How to Select a Drain Valve

Here are some guidelines that can help you select a condensate drain valve. The article outlines a two step process to selecting a condensate drain valve.
  1. One: choose the best type of valve for your application.
  2. Two: match the operating conditions with the drain valve's specifications.
To buy see our our drain valves main page.

Ball Valve Drains

Sure Drain
If you need to drain an air receiver or other similar pressure vessel the best choice is a ball valve drain. Compared to other types of drain valves ball valve drains are not affected as quickly by dirt, oily sludge, rust, and the other gunk that comes out of receiver tanks. Motorized ball valve drains with timers are a little more expensive than direct acting drains, however the headaches saved probably make the expense worthwhile.

When you have a large amount of pipe scale and other gunk your best choice is a ball valve style drain valve. Common dirty drain valve applications include:
TEC 44 Ball Valve Drain
Ball Valve Drain
bulletAir receivers (tanks)
bulletDeliquescent air dryers
bulletAftercooler separators
Standard electronic solenoid drain valves can be installed on air receivers and in other dirty applications; however, you should install a strainer with these drains to allow easy access and protection from pipe scale and other contaminants.

No-Loss Drains

No Loss Automatic Drain Valve
No-loss drain valves eliminate the compressed air consumed by other types of drains. The return on investment is often weeks.

A no-loss drain valve collects condensate in a small reservoir and discharges it when a certain volume has been reached without consuming any compressed air. So no-loss style drains reduce the amount of compressed air consumed. For example a DEHYDRA52 collects 52 ounces of condensate before it cycles discharging the condensate to drain.

In a large well maintained system, no-loss drains can save thousands of dollars a year paying for themselves normally in less then 3 months. So, no-loss drains are a good choice for systems
over 1000 SCFM who have done a compressed air audit and have an active leak monitoring program. Another reason you may want a no-loss drain is because some are pneumatically operated like the DEHYDRA52 and ROBODRAIN. So if you don't have power available, you can use these drains without running new electric.

Gravity type condensate oil/water separators that are fed from no-loss drains work better because the condensate is not constantly emulsified by the blow down you get from electronic drain valves. Chemical adsorption oil/water separators like the PURO models are not effected by blow down from drains because they don't use gravity separation tanks.

A niche no-loss drain application is in conjunction with centrifugal air compressors. On centrifugal air compressors two no-loss drain valves are recommended at each intercooler location. This is to protect the expensive compressors from potential damage from a drain trap failure. At the same time, an electronic drain may fire to often or not enough either trapping moisture or wasting air here.

Direct Acting Drains

Direct acting electronic drain valves are less expensive than no-loss and ball valve drains. Most electronic drain valves let you set the drain to come on once every 10 seconds to 45 minutes and remain open for 0.10 to 10 seconds.
Optimum Series
Electronic Drain Valve
The condensate is blown out of the drip leg or filter housing with some compressed air. Electronic drain valves are normally used on drip legs, separators, filter housings, and nearly anywhere else in the compressed air system where condensate collects.

If the condensate contains a large amount of dirt, a strainer should be added to the electronic drain valve. The strainer will stop the dirt from clogging the drain valve orifice. The size of the drain's orifice affects how much compressed air will be expelled with the condensate each time the drain fires. Operating pressure and discharge time are also factors.

Diaphragm Drains

Diaphragm Drain
Diaphragm style electronic drain valves have larger orifices than most direct acting drain valves. Because of the larger orifice it is generally accepted diaphragm drain valves are less likely to foul than direct acting valves. Diaphragm drain valves do use more compressed air than their direct acting cousins. In the end, the choice between direct acting and diaphragm drain valves is really a coin toss. Both are good electronic drain valves and can be used in the same applications. A strainer should be used with a diaphragm valve in dirty applications.

Operating Conditions

Of course there are some basic operating conditions to consider when selecting any drain valve. They include:
bulletAmount of condensate being discharged
bulletMaximum temperature
bulletMaximum pressure
bulletValve body material
bulletDischarge and interval time
bulletNPT Connection
bulletOrifice size
bulletType of valve (discussed at length above)
From the lengthy discussion above you've probably concluded correctly the most important factor is the type of valve. Once you have decided between...
bulletBall valve
bulletDirect acting
The other specifications help you choose the best fit for your situation. Most drain valves can handle nearly any condensate load, but best practice in large air systems (1000 SCFM larger) is to use ball valve drains and large no-loss drains in applications closest to the air compressor including the air receiver and aftercooler separator. The next thing to consider is the pressure you are operating at and the air's temperature. Drain valves for high temperatures and pressures are readily available. However, most are rated around 200 F and 250 PSI because most compressed air systems operate at less than these maximums.

The valve body material is normally brass or bronze or stainless. Stainless steel valves are commonly used in corrosive environments, sanitary applications, and in systems piped in stainless. If chemical compatibility is a concern with your process be sure to check the valve body material. Some drains like the Optimum series are NEMA4. Explosion-proof NEMA7 drain valves are a custom product. The closest standard product to NEMA7 is a pneumatically operated no-loss drain valve.

Drain valves come in nearly all electric formats making it easy to match a drain with what you have available at the installation point. Most 120 VAC drains come with a six foot cord and plug ready for a standard outlet. Drain valves are available in...
bullet120 VAC
bullet220 VAC
bullet24 VAC
bullet24 VDC
bulletand more
So, you can generally select a drain by the electric you have available at your installation point. Additionally pneumatically operated drain valves like the no-loss ROBODRAIN don't require any electric.

The connection size can be selected to match what your installing the drain valve on. For example a 1/4'' NPT connection at the bottom of a filter bowl would take a 1/4 NPT drain valve. Drain valves have female NPT connections. Don't always blindly match the drain to the connection size also consider the application. For example, a 1/4'' NPT drain valve is not a good choice for a 1500 gallon air receiver.

Hopefully this short article helped you select a drain valve for your compressed air system. eCompressedair offers a full line of compressed air drain valves online. For help offline call us at 704-947-1967.