Why Is Moisture In My Pneumatic System?

Post By: Tom Rowse On: 02-10-2023 Read Time: 5 minutes - Guides - Pneumatics

From automotive manufacturers to food production facilities, many industrial automation functions rely on pneumatic systems to power mechanical components.

Pneumatic systems operate with compressed air stored in a high-pressure compressor tank to generate energy. The air is supplied from the compressor tank (or receiver tank) to the system through valves and pipes to move actuators, pistons and other machine parts.

How Moisture Appears

Air naturally contains water vapour, oils, and dust particles. When the receiver tank takes in air from the atmosphere, it also absorbs these elements. Because pressurised air held in receiver tanks generates more heat, atmospheric heating and cooling cycles cause the air in the tank to cool. When these temperature fluctuations occur, the air can no longer hold so much vapour, causing water droplets or condensation to form in the air system.

The higher the velocity in the tank, the lower the pressure and the temperature. This effect further condenses vapour into water and it can also make water droplets freeze into ice crystals – even if the ambient temperature is higher than freezing. Condensation and ice crystals damage sensitive pneumatic components, which is why it’s important to invest in tools to manage moisture.

Equipment failure and an undersized unit can also cause the build-up of moisture in the system.

Why Is It Necessary To Reduce Moisture In Pneumatic Systems?


Corrosion is the main problem caused by moisture in pneumatic systems. It is the chemical reaction between water, oxygen, and metal. Metal receiver tanks are susceptible to rust, so any water in the tank will oxidise the metal interior and transfer rust throughout the system. Rust also affects electronic components and can cause pipe scale and rust to form.

Rust in the interior of piping blocks the passage of air, which narrows air pathways, increasing corrosion and clogging the circulating tubing. As time goes on, pipe scale and rust break away from the piping’s interior, causing even more damage as it reaches other parts of the pneumatic system.

Moisture is also a breeding ground for bacteria, which can be disastrous for food plants and other industries that rely on highly sanitised conditions.

Damage To Pneumatic Components

Pneumatic system components are intricate and precise, so any moisture or dirt particles can clog their fine passageways, causing poor performance. The inner workings of pneumatic components include rubber seals for functionality and protection against wear.

Moisture can make these seals stiffen or swell with moisture, damaging components and causing system failures. Excess water can also cause sudden changes in water pressure, which damages cylinders and valves and can even cause them to burst.

Plant Air Contamination And Reduced Efficiency

Industrial processes that rely on compressed air need the air to be moisture-free and clean to function properly. If pneumatic systems are not free of bacteria, mould, rust, and debris, these contaminants can seep into the air passageway during processes. For a food processing plant, this can cause health hazard concerns.

Similarly, pneumatic systems used in paint booths need to be free of moisture otherwise the paint finish may contain blots and lack quality. Any moisture in compressed systems will also reduce the efficiency of equipment, leading to increased costs from replacements.

Increased Costs

If moisture reaches sensitive pneumatic systems, it can impact controls, interfere with productivity, and lead to maintenance costs from downtime to source and replace damaged pneumatic parts.

One example of this is filter and circuit damage caused by recurring pressure drops in filters over time. Another example is food manufacturers that use compression systems to dry the packaging of perishable foods. If moisture and bacteria seep into compressed air systems, food quality and shelf life will be affected by contaminants sealed into the packaging.

Why Is Moisture In My Pneumatic System

How To Reduce Moisture?

Removing moisture from an air compressor tank depends on the following:

  • The compressed air dew point – the point at which water vapour in a volume of air cools and condenses to form a liquid at the same rate it’s evaporating
  • Ambient air temperature
  • Air compression pressure ratings
  • The plant’s processes and airflow dynamics

After analysing this information, there are several measures that can remove water from the compressor’s system:

Draining Moisture

It’s important to drain air compressors regularly, and more so during the warmer months of the year. Air compressors usually have a drain for accumulated water to be released, but a drain can also be installed elsewhere in the system – automatic (timer-controlled) or manual.

Creating Consistent Temperatures

If the air compressor unit is outdoors, extra care must be taken to reduce moisture during hot weather. For indoor compressors, keeping the compressor’s housing room well-ventilated and dry reduces the reliance on air-drying equipment. In addition, the compressor will be less likely to overheat. Insulating the compressor, adding a dehumidifier and fixing leaks in the room also improves temperature control.

Air Drying Systems

While drains and traps work well in disposing of water, air driers are even more efficient in eliminating water from the system. Refrigerated air driers cool the air to a low temperature for the water to condense, which can then be collected separately. Refrigerated systems are suited to moisture-sensitive industries.

Desiccant air driers contain hygroscopic materials in the unit’s drying towers. As air passes through these absorbent substances, the fibres absorb moisture and the dried air flows out. Typically, desiccant drying systems are regenerative types, meaning they have two towers. One tower actively dries compressed air while the second prepares for the next cycle’s intake.

Better Design

We know that water vapour occurs when hot air cools, so take this into account when designing a compressor system that helps prevent rapid temperature changes. Choosing more rust-resistant materials can also prevent oxidation-type contamination. Another measure is connecting piping at the top of the system rather than the bottom, which provides drier air and reduces moisture.

Keeping Compressors Moisture-Free

To sum up, automation machinery that relies on compressed air will always generate moisture to some extent. Moisture can have detrimental effects on systems, bringing rust, debris, and bacteria to the system. To maintain efficiency, it’s important to invest in technology to remove moisture, so equipment is contaminant-free and running at optimal capacity.