Oil in air tanks

Oil is lighter than water and will displace the oil on the bottom of the tank as it cools and condenses back into liquid. Over time, this will rust out the bottom of the tank. Take it from me, I work with oil storage tanks all the time from Kero to #6 oil and none of them are immuned to rust. #6 oil tanks are perhaps the best protected since the oil is so thick but I have seen these rust out and fail as well.

I'm not picking bones with anyone over this, just reinforcing my point that draining the tank often is best. I failed to mention in my first post that you can get auto drain devices, commonly called "spitter valves" that attach directly to the tank drain fitting. Some are electric powered running off 120 Vac and can be set to cycle the valve for X seconds every X minutes. Another type gets connected to the unloader (usually only found on larger commercial compressors) so that when the unloader opens, a pulse of air causes the valve to open for a short time or "spit". Others are float type that when water/oil is collected, the float opens the valave and expells the fluids and closes when empty. Personally, I drain my tanks and lines at the start and end of each day but for my customers who I know are not going to do this, I install the auto drains on all the tanks and drop loops in the system. I most favor the float type auto drains for economy and ease of installation. There are a number of good auto drain devices available, depending on type, size and quality for $30 and up.

Something else I failed to include is for those of you with down stream storage tanks (those separate from the main compressor tank) I install a spinner type separator prior to the tank and a check valve between the tank and separtor. The separator will catch a good portion of the water before it can enter the tank and the check valve prevents and trapped water from being carried back into the line with the back flow of air (all storage devices require a pressure safety relief). Good quality separators have NPT threaded drain connections that allow for easy and quick installation of an auto drain on them and some are available with an auto drain built into them. A spinner separator with auto drain will run you around $45 and up depending on type and size.

One more thing and I'll shut up. For those of you who live in areas with high humidity, adding an aftercooler between the compressor output and receiver tank is a good idea. Once again, these come in all shapes, types and sizes from radiant air cooled with no moving parts to refrigerant cooled for lots of bucks. Most common ones I install are forced air cooled. These have a fan that blows air across the radiator core and works the same as the rad in your car. Some come with condensate collectors and auto drains and some don't. Decent ones start around $300 but are well worth it to save your system equipment and tools if you have a lot of moisture problems.

Sorry for not putting this in the first post.

One thing I do with new systems is serious overkill because it never fails that six months or a year later, the customer wants more air or more attachments. I did a garage, new system to supply a one man paint booth and three mechs. I talked the customer into buying a twin 15 hp quincy with only one motor and pump so the second one could be easily added "when" needed. He gave me a lot of grief over the cost especially when I spec'ed 2" pipe for the main loop and lots of 2" tee's and valves through the shop on the main. About 2 months after installing it, he wanted to add another lift, very pleased when I was able to connect it up without shutting down the system or taking a lot of time to do it. About 14 moths later, we added the second pump and motor, to supply the new addition of the garage, 10 new mechs, two more paint booths and a moderate size sand blast booth. Never shut the system down doing any of these additions so he did not loose a minute of work time. The additional up front cost became a real money and time saver in the long run.