What Are Automatic Drain Valves? Importance & Types with Compressed Air Dryers

Wherever there is compressed air, there is moisture. Ambient air naturally contains water vapor, and when it’s drawn into a compressor and pressurized, that vapor becomes highly concentrated. As the hot compressed air cools, the vapor condenses into liquid water, leading to corrosion, contamination, and equipment failure if not properly managed. A complete compressed air system includes both a dryer to remove vapor and an automatic drain valve to remove liquid condensate.

Automatic drain valves remove mixtures of water and compressor lubricants from compressed air systems. An automatic drain valve eliminates the need for a maintenance worker to patrol the plant, manually dumping liquid from the air system.

The Importance of Using Compressed Air Dryers

In the process of generating and distributing compressed air, moisture condensation is inevitable. It usually contains oil and other contaminants that can sometimes be particularly aggressive.

Companies recognize the pitfalls that accompany contaminated air–increased maintenance, higher operating costs, premature equipment failure, and replacement, as well as an overall decrease in productivity. Deliquescent D-Series Dryers, Portable Compressed Air Dryers, Regenerative Desiccant Compressed Air Dryers, In-line Desiccant Dryers, and Moisture Block Dryers remove those harmful toxins and eliminate water from compressed air lines, reducing any condensation or rusting.   

Also known as “salt dryers,” deliquescent compressed air dryers protect against freeze-ups in winter and liquid carryover in summer, operating alongside automatic drain valves to discharge collected condensate.

The amount of moisture air can hold depends on its temperature. As compressed air cools, the temperature at which vapor begins to condense is called the dew point. Keeping the system’s dew point below ambient temperature ensures “dry” compressed air and prevents downstream moisture issues.

Benefits of Using Automatic Drain Valves

As dryers remove vapor from compressed air, the resulting condensate must also be drained to prevent overflow or back pressure. Van Air Systems provides an economical and compliant solution that meets current EPA regulations.

For example, a typical 50 HP compressor can generate up to two gallons of water per hour—16 gallons in a single shift. Automatic drain valves discharge this moisture safely and consistently, while oil/water separators ensure that contaminated condensate is properly treated instead of entering groundwater or sewer systems.

Applications of Compressed Air Dryers

Compressed Air Dryers with Automatic Drain Valves can be used for:

• Auto Repair / Body Shops
• CNC Machine Shops
• Service Trucks
• Dry Cleaners
• Paint Shops
• HVAC Systems
• Manufacturing Plants
• Home Workshops
• Dairy Farms 
• Off-Shore Operations
• Dental Labs
• Chemical Plants
• Process Equipment
• Food Packaging

Compressed Air Dryers with Automatic Drain Valves can prevent:

• Liquid-related damage
• Excessive liquid build-up 
• High-cost maintenance
• Noise hazard 
• Loss of compressed air
• Liquid carryover downstream

Types of Drain Valves 

Automatic Drain Valves

As the name implies, auto drain valves remove human labor from emptying drying storage tanks. An automatic drain valve eliminates the need for a maintenance worker to patrol the plant, manually dumping liquid from the air system. Here are a few different auto drain valves available:

• Solenoid Electric Drains 
• Pneumatic Zero Loss Drains 
• Motorized Timer Ball Valve 

Timered Solenoid Automatic Drain – EDV Series

Best fit: Ideal for clean condensate lines such as coalescing filters.

These drains are the most economical drains on the market.  They use a solenoid to open and close a needle valve. The downside to these valves is that they clog up when there are heavy particulates in the drain lines.  Since these valves only have a needle seat drain, they often clog up. If your condensate line is clean, like on a coalescing filter, then the EDV timered solenoid drain valve would be a perfect solution.

Motorized Automatic Drain Valve – MDV Series

Best fit: Best for systems with heavy particulate or variable flow conditions.

These automatic drain valves are built like a tank and can handle heavy particulates without clogging up. The best part about our MDV drain valves is that they can be wired to upper and lower limit liquid level sensors to be used as a zero loss drain valve.  You can operate the MDV in Timer Mode, Switch Mode, or both. Using high-powered actuators and a full ported ball valve, nothing will stop these valves from opening and closing. Our valves can snap a #2 pencil if it gets in the way, so keep your fingers clear when it begins to rotate.  

Pneumatic Drain Valves – PDV Series

Best fit: Suited for applications where zero air loss is critical.

These automatic drain valves are used when you cannot have any loss of compressed air.  They work by allowing the condensate to gravity feed into the valve's condensation reservoir.  When the liquid in the reservoir rises to a point where the float lifts off the seats, control air pressure is sent to the pneumatic piston to open the normally closed ¾ ported ball valve.  When the liquid is evacuated and the float returns to the seat inside the reservoir, the control air pressure is cut off and the pneumatically operated piston slams shut. The most unique part about our PDV series is that our trigger mechanism does not touch the liquid condensate so there is no chance for sediment to build up and prevent the float from reseating.  This means that our zero loss drain valve will always reseat and close unlike some of the others on the market.

Need Help?

Van Air Systems provides more than just an affordable solution to problematic electric and diesel air compressors with pristine automatic drain valves. With 65 years of diverse technical experience behind us, Van Air Systems has grown into a leading manufacturer and supplier of absorbent desiccants for natural gas and compressed air deliquescent dehydration. Throughout that time, our company has worked to produce a wide array of energy-free products that improve the drying process. Regardless of your industrial dehydration equipment needs, we at Van Air Systems are confident in our abilities to provide cleaner solutions at an economical rate.

As a top manufacturer and supplier in our industry, our products continue to act as energy-free alternatives for your commercial coating, blasting, and industrial dehydration needs. Explore our full product line of compressed air and natural gas dryers, automatic drain valves, air and gas filters, and other accessories today.