Drain valves are a crucial part of the compressed air system. There are three types of automatic drains: float operated drains, electronic sensor drains and electronic timer drains.
Float Operated Drains: 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.
Electronic 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. 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.