Check valve?

New check valve. It runs perfectly the first time.

Because at start up under load it is pulling more that your breaker can handle. If it pulls 19 amps from a dry start it will pull over 20 on restart. All compressors are harder to start with a load.
That is why folks have the same problems when using generators and extension cords. They work on a dry start but then need the load start amps and blow the breaker.
An air compressor using a genny will need a genny 3 times the wattage the compressor pulls from a dry start running watts.

I had a similar problem and the problem was the "unloader valve." It is a sort of check valve, but I don't know if it is the same one you replaced. This valve operates to relieve pressure between the tank and the motor after the motor shuts down. If it doesn't do that, when the motor tries to start next time the piston would have to overcome the pressure in the tank, which would require a very strong motor or cause the motor to work too hard, blowing the breaker. Don't know if that helps, but good luck.

It never had an underloader valve, but I put one on it thinking the same thing. No difference, I think the only answer is to beef up the breaker to a 25 or 30 amp. I understand the older it gets the more it will draw.
Thanks for the info I'll let you know when I change the breaker.
Roger

Be careful,Rog. If the wire from breaker to wall plug is too small,you could create a fire hazard going to a larger breaker.
Mike

I ran 12gauge to the outlets with a straight run to the breaker panel it should'nt be a problem. Thanks for looking out for me.
Roger

Have you tried it on different circuits? Maybe your breaker is getting a little twitchy.

What about the starter Capacitor? Also, too heavy an oil in the crankcase will put a load on the motor. I know mine struggles in the dead of winter when the oil gets thick.

I have 2 dedicated lines from the panel to the garage both 20amp and 12 gauge wire. I think all I can do is go up with the breaker.

Roger,

I hear you on just installing a "superfuse" and being done with it, but there just has to be an answer here. Worth looking into further IMHO because if this problem arose gradually, maybe it is still getting worse and will eventually overcome the new breaker.

Can you read anywhere on the compressor where it states the amperage rating? Curious how far away that is from what it is actually drawing.

What make/model compressor is it?

Presumably it worked just fine in its current location and just recently starting doing this? If it has always done this (like if you bought it used) I wonder whether the breaker is GFCI?

Is the centrifigal switch that switches from start to run windings working OK?
Mike

Are you sure you have the unloader valve installed right? Do you hear air bleeding off when it's done pumping? If it's working right it should start just as easy as with no pressure in the tank. Also check the contact points in the switch Mike mentioned, they can get dirty and not make good contact when shaking a little. Had a old sears compressor that did that, clean the contacts off and it would work good again. Steve

Well guys, the start switch is new that was the first thing I changed and it worked fine for a while.Then I put an underloader valve on beceause it didn't have one that works fine. It's a WB Brown model. The shop said that the capacitor is ok.I will check the amp rating tonight. I checked the breaker last night and it is a regular 20 amp. And the wire is 12/2. The bleeder blows off correctly and the switch is clean.It runs fine on an empty tank the first time thats it. Still scratching my head. Does anyone know how high I can go with the breaker on 12/2 wire thats about 100 ft from the panel?
Roger

Check valve coming out tank is leaking inside line after compressor cuts off that pressure cause hard start. Take line from tank after pumps up pressure any leak from check valve is to much. This be large line from compressor to tank not switch line that gauge is in. This fitting looks like regular fitting until get off in hand you see check in it. It has no spring closed by back pressure in tank can be very hard fitting to find go to place that rebuilds air compressors large cities with air and lube business is only places I have found them most people buy new unit.

O bleed air from tank before removing fitting it be hard find after goes throw roof.

If the check valve was leaking it would bleed out the underloader valve yes? I took it out a while ago and it seems to work ok.

The switch Ladylake and I are referring to is inside the motor,Rog. If it isn't working right,the motor will start but won't have full torque ie: it will start OK w/ tank empty but will bog down against an almost full tank.
Mike

Where do I find this switch? Is this the restart/ overheat button?
Roger

I think you will find that copper No. 12 romex is rated for 20 amps .... the breaker is protecting the wiring and upping the amperage on the protection device to something greater than the wire is rated to carry is asking for a fire....

The centifugal switch is located under the cover on the back end of motor. It works similar to a governor in that it holds one of two sets of contacts closed(start circuit) until motor reaches a set rpm and then switches to another set of contacts(run circuit) utilizing centrifugal force. if the first set is corroded or can't make contact,the motor won't deliver full torque.
HTH,
Mike

Mike, I took off the back of the motor and cleaned the contacts on both of these switches. Put it back together and tried it. It started but only ran a few seconds before blowing the breaker. To make sure I tried it in the other 20 amp curcuit I have in the garage and the same thing happen. Did I do something wrong.
Roger

Did it get up to full speed before the breaker tripped? I think there's one of three things wrong:the motor,the compressor or the breaker.Have you tried switching the breaker w/ another 20 amp one in the panel?I wish you had a clamp on style ammeter to hook over the black wire right at the breaker and get a reading while someone else started the compressor.This would tell exactly how many amps it's pulling at start.
I just reread all the posts on this and you said it's 100' on this circuit and it's a dedicated circuit ie: there are no connections except at breaker and wall receptical. Have you checked all connections on this circuit? Especially the black wire connected to the breaker.If this is not a good connection,it will create heat which will make a good breaker trip.
If this compressor worked fine on this circuit up to this point in time,something has changed. You've done everything to the motor except change it,so I think there's a problem in the circuit somewhere. I don't know if this comp is on wheels. If so, take the cover off breaker panel,make up a short 12 ga cord w/ a male plug on the end and connect it directly to breaker for that circuit and try the compessor there.If it runs fine there then I'd say you've found the problem.
HTH,
Mike

Did the shop that you took the compressor to say that
the 19 amps was starting amps, or running amps?
If you look on the name plate of the motor, it should
give an amperage rating, which is the running amperage.
Starting amperage can be as high as 8 times this number.
When the armature of an electric motor is at a stand still,
it takes a lot more amps to just get it in motion and
will draw a higher starting current for just a fraction
of a second, (until the armature gets under motion),
and then start to drop until the motor is up to speed,
and then draw what the name plate says. The name plate
may give running watts, which you can convert to amps
by dividing it by the voltage, which should be no lower
than 115 and no higher than 126. It may also give a
figure known as Volt-amps, which you can use as amps
in this case. Good luck, and keep us posted of your
findings.

It seems like it got up to speed then blew. I tried another outlet also direct line, the same thing happened.The motor is rated for 15 amps running and is drawing 19 amps running. I heard a chatter when it was running but it ran for such a short time I couldn't figure it out. This compressor use to run fine. The panel is in the basement with no access for me to put the compressor to test it down there.When I cleaned the centrifugal switch it seems worse. It's got to be something in the motor as everything else is new or working fine.

I can only suggest a new motor.
Mike

chatter is what it does when the centrifugal switch is dirty or shot and it will trip the breaker fast. What kind of shop is the compressor in? Mine was in a dusty wood shop and I had to clean that switch often. Steve

Disconnect the load, mechanically, from the motor.
It may be as easy as taking the belt off, or you
may have to remove the motor. Then see how the
armature turns by hand. I'm thinking maybe the
bearings are bad? Also, at this time see how
the compressor feels as you turn it by hand.
If nothing is evident at that point, I would
recommend you take just the motor to a good
motor shop, not a compressor shop.

OK, took the belt off after cleaning all the contacts inside and it runs fine. Put the belt back on and the first cycle filled the tank and shut off. Blew air out and when it started the second time it did the same thing, but I noticed the back of the motor was hot so I blew air on it for a while and tryed again,. This time it started and mad a clicking sound and I could see arching through the motor, finally it blew the breaker and a puff of smoke came out of the motor. Time to buy a new motor, how much time can one person put in on a project before going crazy. Thanks for all you help, i'll let you know how I make out.
Roger

I was afraid that would end up being the problem. Check voltage drop at motor when tank is almost full when you install the new one. I keep thinking 100'of 12 ga wire pulling the amps the comp requires may be what brought on this problem.
Mike

I think 100' of No. 12 is a long run too. Is there any way you get the compressor closer to the breaker box and use some 1/2" copper pipe to get the air where you need it. Steve

No the panel is in the basement at the other side of the house from the garage and I roll it around the garage depending on what I need it for. I'm looking at a new motor that draws 12amps running. See what happens, otherwise I run a new line of #10 wire.
Roger

As long as you are getting a new motor, why not
give some thought to a 240 volt. You'll have to
do a little electrical work, but the voltage
drop problem won't be as bad. Besides,
if you don't have 240 volts in your shop, this
would be a good time to get it.
And if you do go 240, you may need new switches
on the compressor, check their rating.

I already have 240 volts in the garage for an electric heater but I was hoping to be able to move this around inside and out. If I have to I can switch the voltage on the motor later if there still is a problem.Thanks
Roger

I gave up. Got a new motor same exact specs, put it on and started it up. It would not turn the pump fly wheel. So I took the belt off and the motor ran fine. Tried the pump and it also turned fine with no pressure it the head because I took off the line to the tank. Tried again with no pressure and the motor labored to turn the pump. Thats it I said to myself way to many hours in this thing. I took off the new motor and sent it back. Went out and bought a new unit. Wheeled the old one out to the curb. Now I have air again after 3 months of trouble.....