Bleeding Compressor

I have a small (25L) workshop compressor. After pumping up a tyre I bled the tank and noticed that the water bleed valve is located at the 5 o-clock position (viewed from the rear).

I tilted the compressor to bring the valve to the 6 o-clock position and noticed some extra water being drained from the tank.

This caused me to ponder why would the valve be located where it is (5 o-clock) and what are the dangers of leaving water in the tank?

* Danny M *

I too have use of a small compressor and am the only person that bothers to bleed it, the bleed valve is at 6 o'clock but is so near the floor that I have to tip the machine over to get to it and then tip it back to normal. The valve set to one side may save you tipping it over?

Clive

Mine is the same as yours Dannyand has to be tilted to get the last bit out. Maybe it would be hard to see if right at teh bottom and get forgotten?

Funnily enough I took it upon myself to drain my hydravane thats in a garage today

A small amount of water shot out but then a small amount of air in spite of the tank being full ( 130 psi)

what stops all the air rushing out? its a 10mm bore valve...whats inside the tank around the drain

Why I asked the question is that I am concerned that with the valve at 5 o-clock a small amount of water is left in the tank after draining.

I would assume/hope that the interior of the tank is suitably coated to resist the effect of any stored water, as when pressurised to 150 psi one would not want to be around if a rust spot developed inside the tank.

These things are sold and approved as 'fit for purpose', mine is about 15 years old and drained after every use but only on the last use did I think to tilt it to see if there was any residual water.

I noticed that boilers, bottled gas tanks and diving tanks have a strict testing regime but compressors seem to be exempt.

* Danny M *

Ian,

There is nothing to stop air coming out unless you have an auto drain valve fitted which I doubt as you say you drained it, most likely a piece of crud or congealed oil.

Danny I doubt they are coated inside, they will be bare metal normally.

Martin P

Compressors are not exempt if you are in business, cranes and compressors have to be inspected every year of your insurance is null and void.

I fully support what John says, our dehydrator tanks and bottles had to be tested every year, pressure?, 2 PSI !

Frank

Quite so. PSSR for administration and PUWER for maintenance.

However it is not compressors per se but receivers and piping. With hydraulics it is accumulators only.

Just a guess but could there be a bent pipe inside the bleed valve that reaches the bottom.

Roy

"I tilted the compressor to bring the valve to the 6 o-clock position and noticed some extra water being drained from the tank."

Kind of suggests that there is no tube

My compressor tank rusted through because I left it in the shed, even after draining it. It's only a small Shhh silent model mostly used for air brushing. Clarke want £85 +VAT +P&P for a new one. I did find a supplier of stainless receiver tanks a while back (about double the capacity and half the cost) and thought about adapting the compressor unit to fit. But I'd rather be safe and not attempt something potentially dangerous.

Ed.

I have a small JCB compressor and the drain valve is similarly positioned slightly above the lowest point. This afternoon I was using the compressor to blow out some debris from some tapped holes and was alarmed to find some water drops coming out of the blower gun. Is this normal, it is the first time I have noticed it, and can anything be done to prevent it?

I then checked the drain valve and tilted the compressor and some rusty water dribbled out. The water that came out of the blower gun was not rusty.

Doug

Not only is it normal, it is unavoidable. Increased pressure forces some of the water vapour back into liquid form. More forms in a receiver when the air cools to ambient temperature.

A separator helps but then dryers are used. Drying is expensive and not practical for home use.

Perhaps the tank was originally designed to be vertical.

At work about 20 years ago we had a seldom used test faciity that needed a small compressor. It was bricked up underneath an outside staircase that had obviously seemed a good way to mask the noise. One day the seperator in the lab that we were used to emptiying filled right up suddenly. The old technician showed me the tap on the drain extension he had had the forethought to install. After he died and I left I wonder if they used it again and what they did. (factory now houses of course)

Doug,

If there is moisture in the surrounding air, it will condense in the compressed air lines and drip out the end of the gun. ( the air cools as it expands, like in a refrigerator). I use a moisture separator, attached to the compressor outlet to trap moisture. Important if you are spraying paint.. If high air humidity, I add a second separator to the end of the air hose before it goes into the spray gun.

Paul.

When I bought my compressor, the advice given was to always drain after use, and to leave the drain valve open.

Despite this, when the compressor is moved, some water drains out. Draining with a full tank, usually results in a moisture cloud, followed by a stoppage. Eventually the ice melts (The air expands and cools and takes heat from it surroundings, reducing the temperature below freezing point - hence the ice) In the days when I worked for a large bus company, the large twin cylinder compressor in our depot would do the same when drained each week. It took so long to melt that we used to open the drain as we went for a cup of tea, so that it could drain/ice up/melt and continue draining while we took a break.

Howard

My home built compressor is mounted on the floor, with the receiver mounted vertically above it, between the compressor and tank is a self draining water trap, at zero pressure this is open, and after start up it closes at about 10 psi after blowing any water out, I have a little tin under the vent, it's got a little bit of oil in it, possably floating on a few drops of water.

Ian S C

Here is a simple automatic drain valve that can directly replace the standard item:

http://s1149.photobucket.com/user/steamdave/media/drainvalve.jpg.html

 I've got a drawing in pdf format, but not sure how to put it on here.

Dave
The Emerald Isle

Edited By steamdave on 21/05/2015 11:09:34

Edited By steamdave on 21/05/2015 11:16:36

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Dave,

You will need to convert it to jpg

We mere mortals are not allowed to post pdf

... If it's not easy for you to convert, I can do it for you.

MichaelG.