Selection methods and factors to consider when choosing water ring vacuum pumps
2026-01-13
The selection of a water ring vacuum pump should be based on the required air volume in the system to determine the appropriate pump model. Although the performance parameters of a water ring vacuum pump are greatly influenced by its design and manufacturing process, the operating environment and usage requirements also have a profound impact on its actual performance. Below we take a closer look at the methods for selecting a water ring vacuum pump and the key factors to consider during the process.
Selection table for water ring vacuum pumps
| Model | Main Features | Absolute vacuummmHg | Working vacuum level mmHg | Pump speed range m3/min | Sealed form. |
| S.K. | Single-stage water ring vacuum pumps of domestic production are characterized by a simple design and ease of maintenance. Currently, they are the main type of low vacuum water ring vacuum pumps in China. | -700 | -300~-650 | 0.15~120 | Sealing, mechanical seal |
| 2SK | Domestic designed two-stage water ring vacuum pumps, equivalent to two SK water ring pumps operating in series, have a higher vacuum level and higher pumping speed under high vacuum conditions compared to single-stage water ring pumps. Currently the main water ring vacuum pumps in China. | -735 | -300~-700 | 1.5~30 | Sealing, mechanical seal |
| 2BV | Using Siemens technology, coaxial motor and pump design, compact structure, high efficiency, superior vacuum levels and stable performance, This model will gradually replace the SK and 2SK series water ring vacuum pumps with pumping speeds from 0.4 to 6 m³/min. | -735 | -300~-700 | 0.45~8.33 | Mechanical seal |
| 2BE1 | Using Siemens technology, these pumps provide high efficiency, excellent vacuum levels and stable operation, and will gradually replace water ring vacuum pumps of the SK and 2SK series with pumping speeds from 6 to 120 m³/min. | -735 -640 | -300~-700 -300~-600 | 5~400 | Sealing, mechanical seal |
| SZ | Soviet technology from the 1950s, characterized by low efficiency and high energy consumption, was gradually phased out by the early 1980s. | -640~-700 | -300~-650 | 1.5~27 | Packaging |
| SZB | Mainly used for existing users. | -600 | -300~-550 | 0.33~0.66 | Packaging |
1. Vacuum level required by process specifications
The operating pressure of the vacuum pump must meet the process pressure requirements. When choosing a pump, its vacuum level should exceed the level of vacuum equipment by half an order of magnitude. (For example: if the process requires a vacuum level of 100 Pa (pressure), the selected vacuum pump must achieve a vacuum level of at least 50 Pa to 10 Pa). Generally, if the required pressure exceeds 3300Pa, water ring vacuum pump should be preferred as the vacuum device. If the pressure requirement is below 3300Pa, the water ring vacuum pump should not be selected; Instead, a rotary vacuum pump or a vacuum pump with a higher vacuum level should be selected as the vacuum device.
II.Pump performance required for the process (pumping speed)
Vacuum pumps require a certain pumping speed (i.e. the ability to remove gases, liquids and solids at operating pressure), which is usually measured in m³/h, l/s or m³/min. Specific calculation methods can be determined using the formula below for your own selection. Naturally, choosing a vacuum pump is a complex process that requires appropriate experience and consideration of other factors.
S = (V/t) × ln(P₁/P₂)
Where:
S—vacuum pump pumping speed (l/s)
V - volume of the vacuum chamber (l)
t - time required to achieve a given vacuum level (s)
P₁ - initial pressure (Pa)
P₂ - required pressure (Pa)
III. Determination of the composition of the substance to be removed
1.Determine whether the substance is a gas, liquid or solid. Be careful when selecting a rotary vacuum pump if the gas contains water vapor or traces of impurities such as particulate matter and dust. If a high level of vacuum is required, install a filtration system to purify the gas before using the rotary vacuum pump as vacuum generating equipment.
2. Determine whether the substance being removed is corrosive (acidic or alkaline? What is its pH value?). If the gas contains corrosive acids, alkalis or organic compounds, filtration or neutralization must be carried out before selecting a rotary vacuum pump.
3.Does the substance being removed contaminate rubber or petroleum products? Select the appropriate vacuum equipment depending on the specific environment. If the gas contains significant amounts of vapors, particulates or corrosive gases, consider installing auxiliary equipment on the pump inlet line, such as capacitors or filters (check with our technical engineers for specific details).
4.Does the noise, vibration or appearance of the vacuum pump affect the factory environment.
5.As they say, you get what you pay for. When purchasing vacuum pumps and equipment, prioritize factors such as equipment quality, transportation costs, and maintenance costs.
Factors to consider when choosing water ring vacuum pumps
Before looking at the factors to consider when choosing water ring vacuum pumps, let's first look at how they work.
1.The operating pressure of the liquid ring vacuum pump must meet the vacuum equipment requirements for extreme vacuum and operating pressure. For example, if a vacuum coating requires a vacuum level of 1×10⁻⁵ mm Hg. Art., the selected vacuum pump must reach at least 5×10⁻⁶ mmHg. Art. As a rule, the vacuum capacity of the pump should exceed the equipment requirements by half an order of magnitude.
2. Correctly select the operating point of the liquid ring vacuum pump. Each pump type has a specific operating pressure range. For example, diffusion pumps operate in the range from 10⁻³ to 10⁻⁷ mmHg. Art. Over this wide pressure range, the pump's pumping speed varies with pressure. The stable operating pressure range is from 5×10⁻⁴ to 5×10⁻⁶ mm Hg. Art. Therefore, the operating point of the pump must be selected within this range, and its continuous operation at a pressure below 10⁻⁸ mmHg is not allowed. Art. Likewise, although a titanium sublimation pump can operate at a pressure of 10⁻² mmHg. Art., its working pressure should ideally remain below 1 × 10⁻⁵ mm Hg. Art.
3. At operating pressure, the water ring vacuum pump must be able to remove the entire volume of gas generated during the operation of the vacuum equipment.
4.Correctly combine water ring vacuum pumps. Due to the selective characteristics of vacuum pumps, a single pump may sometimes fail to meet pumping requirements. In such cases, it is necessary to combine several pumps so that they complement each other and meet the pumping requirements. For example, titanium sublimation pumps have a high pumping rate for hydrogen, but cannot pump out helium. Conversely, triode sputter ion pumps (or diode asymmetric sputter cathode ion pumps) have a specific argon pumping rate. The combination of these two types provides an excellent vacuum level for the vacuum system. Additionally, some vacuum pumps cannot operate at atmospheric pressure and require a pre-vacuum; others discharge at subatmospheric pressure and require a booster pump. Therefore, pump combinations are always necessary.
5. Requirements for oil contamination for vacuum equipment. When absolutely oil-free operation is required, choose oil-free pumps such as liquid ring pumps, molecular sieve adsorption pumps, atomized ion pumps or cryogenic pumps. For less stringent requirements, oil-lubricated pumps with additional fouling control measures such as cold traps, baffles or oil traps can be used to achieve clean vacuum conditions.
6.Understand the composition of the exhaust gas: Determine whether the gas contains condensable vapors, particulates, dust or corrosive components. When selecting a vacuum pump, knowledge of the gas composition is necessary to select the appropriate pump for the specific gas being removed. If the gas contains vapors, particles, or corrosive gases, consider installing auxiliary equipment in the pump inlet line, such as condensers or dust collectors.
7.Assess the environmental impact of oil vapors emitted by the vacuum pump. If contamination is unacceptable, choose oil-free vacuum pumps or vent oil vapors to the outside.
8.Evaluate whether the operating vibrations of the vacuum pump affect the process or the environment. If the process does not tolerate vibration, select vibration-free pumps or take measures to eliminate them.
9.Consider the purchase price of the vacuum pump along with operating and maintenance costs.
The above describes the methodology for selecting water ring vacuum pumps and the key factors that must be considered when choosing such equipment. We recommend that, whenever possible, equipment be selected in accordance with established standards. These vacuum pumps are manufactured in strict accordance with these standards to ensure reliable quality. They are supported by a dedicated after-sales service that guarantees comprehensive service after purchase.
