Automatic Drain Valves

Types and function:

Drain valves are a crucial part of the compressed air system. Browse eCompressedair's online selection of drain valves here.

Condensate drain valves remove condensate from the air system without losing excessive compressed air and without shutting down the system. Condensate can have harmful effects on a system when not removed. For instance, moisture can wash lubrication from air tools and production equipment causing downtime and maintenance; an inconsistent supply of dry air can cause production quality problems; and excessive rust and scale can form in the air distribution system. Also, water can back up into the compressor and wreck the machinery, air dryers can become overloaded, and in-line filters can be destroyed. There are two basic types of automatic drain valves: automatic and manual.

• Automatic: There are three types of automatic drains: float operated drains, electronic sensor drains and timer drains.
  • Float operated drains (fig. DV1-1): These drains automate the dumping of condensation by using a float to initiate the draining action. As condensate flows into the drain housing, the float rises. When the condensate rises to a specific level the drain opens and allows the condensate to be discharged. Float-operated drains discharge condensate only when condensate is in sufficient quantity. Other types of drain valves can open when no condensate is present resulting in a loss of compressed air. Some float operated drains are also no-waste drain valves. They incorporate a liquid seal that prevents compressed air loss during the drain discharge cycle.
  • Electronic sensor drains: An electronic sensor probe inside the drain reservoir initiates the discharge command. When the condensate reaches the probe, an electrical connection closes, opening a solenoid valve. When the condensate level drops below a second, low-level probe, the valve closes. This cycle is repeated as the condensate level rises and falls within the reservoir. This valve also saves compressed air because the valve closes before all of the condensate is discharged. Electronic sensor drains have few moving parts that aid in reliable operation.
  • Timer drains: These drains incorporate a solenoid valve and an electric timer. The timer usually has two settings: time between valve openings (usually in minutes) and amount of time the valve stays open (usually in seconds). The drain comes with an electrical cord that can be plugged into a wall outlet. By matching these two settings to the amount of condensate a system produces the condensate can be removed from the compressed air system. The goal is to set the timer long enough to empty all of the condensate but not so long that compressed air is wasted. A combination isolation valve and strainer, if not standard, is highly recommended. This keeps objects from plugging the orifice inside the automatic drain valve, which will keep condensate from being released.
• Manual: Manual drains are valves that are opened manually to dump condensation. Some operators choose to leave the valve partially open all the time. This method will drain condensation constantly, but also wastes compressed air by allowing a continuous leak. The kW power rate will determine the energy cost of producing compressed air.

Installation and maintenance recommendations:

• Flush out the piping system to remove dirt and other foreign particles before installing valves.
• To facilitate gravity draining, install the valve and drip legs at all low points in the system and at any point where the air line drops to go around an obstruction. However, these points should not be near a heat source, as the valve may become delayed in opening.
• Install valves to ensure that water flows through the entire line, avoiding stagnant sections and dead legs.
• Install the valve so that water flows in the proper direction and is pitched down. Flow should be discharged through an air gap.
• Include strainers just ahead of the drain valves to protect against dirt. The strainers should be cleared periodically to avoid dirt accumulation.
• The most common cause of valve malfunctioning is misapplied discharge piping. The drain valve should empty directly into waste. If discharging piping into a drain, install a valve directly above the drain.
• Follow manufacturer's installation procedures that come with the valve. Some valves require vent lines, balance lines or both for proper operation.

Note: Since the condensate will contain a mixture of water and lubricating oil, be sure to drain all condensate in a manner approved by all federal, state and local regulatory agencies. Oil/water separators are available to assist in this function.

Maintenance of drain valves is really quite simple. Manual drains should be drained and checked daily, and automatic drains should be tested daily.