Compressor-Pump & Service, Inc.

The Role of the Drain Valve in an Air Compressor

By In Information On May 11, 2018

The majority of industrial air compressor generate between 100 and 175 psig. This pressure allows air compressors to accomplish a nearly limitless array of tasks. To ensure proper functioning and safety, an air compressor contains numerous valves meant to help regulate the flow of air and pressure.

previous article explored two key valves in an air compressor: the unloader valve and its related check valve. This article will discuss another key valve — the drain valve — and the vital role it plays in the life of an air compressor.

Water Vapor

Most industrial air compressors use one of two means — pistons or a rotating screw — in order to compress air inside a sealed chamber. Naturally, this process involves the machine taking in atmospheric air around the compressor. This air contains water vapor.

An air compressor increases the pressure some of the moisture drops out in water molecules. Also, as the air is cooled back down to ambient temperature, the water vapor condenses into liquid and more moisture drops out. This water accumulates at the bottom of the tank. For examples, a 200 CFM compressor (25 HP) will produce 18 gallons of water per day.

Drain Valve

Water in your compression chamber will soon lead to serious problems, especially rust and corrosion. Left unchecked, such corrosion will eat right through the sidewall of your air receiver. Excessive water may also cause your compressor’s air dryers to become overloaded and to stop functioning properly. All this leads to moisture downstream, causing excessive wear on tools and other air-operated equipment.

In order to prevent these problems, all air compressors have a drain valve on the bottom of the air receiver. The drain valve allows water to flow out of the system.

Drain Valve Types

The simplest type of drain valve — a manual drain valve — remains closed until manually opened by a user. The operator is responsible for periodically draining condensate from the tank. For smaller air compressors, this task shouldn’t be too overwhelming.

A manual drain valve isn’t practical for industrial air compressors. Instead, such air compressors use one of three valve types.

The first of these — a float-operated drain — consists of a special housing built around the drain valve. As water builds up in the tank, it flows into this housing. The rising water level causes a float inside the housing to rise. Upon reaching a pre-set level, the float triggers the drain to open, and the water drains out. Some compressed air is lost with this type of valve. In larger air compressor systems this can waste electricity.

The second type of drain valve — a timer-controlled drain — takes a different approach. The valve does not measure the water level. Instead, it uses an electrical timer to open and close the valve at times designated by the user. Because the water in the compressed air is dependent on the atmospheric relative humidity the amount of liquid produced varies. Again, compressed air can be lost and energy wasted.

The third type of drain valve — a zero-loss drain — uses a different triggering mechanism. A sensor probe monitors the presence of water in the valve. When the water builds up enough, the probe sends an electrical signal to a solenoid that opens the drain but stops the flow prior to the release of any compressed air.

A timed valve makes sense for air compressors used in highly regulated settings. Once the accumulation rate of water has been determined, the valve can be set to open up at appropriate times. This allows drainage to be balanced against the air loss that can occur when a drain valve opens.

As you can see, the drain valve plays a vital role in the health of an air compressor. For more information about the type of drain valve best suited for your air compressor, contact the pros at Compressor-Pump & Service, Inc.

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