Selection of vacuum pump

Selection of vacuum pump, you need to pay attention to the following matters:

1,Vacuum pump working intensity of pressure should meet the requirements of the limitation vacuum and working intensity of pressure of vacuum device. Such as: a vacuum drying process requirements 10mmhg working vacuum degree, ultimate vacuum of the selected vacuum pump is at least 2mmhg; it is best to be 1mmhg. Usually, the ultimate vacuum of chosen pumps will be a half to one order of magnitude higher than the working vacuum of vacuum device.

2,Correctly select vacuum pump’s working points. Each pump has a certain working pressure range, such as: working pressure range of 2BV series water ring vacuum pump is 760mmHg~25mmHg (absolute pressure); in such a wide range of pressure, pumping speed of pump changes with intensity of pressure (changes in detail refer to the pump performance curve); the stable working pressure range is 760~60mmHg. Thus, the pump operating point should be selected within the range, and not let it work for a long time in 25 ~ 30mmhg.

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

4,Correctly combine vacuum pumps. The vacuum pump has a selective pumping gas, therefore, sometimes using a pump cannot meet the pumping requirements, need several pump combination, complement each other in order to meet the pumping requirements. Such as titanium sublimation pump has a high pumping speed of hydrogen, but not pumping helium, however the three pole sputtering ion pump, (or ambipolar asymmetric cathode sputtering ion pump) has a certain pumping speed on argon; if combine the two kinds of pumps together, they will make a vacuum device to get a better vacuum degree. In addition, some of the vacuum pumps can’t work under atmospheric pressure, they need to pre-vacuum; some of the vacuum pumps’ outlet pressure is below atmospheric pressure, they need backing pump; therefore, pump combination is needed.

5,Requirements of vacuum equipment for oil pollution. If the equipment demands oil free, they should select a variety of non - oil pump, such as: water ring pump, molecular sieve adsorption pump, sputter ion pump, cryogenic pumps etc. If the requirement is not strict, a pump with oil can be chosen, plus on a number of oil pollution prevention measures, such as adding cold trap, baffled, block the oil wells, etc., they also can achieve clean vacuum requirements.

6,Learn composition of gas to be pumped, whether gas contains condensable vapor, dust particles and corrosion. When choosing vacuum pump, it needs to know the gas composition, and the corresponding pump should be chosen according to the pumped gas. If the gas contains steam, particles and corrosive gases, it should consider to install auxiliary equipment in the pump inlet pipe, such as condensers and dust collectors.

7,Impact of oil vapor discharged from the vacuum pump on the environment. If the environment does not allow pollution, you can choose a non-oil vacuum pump, or discharge the oil vapor to the outside.

8,Whether vibration, which is generated when vacuum pump works, impact the process and environment. If the process is not allowed, it should choose pumps without vibration or take anti-vibration measures.

9,Vacuum pump price, operation and maintenance costs.

Selection of water ring vacuum pump

Selection of water ring vacuum pump
The type of pump mainly depends on the amount of gas, vacuum or exhaust pressure required by the work.

Pump work, you need to pay attention to the following two aspects:

• The pump should work in the effective region as much as possible, namely within the zone of the critical vacuum or critical exhaust pressure.
• It should avoid to work under conditions of near maximum vacuum or maximum exhaust pressure. If operate within this region, not only efficiency is very low, but also the work is not stable, easy to produce vibration and noise. For vacuum pump with high vacuum, if operate in this region, cavitation often happens; a clear sign of this phenomenon is the pump noise and vibration. Cavitation will cause damage to the pump body, impeller and other parts, and then cause the pump cannot work.

According to the above principles, when vacuum or gas pressure needed by a pump is not high, it is preferential to choose in the single-stage pump. If vacuum or exhaust pressure is high, single-stage pumps are often unable to meet, or pump under high vacuum still large capacity, which requires the performance curves at higher vacuum degree relatively flat, the use of two stage pump. If the vacuum degree is above -710mmHg, water ring- air pump or water ring - Roots vacuum units can be chosen as the pumping vacuum device.

Choose vacuum pumps according to the required air amount of the system

After the initial selection of the pump type, model of the vacuum pump should be chosen according to the required air amount of the system.About calculation of vacuum pump pumping speed and time, please refer to the vacuum calculation formula in our website　Formula of vacuum.

To various types of water ring vacuum pumps and compressors, we have collected their own characteristics as follows, in order to facilitate user selection

The water temperature has bigger impact on the water ring vacuum pump, whose performance curves are measured in 15℃ water temperature conditions, so in the practical choice of water ring vacuum pump, its pumping speed should be corrected.

Modification values of the actual pumping speed of the water ring pump can be calculated according to the Q_t=Q₁₅K，K＝（P₁-P_t）/（P₁-P₁₅）where：
Q_t-air volume when water temperature is t℃m³/min Q₁₅-air volume when water temperature is 15℃ m³/min
P₁-water ring pump suction pressure, inmmHg P_t-saturated steam pressure when water temperature is t℃, in mmHg
P₁₅-saturated steam pressure when water temperature is 15℃, in mmHg K－volume correction coefficient

The K value of water ring vacuum pumps under various temperature and pumping pressure can refer to the following table.