Air Compressor Question

  • Advertise with us

« back to Power Tools, Hardware and Accessories forum

Forum topic by Jeffjr02 posted 08-05-2015 08:39 PM 937 views 0 times favorited 6 replies Add to Favorites Watch
View Jeffjr02's profile


134 posts in 1268 days

08-05-2015 08:39 PM

Topic tags/keywords: air compressor

I recently got a nice older model Craftsman compressor. It’s a 4 hp belt driven, 20 gal model that puts out something like 7.5 CFM at 90 psi. Anyways, after looking at it a bit I realized that there is no factory installed drain on the bottom of this thing. It does have the large cast plugs on each end of the tank, but they look like they have possibly never been removed. There isn’t any water in it sloshing around, so water had to get out somehow. I have read somewhere that some better compressors have a cooling mechanism to remove condensate before it enters the tank, so I’m not sure if that’s the method used here. But I cannot for the life of me understand if/what I need to do to maintain this thing. It doesn’t have a model number anywhere that I can find, but it must be at is 30 years old. It has the original DeVilbiss factory plate with a manufacturer number and the Sears sticker with a handful of specs but nowhere is there an explicit model number. This thing looks like it’s in beautiful shape for its age, it only has some minor paint coming off the galvanized tank. I believe that I could take it to a welder and have them install a drain plate/hole so I can install a valve, but if it’s completely unnecessary I would like to keep the money and the condition of the tank. (Wire brushing and weld burns sure aren’t pretty). Anyone else have a machine like this?

6 replies so far

View Bill White's profile

Bill White

5149 posts in 4200 days

#1 posted 08-05-2015 09:36 PM

Could be done, but welding a pressure tank must be done very carefully. Ya sure don’t want that puppy blowing up on you.
Betcha that there is a line dryer somewhere in the system.


View JoeinGa's profile


7740 posts in 2247 days

#2 posted 08-05-2015 10:05 PM

I’ve seen air tanks where the drain was actually up on the side. There was a tube inside that reached to the bottom of the tank, and the valve was placed outside. When the valve is opened, the pressure forces the water up and out. Check those openings in the side, could have been there.

-- Perform A Random Act Of Kindness Today ... Pay It Forward

View Jeffjr02's profile


134 posts in 1268 days

#3 posted 08-06-2015 04:03 AM

Is it possible the pressure relief valve on top is the sole method of getting water out? He is sitting dead center on top.

View TopamaxSurvivor's profile


18425 posts in 3916 days

#4 posted 08-06-2015 04:53 AM

I have a small compressor, don’t recall the brand or hp right now, but in 25 years, I have yet to have any water to drain. Not sure why. Here on the coast of WA, there is enough humidity in the air to form condensation on anything cold setting out. We don’t have rust problems like they do in the midwest.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View timbertailor's profile


1594 posts in 1664 days

#5 posted 08-06-2015 04:33 PM

That is a lot of HP for only 20 gallon tank. Also seems rather inefficient if you are only getting 7.5 cfm @90psi.

Would probably have to go through pressure testing to make sure it is safe to use or if any modifications were made.

-- Brad, Texas,

View Jeffjr02's profile


134 posts in 1268 days

#6 posted 08-06-2015 05:02 PM

I have already used it. I’m just afraid to use it too much without knowing how to drain it. The thought of it rusting out really scares me, even though like I said there is no water in it at present. I’m not worried about the quality of this unit in it’s present state. It is in phenomenal shape for it’s age cosmetically. The tank could use some touchup painting but it’s nowhere close to needing a full repaint. It’s from 1985 and without being an expert it seems obvious to me that the tank is original. I do love this compressor though. It fills up very fast and is super quiet.

I don’t suppose that some of the potential CFM is bled off in somehow drying out the air? The maximum supplied air is around 7.5 (not sure of the exact because I don’t have a picture of the label with me), but the actual displacement is somewhere north of 11 CFM according to the label.

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics