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View Full Version : To drain or not to drain.



Mike Burch
01-14-2010, 12:05 AM
I use my compressor only about once a month, and I have been in the habit of draining the air out of it when I've finished, on the grounds that leaving the tank in the least stressed condition would be best for it.
It recently occured to me, though, that cycling the tank through compression/decompression each time I use it might actually be worse for it than simply leaving it under pressure all the time.
On the third hand (eh?) it might not make a blind bit of difference.
Is there a general consensus of opinion about this?

Paul_NJ
01-14-2010, 12:11 AM
I use my compressor only about once a month, and I have been in the habit of draining the air out of it when I've finished, on the grounds that leaving the tank in the least stressed condition would be best for it.
It recently occured to me, though, that cycling the tank through compression/decompression each time I use it might actually be worse for it than simply leaving it under pressure all the time.
On the third hand (eh?) it might not make a blind bit of difference.
Is there a general consensus of opinion about this?

I think it's door number 4. I crack the drain valve long enough till it stops blowing water, and then shut it again. You don't have to blow it all the way down. That's how the auto drain valves work.

Ken_Shea
01-14-2010, 12:24 AM
I'm with Paul, with the exception I usually let is set for an hour or so and re open the valve till I see nothing, almost always some comes out at that time.

That said, this is often never done at any regular intervals and even unnecessary over evacuating is better then not at all.

bobw53
01-14-2010, 12:39 AM
When I was younger and still living back home and using the old mans compressor. I always cracked it and left it open. Cheapie roll around 20
gallon. He always claimed it was so that air could circulate freely and it
had less of a chance of rusting. Any pooled water would evaporate instead of sit in the tank.

It must work, 25 years on that cheap POS compressor. Sometimes that thing would sit for 6 months.

gnm109
01-14-2010, 01:08 AM
I blow my 80 gallon compressor down about once a month. I shut the breaker off and then open the drain valve until there is no water coming out.

I'm not as cocerned about the expansion and contraction on the tank as I am the extra electricity and the wear and tear on the compressor and motor if I were to do it every day. Once a month is plenty. I don't have time for a daily cleanout. It doesn't have much water in it on a monthly basis so wouldn't be worthwhile to do it more frequently. .

Ed ke6bnl
01-14-2010, 03:46 AM
I have an automatic drain goes off every 45min and for about 8 secounds. My guess is that total draining air is a waist of time and electricty to refill. My quess is that the fill up procedure will introduce a whole lot of moist air into the tank ED

Richard-TX
01-14-2010, 05:14 AM
I open the drain on my tank for about 5 seconds every other day whether I use the compressor or not. I always get water.

rockrat
01-14-2010, 08:32 AM
I have an automatic drain goes off every 45min and for about 8 secounds. My guess is that total draining air is a waist of time and electricty to refill. My quess is that the fill up procedure will introduce a whole lot of moist air into the tank ED

Do you know the maker of that valve? I have been looking around town for something similar to that but all I find are the low pressure actuated types.

rock~

Boucher
01-14-2010, 08:55 AM
The best Auto drain system that I have seen was on a big truck that I had. It had a regulator looking thing mounted on one tank that ejected a small squirt of air/water each time the compressor cycled. It did a great job of keeping the moisture down in the air brake system. I have been thinking about going by the junk yard to see if I might find one.

Those old truck air tanks make an good moisture trap when mounted vertically with the incoming air located on the side, the outlet on the top, and drain on the bottom.

Draining an air compressor down is a waste of time. I turn the breaker off on mine if I am going to be gone for a week or two.

SpyGuy
01-14-2010, 10:02 AM
The best Auto drain system that I have seen was on a big truck that I had. It had a regulator looking thing mounted on one tank that ejected a small squirt of air/water each time the compressor cycled.

Harbor Freight sells an Automatic Compressor Drain (http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=46960) that works exactly as you described... and for just $10!

The only downside to these types of automatic drains is if the compressor is used infrequently. In that case, it won't automatically drain the water that condenses after the last use cycle (and that's when the most water will condense out in the tank as the compressed air will have time to reach ambient temperature). Of course, there is a bypass valve so you can still manually drain the tank to flush out that water after the tank has had time to cool. Evacuating the water that condenses during the compressor's downtime is the primary advantage of the timer-based automatic drains. But those units are considerably more expensive.

lazlo
01-14-2010, 10:08 AM
I think it's door number 4. I crack the drain valve long enough till it stops blowing water, and then shut it again. You don't have to blow it all the way down. That's how the auto drain valves work.

I do the same as Paul and Ken -- I crack the valve long enough for it to stop blowing water when I finish-up in the shop, and leave it under pressure 24/7.


The best Auto drain system that I have seen was on a big truck that I had. It had a regulator looking thing mounted on one tank that ejected a small squirt of air/water each time the compressor cycled.

Those are unloader drains. They're triggered when the pressure unloader valve cycles, when the compressor tops-off the tanks. I have one on my Champion, and I installed the Harbor Freight version on my Ingersoll Rand before that -- they work really well. Note that the Harbor Freight version requires you to cut/splice the hard copper plumbing on the compressor's unloader circuit -- it's not a bolt-on kit.

pcarpenter
01-14-2010, 10:24 AM
Here is what has worked for me:

Based on a tip I saw years ago in Hot Rod or some other car magazine, I went to a truck parts supply place and bought a truck air tank bleeder valve. It's a spring loaded dealy with a cable attached to a center shaft. You just pull the thing sideways and it bleeds, but returns to closed when you let go. I have an 80 gallon vertical tank and bending down means that it would not get drained as often as it should. With this cable attached, I just give it a tug on a regular basis and it keeps water from ever building up much in the first place. I figure it's better to let the water out almost as fast as it condenses if possible so I make this part of the routine in the shop. I had one of the HF auto-drain thingies, but did not have clearance for it at the bottom of the tank, under the plinth it sits on.

The other thing I did was to get a normally open relay sized large enough to handle the full load of the 5HP motor on my compressor. It has 120V holding coils and my light circuit was tapped to feed the holding coil. When the lights go off, the compressor will not run.....there goes the problem of putting a bunch of wear and tear on the compressor. I am sure it would be an issue in my case too. I have left the ball valve shutoff open a time or two and in each case, when I turned on the shop lights, the compressor fired off. I have a pipe leak somewhere. Small enough I can't hear it but big enough to let the compressor drain down slowly. I have cast iron lines that run up and across the ceiling to an automatic hose reel and the leak is there somewhere. Even if this were not an issue, a hose burst could put a lifetime of wear on that compressor in a day or less if you weren't around.

Paul

Carld
01-14-2010, 10:39 AM
I have an American Kellog air compressor that was made in 1956 and as far as I can determine it has had pressure in the tank for all those years except for the few times it was moved or for sale. It was not out of use very much at all as far as I can find out.

It's a vertical tank and I drain it often, service it and that's all.

thistle
01-14-2010, 11:38 AM
some bright sparks at work were complaining that thevertical tank air compressor was cycling way too much and was probably needing replaced, yes it was almost full of water, drained it and all was good.

on my compressor which only gets intermittant use i leave the drain slightly cracked so it slowly leaks, dont get any water in it that way

Mike Burch
01-14-2010, 05:08 PM
Gentlemen, many thanks for all the useful replies.
My compressor is a Chinese-made portable, a nominal 15cfm (a figure which it might possibly achieve if I get around to fitting a decent air-cleaner that will let the two cylinders breath properly), with a horizontal 13 US gallon tank.
I think that from now on I will drain off the condensation when I finish using the thing, but otherwise leave it full.
Thanks again,
Mike.

SpyGuy
01-14-2010, 05:27 PM
on my compressor which only gets intermittant use i leave the drain slightly cracked so it slowly leaks, dont get any water in it that way
Wow, that's an expensive way to drain a little bit of water, especially for a compressor that's used intermittently. Not only does it waste a LOT of electricity, but it also puts a lot of unnecessary wear-and-tear on the pump and motor.

If it's too hard to drain manually, why not get an auto-drain?

SpyGuy
01-14-2010, 05:34 PM
For those who don't like crawling on the floor to get to the manual drain under the tank (or for the gentleman who had no room under his tank for an auto-drain), there is a better way....

Just run some tubing or pipe from the bung (the threaded drain port that's welded to the tank) to a remote location that has more clearance and is more accessible. I prefer to use copper tubing, but there are many ways to skin this cat.

dp
01-14-2010, 06:10 PM
I installed one of the HF auto-drains and now I don't have to drain it down - that valve leaks so bad it's drained down daily. Prior I would drain it to blow out the water. I have a shut-off valve at the tank that I leave off when not in use so if an airhose end pops off for any reason the hose won't beat my shop contents to a pulp.

Prototyper
01-14-2010, 06:17 PM
I have an automatic drain goes off every 45min and for about 8 secounds. My guess is that total draining air is a waist of time and electricty to refill. My quess is that the fill up procedure will introduce a whole lot of moist air into the tank ED
Wow! That is an awful lot of air being expelled with a tiny bit of condensate. Unless you are using air continuously, that seems a bit excessive. At work, we have 4 compressors, 2 of which are 350 HP Quincy screws, with a 5000 gallon receiver. On that setup, we are draining at frequent intervals, but then again, we are producing >3500 CFM.

In my home shop, I have a 5HP Quincy recip. with an 80 gallon receiver. I leave it pressurized continuously, except when I go out of town. I do have a solenoid valve that cuts off air supply to my copper piping network, hose reel, hoses, etc. I turn this off whenever I am done in the shop. Gives me peace of mind knowing that a hose won't fail and run the compressor to death while I'm at work.

I use a fair amount of air every evening, usually cycling the compressor a few times each day. I have a timed motorized ball valve type drain like this (http://cgi.ebay.com/DynaQuip-Automatic-Drain-Valve-for-Air-Compressors_W0QQitemZ190362529267QQcmdZViewItemQQp tZBI_Air_Compressors?hash=item2c527dadf3) on the receiver, that dumps into a bucket. I have it set to drain once every 24 hours. It works great, and the water is always pretty much clear, with no rust or oil to speak of in it. Not bad for a compressor and receiver that dates back to the mid 70's!

Jon

Boucher
01-15-2010, 02:48 PM
I do the same as Paul and Ken -- I crack the valve long enough for it to stop blowing water when I finish-up in the shop, and leave it under pressure 24/7.



Those are unloader drains. They're triggered when the pressure unloader valve cycles, when the compressor tops-off the tanks. I have one on my Champion, and I installed the Harbor Freight version on my Ingersoll Rand before that -- they work really well. Note that the Harbor Freight version requires you to cut/splice the hard copper plumbing on the compressor's unloader circuit -- it's not a bolt-on kit.

Robert: The ones on the trucks are not connected to anything other than the air line in and the tank on the out. The truck regulators just hold the compressor valves open as the compressor is turning continuously when the engine is running.

Regarding the big volume compressors I ran 600 to 900 scfm 250 psi compresors on the air drilling rig and I just cracked the receiver tank valve and just let it dribble water. You would be amazed at how many dumb asses there are that would walk around the Rig and close that valve. In an 8 hr run that tank would catch 5-10 gallons of water on a humid day.

Ed ke6bnl
01-15-2010, 04:19 PM
My compressor at home is now hooked up to my garage lights through a
contactor that will turn off the compressor when the garage light are turned off and when no one is working in the garage. I have caught the compressor running with the pop off blowing air and one other time with a air lone blew. so this makes me feel safer. ED

lazlo
01-15-2010, 04:26 PM
Robert: The ones on the trucks are not connected to anything other than the air line in and the tank on the out. The truck regulators just hold the compressor valves open as the compressor is turning continuously when the engine is running.

Well, that's one way to do it! :)

Here's a picture of a guy who installed the Harbor Freight "auto-drain" (which is triggered by the compressor's unloader): the tee and the black plastic tubing come with the kit. I threw-away the cheap black vinyl tubing and used 1/4" copper ice machine tubing:

http://www.paragoncode.com/shop/compressor/reinstall_line_b.jpg

This is on the smaller sized compressors where the unloader valve is built into the pressure switch. On my Ingersoll Rand, and most pro-sumer and industrial compressors, the unloader is built into the head plumbing, and you have to splice the hard pipe. It wasn't fun.

Mine never leaked, but when I sold the IR recently when I upgraded to a Champion, MikeyD slid it across the floor and it sheared the right-angle tap off the bottom :) It was an easy fix, but the HF unloader valve is about the size of a peach (say, somewhat smaller than a racquetball).