Air compressor, VFD and unloader valve - Page 2
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  1. #26
    Join Date
    Dec 2008
    Location
    Lockhart,Tx (BBQ capitol of the world)
    Posts
    496

    Re: Air compressor, VFD and unloader valve

    You may still have issues with the settings on your VFD but getting it to unload properly is a good first step.
    There are others on here that know a heck of a lot more about VFD's than I do(which is almost nothing)!
    Keep us updated.

    One and a half to two turns of regular teflon tape should work just fine.
    Any more than two turns is just wasting tape!

  2. #27
    Join Date
    Apr 2006
    Location
    Soda springs,Id
    Posts
    4,287

    Re: Air compressor, VFD and unloader valve

    By the looks of the paint on the 2nd stage I'm thinking that unit has done some sandblasting or DA sander duty.

    Lee, I'm curious as to what the VFD cost against what a 5 HP single phase motor would.
    Mike
    Ol' Stonebreaker
    "Experience is the name everyone gives to their mistakes"

    Miller 175 mig
    Miller thunderbolt ac/dc stick
    Victor O/A setup
    Makita chop saw

  3. #28
    Join Date
    Jun 2013
    Posts
    55

    Re: Air compressor, VFD and unloader valve

    Thanks all

    I think the VFD settings should be ok, as long as I get the pistons to unload reliably. There are fancy things you can do with VFDs on a compressor, but I'm just looking to start the motor :-)

    Mike: the VFD was $50 from eBay. It's a gamble buying them, as they are usually sold "as-is", the capacitors may need reformed, and if someone has previously tried to power it up without reforming the caps, it may well be DOA. But, I've had pretty good luck with eBay VFDs.

    Side note: I do have an RPC as well, for 3ph power. It's a 5hp unit, so it would struggle to run a 5hp compressor. Upgrading to a 10hp unit is in the pipeline, but by the time I run new wiring for a bigger breaker, I'm looking at close to $1500ish. Some day, but I can't justify it right now. I'm not making money with my machines. Same story with a 5hp single phase motor - it would trip the 20amp breaker right smart.







    Sent from my SM-N920T using Tapatalk

  4. #29
    Join Date
    Jun 2013
    Posts
    55

    Re: Air compressor, VFD and unloader valve

    In other news...

    I got the existing check valve out. That thing was in there good and tight! Had to break out the propane torch to free it up.

    I pulled it apart and cleaned it. Think I found the problem. The ball is pretty chewed up, and was actually sitting down inside the spring, essentially trapped and unable to float (see the second picture)

    Good! Hopefully the replacement does the trick.

    Thanks,

    Lee

    Sent from my SM-N920T using Tapatalk

  5. #30
    Join Date
    Jan 2005
    Location
    St. Johns, Michigan
    Posts
    86

    Re: Air compressor, VFD and unloader valve

    I bought a used 1966 Kellogg decades ago for $150.00 threw new belts on it cleaned the air filter changed the oil and was good to go. Shortly after that It would start fine when there wasn't much pressure in the tank but as soon as it had built up pressure the motor would struggle to start, You guys sound like you know one Hell of a lot more than I do about air compressors, Luckily for me I called a local compressor shop and told the tech what it was doing, he set me straight on a new check valve, didn't cost much and it still runs like a top 36 years later. Hopefully your new check valve will do the trick for you too.
    Pete




    ESAB SVI300
    ESAB MIG 4 HD
    MILLER PASSPORT 180
    MILLER DYNASTY 300DX
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    C&K WF-3

  6. #31
    Join Date
    Jun 2013
    Posts
    55

    Re: Air compressor, VFD and unloader valve

    The new check valve fixed it :-) now working as intended.

    Thanks everyone for your help!

    Lee



    Sent from my SM-N920T using Tapatalk

  7. #32
    Join Date
    Jan 2005
    Location
    St. Johns, Michigan
    Posts
    86

    Re: Air compressor, VFD and unloader valve

    Awesome... Cheap fix is always a good thing..
    Pete




    ESAB SVI300
    ESAB MIG 4 HD
    MILLER PASSPORT 180
    MILLER DYNASTY 300DX
    MILLER COOLMATE 4
    MILLER 30A
    MILLER SPECTRUM 2050
    C&K WF-3

  8. #33
    Join Date
    Apr 2006
    Location
    Soda springs,Id
    Posts
    4,287

    Re: Air compressor, VFD and unloader valve

    Glad you got it working right. If you are doing something using a lot of air I'll recommend using the other unloader so the motor runs continuous else it will overheat. I learned this doing sandblasting with a Jenny compressor borrowed from my BIL. No harm done, just kicked the overheat breaker on the motor.
    Mike
    Ol' Stonebreaker
    "Experience is the name everyone gives to their mistakes"

    Miller 175 mig
    Miller thunderbolt ac/dc stick
    Victor O/A setup
    Makita chop saw

  9. #34
    Join Date
    Dec 2013
    Location
    Mount Tabor VT
    Posts
    4,677

    Re: Air compressor, VFD and unloader valve

    Quote Originally Posted by mla2ofus View Post
    Glad you got it working right. If you are doing something using a lot of air I'll recommend using the other unloader so the motor runs continuous else it will overheat. I learned this doing sandblasting with a Jenny compressor borrowed from my BIL. No harm done, just kicked the overheat breaker on the motor.
    Mike
    Years ago my father in law had a tennis court 200 feet in elevation higher than Otter Creek. There was a pump 5' above the creek to pump water to the tennis court. Pumps lasted an average of two years.
    I went to F W Webb looking for a solution. The pump guru there said "Remove the pressure switch."

    This did not compute. If the pump runs all the time, how can this extend pump motor life?

    He explained that starting is where heat is generated, and load is about moving water. Once pressure rises to a point where water isn't actually moving, the impeller free wheels, only overcoming friction of the water.

    As it neither starts, or moves large volume, it generates little heat in the motor.

    An air compressor is positive displacement, so it won't free wheel, but it will make less heat if it doesn't stop, and start.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

  10. #35
    Join Date
    Mar 2018
    Location
    New Zealand
    Posts
    108

    Re: Air compressor, VFD and unloader valve

    Quote Originally Posted by Willie B View Post
    Years ago my father in law had a tennis court 200 feet in elevation higher than Otter Creek. There was a pump 5' above the creek to pump water to the tennis court. Pumps lasted an average of two years.
    I went to F W Webb looking for a solution. The pump guru there said "Remove the pressure switch."

    This did not compute. If the pump runs all the time, how can this extend pump motor life?

    He explained that starting is where heat is generated, and load is about moving water. Once pressure rises to a point where water isn't actually moving, the impeller free wheels, only overcoming friction of the water.

    As it neither starts, or moves large volume, it generates little heat in the motor.

    An air compressor is positive displacement, so it won't free wheel, but it will make less heat if it doesn't stop, and start.
    the catch is there can be other consequences. eg the impeller on the water pump cavitates and gets eaten away.
    so you do need to be careful with what tricks you use.
    i'm inclined to fix the issue. if pump was cooking its motor then its probably running an undersized motor that struggled on the restart.

    an air compressor still has load on a motor even when unloaded, so its still producing heat (and still using power $$) plus your often increasing the compressor usage hours a fair bit (compressor wear).

    as the compressor has a VFD you can use a pressure sensor and program the VFD to slow down a bit so its output is less and is closer match to what you use.
    the other way is to simply increase storage. that extends the off time and increases cooling time.
    you can also have electric fans so its being fan cooled even when its not running.

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