Condensate Drain


A condensate drain is a type of valve used to drain condensate. They are one of the most ignored and yet most essential components of compressed air systems. They remove condensate along with contamination from the system, preferably without losing excess compressed air and without the need to shut down the system. They play a crucial role in enhancing the longevity of the compressor unit and the entire compressed air system, including the sub components, driven equipment, and instruments.

Compressed air

Compressed air is air that is compressed to a higher pressure than atmospheric pressure. Usually, the pressure is 5-8 bar. This compressed air is transported through a system of pipes. After that, it is released back to the atmosphere through pneumatic equipment or other applications that use the pressure for a certain purpose.

It is for example used in industrial processes to power pneumatic equipment such as power tools, spray paint, air motors etc. It is also used in breaking systems of trains, buses and large trucks or to start engines of large ships. It is even used for pneumatic post, for example in banks.

Moisture in compressed air

The air that we breathe is not suited to turn into compressed air directly. It needs to be treated first. Atmospheric air is full of pollution. One cubic meter of air can easily contain 100 million airborne particles. They consist of soot, pollen, dust, organic compounds, water vapour etc. The invisible moisture in the air is called water vapour. By compressing air, the amount of water vapour increases because water vapour is not compressible. Air compression causes the air temperature to rise significantly. Therefore, the air is still able to contain the water vapour at that point. But as it begins to cool, the water vapour begins to condensate. The condensate consists of water, compressor oil, dirt and other contaminants which therefore need to be periodically drained from the system to avoid damages to equipment and maintain efficient compressed air delivery. Condensation is a serious problem in compressed air systems and is one of the major reasons for failures and breakdowns.

Types of condensate drains

Drain valves can be broadly classified into manual and automatic condensate drains.

Manual condensate drains valves

As the name suggests, manual drain valves are opened manually to evacuate the accumulated condensation.

Two major concerns with manual valves are:

  • Operators can forget to drain causing excess condensate to accumulate in the system.
  • Operators can leave them partially open all the time. This method does drain the condensate constantly but leads to continuous waste of compressed air.

Automatic condensate drains

Automatic condensate drains function without manual intervention. They operate efficiently to drain condensate from compressed air systems. Most of them are electrically operated but some can operate without the use of electricity. There are roughly three types of automatic drain valves:

Electronic Timer Drains

Electronic timer drains incorporate a solenoid valve and an electric timer. The timer usually has two types of settings:

  1. ON period. The amount of time the valve needs to stay open.
  2. OFF period. The time between openings.

Many timers have two rotary control knobs on the face of the timer module. Usually, the ON period can be set from 0 to 10 seconds and the interval time of the OFF period from 0 to 45 minutes. Other timers have a digital display with push buttons and a wider range of program settings.

Electronic timer drains are a very popular choice, easy to install, cost-effective and have a reliable operation when installed with an inlet strainer. Upon actuation, the solenoid is energized, the condensate drain opens and the cycle time begins. At the end of the pre-set “ON” time, the solenoid is de-energized and remains so until the interval time is over.

The two settings need to be adjusted to the size of the compressed air system in such a way that all condensate is discharged with a minimum loss of air. The ON time needs to be set long enough to drain all the condensate but short enough to not waste any compressed air. The OFF time needs to be set long enough for some condensate to have accumulated but not too long to avoid problems in the system due to condensate. This requires some initial manual fine-tuning, but once it is set, it is both effective and reliable. The use of an inlet strainer on the solenoid valve is highly recommended. This keeps contaminants from clogging the orifice inside the condensate drain and ensures its proper working and longevity. Disadvantages of this drain type are that the valve may not open long enough to eject all the condensate or may stay open too long wasting compressed air. The oil particles contained in the condensate can undergo change partly because of high velocities and direction changes, forming stable emulsions and causing problems with proper condensate separation and ejection. It is recommended to regularly check the drain settings.

Directly to electronic timer drains

CD-014BA Automatic analog condensate drain CD-014SD Automatic digital condensate drain

Automatic analog and digital condensate drains

Electronic Level-controlled Condensate Drains

These drains are also called “Zero Air Loss” drains and have an electronic capacitive sensor monitoring the condensate level. The electronic capacitive sensor probe placed inside the drain reservoir controls the discharge by initiating the discharge command to a built-in indirect operated solenoid valve. When the condensate reaches the probe, the solenoid valve is actuated and opens. This drains the condensate and as its level drops, the probe senses this and closes the valve again. This cycle is repeated as the condensate level increases and decreases in the reservoir.

This valve avoids loss of compressed air as the valve closes before all of the condensate is discharged. Electronic sensor drains have few moving parts which ensure a reliable operation. The sensor works on all types of condensates like water, water+oil, and water+oil+contaminants.

Electronic condensate drain with capacitive level sensor and timer controlled solenoid valve

Electronic condensate drain with capacitive level sensor and timer controlled solenoid valve

Float Operated Condensate Drains

These valves have a simple construction and operate using a float type system. This float automates the process of condensate draining by opening and closing the valve after a certain amount of condensate is accumulated.

As condensate is collected and flows into the drain housing or filter bowl, the float rises. When the condensate rises to a certain level, the drain valve opens and discharges the condensate. These drains operate only when a sufficient quantity of condensate is present. Usually, a manual override is provided which allows for drainage of the system on demand or during cleaning. Most float-operated drain valves leave a small amount of condensate in the reservoir when discharging, this prevents the loss of valuable compressed air.

In most of these drain valves, the float directly operates the discharge valve through a lever mechanism. The disadvantage is that the force applied by the lever mechanism to the valve seal is relatively low, which results in a lower reliability. Some drain valves solve this problem by using permanent magnets. In these drain valves, the float mechanism is not directly connected to the valve. Instead, the float mechanism moves a permanent magnet. The valve is closed by a ferromagnetic plunger which rests on the valve seat, just like in a direct operated solenoid valve. When the condensate level rises, the magnet moves towards the plunger. The plunger is attracted by the magnet and the valve opens. As the condensate level drops, the magnet moves away and the valve closes again. This mechanism provides a more reliable and robust sealing than a traditional float operated drain valve. Float operated drain valves are a good choice when no electricity is available.

Selecting the Proper Automatic Condensate Drain

The general engineering criteria that influence the selection of the right automatic condensate drains are:

  • Temperature
  • Pressure
  • Environment

However, the financial factor should also be taken into consideration. Compressed air is about 10 times more expensive than electricity as a power source to operate tools or equipment. Therefore, avoiding loss of compressed air to limit energy costs is important.