Draining down compressors

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Draining down compressors

This topic has 29 replies, 21 voices, and was last updated 15 December 2017 at 11:05 by Dazza.

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7 December 2017 at 19:21 #330945
peak4
Participant
@peak4
I recently bought a second hand Clark Boxer 55 50L 3 HP V twin air compressor for the new workshop/garage.

I'm aware of the need, and reason, to drain down air condensate from the pressure vessel on a daily basis; to prevent corrosion and water build-up.

The previous owner said that what he did, was to slightly crack open the drain cock on a permanent basis and just allow it to drip. I've been doing this, dripping into an ex-ready meal aluminium container with a couple of paper towels in it to prevent any splashing, though there's not much water drips out.

Any thoughts on the wisdom of continuing this practice, or am I better just fully closing the drain cock, and draining daily whenever I use it?

As it's set at the moment, without using any air myself, there is enough leakage out of the drain cock for the motor to kick in every half hour or so. I always turn off the compressor when I pack up for the night and let it de-pressurise itself.

Also, I spray a VCI emitting aerosol wax into various bits of Landrover, to help stem the internal corrosion. I was wondering about a quick spray into the 50L pressure vessel: Any thoughts on that one??
It's Corroless CCI400 wax that I use. (see the link for details.) Being a second hand compressor, it's too late to use one of the various fuel tank sealants, as there will almost certain be come corrosion in place that I wouldn't want to seal in.

Thanks

Bill

Edited By peak4 on 07/12/2017 19:22:53
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7 December 2017 at 19:21 #25685
peak4
Participant
@peak4
7 December 2017 at 19:49 #330951
David George 1
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@davidgeorge1
Hi Bill I would never leave a drain open on a compressor as you would never recover the cost of running air for no reason, it costs to produce compressed air and as long as you drain regularly at the end of every use you will not have any significant build up of condensate. I am not sure of the coating of the inside of the tank with the anti corrosion that you have as the chemicals in it dont look very healthy and may come out with the air in use.

David
7 December 2017 at 20:59 #330967
peak4
Participant
@peak4
David, I wasn't suggesting coating the inside of the tank, more just adding a bit, such that it works in the same way as the brown VCI paper that one might use to line a tool drawer.

I'm not sure if the constant air flow would remove the active VCI ingredient too quickly.

The extra cost of running the compressor would be negligible in my case, as the workshop's not in daily usage, and the drain cock's barely cracked, not wide open; I can't hear air escaping and it just drips a bit of water out.
7 December 2017 at 21:24 #330971
SillyOldDuffer
Moderator
@sillyoldduffer
Thinking aloud in total ignorance, I wouldn't be happy compressing a mixture of air and oil.

I don't suppose the mix would be hot enough to ignite in the tank but I can imagine the thing behaving like a baby flame-thrower if the output caught fire, say due to a spark. It might even flash back and explode in the tank. Fifty years ago I might have tried it for fun. Now I'm yellow!

Dave
7 December 2017 at 22:16 #330981
Clive Hartland
Participant
@clivehartland94829
The air is compressed and gets heated, later as the tank cools down it condenses the water vapour which goes to the bottom of the tank and accumulates over a period of time. Worst are long runs of pipe where you should have drain points every 30 Foot. daily draining will produce little water and I used to do a 7 day cycle where oil, draining and mechanical checks were made. Air filters come loose and rattle. I have even had the wheels come off!
7 December 2017 at 23:24 #330992
ChrisB
Participant
@chrisb35596
Posted by SillyOldDuffer on 07/12/2017 21:24:05:

Thinking aloud in total ignorance, I wouldn't be happy compressing a mixture of air and oil.

I don't suppose the mix would be hot enough to ignite in the tank but I can imagine the thing behaving like a baby flame-thrower if the output caught fire, say due to a spark. It might even flash back and explode in the tank. Fifty years ago I might have tried it for fun. Now I'm yellow!

Dave

At 7bar delivery pressure it will surely not ignite, not even with a spark….if it were an oxygen bottle…that's an other story…
7 December 2017 at 23:44 #330993
Bazyle
Participant
@bazyle
I feel that a permanent drip means there a permanent small puddle inside just enough to get over any lip where the drain is welded in. I like a big rush of air at the end of a session that will carry over any reluctant drips and the flow will dry out the valve too.

We had a small compressor at work for an equipment vibration test chamber and it was a bit noisy. So it was plumbed in outside in the space under some steps. Still noisy so it was bricked up. No they weren't so dim they didn't allow for the drain and fitted a pipe and tap coming out of the bricks. Problem was only a couple of us knew why there was a funny little tap sticking out of the wall and the rig could go for months, years even without being used. One of us retired and I move to the other end of site so they lived with it spewing water into the glass water trap for months thinking that was how it was supposed to operate.
7 December 2017 at 23:57 #330994
I.M. OUTAHERE
Participant
@i-m-outahere
Bill any corrosion that the tank will suffer from has already started so the aerosol will do nothing to it .

I wouldn't put anything in the tank especially any type of oil or wax as it could get dragged through by the air into your airline and will wreak havoc on you if you ever need to spray paint anything or use the supply for a plasma cutter.

I simply dump the air out of the draincock and the drain on my regulator then back of the regulator pressure knob to release any tension on the diaphragm after use but if you use yours daily you would leave that set as is . It isn't to hard to get into the habit of dumping the air at the end of the day and even if you miss a few days it won't hurt anything .

If the drain is hard to access you could fit one of those spring loaded blowdown valves like they use on truck air tanks and set up a pullcord to operate it , that way you don't dump all the air and only need to give the cord a tug for a few seconds on your way out of the shop at the end of the day .

Ian.
7 December 2017 at 23:58 #330995
peak4
Participant
@peak4
Posted by Bazyle on 07/12/2017 23:44:10:

I feel that a permanent drip means there a permanent small puddle inside just enough to get over any lip where the drain is welded in. I like a big rush of air at the end of a session that will carry over any reluctant drips and the flow will dry out the valve too.

Thanks Bazyle, that was exactly my own thoughts, which is why I raised the question.

I didn't mention it myself as I didn't want to prejudice anyone else' thoughts.

I'm actually in agreement with you, and was thinking about obtaining a valve to use as a drain cock, rather than the daft current arrangement which requires fiddling underneath with a spanner.

Within reason, I'm not bothered about the safety implications of compressed air and oil/wax in this case, as it's an oiled compressor, so if I gave a go at paint spraying, I'd probably need an inline filter/condenser fitting before the spray gun anyway.

Cheers

Bill
7 December 2017 at 23:58 #330996
I.M. OUTAHERE
Participant
@i-m-outahere
Bill any corrosion that the tank will suffer from has already started so the aerosol will do nothing to it .

I wouldn't put anything in the tank especially any type of oil or wax as it could get dragged through by the air into your airline and will wreak havoc on you if you ever need to spray paint anything or use the supply for a plasma cutter.

I simply dump the air out of the draincock and the drain on my regulator then back of the regulator pressure knob to release any tension on the diaphragm after use but if you use yours daily you would leave that set as is . It isn't to hard to get into the habit of dumping the air at the end of the day and even if you miss a few days it won't hurt anything .

If the drain is hard to access you could fit one of those spring loaded blowdown valves like they use on truck air tanks and set up a pullcord to operate it , that way you don't dump all the air and only need to give the cord a tug for a few seconds on your way out of the shop at the end of the day .

Ian.
8 December 2017 at 01:11 #330997
duncan webster 1
Participant
@duncanwebster1
Why not fit a solenoid operated normally open valve to the drain, then when you shut the compressor down it has to blow down.
8 December 2017 at 03:50 #331001
I.M. OUTAHERE
Participant
@i-m-outahere
Moderators please feel free to fix my double post .

I never thought of that Duncan !

Could be in idea for my bigger compressor as i rarely use this unit as i have a cheapie mounted in my mill cabinet that does the general work and if it dies I don't care !

Ian.
8 December 2017 at 10:52 #331034
Ian S C
Participant
@iansc
My compressor, a home built assembly of bits and pieces has a water trap with an automatic drain that closes at 5psi on start up. The tank is a low pressure aircraft oxygen cylinder, mounted vertically, with the input at the bottom, and the exit at the top. Its a fixed unit.

Ian S C
8 December 2017 at 11:04 #331041
Russell Eberhardt
Participant
@russelleberhardt48058
Just a thought – would an automatic cylinder drain cock as used on model locomotives work?

Russell
8 December 2017 at 11:14 #331044
Paul Lousick
Participant
@paullousick59116
An automatic cylinder drain cock on steam engines is similar to a pressure relief valve. If there is condensate/water in the cylinder, the extra pressure generated because it does not compress like steam/gas is exhausted thru the relief valve instead of blowing out the end of the steam chest,

Paul.

Edited By Paul Lousick on 08/12/2017 11:15:12
8 December 2017 at 11:15 #331046
Howard Lewis
Participant
@howardlewis46836
When I bought my compressor from the local compressor specialist, the advice was to leave the compressor with the drain valve open, when not in use.

Running with the valve just cracked open will mean that the compressor runs, if not continuously, for more than it's designed duty cycle, so it will wear out much sooner. (Again, the advice given by the same specialist, but in another context. This was after a compressor had failed; for just that reason).

Compressing any vapour, below its critical point will cause it to condense, and water vapour in the air will liquefy. Which is why the advice to drain is given. Releasing the pressure, rapidly, allows the air to expand, and will reduce the temperature, and it is likely that the condensation will freeze, so that the drain will block, until the ice thaws out.

It will be a good idea to fit, if not already present, a water trap to prevent condensate being passed down the line.

If the installation is one with a permanent air line around the shop, the take offs should point upwards, ideally, with a downward pointing drain, using a four way fitting, or a TEE at the end of the line.

Howard
8 December 2017 at 11:21 #331049
larry Phelan
Participant
@larryphelan54019
Just drain it every day no big deal.
8 December 2017 at 12:23 #331058
KWIL
Participant
@kwil
Larry, that is a good idea if you can get down to floor level easily. The older you get, the further away the floor becomes
8 December 2017 at 13:59 #331067
duncan webster 1
Participant
@duncanwebster1
Posted by Paul Lousick on 08/12/2017 11:14:19:

An automatic cylinder drain cock on steam engines is similar to a pressure relief valve. If there is condensate/water in the cylinder, the extra pressure generated because it does not compress like steam/gas is exhausted thru the relief valve instead of blowing out the end of the steam chest,

Paul.

Edited By Paul Lousick on 08/12/2017 11:15:12

No it's not, it has a loose ball on the seat which falls away if there is no pressure. It is supposed to not reseat if there is water present, but I've never understood why, and there are mixed reports of their effectiveness. In any case it's not what one needs in this instance
8 December 2017 at 14:22 #331069
Nishka
Participant
@nishka
You could always fit an auto drain like this:

Picture from Mig-Welding.co.uk – link: **LINK**

Plenty on eBay for under £20.00

Nishka (must get one for my compressor!)

Edited By Nishka on 08/12/2017 14:23:13

Edited By Nishka on 08/12/2017 14:24:01
8 December 2017 at 15:07 #331074
mechman48
Participant
@mechman48
FWIW…I have a Clarke Ranger 7, not in daily use, but when I've finished with it I always open drain valve, blow down & leave the valve open until next required.

George.
8 December 2017 at 18:24 #331096
ChrisH
Participant
@chrish
Bill, you say it's an oiled compressor, by which I take it you mean it's not an oil-free compressor but has oil in the crankcase. Therefore some oil will always get by the piston rings and into the compressed air stream; whether that coats the inside of the air bottle nicely is another issue! If you want to paint spray you will need a filter/dryer in the line anyway, get one that catches oil!

You could use an auto-drain trap tee'd off the drain line, Spirex-Sarco used to sell them I think, they have a little disc inside that the water (condensate) builds up behind and it auto lifts every now and then if you really wanted it. The simplest is to just open the drain valve at close of play each day and leave it open until you switch on again.

Chris
8 December 2017 at 23:25 #331154
Paul Lousick
Participant
@paullousick59116
Hi Duncan,

These are what I was referring to as automatic cylinder drain cocks. Shown here on a Avelling and Porter engine. They have a manual lever to open the valve and also a spring loaded vent to atmoshere. (and not suited to the compressor application).

"It is supposed to not reseat if there is water present, but I've never understood why"

The ball in your descriibed valve probably seals whether there is water present or not and is open when there is no pressure. And when open would allow any water to drain out. (this should work on the compressor)

Paul.

Edited By Paul Lousick on 08/12/2017 23:37:12
9 December 2017 at 00:46 #331162
peak4
Participant
@peak4
Posted by ChrisH on 08/12/2017 18:24:40:

Bill, you say it's an oiled compressor, by which I take it you mean it's not an oil-free compressor but has oil in the crankcase. Therefore some oil will always get by the piston rings and into the compressed air stream; whether that coats the inside of the air bottle nicely is another issue! If you want to paint spray you will need a filter/dryer in the line anyway, get one that catches oil!

Chris

Yes exactly that, a V twin with a wet sump, just like my Ducati; it seemed a double negative to say that it it's none oil-free. I appreciate that I'll need a drier/filter for spraying but I think a plasma cutter would make a bit of a mess of my nice new floor tiles.
My intention was to add a valve drain cock, rather than the current one which needs a spanner to vent the air tank.

To save needing to lie down to access the underneath of the tank to drain it, I was going to mount the dump/drain valve at the end of a longer length of copper pipe, attached to a union at the base of the tank.

Provided there is a low "swan neck" in the copper pipe, the volume and velocity of the escaping air should clear any condensate quite happily. Being a copper vent pipe, any few remaining drops shouldn't cause corrosion issues either. I also need to add a third wheel to raise one end, instead of the current lump of wood, so any condensate runs towards the drain vent, rather than away from it.

When I used to work for BT before retirement, all the underground cables were run at positive air pressure to help prevent water ingress through leaks in their outer membranes. The ECP (External Cable Pressure) racks in each exchange had a compressor which ran through a drier of some sort which occasionally vented; (normally into a milk bottle), at the base of the rack. After that, the air then went though an axial vessel containing some sort of moisture absorbent granules,via flow-meters into the cable chambers.

Thanks for all your replies

Bill
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