Tools, Sharpening and Power Machinery - Air compressor tank draining and rust

I recently got my first compressor (Craftsman 19541, horizontal tank). I want it to last a good long time, and I especially don't want the tank to explode. I drain it after each use but it seems to me that It's probably impossible to get every last bit of water out of it. How dry does it have to be to keep it from rusting?

Here are two things I've observed, and I'd like to hear your thoughts on them:

1. Once after using it I drained it completely (or so I thought, see #2 below) and then closed the drain valve. About a week later I opened the valve and was surprised that some air came out. Could this just be because the tank was colder when I closed the valve after draining than it was when I reopened it a week later? I then moved the compressor with the valve open and some water came out. The water was brownish but after the water dried it left an oily residue so I'm hoping that the brown color was either from compressor oil or some kind of oily anti-corrosion coating on the inside of the tank (is there such a thing?) rather than rust. Could any significant damage have occurred from having a little pressure and water in the tank for a week or so?

2. Sometimes when the compressor is draining, the air flow slows down to almost nothing, then there's a popping sound and the air flow speeds up again. This process can repeat several times. The only explanation I can think of is that when air is flowing quickly the valve gets cold enough for the water going through the valve to freeze, then when the flow slows down the ice melts and the valve clears. Does this make sense? Is this a normal thing that all compressors do?

Thanks!

First, the popping sound you hear is sediment being forced through the small hole in the drain plug. Place your hand under it and it will sting you quite nicely. But it is normal. At least you are getting rid of it. What I do is close the valve when the pressure is reduced and open it back up. It will dislodge the solid particles and blow them on out as it should. Above all, drain it daily. The rust colored water, as far as I can tell, is normal, as all my compressors have done it from day one. I also leave the drain open when storing it so any residual water can find its way out should it get lost in the tank ;). Fluctuations in temperature can cause pressure to build or reduce and it is, also, normal.

You can't completely stop rust in a tank. They are actually considered to be "wet" tanks. Just drain it like chandler said and it'll last forever. My small compressor's drain is always open when not in use. The big one only gets partially drained about once a week, because blowing down a big tank is a chore and a half. And it's 35 years old.

Not sure where I found them, but there exists a purge valve you can install on your drain that is also hooked to a live line, such as the pitot tube to the switch. When the compressor turns off, about 3 seconds later this valve spits out accumulated water at the valve. Granted, it may not get it all if there is alot, but it does a "per cycle" purging. I have very little water in my large compressor since I installed it.

I have a 2hp 8 gallon central pneumatic compressor.
I drain it from the lever valve on top as well as the plug at bottom. I haven't gotten any water out of the bottom valve as of yet but notice some rust where the connector snaps onto the hose.

Someone mentioned to me that rustoleum sells an oil that you can pour into the tank then pressurized the tank then release the air and it helps to reduce rust in the tank.

Does anyone know of this product or anything similar?

Welcome to the forums macbqe!

You should always drain the tank from the bottom. That allows the air pressure in the tank to force any water out the bottom.

Someone mentioned to me that rustoleum sells an oil that you can pour into the tank then pressurized the tank then release the air and it helps to reduce rust in the tank.

Does anyone know of this product or anything similar?

If you pump is oil lubed, you'll have oil in the tank anyway :) Adding more oil to the tank will only contribute to gumming up your lines, filters and tools. Don't lose any sleep over a little tank rust, they are designed to take it.

And if you have excessive oil in your tank you can forget painting with it, unless you install a post filter.