LN solenoid valve service

3D Model About this item

This is a maintenance procedure for servicing a solenoid valve used to supply liquid nitrogen. This service is required before installing the a new valve, and also may resolve the problem when a valve sticks open or closed.

If the valve is installed on the LN cylinder (tank), first close the cylinder's manual LN valve.
Shut down and remove power from the system that controls the valve.
Unplug the coil's electrical connectors.
Familiarize yourself with the exploded view diagram at right.
Pry up and remove the "red hat" cap.
Remove the ID plate as follows:
Note: The ID plate holds the coil in place on the valve body.
- Find the notch in the green coil casting at the center of ID plate's bottom edge. The bottom edge is the one nearest the wires (toward the left in the exploded view).
- Slide a thin tool, such a small screwdriver or knife, slightly beneath the edge of the plate at the notch.
- Firmly force the coil down onto the valve body to compress the coil spring. With the spring compressed, gently pry to lift the bottom edge of ID plate so its hole goes up and over the raised area at the middle of the coil. The plate can then be shifted so the larger half of its hole clears the top of the core housing.
Lift the coil to remove it from the core housing and valve body.
Use a wrench to remove the nut from the valve body.
Note: This frees the core housing and its contents. Prevent these parts from falling.
Carefully remove the three core parts (core housing, core spring and core) from the valve body and place them in a small container for cleaning. Note: The plastic or rubber tip is a permanent part of the core. Do not attempt to remove it. If the tip is removed or broken, the core must be replaced.
Inspect the O-ring for damage and replace it if necessary (SAE AS568 size 018). A PTFE O-ring is better than rubber. Do not use any lubricant.
Thoroughly clean and rinse the core parts and valve body using only isopropyl alcohol or ethanol. Do not neglect the interiors of the core housing and core. A minute or two of sonication is ideal, but a squirt bottle is sufficient if done thoroughly.
Completely dry the cleaned parts. The fastest way to do this is with clean compressed air. However, other drying methods can be used if necessary, such as moderate warming or vacuum. The parts must be completely clean and dry before reassembly, especially the interiors of the core and core housing.
Re-assemble the valve in the reverse order of disassembly. Note that the wider end of the core spring goes into the core; the tapered end goes up into the core housing. Do not over-tighten the nut. It only needs to be snug enough to remain secure against normal use and vibration. The assembly is sealed by compressing the O-ring; once that's accomplished and the nut is secure, further tightening is harmful, not helpful.

A 3D model of the valve may be viewed here.