pressure to 1 Torr: t = 8 V/S (empirical formula)
(V is the volume, S is the pumping rate, and usually t is selected within 5 to 10 minutes.)
8. Maintain pump selection:
S dimension = S before/10
9. Estimation of pumping speed of diffusion pump:
S = 3D2 (D = diameter cm)
10. Front 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 is stopped (mmHg)
P2-pressure reached in the vacuum chamber after time t (mmHg)
t-time (s) for pressure to rise from P1 to P2
12. Selection of pumping speed of rough pumping pump:
S = Q1/P pre (l/s)
      S=2.3V•lg(Pa/P预)/t
S-effective pumping speed of mechanical pump Q1-leakage rate of vacuum system (torr l/s)
P pre-required pre-vacuum degree (Torr) V-vacuum system volume (L)
t-time required to reach P pre-time Pa-atmospheric pressure (Torr)
13. Selection of pumping speed of front pump:
Transmission pumps with exhaust port pressure lower than one atmospheric pressure, such as diffusion pump, oil booster pump, Roots pump, turbo molecular pump, etc., need a front-stage pump to maintain its front-stage pressure lower than the critical value when they work. The selected front-stage pump must be able to discharge the maximum gas volume of the main pump. According to the principle of constant flow rate of each section in the pipeline, there are:
  PnSg≥PgS 或 Sg≥Pgs/Pn
Sg-effective pumping speed of pre-pump (l/s) Pn-critical pre-pump pressure (maximum discharge pressure)(l/s)
Pg-vacuum chamber high working pressure (Torr) S-effective pumping speed at Pg when the main pump is working. (l/s)
14. Calculation formula of pumping speed of diffusion pump:
S = Q/P =(K • n)/(P • t)(l/s)
In the formula: S-pumping rate of the tested pump (l/s) n-lifting number of the oil column in the dropper (grid)
t-the time required for the oil column to rise n cells (seconds) p-the pressure measured near the pump port (torr)
K-dropper coefficient (l/s) k = v0 (l/n) (y0/ym) pa △ vt
Where V0-the original volume of the dropper and vacuum hose (liter) L-the length of the scale part of the dropper (mm)
N-number of cells (cells) of the scale part of the burette Y0-specific gravity of the oil (g/cm3)
γm-specific gravity of mercury (g/cm3) Pa-local atmospheric pressure (torr)
△Vt-the corresponding volume of one grid on the scale of the dropper (liter/grid)
15, rotary vane vacuum pump geometric pumping speed calculation formula:
S = πznlkv (D2-d2)/(24 × 104) (l/s)
Where: z is the number of rotating discs, n is the rotation speed (rpm), l is the length of the pump cavity, d is the diameter of the pump cavity, d is the diameter of the rotor (cm),Kv is the volume utilization coefficient (generally 95%).
16. O-type rubber groove depth B = 0.7D
D is the rubber diameter, groove width C = 1.6B
17. Square rubber groove depth B = 0.8A
A is square rubber side length, groove width C = 1.67B
When selecting a vacuum pump, you need to pay attention to the following:
The working pressure of the vacuum pump should meet the requirements of the ultimate vacuum and working pressure of the vacuum equipment. For example, vacuum coating requires a vacuum degree of 1 × 10-5mmHg, and the vacuum degree of the selected vacuum pump should be at least 5 × 10-6mmHg. Usually select the pump vacuum is higher than the vacuum equipment vacuum half to an order of magnitude.
Correctly select the working point of the vacuum pump. Each pump has a certain working pressure range, such as: diffusion pump is 10-3 ~ 10-7mmHg, in such a wide pressure range, the pumping speed of the pump varies with the pressure, and its stable working pressure range is 5 × 10-4~5 × 10-6mmHg. Therefore, the working point of the pump should be selected within this range, and it should not be allowed to work for a long time under 10-8mmHg. Another example is that the titanium distillation pump can work under 10-2mmHg, but its working pressure should be less than 1 × 10-5mmHg.
3. The vacuum pump should be able to discharge all the gas generated during the process of vacuum equipment under its working pressure.
4, the correct combination of vacuum pump. Because the vacuum pump has selective pumping, sometimes a pump can not meet the pumping requirements, and several pumps need to be combined to complement each other to meet the pumping requirements. Such as titanium submersion pump for hydrogen has a high pumping speed, but can not pump helium, and three-pole type sputtering ion pump, (or two-pole type asymmetric cathode sputtering ion pump) for argon has a certain pumping speed, the combination of the two, will make the vacuum device to get a better degree of vacuum. In addition, some vacuum pumps cannot work at atmospheric pressure and require pre-vacuum; some vacuum pumps have outlet pressures lower than atmospheric pressure and require pre-pumps, so they all need to be combined.
5. Requirements of vacuum equipment for oil pollution. If the equipment is strictly required to be oil-free, various oil-free pumps should be selected, such as water ring pump, molecular sieve adsorption pump, sputtering ion pump, cryogenic pump, etc. If the requirements are not strict, you can choose an oil pump, plus some anti-oil pollution measures, such as adding cold traps, baffles, oil traps, etc., can also meet the requirements of clean vacuum.
6. Understand the composition of the pumped gas, whether the gas contains condensable vapor, whether there is particulate dust, whether it is corrosive, etc. When selecting a vacuum pump, you need to know the gas composition and select the corresponding pump for the pumped gas. If the gas contains steam, particles, and corrosive gases, it should be considered to install auxiliary equipment on the inlet pipeline of the pump, such as condenser, dust collector, etc.
7. How does the oil vapor discharged from the vacuum pump affect the environment. If the environment does not allow pollution, you can choose an oil-free vacuum pump, or the oil vapor discharged to the outdoor.
8. Does the vibration generated by the vacuum pump affect the process and the environment. If the process is not allowed, should choose no vibration pump or take anti vibration measures.
9. The price, operation and maintenance cost of the vacuum pump.
Selection of Water Ring Vacuum Pump
Determination of 1. pump type
The type of pump is mainly determined by the amount of gas, vacuum or exhaust pressure required for work.
When the pump is working, you need to pay attention to the following two aspects:

As far as possible, it is required to operate in the mailbox area, that is, in the area of critical vacuum or critical exhaust pressure.

Avoid operation near maximum vacuum or maximum discharge pressure. In this area, not only the efficiency is very low, but also the work is very unstable, easy to produce vibration and noise. For vacuum pumps with high vacuum, cavitation often occurs when operating in this area. The obvious sign 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 principles, when the vacuum degree or gas pressure required by the pump is not high, it can be selected in the single-stage pump. If the degree of vacuum or exhaust pressure is high, the single-stage pump often can not meet, or, the requirements of the pump in the case of a higher degree of vacuum still have a larger volume, that is, the requirements of the performance curve in a higher degree of vacuum is flat, can choose two-stage pump. If the vacuum degree is required to be above -710mmHg, the water ring-atmospheric pump or the water ring-Roots vacuum unit can be used as the vacuum device.
If it is only used as a vacuum pump, it is better to use a single-acting pump. Because the structure of the single action pump is simple, easy to manufacture and maintain, and in the case of high vacuum cavitation resistance is good.
If only for the use of a larger volume of the compressor, the use of double-acting pump is more appropriate. Because the double-acting pump has large air volume, small size, light weight, and the radial force can be automatically balanced, the shaft is not prone to fatigue fracture, and the pump has a long service life.
2. select the vacuum pump according to the amount of gas required by the system
After the initial selection of the type of pump, for the vacuum pump, but also according to the amount of air required by the system to choose the pump model.
Regarding the selection of pumping speed and the calculation of pumping time of vacuum pumps, we can refer to our company's website for various types of water ring vacuum pumps and compressors. We specially collect their respective characteristics as follows to facilitate the selection of users.
Code Main Features Ultimate Vacuum Degree
mmHg working vacuum
mmHg pumping speed range
m3/min Seal form
sk domestic design single stage water ring vacuum pump, simple structure, easy maintenance. At present, the domestic mainstream low vacuum water ring vacuum pump. -700 -300 ~-650 0.15~120 packing,
mechanical seal
2sk's domestic design of two-stage water ring vacuum pump is equivalent to two SK water ring pumps used in series. Compared with single-stage water ring pump, it has the characteristics of high vacuum degree and high pumping speed under high vacuum. At present, the domestic mainstream water ring vacuum pump. -735 -300 ~-700 1.5~30 packing, mechanical seal
2BV adopts Siemens advanced technology, coaxial pump, compact structure, high efficiency, high vacuum, stable performance, will gradually replace SK, 2SK series of 0.4 ~ 6m 3/min pumping speed of the water ring vacuum pump. -735 -300 ~-700 0.45~8.33 mechanical seal
2BE1 adopts Siemens advanced technology, high efficiency, high vacuum, stable performance, will gradually replace SK, 2SK series 6~120 m3/min pumping speed of the water ring vacuum pump. -735 -640 -300 ~-700 -300 ~-600 5~400 packing and mechanical seal
SZ Soviet technology in the 1950 s was low in efficiency and high in energy consumption. It was eliminated in the early 1980 s and was mainly used by old users. -640 ~-700 -300 ~-650 1.5~27 packing
SZB Soviet technology in the 1950 s had low efficiency and high energy consumption. It was eliminated in the early 1980 s and was mainly used for water pump diversion. It has been replaced by SK series water ring pumps. -600 -300 ~-550 0.33~0.66 packing
2SY is mainly used in water ring compressor, the maximum discharge pressure is 0.6MPa -- 6~30 mechanical seal
The 2YK structure is basically the same as the 2SK series, and the pumped medium can be used as the working fluid, and the ultimate vacuum degree changes with the saturated vapor pressure of the pumped medium. The limit vacuum degree in the table is the limit vacuum degree when the working medium is transformer oil. -755 -300 ~-720 1.5~30 mechanical seal

When selecting a vacuum pump, you need to pay attention to the following:

The working pressure of the vacuum pump should meet the requirements of the ultimate vacuum and working pressure of the vacuum equipment. For example, vacuum coating requires a vacuum degree of 110-5mmHg, and the vacuum degree of the selected vacuum pump should be at least 510-6mmHg. Usually select the pump vacuum is higher than the vacuum equipment vacuum half to an order of magnitude.

Correctly select the working point of the vacuum pump. Each pump has a certain working pressure range, such as: diffusion pump is 10-3 ~ 10-7mmHg, in such a wide pressure range, the pumping speed of the pump varies with the pressure, and its stable working pressure range is 510-4 ~ 510-6mmHg. Therefore, the working point of the pump should be selected within this range, and it should not be allowed to work for a long time under 10-8mmHg. Another example is that the titanium distillation pump can work under 10-2mmHg, but its working pressure should be less than 110-5mmHg.

3. The vacuum pump should be able to discharge all the gas generated during the process of vacuum equipment under its working pressure.

4, the correct combination of vacuum pump. Because the vacuum pump has selective pumping, sometimes a pump can not meet the pumping requirements, and several pumps need to be combined to complement each other to meet the pumping requirements. Such as titanium submersion pump for hydrogen has a high pumping speed, but can not pump helium, and three-pole type sputtering ion pump, (or two-pole type asymmetric cathode sputtering ion pump) for argon has a certain pumping speed, the combination of the two, will make the vacuum device to get a better degree of vacuum. In addition, some vacuum pumps cannot work at atmospheric pressure and require pre-vacuum; some vacuum pumps have outlet pressures lower than atmospheric pressure and require pre-pumps, so they all need to be combined.

5. Requirements of vacuum equipment for oil pollution. If the equipment is strictly required to be oil-free, various oil-free pumps should be selected, such as water ring pump, molecular sieve adsorption pump, sputtering ion pump, cryogenic pump, etc. If the requirements are not strict, you can choose an oil pump, plus some anti-oil pollution measures, such as adding cold traps, baffles, oil traps, etc., can also meet the requirements of clean vacuum.

6. Understand the composition of the pumped gas, whether the gas contains condensable vapor, whether there is particulate dust, whether it is corrosive, etc. When selecting a vacuum pump, you need to know the gas composition and select the corresponding pump for the pumped gas. If the gas contains steam, particles, and corrosive gases, it should be considered to install auxiliary equipment on the inlet pipeline of the pump, such as condenser, dust collector, etc.

7. How does the oil vapor discharged from the vacuum pump affect the environment. If the environment does not allow pollution, you can choose an oil-free vacuum pump, or the oil vapor discharged to the outdoor.

8. Does the vibration generated by the vacuum pump affect the process and the environment. If the process is not allowed, should choose no vibration pump or take anti vibration measures.

9. The price, operation and maintenance cost of the vacuum pump.

Selection of Water Ring Vacuum Pump

Determination of 1. pump type

The type of pump is mainly determined by the amount of gas, vacuum or exhaust pressure required for work.

When the pump is working, it is necessary to pay attention to the following two aspects: as far as possible, it is required to run in the mailbox area, that is, in the area of critical vacuum or critical exhaust pressure. Avoid operation near maximum vacuum or maximum discharge pressure. In this area, not only the efficiency is very low, but also the work is very unstable, easy to produce vibration and noise. For vacuum pumps with high vacuum, cavitation often occurs when operating in this area. The obvious sign 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 principles, when the vacuum degree or gas pressure required by the pump is not high, it can be selected in the single-stage pump. If the degree of vacuum or exhaust pressure is high, the single-stage pump often can not meet, or, the requirements of the pump in the case of a higher degree of vacuum still have a larger volume, that is, the requirements of the performance curve in a higher degree of vacuum is flat, can choose two-stage pump. If the vacuum degree is required to be above -710mmHg, the water ring-atmospheric pump or the water ring-Roots vacuum unit can be used as the vacuum device.

2. select the vacuum pump according to the amount of gas required by the system

After the initial selection of the type of pump, for the vacuum pump, but also according to the amount of air required by the system to choose the pump model. For the selection of pumping speed and the calculation of pumping time of vacuum pump, refer to the vacuum calculation formula of our company's web page.

In the face of various types of water ring vacuum pumps and compressors, we specially collect their respective characteristics as follows to facilitate user selection.

(Absolute vacuum does not exist)

Example 3: If the indication value of the table is 0.08, then P = 1 × 105(1-0.08/0.1)= 2 × 104 Pa
The vacuum index value of this product is <267Pa, which indicates that the product can still work normally under the low vacuum state of 267Pa (surface indication value is about 0.0997, close to -0.1). The vacuum degree of the product mainly depends on the performance of the supporting vacuum pump.

Vacuum unit of measurement conversion is as follows:
0.1Mpa = 1 × 105 Pa = 760mmHg = 1 atmosphere
1 Torr = 1mmHg = 133.33Pa
2 Torr = 0.00026666Mpa ≈ 267Pa

(2) The reading of the vacuum gauge can be displayed with intuitive numbers. But the price is more expensive, generally applicable to scientific research units. If the user needs, the company can order supply.