Freezing air tools

[SORNagain]

Hi Folks,

I tend to do little fabrication in the summer for fear of disturbing my neighbours, who live in fairly close proximity. In the winter though, with their windows shut, I think it's fair game. Trouble is, as the weather gets colder so do my air tools, to the extent that they freeze up and nearly give me frost bite!

Obviously wearing gloves is not a problem, but the tool freezing up is. I get ice forming in the control valve which gradually impedes the flow of air until the tool is un-usable. Last winter I got better performance by not wearing gloves - the heat of my hand helped to keep it thawed out. Pretty uncomfortable way to work though.

So I can either eliminate the moisture or heat the air in some way. I drain the reservoir regularly and have a moisture trap as part of the regulator, but the problem persists.

I am guessing this must be a fairly common problem. Any ideas? I am thinking of a fan heater on the air reservoir or some kind of inline heater post regulator....? Almost any suggestions welcome

[dirtyninety]

My airtools freeze up all year round, even on hot days.

i think a fan heater post regulator should help with the problem, on the outlet to the air tank, but becareful as you dont want it to warm, or it will raise the pressure and potentially could pop your tank!

as pressurized gas is released (expands) it absorbs energy (heat) thus freezing water molecules if there is not enough energy to keep it above freezing point.

[simonr]

What about making a coil of copper 'micro bore' tube (it comes in 8mm & 10mm outside diameter from plumbing merchants) and getting a tea urn (I bought one for about £20 on eBay) - then dangle the tube in boiling water and connect in line with the air line.

Added to that - you will have a ready supply of hot water for warming mid-job tea!

Si

P.S. My tools do not freeze up because I have a condenser and a decent water trap. The tools only care about getting cold if there is water vapor in the air to freeze!

[SORNagain]

Thanks guys, love the tea urn Idea!

I think that part of the problem might be that during continuous use the air receiver becomes very hot (its only a 50ltr tank so not much surface area). This might allow the air inside to get quite humid, carrying the moisture through instead of letting it condense out at the bottom. Maybe I ought to be cooling it not heating it!

I am guessing a condenser isn't a cheap bit of kit? Also my water trap is a Clarke special, so maybe I should invest in a better one....

[Jon White]

I've had this - i solved it by running a 10metre air hose up above the compressor, in a coil, and then dropping it down to a moisture trap. Then taking my outlet hose up high out of the moisture trap, before taking it off to where I was working. The first coil allows the air to cool and hence the water to re-condense before it gets to the moisture trap, as the air coming out the receiver was too hot to allow it to condense until it got to the tool.

This worked for me!

Jon

[CwazyWabbit]

That's a neat idea Jon

[SORNagain]

Another great idea, and easy to try too. Sounds exactly like the problem I have, because now I think about it it doesn't ice up to start with, only after a while. (consistent with the reservoir heating up!) Fortunately I have quick release connectors between the reservoir and the regulator so it's just a case of putting an extension hose in there to test it.

[LandyManLuke]

I have used copper pipe between the tank and the regulator, as well as between my back up compressors and the tank. This works well for allowing the water to condense out of the air.

I have built a 2m tall U that has a leg at the bottom (like a lower-case mu), hot air goes in the top of one side, cooler air comes out of the top of the other side. The leg has a purge valve on it.

[simonr]

That's pretty much how my condenser works, except it uses two oil cooler type radiators for the verticals of the U connected to a tank at the bottom and has the compressor motor drive a fan blowing on the coolers. There is a low pressure purge valve in the bottom so it stays open until the pressure reaches a certain point. The air venting through the valve purges the water too.

Mine came as part of the compressor - but it would be dead easy to make!

Si

[dirtydiesel]

I use composite tools and despite it getting down to -8 in the workshop earlier this year i didn't have any problems.

[SORNagain]

Thanks everyone, I knew I couldn't be the only one with this problem!

Sounds like ideally I need to cool the air down before it makes it into the reservoir, but that would mean changing the pipework on the compressor itself which I am not keen to do. So I will give the 10m hose a go, see if it is any different, and then possibly get some copper tubing to make a condenser.

Odd that I started this thread thinking I would have to heat something up, when in actual fact I need to cool it down! I could still heat the air after the regulator I suppose, but there is little point if I can keep the moisure content low enough.

As an aside, any one know how to work out what temperature I would need to heat to at 90psi, to ensure the exhaust stays above 0degC at 0psi? Looked at (P1V1)/T1 = (P2V2)/T2 but without knowing the volumes it's a bit tricky. PV is only constant at a constant temperature. I guess I need a coefficient of squashiness somewhere so I can work out the volumes....?

[landroversforever]

I think heating the air is going to cause more problems... If the air is cool and dry then there will be nothing to freeze!!

[SORNagain]

Think you are right.

One of my neighbours has left an old fridge freezer out for the bin men. Hoping to use the radiator on the back of it as a good condenser! :-)

[simonr]

The condenser does not need to be on the feed in to the compressor as the reservoir will condense out much of the water on it's own. It will work just as well on the outlet.

The condenser on a freezer might work, but I would worry about the bore of the pipe restricting flow too much. The flow at a given pressure is proportional to the fourth power of the diameter - so double the diameter gives 16 times the flow and vice versa.

An oil cooler is a good option - even one of the land rover gear oil coolers. They will not restrict the flow and are big enough bore that the water can easily flow out the end into a trap without being blown past it by the air.

Si

[SORNagain]

Thanks Si,

It is a bit thin...about 6mm OD. It has loops at top and bottom and I was going to cut these & parallel them up, but if the restriction is prop to d^4 then I guess this is not such a good idea. Think I will keep it simple with a bit of microbore heating pipe!

[LandyManLuke]

One of my neighbours has left an old fridge freezer out for the bin men. Hoping to use the radiator on the back of it as a good condenser! :-)

I'd be after the compressor!!

I use 2 fridge freezer compressors to fill a 300L tank. They run continously when I'm in the workshop, with a break now and again to let them cool. I've extended the run period by mounting a fan on each one.

[SORNagain]

Wow. I thought there was oil in the refrigerant so you couldn't do that. What pressure are they good for?

[LandyManLuke]

There is lubricant in the refrigerant, but they run ok without. They're easily good for 150 psi, I only run mine to 120 psi most of the time.

Whilst the output pressure is good, the flow is very low. Freezer compressors seem on average to better fridge compressors, which makes sense, but it's not much. The 300L tank means that I have the reserve to run high volume tools, as long as the compressors have been running long enough to charge the tank.

I've fitted a filter to the inlet, and watch the temperature as you can overheat them - in their usual life, duty cycle is much lower compared to how I use them, hence the fans.

They can be a pain to start, they don't like being too cold or too hot, but it's worth it for the noise-free filling they give.

[SORNagain]

Useful to know. That and a gas bottle is one very cheap compressor!

[CwazyWabbit]

There is lubricant in the refrigerant, but they run ok without. They're easily good for 150 psi, I only run mine to 120 psi most of the time.

Whilst the output pressure is good, the flow is very low. Freezer compressors seem on average to better fridge compressors, which makes sense, but it's not much. The 300L tank means that I have the reserve to run high volume tools, as long as the compressors have been running long enough to charge the tank.

I've fitted a filter to the inlet, and watch the temperature as you can overheat them - in their usual life, duty cycle is much lower compared to how I use them, hence the fans.

They can be a pain to start, they don't like being too cold or too hot, but it's worth it for the noise-free filling they give.

The people on spudfiles claim to get 300psi out of freezer compressors that must be a scary spudgun!

[Team Idris]

Yep, it sure is a funny old science. Myself and Darren at work built an aluminium-oil-cooler brazing oven which had trouble with humidity. We assumed heat (600 deg.c) would make it dry inside. But all we got was a sealed box of highly corroding air Took us a while to figure that one We're experts now

So knowing this, on installing the new big compressor I piped it into a large tank first (cooling), and then into a smaller secondary drying tank for water collecting.

For coolers, my work mate Simon swears that those intercal/oxford/mocal coolers will do 100psi ? If you've got one lying about, it would save space.

As far as I can tell on tool cooling effect, if it was a 75% efficient compressor with a 1kW motor, running continually, you'ld have roughly 750watts of of cooling in the tool. I think the air inlet would have to be so hot it would burn you. But here's the math;

watts = mass flow rate * specific heat capacity * temperature

The mass flow rate is in kg's per second, so it works for any fluid. Air is 1kg per cubic meter (and car oils about 0.7kg per litre).

The specific heat capacity for air is about 1000 per kg ( about 200 for oils and about 4200 for water)

The temperature is the difference betwen what you have and what you want.

Taking a typical screwfix unit; 120 lit/min Free Air Delivery is 0.002 kg/sec. 1.5kW motor at maybe 70% efficient. Run the math backward.....

(1500*0.7) divided by (0.002 *1000) = 525 deg.c

So definate chance of burning if my math is right? And I garantee that the above math doesn't match reality on an open ended circuit. But its kept me busy for while

Try it on somthing closed-system like power steering, or hydraulic winch and its pretty acurate

[simonr]

For coolers, my work mate Simon swears that those intercal/oxford/mocal coolers will do 100psi ? If you've got one lying about, it would save space.

I concur with that - 100psi easy, 150psi doesn't seem to cause any problems either. My cooler is just a pair of these side by side (rectangular coolers) with the inlet and outlet at the top and the bottom two ports attached to a collection tank for the water. The fan is the same diameter as the two coolers side by side so blows on both of them. It's astonishing how much water comes out of the thing.

Si

[SORNagain]

Looks like heating the air is not the answer then! Would only cure the symptom anyway, not the cause.

I have found an Eberspacher heater matrix with fan attached, which is quite compact. Its brazed copper construction, so should be ok for a few PSI. Beacuse of its size I will probably bite the bullet and install between the pump & reservoir, and bolt it onto the frame of the compressor itself. That way I can just wire the fan in parallel with the motor, since it only needs to run when the compressor is running.

Thanks for your suggestions everyone, they have been very helpful!

[integerspin]

When I put my first compressor together I had a water problem. I went to see the old boy I bought the electric motor off and he was using a setup with a 6foot high 2" steel pipe between the pump and receiver and an old

gas cylinder after the reciever, before any filtering or regulation. I copied the set up and used it for spraying,

and running air tools pretty much all the time. I never saw any signs or water after the first filter, I don't think I ever had to drain the second filter. I altered the setup and removed the pipe and cylinder a few years ago. I don't use a lot of air now and didn't think I would have any problems. The next time I was blasting I had water in the air. I added a new tank before the filters and it seems to have cured it.

I ran a large road compressor for blasting at one time and there is obviously a lot of water to get out of the air. I ended up with the air piped through roughly a metre cube of condensor which sat in a huge water tank, we had to leave a drip leg drain part open for the water to run out of. We went to a local air conditioning place and they pointed at some shelves and said it was all scrap take what you want, we had several of the largest condensors.