Vacuum Pump Oil – The Surprising Maintenance Step

Vacuum pumps are mechanical devices that are used to remove gas molecules from a sealed volume to create a partial vacuum. There are several different types of vacuum pumps that operate on different principles:

  • Rotary vane vacuum pumps use a rotating rotor with sliding vanes to sweep gas molecules out of an enclosure and exhaust them. They are commonly used in industrial applications.

  • Scroll vacuum pumps use two interleaved scrolls to compress and transport gas. They can achieve medium and high vacuum levels. Scroll pumps are often used in analytical instruments.

  • Diaphragm vacuum pumps contain a flexible diaphragm that moves up and down to create suction. They are used widely in medical applications.

  • Diffusion pumps contain no moving parts. Instead, they use oil vapor to direct gas molecules out of the chamber. They are able to reach ultra high vacuum levels.

  • Turbomolecular pumps use high speed rotating blades to impart momentum to gas molecules and force them out. They are commonly found in scientific research applications.

Vacuum pumps have a wide range of uses across many industries including manufacturing, food processing, medical technology, analytical instrumentation, and scientific research. They are a key component for many processes that require controlled environments at sub-atmospheric pressures. Some common applications include vacuum coating, freeze drying, vacuum packing, vacuum forming, distillation, and space simulation chambers. The ability to achieve and control vacuum conditions is critical for many industrial and scientific processes.

How Vacuum Pumps Work

Vacuum pumps work by creating a pressure differential to remove gas molecules from an enclosed space. This creates a partial vacuum with a lower pressure than atmospheric pressure. There are several basic parts and principles that allow vacuum pumps to work:

Moving Parts – Vacuum pumps have moving parts like rotors, vanes, pistons, diaphragms, or impellers that operate with motors to mechanically create suction. The motion of these parts expands the volume inside the pump so gas molecules rush in. Then the volume is compressed to push the molecules out through the exhaust. This cycling action generates continuous suction to evacuate air and gases.

Inlet and Outlet – All pumps have an inlet and outlet. The inlet is connected to the vacuum chamber. As the pump operates, it sucks gas in through the inlet. The gas gets trapped and compressed inside the pump, then expelled through the outlet. This maintains the negative pressure at the inlet to keep pulling in gases.

Seals – Tight seals are crucial to prevent air leaks into the vacuum chamber. Well-designed shaft seals, gaskets, and o-rings allow the pump’s moving parts to operate without letting air sneak into the inlet side. Proper seals ensure the pump can sustain maximum vacuum.

Check Valves – Check valves are one-way valves that allow gas to flow in only one direction through the pump. On the inlet side, they open to allow gases to be drawn into the pump. On the outlet, they open to let gases escape but then close tightly to avoid backstreaming into the inlet. This maintains the pressure differential.

By using these principles, vacuum pumps continuously evacuate air and gases to create strong, steady vacuum suction. The lower pressure inside the vacuum vessel compared to atmospheric pressure outside is what allows pumps to effectively remove gas molecules.

Importance of Vacuum Pump Oil

Vacuum pump oil serves several critical functions that are vital for proper operation and longevity of the vacuum pump. Some of the key functions and importance of vacuum pump oil include:


  • Provides lubrication between moving parts like bearings, rotors, vanes to reduce friction and wear
  • Prevents metal-to-metal contact between components
  • Allows smooth operation and prevents seizing up of parts


  • Forms a sealing film between clearances in the pump to maintain vacuum
  • Prevents leakage of air and loss of vacuum
  • Keeps pumped gases from leaking back into the system


  • Absorbs and dissipates heat generated during compression
  • Prevents overheating of pump components
  • Removes heat from critical areas like bearings


  • Keeps interior surfaces of pump clean
  • Suspends contaminants and particles caused by wear
  • Prevents buildup of sludge, carbon, and deposits

Proper lubrication and sealing allows the pump to reach deeper vacuum levels. Cooling prevents overheating damage. And cleaning maintains pump efficiency and performance. Using the right vacuum pump oil is critical to maximize pump life.

Types of Vacuum Pump Oils

When selecting a vacuum pump oil, you’ll typically choose between mineral oils and synthetic oils. Both have their advantages and drawbacks.

Mineral Oils

Mineral oils are derived from crude oil that has been refined through a process called fractional distillation. They are composed of hydrocarbon chains of different lengths, giving them a variety of viscosities.

Some pros of mineral oils:

  • Inexpensive compared to synthetics
  • Readily available
  • Good lubricity properties

Some cons of mineral oils:

  • Shorter service life than synthetics due to oxidation
  • Not as thermally stable as synthetics
  • Lower flash points than synthetics

Overall, mineral oils are a good budget-friendly option for low to moderate temperature applications where extended oil change intervals are not critical. They provide adequate lubrication at a low initial cost.

Synthetic Oils

Synthetic oils are produced through a chemical process to create customized hydrocarbon structures with enhanced properties. The molecular chains, additives, and viscosity can be precisely dialed in.

Some pros of synthetic oils:

  • Extended service life, often 2-3X longer than mineral oils
  • Excellent thermal stability at high temperatures
  • Higher viscosity indexes for use across wider temperature ranges
  • Higher flash points for safety

Some cons of synthetic oils:

  • More expensive upfront cost than mineral oils
  • Limited availability – may need to purchase directly from an industrial supplier
  • Overkill for some low temperature or intermittent use applications

Synthetic oils are ideal for demanding applications requiring high temperatures, continuous operation, and extended oil change intervals. Their advanced formulation pays off in extended equipment life and less downtime.

Vacuum Pump Oil Properties

Vacuum pump oils have several key properties that determine their performance and suitability for different applications. Some of the most important properties to consider are:


  • Viscosity refers to a liquid’s resistance to flow. For vacuum pump oils, the right viscosity helps create an effective seal between moving parts while minimizing friction.
  • Oils with higher viscosity tend to offer better sealing and lubrication. However, too high of a viscosity can lead to excessive drag in the pump. Lower viscosity oils flow more easily but may not provide adequate lubrication.
  • Most vacuum pump oils have a viscosity rating between ISO 32 and ISO 100. The optimal viscosity depends on the pump design and its operating speed.

Vapor Pressure

  • Vapor pressure indicates how easily the oil evaporates. Lower vapor pressures are better for vacuum applications.
  • If the vapor pressure is too high, the oil can evaporate inside the pump, contaminating the vacuum chamber. It can also lead to the release of volatile organic compounds (VOCs).
  • High-quality vacuum pump oils are specially engineered with low vapor pressures to prevent evaporation issues.


  • Demulsibility refers to an oil’s ability to separate from water, which can condense inside pumps.
  • Oils that resist emulsifying allow water droplets to coalesce and drain out rather than staying dispersed in the oil.
  • Good demulsibility prolongs oil life and prevents corrosion inside the pump.

Pour Point

  • The pour point is the lowest temperature at which the oil will flow.
  • Vacuum pump oils need adequate flow at low temperatures for cold starting. A pour point below -10°C is typical.

Flash Point

  • The flash point is the temperature at which the oil gives off flammable vapors. It indicates the oil’s fire resistance.
  • Most vacuum pump oils have high flash points over 200°C for safety when operating pumps at higher temperatures.

Selecting the Right Vacuum Pump Oil

Choosing the proper vacuum pump oil is crucial for optimal pump performance and longevity. There are several key factors to consider when selecting vacuum pump oil:

Pump Type

  • The type of pump you have determines the oil requirements. Rotary vane, piston, screw, scroll, and other pump designs call for oils with specific properties. Always consult your pump manual for the manufacturer’s oil recommendations.

  • Common oil types used include mineral oils, synthetic hydrocarbons, polyalphaolefins (PAOs), polyalkylene glycols (PAGs), silicones, fluorinated fluids, and more. Each has advantages and disadvantages.

Operating Temperature

  • Consider the temperature range your pump operates within. Oils are formulated for low, medium and high temperature ranges. Using the wrong viscosity oil can lead to issues.

  • For high heat applications, choose an oil with good thermal stability and a high flash point. For cold environments, select an oil that flows well at low temps.


  • The oil’s viscosity grade must match the pump requirements. Thinner oils may not provide enough lubrication. Thicker oils can lead to high drag and inefficiency.

  • Most pumps use ISO VG 32, 46 or 68 oils. Double vane pumps tend to use lower VG fluids. Check your manual for the recommended viscosity.

  • Viscosity index (VI) indicates how much an oil’s viscosity changes with temperature. Higher VI oils maintain viscosity better as temps fluctuate.

Properly selecting vacuum pump oil requires understanding your pump’s needs in terms of design, operating temps, required viscosity, and oil properties. Refer to manufacturer guidelines and choose quality branded vacuum oils.

Changing the Vacuum Pump Oil

Proper oil change intervals and procedures are critical for vacuum pump health and performance. Here are some best practices when changing vacuum pump oil:

Drain Intervals

  • Follow the vacuum pump manufacturer’s recommendations for oil change intervals. This is usually every 500 hours of operation or 6 months, whichever comes first.

  • Consider used oil analysis to determine if the oil can safely go longer between changes. Analysis tracks viscosity, acidity, wear metals, and contaminants.

  • Change oil more frequently with heavy usage or in dirty environments. Frequent changes remove damaging contaminants.

Used Oil Analysis

  • Used oil analysis involves sending a sample to a lab for testing key oil properties. This reveals how the oil is holding up.

  • Analysis can potentially double oil change intervals if the oil is still in good condition. Cost of testing is offset by less frequent disposal and refills.

  • Testing can diagnose wear issues inside the pump by tracking rising metal content. Proactively address wear before failure.

Fill Procedure

  • Thoroughly drain used oil while hot through the pump’s drain port into an approved container. Hot oil drains quickly and completely.

  • Replace the drain plug. Wipe away spills and dispose of rags properly to prevent fires.

  • Refill pump through the fill port with new vacuum pump oil to the proper level. Don’t overfill.

  • Briefly run the pump to circulate the clean oil before returning to service.


  • Properly dispose of used oil according to local environmental regulations. Do not dump down drains or into the ground.

  • Many municipalities and waste management companies accept used oil for recycling or energy reclamation. Reusing oil is more sustainable.

  • Storing small amounts until enough accumulates for proper disposal is an option. Use sealed containers in a safe location.

Signs of Vacuum Pump Oil Problems

Vacuum pump oil can develop issues over time that indicate it needs to be changed. Being aware of these signs can help prevent damage and extend the life of the pump. Some common signs of vacuum pump oil problems include:


As vacuum pump oil ages and circulates through the system, it can become contaminated with particulates, moisture or other fluids. Contaminants degrade the oil’s lubricating properties and can abrade internal surfaces. Evidence of contamination includes discoloration, cloudiness, or the presence of particles or water droplets. Oil analysis can identify specific contaminants.

Viscosity Changes

The viscosity of vacuum pump oil can increase or decrease over time. Thickened oil may indicate oxidation and polymerization. This reduces the oil’s ability to flow and provide adequate lubrication. Thinned oil could mean fuel or solvent contamination. Checking the oil’s viscosity and comparing to fresh oil is a way to identify viscosity issues.


A foamy or bubbly appearance when circulating or churning can indicate the presence of moisture. It also reduces the oil’s lubricating effectiveness. Foaming oil needs to be changed as moisture can corrode internal pump components.


Vacuum pump oil that smells burnt or rancid is likely oxidized. Strong fuel odors may signal contamination. Unusual odors are a red flag the oil needs changing. The oil should have little discernible scent if in good condition.

Best Practices for Vacuum Pump Oil

Proper care and maintenance of vacuum pump oil is crucial for optimal performance and longevity of the pump. Here are some best practices to follow:


  • Store oil in a cool, dry place away from direct sunlight and extreme temperatures. Heat and contaminants can degrade oil over time.
  • Use sealed containers and check for leaks periodically. Moisture absorption can negatively impact oil properties.
  • Avoid cross-contaminating oils. Store different oils separately.
  • Follow first-in-first-out (FIFO) inventory management. Use older oils first to avoid extended storage periods.


  • Wear protective equipment like gloves and goggles when handling oil. Avoid skin contact.
  • Use a pump or funnel when transferring oil to prevent spills. Wipe up any spills immediately.
  • Keep the oil fill port and surrounding area clean when adding oil. Avoid introducing contaminants.


  • Use a vacuum dehydrator or in-line filter to remove moisture and particles from oil during operation.
  • Filter oil before adding it to the pump or reservoir. Particle contamination can damage internal components.


  • Test oil samples regularly to check condition and contamination levels. Look for water content, acidity, and metal particles.
  • Oil analysis can identify issues needing attention before equipment failure occurs. It also determines optimal change intervals.

Record Keeping

  • Document oil change dates, oil types, filter changes, operating hours, and analysis results.
  • Records help optimize maintenance scheduling and identify trends over time.
  • Note any unusual operating conditions, noise, leaks, or performance changes.


Proper lubrication is critical to vacuum pump reliability and performance. Selecting the right oil prevents premature wear, corrosion, and failure. The oil creates a seal between moving parts, provides cooling, and carries away contaminants. Using the manufacturer’s recommended oil is ideal, as it’s designed specifically for that pump’s components and operating conditions.

Factors like viscosity, vapor pressure, demulsibility, and chemical composition determine oil suitability. Oils for rotary vane or piston pumps often have higher viscosities than diffusion or turbomolecular pump oils. Synthetic oils withstand high temperatures and have low vapor pressures. Demulsible oils resist emulsifying with water, preventing corrosion. Additives enhance performance.

Routinely checking oil levels, changing at recommended intervals, and watching for signs of contamination keep vacuum pumps running smoothly. Clean oil is vital. By properly maintaining vacuum pump oil, you safeguard your investment and avoid costly downtime. Proper lubrication practices maximize vacuum pump life.

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