industrial instrumentation basics

Auto Drain Valves: How They Work and How to Get the Timing Right Anywhere compressed air is present in a plant — receivers, filters, dryers, FRL (filter-regulator-lubricator) units — condensate is quietly forming inside. Auto drain valves are the unglamorous devices tasked with clearing that water out before it causes real trouble: rusted piping, water hammer, contaminated instrument air, or a downstream solenoid valve that sticks because of grime carried in the water.   What's Inside One Open one up and the internals are straightforward: a solenoid valve — usually two-way and normally closed — sits on the drain port, controlled by a small timer circuit board. That board typically offers two adjustable settings, ON time and Interval time, and often a manual test button. ON time is how long the valve stays open during a drain cycle, generally somewhere between 0.5 and 10 seconds. Interval time is the wait period between drain cycles, ranging anywhere from 30 seconds to 45 minutes ...