The thermoforming packaging machine suddenly takes longer before the film sits cleanly. The vacuum clamping table on the CNC router no longer holds thin panels firmly. The dryer does not reach its usual pressure. Behind all three cases is the same component: a vacuum pump that no longer delivers what the process requires – or that never really suited the process in the first place.
Vacuum pumps come in many types. Each has a pressure range in which it works well, and media that it tolerates well or badly. If you need to replace a pump or select a new one, you should know these differences.
This guide explains the most important industrial vacuum pumps, classifies them by pressure range and application, and shows which details you need for selection and replacement.
Understanding vacuum: pressure ranges and pumping speed
Vacuum means a pressure below atmospheric pressure, which at sea level is around 1013 mbar. In practice, vacuum is usually stated as absolute pressure. The smaller the number, the better the vacuum. The common classification:
| Range | Absolute pressure | Typical applications |
|---|---|---|
| Rough vacuum | Atmosphere to 1 mbar | Packaging, holding and clamping, conveying, degassing |
| Medium vacuum | 1 to 0.001 mbar | Vacuum drying, distillation, freeze drying |
| High vacuum | 0.001 to 0.0000001 mbar | Coating, heat treatment, analytics |
| Ultra-high vacuum | below that | Research, semiconductor technology |
Most industrial applications lie in the rough and medium vacuum ranges. Alongside the achievable ultimate pressure, what counts is the pumping speed, stated in m³/h. It describes the volume of gas the pump moves per unit of time and determines how quickly a vessel is evacuated. Important: pumping speed depends on pressure and falls off close to the ultimate pressure. So look at the pumping speed curve in the data sheet, not just the nominal value.
The main types
Oil-lubricated rotary vane pump
The rotary vane pump is the classic for rough and medium vacuum. An eccentrically mounted rotor with sliding vanes forms chambers that draw in, compress and expel the gas. Oil seals the gaps, lubricates and dissipates heat. Single-stage pumps typically reach ultimate pressures of around 0.1 mbar; two-stage pumps go further into the medium vacuum range.
Strengths: good ultimate vacuum, compact design, wide choice. Weaknesses: the oil can be contaminated by vapours and particles, oil changes are part of regular maintenance, and an oil mist separator is needed at the exhaust. Typical uses: packaging, clamping tables, refrigeration and air-conditioning technology, laboratory systems.
Dry-running rotary vane pump
The vanes are made of a self-lubricating material, usually graphite-based. The pump works without oil in the compression chamber and only reaches rough vacuum. It is suited to clean, dry air, for example in the printing industry or in handling. The vanes are wear parts.
Claw vacuum pump
Two claw-shaped rotors turn against each other without contact. With no friction in the compression chamber, the pump is low-wear and compresses oil-free. It works in the rough vacuum range and is used for central vacuum supplies, in the packaging and wood industries and in conveying systems.
Screw vacuum pump
Two counter-rotating screw rotors convey the gas without contact and dry. Screw pumps reach medium vacuum and tolerate vapours and, to a certain extent, condensate. They are therefore widespread in chemicals and pharmaceuticals, in drying, distillation and solvent recovery. Special versions are available for aggressive or explosive media.
Liquid ring pump
An impeller rotates eccentrically in a casing partly filled with operating liquid, usually water. The rotating liquid ring forms the pumping chambers. The pump is robust and tolerates vapours, liquid carry-over and contaminated gases. Its ultimate pressure is limited by the vapour pressure of the operating liquid and rises with the liquid’s temperature. Uses: chemicals, the paper industry, food, degassing.
Diaphragm pump
An oscillating diaphragm conveys the gas completely oil-free. Diaphragm pumps are small, have a limited pumping speed and work in the rough vacuum range. They are found in laboratories, analytics and as backing pumps for small systems.
Roots pump and turbomolecular pump
Neither works alone; both work together with a backing pump. The Roots pump sits as a booster in front of a rotary vane, screw or liquid ring pump and considerably increases the pumping speed in the medium vacuum range. The turbomolecular pump produces high vacuum and likewise needs a backing pump.
Side channel blower
It produces only a low vacuum but moves large volume flows. Typical uses are pneumatic conveying systems, extraction systems and vacuum lifters with large leaks.
Which type suits which process?
| Process | Commonly used types | What matters |
|---|---|---|
| Vacuum packaging | Rotary vane, claw | fast evacuation, moisture from the product |
| Clamping tables, handling | Rotary vane dry or oil-lubricated, claw, side channel | volume flow with leakage via workpiece and seals |
| Drying, distillation | Screw, liquid ring, rotary vane with gas ballast | vapours, condensate, solvents |
| Degassing of plastic melts | Liquid ring, screw, rotary vane with separator | deposits, monomers, particles |
| Central vacuum supply | Claw, screw, rotary vane | demand-based control, redundancy |
| Coating, heat treatment | Backing pump plus Roots or turbomolecular pump | high vacuum, pumping station |
The selection criteria at a glance
- Working pressure: what absolute pressure does the process really need? A pump that only just reaches its ultimate pressure is working in an unfavourable part of its curve.
- Pumping speed: what volume has to be evacuated in what time, and how large are the leaks in the system?
- Medium: dry air, water vapour, solvents, aggressive gases, particles or dusts? This determines whether oil-lubricated, dry or liquid-sealed is the better choice.
- Oil-free operation: in food, pharmaceutical or cleanroom applications, an oil-free process may be mandatory.
- Explosion protection: if explosive mixtures are pumped or the pump stands in a hazardous area, it must be suitable for the relevant zone. In the EU, the legal basis for equipment is Directive 2014/34/EU.
- Mode of operation: continuous operation, frequent start-stop cycles or operation close to atmospheric pressure affect wear and heating.
- Maintenance and environment: oil changes, vane changes, operating liquid, waste heat in the room and noise level.
Typical faults and their causes
- Ultimate pressure not reached: leaks in pipes and seals, contaminated or emulsified oil, clogged inlet filter, worn vanes.
- Oil in the exhaust or oil loss: saturated oil mist separator, excessive inlet pressure over a long period, wrong oil.
- Milky oil: water vapour condenses in the pump. Operating with gas ballast or an upstream condensate trap can help.
- Overheating: poor ventilation, excessive ambient temperature, continuous operation at high inlet pressure.
- Unusual noises: bearing damage, coupling wear, broken vanes.
Before you suspect the pump, check the system. A vacuum gauge directly at the inlet flange shows whether the pump reaches its ultimate pressure on its own. If it does, the problem usually lies in the plant’s pipes, valves or seals.
Operation and maintenance: how to make the pump last longer
Many vacuum pump failures can be avoided with a few measures. Which of them are important depends on the type:
- Check the oil regularly: with oil-lubricated pumps, the level and colour in the sight glass tell you a lot. Dark, cloudy or milky oil is a signal for an oil change and for vapours or particles in the process. Use the vacuum pump oil approved by the manufacturer.
- Use gas ballast correctly: the gas ballast valve lets a small amount of air into the compression phase. This stops water vapour condensing in the oil; instead it is expelled with the gas. The achievable ultimate pressure is somewhat worse as a result. For humid processes, this is usually the better compromise.
- Let it warm up: a cold pump absorbs vapours into the oil more easily. Let it run for a few minutes with the inlet valve closed before the process, if the manufacturer recommends this.
- Keep an eye on filters and separators: a clogged inlet filter reduces the pumping speed; a saturated oil mist separator increases back pressure and oil loss.
- Keep wear parts in stock: vanes, seal kits, filter elements and coupling parts are good candidates for your own spare parts store for critical pumps.
With dry-running screw and claw pumps there is no oil change in the compression chamber, but gear oil and bearings still need attention. Liquid ring pumps depend on a sufficiently cool and clean operating liquid.
What to specify for replacement or new selection
- manufacturer, type and serial number from the nameplate
- type and, if known, ultimate pressure and pumping speed
- voltage and frequency: the pumping speed is higher at 60 Hz than at 50 Hz because the pump turns faster
- connection size and connection type on the inlet and outlet sides
- medium and process, especially vapours, solvents and particles
- oil or operating liquid used
- requirements for explosion protection or oil-free operation
- photos of the nameplate, connections and installation
When the vacuum pump or its wear parts are missing
Vanes, seal kits, filters and oil mist separators are typical spare parts that are missing during a shutdown. With older pumps, sometimes the whole model is no longer available. KTB Europe is a family business from Hamburg and has been sourcing industrial spare parts of all brands worldwide since 1976. Send us the part number, a photo of the nameplate or a description. If a type has been discontinued, we look for suitable alternatives.
Find out more on the pages on MRO procurement and spare parts management. You can send your enquiry via the contact page. Further reading: industrial pumps from specification to delivery and our checklist for buying a pressure gauge, which also covers vacuum gauges.
Conclusion
The right vacuum pump follows from the working pressure, pumping speed and medium. For packaging and clamping tables, rotary vane and claw pumps are the usual choice; for vapours and solvents, screw and liquid ring pumps; for high vacuum, a pumping station with a backing pump. If you provide the nameplate data, the medium and the mains frequency when ordering a replacement, you will find a pump that suits the process more quickly.
Frequently asked questions
Which vacuum pump is right for my process?
The decisive factors are the required working pressure, the pumping speed and the medium being pumped. For packaging and clamping tables, rotary vane or claw pumps are often used; for vapours and solvents, screw or liquid ring pumps. High vacuum requires a pumping station with a backing pump.
How does a rotary vane pump work?
An eccentrically mounted rotor with sliding vanes forms chambers in the housing that draw in, compress and expel gas. In oil-lubricated pumps, oil seals the gaps and dissipates heat. Single-stage versions reach rough vacuum down to around 0.1 mbar; two-stage versions go further into the medium vacuum range.
Why does my vacuum pump no longer reach its ultimate pressure?
Common causes are leaks in the plant, oil that is contaminated or emulsified by water vapour, a clogged inlet filter or worn vanes. Use a vacuum gauge directly at the inlet flange to check whether the pump reaches its ultimate pressure on its own. If it does, the problem usually lies in the plant.
What does pumping speed mean for vacuum pumps?
Pumping speed indicates the volume of gas a pump moves per unit of time, usually in cubic metres per hour. It determines how quickly a vessel is evacuated. As it decreases with falling pressure, you should look at the pumping speed curve in the data sheet.
When do you need an oil-free vacuum pump?
Oil-free pumps make sense if oil could contaminate the process or the product, for example in food, pharmaceutical or cleanroom applications. Dry screw or claw pumps are also often the better choice if vapours would quickly contaminate the oil.