New Compressor trips breaker on restart fixed

by Jamie
(Langley BC canada)

The Swan tech came out today, and lengthened the discharge line a fare amount by going around the whole compressor unit, giving ample time for the motor to get up to speed before charging the longer line (more volume), sure helped! He also slowed the compressor speed down a little, and that helped lower the running amperage back down to normal, with only a miner CFM loss down from 60 cfm, to about 54 cfm.. no big deal, as at least it is up and running now!


Original problem was that the new Swan SW415 120 gallon compressor and 3 phase 15 hp motor, was tripping the breaker on our phase converter setup, that previously worked with a 15 hp compressor, bu the old one had a valve unloader the new one does not! Now it works fine!

_____________________
Glad to hear it worked out, Jamie.

B.

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New compressor unit installed tripping breaker on restart?

by Jamie
(British columbia, Canada , Langley)

We just purchased a new Swan SW415 compressor with a 120 gallon tank, pressure switch with, mechanical unloader valve, and a 15 hp 230 volt (38amps) 3 phase motor. We only have single phase power, so we have a 3 phase 575 volt 20 hp motor, with start and run capacitors, used as a rotary phase converter. We have a 100 amp fused throw switch to the phase converter, and a 70 amp breaker to the compressor motor.

The old compressor was a 1968 Gardner Denver ADS-1011 with a 80 Gallon tank,pressure switch, and separate electric solenoid, with lines plumbed from both heads, separators, and crankcase vent, as an unloader. This unit also ran on a 15 hp 230volt 3 phase motor, both the same rated rpm, on the motor, ran fine with the same phase converter setup for 15 years!

The problem is that the new compressor will not restart. The compressor starts to turn, when the tank pressure drops to 100psi, then stops, as the 70amp breaker kicks out! The mechanical unloader is plumbed to a small 1/8 NPT hole just before the check valve on the tank, is that enough?

I think that there needs to be a series of lines plumed into the top of each head, and just be fore the check valve, that are plumbed into a solenoid valve that stays open until the motor reaches full rpm, then closes, to allow pressure build up. We had Swan compressor, remove the old unit and install the new one, I right away questioned him about the solenoid valve not being there on the new one...he says it is not needed!

Swan says we need an electrician to provide more inrush power!

But it ran the old one no problem!! Please help, us as our brand new compressor is sitting here not able to restart! And no one to accept blame for it!






Bill responds...

Hey Jamie...thanks for visiting and writing in to about-air-compressors.com.

The unload process takes on a second or two, and I would think that a 1/8" NPT sized hole would do the job effectively.

You can see more about air flow through an orifice here.

You also need to consider that though the motor on the new compressor is rated similarly to the old, that doesn't mean that they require the same inrush.

Of the two options facing you, adding unloader flow capacity would be the least expensive of them. If you do that, and the compressor still blows the breaker on start up, then you will know that the Swan folks were correct, and you will have to supply more inrush current.

Make sure first that any modifications you make to the compressor doesn't void your warranty.

Good luck.

Bill

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Jan 15, 2012
Unloader valve
by: Anonymous

Most of the problems I've read concern a valve problem. Most of the compressors have the unloader valve in the tank where the compressed air line enters the tank. The valve is a check valve that has a spring and a seal in it. A lot of times you can take it apart and clean it, a slight leak will let pressure build up in the piston/cylinder and will increase the load when you try to start it. Look for dirt or chips out of the seal in the valve. Any good repair shop should be able to get a replacement valve. I've cleaned and replaced a lot of these. Rust and dirt is a problem for these valves.

Sep 28, 2009
RE: New compressor installed trips breaker
by: Jamie

Thanks for the speedy reply Bill! Do you no if you can add an unloader to the swan compressors, I don't see any of them pictured on there web site? All I see a what appear to be 1/8" npt plugs in each head, but they could be used to hold tension, on the valve assembly? Or are they some kind of port to add air into, to force the suction vales open, to act as an unloader with a 3 way solenoid valve? Thanks again -Jamie

__________________

Jamie, no I can't. Sorry. I don't know any details about that brand of compressor other than a general overview of function.

Does anyone else out there have an suggestions?

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Sears compressor unloader valve

by robert
(paramus nj)

I have a sears upright compressor from about the mid 1980's i need an unloader valve. Where can i get one? The part is no longer available from sears. And how do i adjust it?






Bill says...

Robert, good to hear from you.

Check your local listings for compressor repair shops or ask the local store where they get their compressors repaired under warranty. Go and see those folks. They should be able to fix you up with an unloader that works.

If your compressor is portable, take it with you when you go in.

As to adjusting the unloader valve, there shouldn't be any. The unloader opens when the cut out pressure is reached, and closes when the cut in pressure level starts the compressor.

Cheers,

Bill

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Unloader valve leaks air when compressor running.

by K. Lee
(S.C.)

Porter Cable 5hp., 60 gallon.

The unloader valve hisses air while the compressor builds pressure, then when cutoff pressure hits, it unloads, and the leakage stops.
I really haven't noticed this before.Is this normal?






Bill answers...

Howdy K. Lee:

In a word, no.

Your unloader valve should be closed when the compressor is running, this allowing all of the air being compressed to be sent down into the tank, and not bled out of the unloader valve.

When the compressor reaches the high pressure cut-out, the pressure switch reacts to that high pressure point, shuts off power to the motor, and then opens the unloader valve to unload the compressed air trapped over the piston.

It does this to help the compressor start more easily next time the low pressure trips the pressure switch to start the motor. If there was air trapped over the piston, the motor would have to work a lot harder to start against that load.

In your case, it sounds as though you have a seal leak of some kind in the unloader valve.

Hope this helps,

Bill

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Jun 11, 2009
Unloader valve hissing
by: Kenny Lee

I just took the unloader off the comp. and took it to the bench, disassembled, cleaned with brakeclean, reassembled even using the old gaskets. Work fine now, no hissing.

_____________________

Excellent Ken, glad to hear it.

B.

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A question about how compressor unloader valves operated.

How do unloaders work in a compressor?






Bill answers...

You can answer this question yourself, Richard.

Simply go to the site map page, scroll down to the "U's", and click on the unloader valve link.

That page will provide you much information about how unloader valves work.

If you still need some help after that, feel free to write back in.

Cheers,

Bill

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Unloader for a two stage gasoline powered compressor

by charles
(jena, Louisiana)

Is the unloader valve the same on gasoline powered and electric powered compressors? If not, what does a gas powered use instead of a unloader valve. I don't want to buy something that I can't use.






Bill answers...

Hi Charles, nice to hear from you in Louisiana.

I fess up to the fact that I don't use and don't have a lot of experience with gas powered compressors.

However, it makes sense that an unloader valve on a gas powered unit will both unload the air over the piston(s) to make an easier restart...and the unloader valve may be connected to a throttling device.

On an electric compressor (unless it's an industrial continuous run type) the unloader valve operates simultaneously with the shut off of the electric motor. Both are driven by the pressure switch, and it's the pressure switch toggling to the off position (shutting off power to the electric motor) that also flips the unloader valve and allows it to dump the air over the piston(s).

On a gas powered compressor, the motor doesn't shut off, and the unloader process may, depending on the model, shut off air intake to the compressor and slow down the motor so there's not so much fuel used when compressed air isn't needed or the tank is full.

Hope this helps,

Bill

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Continuous run unloader - how to adjust?

I am building a compressor from components and I have a new continuous run unloader from princess auto.

It is preset to cut in at 115psi and cut out at 140psi. It says it is adjustable between 100 and 250 psi. I would like to have it cut out at 175 but don't know how to adjust it, I didn't want to mess around with it without some solid advice. I asked the people at princess auto but they didn't have the answer. Any help would be appreciated, Thanks






Bill answers...kind of

Howdy, thanks for visiting and writing in.

Where did you get the continuous run unloader? If you purchased if from Princess Auto, ask them where they got it from.

Were there no manuals or instructions with the unit?

I can't give you any specific directions as I don't know the make, the model or the source.

Check the Repairs page and see if there's a compressor repair depot near you. They will be able to provide details...though it might not be at no charge. I'd take the unit to one of them.

Cheers,

Bill

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My unloader is not dumping air.

by Nat
(London Ontario Canada)

I have a webster compressor head and a typical pressure switch with a unloader built in.

I've taken the unloader mechanism on the head apart, and it seems to want air pressure pushing in which opens a valve emptying the pressure out the intake.

my question is: does the typical pressure switch unloader valve just dump air at the switch or does it send air to the head opening the other valve. I think my situation is the later.

if the typical switch just dumps air then that would explain my problem. but I just know what is common being that this is the first one I've ever worked on.

I would greatly appreciate any help

thanks

Nat






Bill answers...

Hi Nat...and howdy to folks from London Ontario. Been there a bunch of times. Nice town! What's that watering hole out near the airport again? Had some good times there, I think! Can't quite remember? :-)

While I can't speak for all compressors, the ones I'm familiar with are plumbed from the head into the tank, and then there's an air line Tee'd off the line into the tank, usually at the check valve, and that runs over to the unloader valve in the pressure switch.

While the compressor is pumping air into the tank, that air is also trying to get out the unloader valve, but it can't as the unloader valve is shut while the compressor is running.

When high pressure cut-out is reached, the motor stops, the unloader valve opens, and the air that's in the line to the tank and over the piston dumps to atmosphere through the valve in the pressure switch.

The air can't get back out of the tank because of the check valve, so that the unloader valve is open all the time the compressor is stopped doesn't create a problem, unless the check valve doesn't seal properly.

It doesn't make a whole lot of sense to me to think that there's another unloader valve at the compressor head. One does the job, and that's in the pressure switch, or near it.

Hope this helps...

Cheers,

Bill



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Unloader valve and check valve problem...solved!

Thanks very much for your information.

I have two old compressors that are having the same problem, they'll run fine, shut off properly, and then groan horribly when they try to restart.

I haven't tried it yet, but now I'm going to look at the unloader valve and the check valve. Again, thanks very much.

Mike Curtin




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Bill answers...

Mike, you are most welcome.

Bill

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Jan 02, 2011
over pressure
by: sam

hi i have a clarke ranger25 compresser..i had to rewire it.thats when it started to build up to much pressure.i unscrewed all 4 screws at the bottom of the power unit where the pressure dials are then had to put it back together ..thats when the bar dial goes over the 8 but the psi 115 is okcos i can set this psi wit the tap.can i set the bar

Jul 06, 2009
Unloader valve suggestion.
by: Mike Curtin

I'm assuming that the reason for the unloader valve is to give a gas or electric motor a chance to get up to speed before it's under load. It seems to me that if you had a motor that could make full power from a stall (like a steam motor), you wouldn't need the unloader valve.






Bill comments too...

Hi Mike;

The unloader valve for an air compressor has a bit different purpose than just that but you've got it right in principle.

I think the issue is... how do you get an electric motor to run with a fairly low amperage power source. The typical home outlet is 120 VAC and maybe 15 or 20 amps max. The typical home and small plant compressor runs on electricity, and those users don't normally have 220 VAC or greater to ensure enough power supply to the motor.

As you know, AC electric motors need a boost of power (inrush current) to get going, and that's supplied by the capacitor. However, if there's something that's bogging down the motor, it won't start, but rather, pop the breaker as it tries to draw more amperage to start against the load and the capacitor can't provide enough to get past the load. That load is air trapped over the piston.

The "unloader valve" clear that load every time the compressor stops.

Follow the link and read up on the details, if you've like.

Cheers,

Bill

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Unloader valve for gas compressor.

How do I know what kind of unloader valve I need? And do I need a throttle control for the gasoline engine?






Bill answers...

Hello, and thanks for writing in.

As I just answered another visitor to this web site, "it makes sense that an unloader valve on a gas powered unit will both unload the air over the piston(s) to make an easier restart...and the unloader valve may be connected to a throttling device.

On an electric compressor (unless it's an industrial continuous run type) the unloader valve operates simultaneously with the shut off of the electric motor. Both are driven by the pressure switch, and it's the pressure switch toggling to the off position (shutting off power to the electric motor) that also flips the unloader valve and allows it to dump the air over the piston(s).

On a gas powered compressor, the motor doesn't shut off, and the unloader process may, depending on the model, shut off air intake to the compressor and slow down the motor so there's not so much fuel used when compressed air isn't needed or the tank is full."

Hope this helps,

Bill

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