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  1. #16
    Join Date
    Sep 2011
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    Ballarat
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    59
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    3,041

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    Quote Originally Posted by gazza2009au View Post
    Any reason behind that SW? the pumps max psi is 160psi i was thinking along the lines it may dump the air at 125psi before its built up in the tanks
    Nope, I have just realised what "continuous run and dump" means...maybe.
    Does the compressor run constantly then the unloader disengages the (reed?) valves when up to pressure then re-engages them as it calls for air?
    Yeah, disregard my previous post. I have a petrol powered compressor that unloads the valves and drops the revs until the air pressure drops.

    An apologetic Phil

  2. #17
    Join Date
    Aug 2009
    Location
    Sydney, NSW, Australia
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    754

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    Similar what the unloader valve does is unloads the pressure at a pre-set PSI say 90PSI when it closes an 125PSI when the valve opens all the valve does is releases the excess pressure its a mechanical switch saves playing with 240v live electricity and electrical switches that turn a electric drive motor on and off, with my set up the electric motor and compressor run continuously and the unloader valve does all the controlling o the pressure also these unloader valves have adjustable PSI ranges which comes really handy

    if u watch this guys video u can hear the unloader valve at 9mins 40seconds this bloke calles it a blow of valve

    https://www.youtube.com/watch?v=fZVazbgPFUQ

  3. #18
    Join Date
    Aug 2010
    Location
    Near Bendigo, Victoria, AUS
    Age
    67
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    2,615

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    Just noticed this thread.
    If you have a squeeling compressor and the compressor speed picks up with dropping pressure (mor aur drained than the compressor can supply), then you have a slipping belt under high load/pressure. You suspected bearings - the symptom described doesn't match. Easiest way to check is to remove the belt,run the motor and listen to its bearings. Then refit the belt and listen to the compressor bearings in comparison to the motor on its own.
    A second note: you could use the two new tanks in series: that way the first tank cools the air and drops the water out, the second tank then only gets drier air and removes a little more moisture. This is the best way to set up two tanks for spray painting and pneumatic tools. I have seen commercial setups like this a few times.
    Cheers, Joe
    again completely retired - more time to contemplate projects and spend more shed time....

  4. #19
    Join Date
    Aug 2009
    Location
    Sydney, NSW, Australia
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    754

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    Jhovel i think your right i have been using the old compressor a bit lately mostly to blow sanded fibreglass off me and the boat and i think i actually have the wrong belt on it i have a normal A belt i think i may need the belt with the notches cut out on the inside of the belt so it turns around the radius of the pulleys easier and conforms better for a better grip

    i still want this home made compressor so its in the workings and it will be much easier to move in 3 pieces when i need to move house (2 tanks and the pump/motor on a frame)

    is it a must to run copper pipe from the compressor pump to the first tank?

  5. #20
    Join Date
    Sep 2005
    Location
    Bendigo
    Age
    54
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    31

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    You may run into issues with water coming down the line to the tools, this may or may not be an issue for you.
    Compressors normally feed the tank at one end and the outlet is at the other, give time for the moisture to drop out of the air. With your setup when the compressor is running the air to your line will come straight from the compression also adding that any water dropping out in your tanks will be fed straight out the line at the bottom. Your drain will only get rid of collected water but any collected water will go straight down the line to the tools when the drain is not open.
    There are also a lot of articles online that copper tube should not be used for compressed air, all to do with the seam in the tube and potential to rupture.

  6. #21
    Join Date
    Aug 2009
    Location
    Sydney, NSW, Australia
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    754

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    droog i was told to build a DIY drier i have not looked into yet the plan was to just open the bottom valve once or twice an hour of run time to let out any moisture i can run the tanks upright but than i have no way to draining them unless i disconnect and turn them upside down I'm also not exactly sure how much moisture builds up over X amount of running hours as i have only ever drained my Pilot Air tank once when i first bought it

    if my propane cylinders are galvanised on the inside if anyone knows? than i may be able to leave a bit of water in them upright for a little while each time without the steel rusting

    are there any other options or things i should look at while building this DIY compressor?

  7. #22
    Join Date
    Oct 2007
    Location
    Alexandra Vic
    Age
    63
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    455

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    Lets go back to basics on this thing.

    The reason that the original Pilot tank got water inside it is that air contains moisture (humidity). When the compressor is running, it is drawing moist air in, compressing it and feeding it the reservoir. As Droog suggested, air is normally fed to the tank at one end and drawn from the other, with a hope that at least most of the moisture will fall to the bottom of the tank. The manufacturers provide a drain at the bottom of the tank, and hope that this will be used on a daily basis to stop having water sitting in the tank on a semi permanent basis. This is bad for two reasons, it will corrode the tank, and significant standing water in the tank will increase the moisture content of the air leaving the tank to work for you. If your current tank is severely corroded, it is because it was not drained frequently when being used.

    The unloading valve operates with the pressure switch that controls the motor operation. They are normally a combined electrical/pneumatic device. The electrical side of the unit operates the motor when pressure falls below a workable value, typically 95PSI, and shuts the motor off when the pressure gets to a rated pressure, typically 120PSI or so. The pneumatic side connects from the manifold connecting the compressor to the check valve, and has a valve that opens and dumps the air in the manifold to atmosphere when the electrical side side switches off the motor. This valve automatically reseats itself once the manifold pressure drops to atmospheric pressure. The purpose of this is to allow the motor to get started without having to work against tank back pressure. The motor may fail to start, or draw significantly more starting current for much longer if the unloading valve is not operating properly. In either case, it should blow a fuse or trigger a breaker, but if these are tampered with, it will cook the motor in a very short time.

    You have a 4HP 3KW electric motor to power your yet to be assembled compressor. Single phase or three phase? Unless you intend to use it in a building with plenty of three phase outlets available, you will need a fairly expensive rewire to provide power for the motor, say a 32A outlet, with cable and breakers to suit if single phase, or maybe a complete new service if 3 phase and the premises are not so equiped. Oh, the electrical side of the unloader valve will need to be rated to handle the current as well, for single phase the break currents could be 20A+ switching the motor off and beyond 100A when starting, or around 12A and 60A respectively for 3 phase. Your average cheap as chips unloader system won't handle that for long, high current ones aren't really cheap because they are designed for industrial use with frequent high power cycling and are expected to last a long time.

    LPG cylinders are not a good choice for tanks because they generally have a single access point, so you don't get the benefit of the air cooling and moisture condensing out that you would get using a regular air receiver. Your plan to use the tanks inverted means that all moisture will stay in the air line, and feed straight to your water traps and tools, overwhelming them. You have probably seen videos about people trying to cut or weld fuel drums and having an unplanned explosion. The same issue applies with LPG tanks as well, except that it harder to purge them properly because there is only one way in and out so you cannot use flow through methods to properly purge them. Gas cylinders need to be tested every 10 years and you can't get them refilled if they are out of test. Old style ones were locally made and it was intended that most would be able to pass test at 30 years . This was intended as a safety feature when it was introduced, but now the cylinders are made in China to the lowest possible cost and are not intended to be tested, they are intended to be used for 10 years then scrapped, rather than being tested and reused if they pass.

    Copper pipes will corrode when exposed to a high moisture air flow, and are also significantly different from the materials the ferrous metals used in compressors and receivers to induce electrolytic corrosion at joints over time. This means that your compressor plumbing can corrode from the inside without notice and burst, and bursts involving compressed air are not healthy.

    Something that opens the drain occasionally (or regularly) is an auto drain, not a drier. It will reduce accumulation of moisture in the system by regularly bleeding it off, but it won't actually remove moisture from flowing air like a dryer does, and to be effective, it needs to open long enough to bleed all of the air from the system, so cannot really be used while you need the air system running, they are normally configured to dump the tank through the tank drain when the compressor is switched off at the power, and reset when power is restored.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  8. #23
    Join Date
    Aug 2009
    Location
    Sydney, NSW, Australia
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    Thanks malb i never thought about the moisture to much but what u say makes sense and i never actually thought my motor would pull those kind of amps i only have a 15A 240v outlet the motor is rated at 3000watts i thought i would have been safe

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