How to Drain Air Compressor Tanks

Learning how to drain air compressor tanks correctly prevents internal corrosion and system failure. Neglecting this simple task allows acidic condensate to accumulate, compromising receiver walls and air quality. At Control Gear, our engineers have spent over 50 years maintaining industrial systems across South Wales to ensure they meet strict safety standards.

We will outline the specific drainage procedures, safety protocols, and legal disposal requirements you need to follow.

Why Does Moisture Accumulate in UK Air Systems?

A typical 100kW compressor can generate up to 85 litres of water per shift in UK conditions because atmospheric humidity is concentrated during the compression process. This volume fluctuates based on the intake air temperature and the relative humidity levels found in your specific industrial environment.

Moisture builds up because compressing air concentrates atmospheric water vapour, drastically raising the Pressure Dew Point (PDP). As the hot compressed air cools downstream in the receiver or piping, this vapour condenses into liquid water. This accumulation is a natural physical result of thermodynamics.

The UK’s high relative humidity, often averaging above 80%, significantly increases this volume. Industrial air compressors like the Atlas Copco GA series, a popular range of industrial screw compressors, intake this moisture-laden air. They generate substantial condensate volumes.

A standard 75 kW compressor running at 7 bar can produce over 150 litres of water daily in our climate. I actually measured this on a site in Cardiff last July. The receiver was filling a standard oil drum faster than the maintenance team could empty it.

Leaving this moisture unchecked leads to rapid internal corrosion of carbon steel tanks. The water mixes with compressor oil and particulates to form an acidic sludge. This mixture clogs downstream equipment and degrades your air quality below ISO 8573-1, the international standard for compressed air quality. Contact us for a system audit to assess your moisture load.

• Compression Heating: High temperatures allow air to hold more water vapour.
• Aftercooling: Rapid cooling forces vapour to condense into liquid.
• Saturation: 100% humidity is reached in the piping.

Understanding the volume of fluid produced leads us to the composition of that fluid.

Is Condensate Just Water or Hazardous Waste?

Condensate is legally classified as hazardous waste rather than clean water because it contains measurable concentrations of oil and heavy metals from the compressor. Modern oil/water separators are essential to remove 99.9% of this liquid contamination before you can legally discharge the remaining fluid into public sewers.

It acts as a regulated pollutant requiring proper compressed air condensate disposal. Under the Water Resources Act 1991, a key piece of UK environmental legislation, discharging oil-contaminated condensate into public sewers or surface water is a criminal offence.

The British Compressed Air Society (bcas.org.uk) advises that the maximum oil content in discharged water must remain below 20 ppm. Failing to meet this standard puts your business at risk of unlimited fines. To comply, you must treat the fluid using proper condensate management equipment.

We often install the Atlas Copco OSC series, a range of oil/water separators from the leading manufacturer Atlas Copco. These units use multi-stage filtration to remove contaminants before the water enters the drainage system.

Why do you need an OSC separator:

• Legal Compliance: Ensures discharge water meets strict environmental standards (below 20 ppm).
• Cost Reduction: You only pay specialist waste carriers to dispose of the captured oil, not the bulk water volume.
• Risk Mitigation: Removes the liability of accidental groundwater contamination.

Legal compliance requires specific physical methods for removing this fluid from your system.

How Do You Safely Drain Different Compressor Types?

Safely draining a compressor needs isolating the electrical supply and fully depressurising the air receiver before opening any valves to release condensate. You must verify that the pressure gauge reads zero and ensure all stored energy is dissipated to prevent high-velocity fluid discharge injuries.

While modern rotary screw units often automate this via electronic zero-loss drains, smaller piston compressors rely on you manually opening the receiver valve daily. Ignoring this pressure release can turn a simple maintenance task into a dangerous projectile hazard.

What Are the Critical Safety Steps?

We insist on strict protocols before touching any drain valve to prevent injury. You must perform a Lock Out Tag Out (LOTO) procedure to isolate the power source completely. Always wear impact-resistant safety glasses and nitrile gloves, as the ejected fluid often contains oil and particulate matter at high velocity.

Refer to the HSE pressure systems guidance, published by the UK’s Health and Safety Executive, for specific isolation standards regarding stored energy. We offer safety training to ensure your team follows these protocols.

How Do Piston and Rotary Screw Procedures Differ?

Piston compressors, like the Atlas Copco Automan, a common model of piston compressor, typically use a simple manual ball valve at the tank’s lowest point. To drain manually, place a collection container under the valve. Slowly rotate the valve handle until you hear air escaping.

Allow the water to flow until only air remains, then close the valve tightly. Conversely, Atlas Copco, a leading Swedish industrial equipment manufacturer, equips its GA Series rotary screw compressors with electronic water drains (EWD). These actuate automatically based on liquid levels.

Key Drainage Locations:

• Receiver Tank: The primary collection point for bulk water.
• Aftercooler Separator: Often found on rotary units to catch moisture early.
• Distribution Drip Legs: Vertical pipe drops that trap water in the network.

Successful drainage highlights the operational differences between manual valves and automated technology.

Which Drain Valve Technology Offers the Best ROI?

Most facilities achieve 100% ROI in the first year after installing electronic zero-loss drains because these devices eliminate the costly compressed air waste associated with manual or timer valves. They use intelligent sensors to discharge only accumulated liquid without venting the expensive energy you have generated.

Electronic zero-loss drains offer the best return on investment by eliminating compressed air waste during the discharge cycle. Unlike timer-based solenoids that purge valuable air alongside water, intelligent capacitive sensors trigger the valve only when liquid is present. This efficiency reduces energy costs significantly over the compressor’s lifespan.

Why Are Manual and Timer Drains Inefficient?

Manual drains rely entirely on human memory during routine maintenance. This reliance often leads to neglect and dangerous system flooding. Timer drains operate on fixed intervals regardless of actual condensate levels, meaning they blow open even when the pipework is dry.

It is painful to stand next to one of these units and hear that loud hiss of wasted air firing off every few minutes. This wastes expensive compressed air. That lost air represents energy you have already paid to generate, directly inflating your electricity bill.

Why Choose Atlas Copco EWD Zero-Loss Drains?

We recommend upgrading to Atlas Copco EWD drains, intelligent discharge units from the global leader in compressed air solutions. These devices use capacitive sensors to monitor liquid levels inside the reservoir. The valve opens only when the reservoir is full and closes before any air escapes, ensuring zero air loss.

• Manual Valves: High risk of flooding. Relies on operator availability.
• Timer Solenoids: High energy waste. Purges air even when dry.
• EWD Zero-Loss: Maximum efficiency. Savings often cover the buy cost within months.

You can find compatible EWD kits in our catalogue of Atlas Copco parts. Optimising your drainage hardware requires a professional maintenance strategy to ensure long-term performance.

How Can Control Gear Support Your System Longevity?

Control Gear supports system longevity by deploying ISO-accredited engineers to maintain your compressed air infrastructure according to strict manufacturer guidelines. We conduct complete system audits and implement proactive maintenance schedules that prevent corrosion, optimise drainage efficiency, and ensure your equipment meets all UK safety regulations.

As an Atlas Copco Premier Distributor, a designation for partners meeting the highest global technical standards, we extend asset lifecycles through proactive care rather than reactive repairs. This structured approach prevents premature failure in critical components like electronic zero-loss drains and protects your investment.

We back this technical expertise with a 24/7 Emergency Call Out service to handle unexpected drainage or pressure faults immediately. Our team operates under rigorous quality and safety frameworks to protect your facility:

• ISO 9001: The international standard for quality management systems ensures consistent service delivery.
• ISO 14001: Environmental Management standards help us manage condensate disposal legally.
• ISO 45001: Occupational Health and Safety standards govern our safe site operations.

Professional support ensures these maintenance practices become a reliable routine.

Secure Your Air System

Draining is not optional since it is important for maintaining safety and efficiency. For the best results, automate the process with EWD drains to eliminate manual errors. Don’t let moisture corrode your profits. Contact Control Gear today for a system audit or to upgrade your drainage solution.