Unloaders for a twin V compressor

by chuck
(Rockford ILLINOIS)

I am having no luck figuring this out. Hope you can help.


I bought a new v-twin compressor with head unloaders.

I know what unloaders do but I am faced with two types (I think). Check valve w/unloader port and switch with unloader.

I have both available.

Does the check valve unloader port go to the heads and that's it? Do the unloader heads need pressure in the 1/4" line to unload? Or is the switch unloader only used to dump the line between the tank check valve and head?
Ideally I would like to be able to switch between continous run to start/stop mode.
Thanks in advance. Chuck B.






Bill says...

Hello Chuck B.

In every case the unloader is used to dump the air over the piston to ease the compressor start up.

In a two stage compressor air is compressed from one cylinder to the other, pre-compressing it, and allowing the second cylinder to compress it further into the tank.

Both pistons need to be unloaded to allow the compressor easier re-start.

There's usually a check valve in the line between the pistons, and on the secondary piston side, an unloader to allow that higher pressure piston to unload too.

Something must operate the unloader valves. In a single piston compressor, that unloader valve is usually located in or as part of the pressure switch.

You'll have to check your manual to see which goes where. I can't determine it with the info provided.

Cheers,

Bill

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Jun 24, 2012
older v twin
by: Ken

Hi Bill..I bought a older used v twin compressor head that was apart when I got it..I'm putting it back together and wondering which side the output and exhuast is in..One side has the 1/4 inch unloader on it and the other side has a big nut on the top of the head beside the unloader..Any info will be greatly appreaciated..Thanks, Ken

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High Compressor blows fuse during startup

by Minaz
(BC Canada)

Hi we a high Compressor purchased from China made by Changsheng Air Compressor, 380 Volts & 3phase. We use this compressor to blow PET bottles. During the night we switch the compressor off and in morning we turn it on. But lately when we switch the compressor on in the morning, it turns on slowly and in about few second it will blow the 3 30Amps fuse in the switch box. After we replace the fuse, the compressor turns on and it works fine. If the compressor is switched off, the above symptoms reappears. Yesterday we kept the compressor on all nigh and when we came in the morning the 3 30amp fuse where blown. The compressor is set to hold 3MPa, since we need that high pressure to blow our bottles. When we switch the compressor off we drain the compressor tank to about <2MPa. The compressor was working fine till now and this symptoms have started lately.

Oil level ok
Motor belt tension ok
general maintenance...check, such as any loose fittings, punctured pipes, leakage etc.,all seems ok

Could please help us diagnose our problem






Bill says...

I can't be sure as I'm not familiar with your air compressor, yet it sounds to me like you have an unloader valve issue.

Check out this page on unloader valves and see if this makes sense.

Cheers,

Bill

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Apr 09, 2013
BUY AMERICAN
by: Anonymous

It sounds like your BIGGEST ISSUE is the country you purchased from, China. Don,t buy their junk made of 50-100% lead. Buy / Support your own country or the GREATEST NATION, THE USA.

Hope This Helps,
Mark

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Unloader Valve

by GEORGE RIVERS
(Patterson, NY, USA)

I have a reciprocating air compressor with an "unloader" valve with a set point of 125 psi.

It doesn't have an electrical pressure switch so it will just idle after reaching pressure.

I want to install an electrical pressure switch to save energy. However the one I purchased, Hubbell 69JF7LY, is valved wrong for my compressor. Instead of pressurizing the line to balance the pressure differential around the piston, this switch just opens the valve to the outside air. If the port on the pump were going to the compressed side of the piston this would work, but my EMGLO MODEL K pump has the port on the non pressurized side of the piston. Can you recommend a pressure switch that will properly unload this compressor?

THANKS!






Bill ponders...

Hello George.

I'm a bit puzzled by your description of the operation of your "unloader" valve.

You've got an unusual one, for sure. Most unloader valves dump the air from on top of the piston when the compressor reaches cut out pressure and stops, so that on restart, the piston (and the motor to which it's connected to) doesn't have to try to start against trapped pressure over the piston.

Sorry, I've never heard of an unloader valve that balances air, though I'm sure, based on your excellent description, they are out there.

Why not install the unloader valve so that it's the pressurized line going to the tank that's connected to the unloader? If you do, make sure you have a check valve installed downstream of the unloader, so that it doesn't empty your air tank when the compressor stops and the unloader valve opens.

If you haven't seen it yet, here's more info on unloader valves.

Cheers, and thanks for writing in. I hope this helps.

Bill

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Jun 05, 2012
unloader
by: Anonymous

the type of unloader this person is talking about is used on gasoline engines. such as a vehicle with air brakes,or a portable contractors copressor where electicity is not available.

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The unloader valve.

by Kurt Schuppe
(Indianapolis, IN)

May I purchase just the unloader valve and not the whole pressure switch (which W.W. Graingers is telling me I have to)? To me replacing the whole switch does not make since, I am able to remove the unloader switch, it seem I should be able to just replace it. If so, where may I purchase one?
Thanks,
Kurt
arctic4us@yahoo.com






Bill says...

Hello Kurt.

Tell me, what was the diagnosis that told you your unloader valve had failed? Was the plunger being toggled by the pressure switch and no air came out? Or is it once it was toggled it wouldn't close again.

Try taking your unloader valve apart and cleaning it. Make sure the spring is sound. Reinstall and test. You might solve your problem by doing this.

Ask your local compressor store where they get their compressors fixed under warranty. Take your unloader valve there and see if they can help.

Cheers,

Bill


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Motor lopes when trying to start.

Occasionally when I turn on my air compressor it will runh...runh....runh but not fully start. If I release the air from the tank valve it will start normally until the pressure builds up again. When I use some of the air in the tank and it tries to start again the same thing happens. What's the problem?

I have a Task Force 3/4 hp. 1.5 gallon oil-free direct drive compressor. Any advice would be appreciated.






Bill posits...

Hello whoever you are. Thank you for visiting and for sending in this question.

For me, the tip off is that you have to let the air out before the compressor starts.

That sounds like your unloader valve isn't working. Go to the site map and scroll down to unloader valve if you want more info about that.

If the unloader valve isn't working, it can be too difficult for your compressor to start against the air trapped over the piston.

Cheers,

Bill

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Nov 05, 2009
Unloader Valve
by: Michael D

Thanks for your response Bill. I'll try replacing the valve.

Sorry for not identifying myself. Just a guy with a finicky compressor. Thanks again.

Michael D.

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What do the unloader valve do?

by chien van khong
(san jose CA)

I have a carrier unit and the unloader valve is bad now the insurance company won't pay for the damange load beacause of the valve






Bill says...

Hello Chien. Thanks for visiting and writing in.

Essentially, the unloader valve makes it less work for the electric motor to do to start the compressor when the pressure switch calls for more air pressure.

Here is complete info on the Unloader Valve.

If your unloader valve has failed, then your compressor motor or capacitor may have failed as a result.

Hope this helps.

Cheers and good luck.

Bill

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air compressor problem

Hi, My clarke air compressor tends to slow down almost to a halt as it tries to recharge.
I noticed that the motor although almost stops as well it still manages to just about slip the belt. then after a few turns the compressor (pump) slowley begins to turn again.
I have cleaned the control valve and no change.

There doesnt appear to be any resistance in the pump when you turn it by hand.

The motor seams ok as does the belt tension.

Help!!

regards, Phil






Bill says...

Hey Phil... thanks for writing in.

I'm thinking that you've got an unloader valve problem. That the air over your piston isn't discharged when your compressor stops would make the compressor hard to start, and if the breaker doesn't blow, your motor and compressor head will take some time to come up to speed.

When you reach cut out pressure, does the unloader valve dump air? A kind of psssshhhht! and then the compressor stops? If it doesn't, then it's your unloader valve / pressure switch that are likely at fault.

Bill

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Air compressor pump

by roger st.peter
(boston ma)

we have a few sm 1-2 hp port compressors that go out to jobsites

we got one back giving us fits

kicks on comes up to pressure air is comsumed kicks back on rises back up in tank air gets comsumed again

sometimes the pump stutters

we get 1 revolution or 2 from pulley won't fill back up tank out at site they removed pulley cover and would start to push wheel with their boots to get it turning and then it would fill up tank sometimes pump would work 8-10 times in a row then would have trouble and they would be turning it by hand or boot to get it going any ideas? any help would be appreciated thanks






Bill says...

Roger, it's really hard to tell from your description of the problem, but in reading between the lines, I wonder if the unloader valve is working on this unit?

Here is information on unloader valves. Maybe see if this makes any sense as the source of your problem?

Cheers,

Bill

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Circuit breaker on motor pops within 5 or 6 sec after starting up.

by Herb
(B.C. Canada)

I just purchased a 65903 compressor from Harbor Freight Tools and as my shop was wired by a licenced electrician and was inspected by a British Columbia Electrical Inspector, I doubt very much if these problems I am encountering have anything to do with my electrical wiring. The compressor starts and runs for about 5 or 6 seconds and then kicks the breaker out on the motor. I then took the belt off and the motor seems to run ok with the load completely removed, which doesn't do me any good. Do you think that a larger motor should be installed? Your comments would be appreciated.






Bill says...

Check the Unloader Valve. If there is air trapped over the piston, that would lead to the symptom you describe.

Cheers,

Bill

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