Protocols - SOPs

Method To Minimize Service Nitrogen Gas Leaks In Lab

While some labs have privileged access to building gas nitrogen, other labs have to rely on ordering nitrogen cylinders for in-lab use (for nitrogen-drying samples, etc.). In our lab, many of the nitrogen guns used for drying samples are slightly leaky, and if left open overnight for extended periods of time, a compressed nitrogen cylinder can be fully empty in a week or so (even without a major leak in the line). To minimize such leaks we have devised a simple, inexpensive, yet effective solution that involves a motion-sensing solenoid valve:

Here’s a structure of the line:

Compressed N2 tank → Regulator → AC solenoid valve → service line (to air guns).

The AC solenoid valve is wired to an AC power plug that connects to a motion sensor that is plugged into the outlet in the lab (outlet should be in visible location so that motion in lab is sensed). Within minutes of no motion in the lab, the solenoid automatically switches to the closed position, thereby saving you gas. Here’s how to set this up (NOTE: you will need a soldering machine and proper insulation!):

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To buy:

1) This (1/4″ Inch Normally Closed Pneumatic Aluminum Electric Solenoid Air Valve 110V AC, $16),
2) This (SensorPlug – Motion Activated Electrical Outlet, $17),
3) This (2-Wire Un-Grounded Power Cable, $7).
4) Two male ¼” NPT ends to connect to valve (one from regulator, and another from the service line).


1) Cut the cable near the female plug end (you will not need this plug end, toss it), and expose the two wires in preparation for soldering to the valve wires.
2) Solder the two wires to the two red wires of the solenoid valve (order does not matter), and insulate properly to avoid shorts and exposed wire!
3) Connect solenoid to compressor and nitrogen service line ends using male NPT connections (use PTFE tape to minimize leaks and tighten properly).
4) Check for leaks in closed position (solenoid is in normally closed position, so no leak should be detected. When main tank valve is turned on an off, pressure should remain same for hours.
5) If no leak, connect SensorPlug to desired outlet in lab (should be visible), and connect power plug to the SensorPlug input. You’re done.