Air Compressor has backpressure?!?!?

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Old 10-08-08, 10:16 PM
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Air Compressor has backpressure?!?!?

First time posting....I have read through any other threads that looked like this and didn;t quite find the answer...

I have a 15 gal or so horizontal 3 hp Sears compressor (mod.919.176830) and this is what happened:

Turn motor on and it runs
builds up pressure to 30-40 psi and then starts to struggle (you can hear the belt) -Electric and motor is all good
I turn the switch off b/c eventually the motor stops and trips house circuit
When I turn it off it bleeds the head properly through the smaller tube-no problem there
I purposely didn;t bleed off the the head and tried to turn it by hand at the exact moments the motor starts struggling and there is definitly a breathing problem there at that moment.
I remove discharge pipe (3/4") and no pressure.
I remove check valve and reconnect discharge to it and run motor and everything works fine (of courase it is not filling tank it is just blowing off to the side throughthe check valve.
So I am left with my only guess going to the intake. This thing seems to exhale fine and teh switches seem to operate, but the wheel does not want to turn after 35 psi...

Question...what should I do now?

Thank you so much for helping us DIY out..I live on an extremely small budget and your professional advice can make or break that budget and my day!
 
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Old 10-09-08, 03:41 AM
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Are you using an extension cord or is it connected to an overloaded cct?
Is this a new unit with the possibility it is wired for 220 volts and connected to 120 volts?

How about the possibility that the check valve is restricted by a broken spring or sludge or the motor windings are bad?
 
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Old 10-09-08, 05:18 AM
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Originally Posted by ryano View Post
First time posting....I have read through any other threads that looked like this and didn;t quite find the answer...

I have a 15 gal or so horizontal 3 hp Sears compressor (mod.919.176830) and this is what happened:

Turn motor on and it runs
builds up pressure to 30-40 psi and then starts to struggle (you can hear the belt) -Electric and motor is all good
I turn the switch off b/c eventually the motor stops and trips house circuit
When I turn it off it bleeds the head properly through the smaller tube-no problem there
I purposely didn;t bleed off the the head and tried to turn it by hand at the exact moments the motor starts struggling and there is definitly a breathing problem there at that moment.
I remove discharge pipe (3/4") and no pressure.
I remove check valve and reconnect discharge to it and run motor and everything works fine (of courase it is not filling tank it is just blowing off to the side throughthe check valve.
So I am left with my only guess going to the intake. This thing seems to exhale fine and teh switches seem to operate, but the wheel does not want to turn after 35 psi...

Question...what should I do now?

Thank you so much for helping us DIY out..I live on an extremely small budget and your professional advice can make or break that budget and my day!
did you buy this unit new? did it come with a molded plug on the input wireing?sounds like the voltage to the motor is low,
the reason your compressor is hard to turn when you stop it with out bleeding off the air is because it is compressing air just like it is supposed to. you said that it runs fine with the air line dissconected from your tank did you happen to check the amp draw and voltage while running hooked up and not hooked up? have you removed the intake air filter and checked it for restriction?

life begins when the kids leave home and the dog dies.
 
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Old 10-09-08, 05:05 PM
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I think you may just be overloading the circuit when the compressor starts to put the full load on the motor. My compressor would do the same thing on a 15 amp circuit. I put in a dedicated 20 a circuit and solved the problem.

B
 
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Old 10-09-08, 09:26 PM
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This seems mechanical

No extension cords in use and it does the same thing no matter 15 or 20 amp breaker. Well, my theory here is that the motor runs fine without any mechanical restrictions like pressure in the tank or the lines. I think it is safe to say that the motor electric is fine. I think that because I ran it with the check valve on the discharge and the discharge hooked up to the head but not hooked up to the tank (it was sticking out so I could see it operate). The motor ran and pumped air just fine. the check valve operates just fine.

I realize the pressure in the head will be there b/c of no bleediing I just wanted to be thorough in my explanation of what I did.

the air intake filter is fine. My question is what voltage to set my multimeter at to test for draw volts and amps...I have never tested draw in anything with my meter.

What are the possibilities inside the intake that could go wrong and not allow the head to "breathe in" at anything over 35 psi because it seems that breathing out is fine. Should I take apart the head?

thanks,
ryan
 
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Old 10-10-08, 11:36 PM
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Help my basement awaits..Check valve lookin good but not so good?

Hey, I am in the middle of finishing my basement and I lost my other compressor so it is buy a new one or resurrect this one.

I was going over this thing again for another 1/2 hr today and it just might make sense to try a new check valve. My question is that this one seems to be just fine...has anyone had one that looked ok and wound up being bad for some reason?

All of my tests seems to indicate that the check valve stops letting air in and shuts at 30 psi or so so the head begins to struggle and the discharge pipe gets real hot.

(I got this off of the side of the road for free) Could be that someone once put in a check valve that once it has 30 psi in the tank will not let the head put in anymore air to the tank?!?! Are they rated ?

Thanks in advance for any advice before I order the valve.

Ryan
 
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Old 10-11-08, 07:23 AM
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symptom of a bad check valve is a "hammering noise" that sounds like it's coming from the tank. it wouldn't hurt to try one but i think you're going to have to pull the head and check the valves for carbon build up or heat damage. those parts are usually not expensive. examine carfully as you take it apart. reed valves are in a particular layered sequence within gaskets and spacers and poppet valves may have different springs for hi and low sides of the airflow.
 
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Old 10-11-08, 12:02 PM
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flaps seem to suck air in

heya, without disassembly of the heads the small flapping valves were taking in air when it was just starting up and trying to build up to the initial 30 psi. Can pressure in the tank of 30 psi affect the valves on the head? To test my check valve theory I put my finger over the discharge tube while it was biulding up presure and teh problem repeated itself (sluggish motor wanting to quit)...as soon as I let my finger off it went to normal operation.

What do yall think?
Thanks,
Ryan
 
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Old 10-11-08, 07:08 PM
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it's tough to solve without seeing the unit. it is possible that the compressor is fighting itself if the valves are not functioning properly. for example, if the exaust side is weak and not closing, it could make it harder for the piston to do it's job. the compressor is really no different than an engine in as much as they are both air pumps.
 
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Old 10-12-08, 11:50 AM
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yes

yeah I hear ya. that is where I was going with all this b/c the motor seems to operate fine even under load so Ithink it is mechanical. I just bought a check valve and will have it in a week through the USPS and once I try it I will surely know what to do next. thanks for all the help so far and stay tuned if possible...I never know if I have help or if you have left for good.

God bless,
ryan
 
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Old 10-16-08, 12:46 PM
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$100 for the answer

OkI am ready to give up money for the answer here!!

I replaced the check valve and took the head off and all seals are good and all flappers seem to be just fine and operating as they should.

I have now committed 25$ to this and want to see it through, not too mention I use my air compressors all the time!

Let me pose this..what affects would time or pressure have on a motor in this scenerio? Keep in mind, the motor ran for as long as I left it on without having it hooked up to the check valve and tank. So it seems as long as there is no pressure being built up this motor keeps on trucking.

Flop shot- anything to look for with these "reed valves" (there are no springs here) that would seem abnormal-they look flat and shiney with no rust and bolted down properly, etc.

Last thing...a motor works harder as the pressure is built up I am assuming...so should I check the capacitor there is only one on the motor?

Pulling my hair out,
Ryan
 
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Old 10-16-08, 05:21 PM
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Lightbulb Don't change any more parts, invest in some test equipment.

You are really going in the wrong direction.

Because you have determined that the compressor is pumping and the pressure will build up you have pretty much eliminated a mechanical problem.
Your unit likely has only a start capacitor which will not affect the operation once it has started.
A clamp on ammeter and a voltage tester would be the tools needed to check any further.
I don't believe throwing parts at it will help.

The correct way to check this is to clamp an ammeter onto one line of the compressor to measure the current draw.
You would then connect a volt meter to the plug feeding the compressor or at the compressor wire terminals.

You then operate the compressor and watch the amps and volts.
The amperage will climb as the pressure rises and when the amperage reaches 12 amps you should check the voltage.
You should have at least 105 volts and the breaker should not trip at 12 amps.

This will tell you what is going on.
If the amperage reaches 12 amps, the voltage is 105 or more but the pressure is not near the cut out pressure you could have a problem with the motor.
If the amperage reaches 12 amps and the voltage drops below 105 volts you may have a problem with the circuit being able to provide enough current.

Oh ya,
One other problem that will cause your symptoms is if the motor pulley has been changed with a larger one which would overload the motor.
 
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Old 10-17-08, 06:46 PM
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greg, I appreciate your help so much and I agree at this point completely about further testing on the motor. I don't own a clamp on meter, so my question is what are the advantages to owning this meter. I have access to many muiltimeters. Should I just use two muiltimeters to accomplish the same thing or is there something I am missing with a clamp on. Looks like I will spend 30$ or more on the meter.

Thanks,
ryan
 
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Old 10-18-08, 05:35 AM
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if the reeds weren't broken burned or clogged then they're fine.
at this point i'm going with Greg although i'm not a motor tech and don't know what the problem could be or if it's repairable.
sorry i couldn't be more help.
 
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Old 10-18-08, 07:04 AM
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The two meters I mentioned do different jobs.

The clamp on ammeter measures amperage which is a measure of current draw and what causes your cct breaker to trip if too high.
A voltmeter measures voltage which you need to ensure is high enough when the motor is under load.

If you have a problem with your circuit where it is unable to deliver high enough voltage, as the voltage goes below 105 volts the amperage will go up tripping the breaker not because of a motor problem but from a low voltage condition.

Using the two meters as explained above will check for this condition.
The clamp on shown can actually measure amperage and voltage as most can do but you need a separate voltage tester so you can read the amperage and voltage simultaneously.
You also while monitoring the volts and amps need to monitor pressure to give you enough info to figure out your problem.
When you put all these readings together your problem may become obvious.

DIY is not always simple.

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