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Thread: Pex for Air?

  1. #1
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    Default Pex for Air?

    I've been meaning to run air around my workshop for a while, but had no compressor. I was toying with trenching a pipe across from another shed and stealing air from its compressor, but that all seemed like a lot of work, and buying another compressor would be a lot simpler. Supercheap have their Stanley belt drive unit on sale at the moment, which is a nice machine for the price, so it seems like the right time to get on with it.

    Having used a bunch of Pex with push-fittings quite successfully for mains water, which here is about 800kPa, I'm thinking using 20mm Pex might be a good, quick installation.

    Anyone tried Pex + push-on fittings for air?

  2. #2
    BobL is offline Member: Blue and white apron brigade
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    We used Polymetric (Philmac style) push fit fit fittings at the mens shed as they were about 25% less than Pex type fittings.
    The 20mm blue line pressure hose was <$40 for a 50m roll.

  3. #3
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    That is a lot cheaper for pipe. Bunnings want $97 for a 50m roll of 20mm Pex. But I already have most of a roll sitting around (I've been running 32mm metric poly and using 20mm Pex for the last 1 or 2 feet to the tap).

    As for the fittings, the Bunnings push-on fittings look to be the same price or cheaper.

    As this will also be pushing air for a plasma cutter, am also considering an intercooler of some kind between the pump and tank.

  4. #4
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    Quote Originally Posted by RustyArc View Post
    Supercheap have their Stanley belt drive unit on sale at the moment, which is a nice machine for the price, so it seems like the right time to get on with it.
    G/day Rusty, this could be worth a look https://www.ebay.com.au/itm/NEW-BELT-DRIVEN-3HP-12CFM-AIR-COMPRESSOR-PORTABLE-300L-MIN-80LT-TANK/233479569407?hash=item365c777fff:g:sO4AAOSwlPFeMUor


    These comps look tempting also https://www.ebay.com.au/itm/WONDER-2...dqA6~#shpCntId dunno anything about them but the spec's look good.
    Last edited by shedhappens; 2nd Jun 2020 at 07:44 PM. Reason: another option

  5. #5
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    Quote Originally Posted by shedhappens View Post
    G/day Rusty, this could be worth a look https://www.ebay.com.au/itm/NEW-BELT...4AAOSwlPFeMUor
    Those are some very good specs for the price - have you got any experience with that unit?

    I've got one of the Stanley belt drive units already in another shed, and was impressed at the quality for the price (~$500 on sale when I bought it). But it's not a particularly big compressor. I've always liked the specs on Peerless compressors, and there was a P17 on Gumtree the other week for $800 which I probably should have gone for. My workshop has a 32A 3 phase supply, so options are endless. However, in reality, the air in the workshop will mostly be used for blowing chips into places they shouldn't be on the lathe and mill, as well as mist cooling, and plasma cutting, the latter being the only application needing any kind of flow rate.

  6. #6
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    Quote Originally Posted by RustyArc View Post
    Those are some very good specs for the price - have you got any experience with that unit?
    No experience, I have been looking at them tho as a m8 is looking to upgrade.
    Did you look at the link for oiless one?

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    Quote Originally Posted by shedhappens View Post
    No experience, I have been looking at them tho as a m8 is looking to upgrade.
    Did you look at the link for oiless one?
    Sorry, only just noticed the other ones you linked to. Previously I did go down a bit of a rabbit hole with those "silent" units - Supercheap do one, and Sydney Tools do as range where they bolt on more of them to get more air.

    As you probably know, the basis for air delivery numbers vary wildly. That Ebay unit just quotes pump displacement, which isn't the same as free air delivery. One upside to "bricks and mortar" stores, which includes Supercheap, is that they commonly quote the CAAA protocol for air delivery, which is based on the time to get from 600kPa to 800kPa scaled by the volume of the tank, i.e. a reasonably good real-world measure of the compressor's delivery around the 100psi (~700kPa) mark.

    I might try and do a bit of a trawl through the compressors on offer and get a measure of which delivers the greatest amount of air for the price and power consumption.

  8. #8
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    I have read many many times of the internob that PEX should not be used but given it appears to be rated for water at 116psi (800kpa) I cannot really see why not. There are many stories of people using it successfully so I would suggest it is the usual snobbery or ignorance coming out - gotta love the internets.

    One area that might be an 'issue' is with moisture. PEX most likely will not cool the compressed air as much as copper or black pipe and therefore the moisture might not condense out. I imagine this might be solved with having the initial section in copper especially if you ran copper up and down the wall a couple of times to provide for more copper surface area.

    I am currently switching too and fro with the copper vs PEX debate. I costed out copper and it will be significantly more. It will also not be as simple/quick to make changes. Dunno.....

  9. #9
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    From what I can tell, Pex is typically rated as PN20, i.e. a working pressure of 2,000kPa, or 290psi. A fair bit of headroom over what any little compressor I'm running is going to produce.

    I've read a fair bit so far about the potential cons of Pex for air, the main one being that while the pipe is probably more than up to the job, the fittings may not be. That argument seems kind of plausible, but then again, in water applications the fittings have to stand up to water hammer events, which I expect would be massive instantaneous pressures, so not convinced the fittings would be a problem. Also, you read of heaps of people who have used it for air with no problems.

    As for cooling, I have a roll of 20mm copper pipe that I'm thinking about fitting between the compressor's pump and its tank to act as an intercooler. Combined with regular draining of the tank, the air coming out should be pretty dry to start with.

  10. #10
    BobL is offline Member: Blue and white apron brigade
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    With Rolls of pipe the orientation becomes important as the water needs to be able to drain otherwise it will pool inside the pipe and exacerbate the problem.

    ON my system I use the finned Copper heating coils from a solar HWS.
    https://metalworkforums.com/f309/t20...sed-air/page-3

    I also have a desiccant trap (see above link) and an auto/man venting of water from the comp tank and two low points in the lines.
    Timing is current 0.5s vent every hour.
    see https://www.woodworkforums.com/f271/...-system-227856.
    Attached Images Attached Images

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    My half-thought-out plan was to come off the pump to a tee, with a foot or two of pipe going down as a water trap to a drain valve, and the other side of the tee going vertical up to the roof then back down into the tank. Downside is that makes for 2 drain valves to purge, one on the tank and one at the start of the copper loop, but given the air in Canberra is generally pretty dry, shouldn't require purging too often.

  12. #12
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    If my understanding is correct PEX pipe is higher grade material than metric poly. If that's the case then you shouldn't have a worry in the world as we used poly pipe in 63mm and 110mm sizes to plumb both air and water at much higher pressures than the home compressor runs when I worked Service Crew hard rock mining. Much higher ambient temperatures too.

  13. #13
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    i just wanted to share my experience with my compressor search, i looked through all the usual places, i found a pilot compressor , it 2m long and about 350mm diamiter. with twin cylinder pilot pump head, and three phase motor. i don,t know the spec,s. i just know ,its nice to not have to wait while its building pressure.
    it has some years on the tank , however the pump head was fairly new. i cleaned and rust converted the inside of the tank . it was $350 so was a good price imo.
    if you keep an eye out, larger capicity ones come up, imo the market for them is limited because people don,t want the big ones, not enough space, and power supply issues.

  14. #14
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    Quote Originally Posted by mick21 View Post
    if you keep an eye out, larger capicity ones come up, imo the market for them is limited because people don,t want the big ones, not enough space, and power supply issues.
    I'd been waiting for the Stanley at Supercheap to come on sale, as it does every few months, and is a good buy at that lower price. At 190LPM free air, it's fine for routine, low-demand applications. That said, if I had more air available, I wouldn't mind running a small sandblasting cabinet, and those want around 350LPM, which looks to be around a 4HP compressor, so if I can find a used 3ph unit of 4-5HP, that could be a good option.

    Hunting around, I came across this gem:
    Peerless 3 phase air compressor | eBay

    But given the sketchy paint job and complete lack of specs or model number, I'm inclined to pass.

  15. #15
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    Quote Originally Posted by RustyArc View Post

    Hunting around, I came across this gem:
    Peerless 3 phase air compressor | eBay

    But given the sketchy paint job and complete lack of specs or model number, I'm inclined to pass.
    i agree, if it was orginial paint, it might give an idea of past treatment/care, it tells a story.

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