How to drain liquids at high pressure

Author: David Connaughton
Blog: Compressed Air The Fourth Utility

Occasionally customers have high pressure compressed air or natural gas lines that need to be filtered to remove oil and water contamination. The problem is, how do you drain out the accumulated liquids? Most automatic drains have a maximum pressure of 150 psig (10 bar), well below the pressure of the filtration vessel. Attaching a valve to the drain could create a dangerous situation. In the diagram above, draining is accomplished by utilizing two valves and a small receiver tank rated at the same pressure as the filter vessel. The receiver could even be a length of pipe as long as its volume is sufficient to hold the amount of liquid that is expected to accumulate between draining. The draining is manual. Initially, the valve closest to the filter vessel is left open to allow liquids to drain into the receiver and must be accomplished by closing the top valve near the filter vessel and opening the bottom valve slowly. It is important to open the bottom valve slowly and carefully because the receiver is at operating pressure. Naturally safety gear like goggles, etc. should be worn.