Moisture Monitor

All air compressors compress ambient humidity and deposit it in the compressed air system. Moisture collects in the tank and then passes on to the rest of the system as we do our daily work. Pretty much everyone who owns a compressor or uses compressor airs knows this and is frustrated by it.

One of the easiest means of addressing the issue is to DRAIN THE TANK DAILY (or more often if you are using the compressor constantly) Most compressor users don't do this, even though it is plainly mentioned in the instruction book and on the YELLOW TAG that is attached to the tank.

Why is draining the tank so darn important any way?

1. As moisture accumulates in the tank the volume of the tank is reduced. As the tank volume is reduced, the compressor has to run more because there is less space to store air. Eventually, the compressor repair guy drives over and drains 100 gallons of water out of the 120 gallon tank and charges you $75 (plus travel) for the service call. Have we mentioned that the compressor running all of the time makes the electric meter spin like a top and tends to wear the compressor out faster?

2. Condensation and the other stuff that collects in the tank cause additional problems, not only in the tank but also to the tools and equipment connected to the air system. The tank can rust out from the inside, which is the number one cause air compressor tank failure.

3. Moisture in the air system eventually ends up at the tool or piece of equipment being used. Water and contamination passing through the tool at high velocity erodes the close tolerance of the tools working mechanism like a rat tail file. As the clearances increase the tool consumes more air. Now, normally when the tool is not working properly the technician corrects the situation by turning up the air pressure on the tool so that it will work, but guess what?

Just turning the pressure up from 90 PSI to 100 PSI will cause the tool to consume at least 16 percent more air, which actually compounds the problem. Oh! and by the way, this causes the compressor to run even more and put greater amounts of water in the tank.

So what can you do?

Actually use the drain valve that every manufacturer installs on the bottom of the tank and drain the air receiver daily, at least. You may have to get down on your knees and look under the tank to find it, but its there. Call your compressor company and ask them to install an AUTOMATIC TANK DRAIN. Depending on the make and model the job will cost as little as $150. Or, purchase one of the many automatic drain valves available and install it yourself. Just a couple of things to remember when you're doing the job:

  • Turn off the compressor and lock out the electrical connection.
  • Vent all compressed air from the receiver and system.
  • Remove the existing manual tank drain valve or petcock.
  • Install a tee fitting into the tank port and install a new manual drain into one leg of the tee. (This will allow you to manually drain the tank if needed.)
  • In the other leg of the tee, install a shut off valve and a strainer after the shut off valve but ahead of the automatic tank drain. (The SOV will allow you to isolate the automatic drain for future maintenance and the strainer will increase the interval between drain maintenance by protecting the drain valve seals from chunks of stuff that settles at the bottom of the tank)
  • Install the automatic tank drain and connect the control wires or pneumatic control tubing.
  • Start the compressor and check the drain for proper operation and leaks.

As my old mechanics teacher told us on the first day of class, "It's always the simplest thing that's the problem." Draining the air tank seems pretty simple wouldn't you agree?