Compressor systems in freezing temperatures

[sealark]

When finished charging just get in the habit of leaving the drain valves open.

 

[cool_hardware52]

When finished charging just get in the habit of leaving the drain valves open.

Thats good practice, but not always possible or completely effective. My compressor has an auto drain system that drains three points, two at the end of interstage coolers and a 3rd after the main after cooler, just ahead of the filter stack. This system uses interstage pressure to hold normally open pneumatic solenoids closed. That means if the pump isn't running the drains will be open. So good so far.

However these drain points have tiny orifices, otherwise total pressure loss would occur when the drains opened, including the interstage pressure that is used to close the solenoids.

Moisture will continue to condense in the after coolers and slowly accumulate in the drain sumps after the pump is shut off, and it takes almost nothing to foul the tiny orifices. In addition the act of draining a high pressure sump through a tiny orifice generates a *lot* of cooling by expansion, often enough to freeze the orifice.

My compressor lives in So Cal. A cold day here is ~40 degrees F and more typically it's 60-100F I still had to add a heaters to the drain sumps to keep them from freezing during draining. I machined new valve / orifice blocks out of aluminum blocks and added cartridge heaters and thermostats, and then insulated the blocks. Works like a charm. With out the heaters the drains freeze even on a summer day.

The good news is on a cold winter day the air will typically be quite dry, but you could still freeze the drains. With manual drains I'd be tempted to increase the bore diameter of whatever is the controlling orifice.

Tobin