Campbell Hausfeld FL-3307 Check valve / Unloader repair - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
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post #1 of 1 Old 03-23-2017, 04:44 PM Thread Starter
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Location: Lake Wobegon, MN
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Campbell Hausfeld FL-3307 Check valve / Unloader repair

I have a Campbell Hausfeld FL-3307 Air Compressor that I brought home from my In-Laws farm this summer.

Was sitting in the granary for awhile. No idea how long. FIL passed this past July.
Drain petcock valve was left open, and tank was dry. Motor would not turn by hand.
Took belt off and compressor pump turned OK by hand and pumped air.
So I loaded it up and brought it home.

Motor was a 2 hp 110V / 220V and was pretty hard to turn by hand. Replaced it with a 1 hp 110V / 220V that I took off a Sanborn compressor I had here that had a leaky tank.

Planning on having the 2 hp rebuilt. It seems like a nice solid USA made motor.

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Compressor w/1 hp installed on it.

Check valve / Unloader worked at first then started giving me trouble by not unloading, and sometimes allowing pressure to escape from the tank.

Once pressure was up to 120 psi motor turned off. But when I would use some pressure and motor tried to restart, it could not turn over and would sometimes blow a breaker if I did not unplug it.
Did some searching on MTF, and elsewhere, and came up with the unloader valve was bad.

Unloader valve is built into the check valve.
It uses a "control leak" system to unload the compressor. P/N is CV-2050, replaced by P/N CV205000AV.
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It is made up of 2 brass fittings. Bottom piece holds the check valve unloader and screws into the tank. Second fitting screws into the first piece and converts it to compression fitting for copper tube that runs up to the top of the pump.
Head pressure is released through the hole in the hex nut of the fitting that screws into the tank.
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Check valve also would not always hold pressure in the tank. If I loosened the top brass compression fitting nut on the compressor head to bleed off the pump, sometimes air continued to flow out of tank until tank was drained.

Took it out and cleaned it put it back in. No go. Tried different ways to put the two brass pieces together with pipe tape or thread dope. Thinking it was how hard I tightened the top brass piece into the bottom valve body. Could not get it to work.
Was starting to think I was missing a piece, as in a fiber washer or O ring between the two brass connectors, or something else. Did not know if FIL had taken it apart. He may have since I found the top compression fitting loose when I first fired it up.
I tried a fiber washer and also an O ring between the two pieces, but no joy.

I was headed towards buying a new one, but before I threw in the towel I decided to take it completely apart and see if I could fix it.
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I used a small screwdriver to pry the push on retainer off the check valve end.
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HINT:Put a shop rag over it while I pried so it did not fly off somewhere.
Had to get all in place then have my wonderful helper put the rag over it.


I laid out the parts in same order as they came out.
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Found the spring that brings check valve up to seal was broken.
Found a spring in one of my "jars of springs I may need someday" that matched pretty close. Seems to be a tad stronger / stiffer than the original. I think if a local hardware store has a display case of different springs, they would have on

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There is a row of small holes in the bottom of the brass piece just above the check valve rubber. They were clean.
Also found there is one tiny hole in one side of the brass valve body up close to where the spring rides in the rubber cup. Not shown in picture. It was plugged. I used a torch tip cleaner to open it back up. What ever gunk was in there was hard to push out. Not sure why that tiny single hole was there, but it must need to be clean and open.

Put it back together the way it came apart. But left broken parts out.
I lined up all parts on the valve and slowly pushed the valve up into the valve body.
Then set it down on work bench to hold valve in place and push the center post up and out of the hole. Put rubber check valve on post and pushed the 3 prong retainer back on.

Hardest part was getting the 3 prong retainer to push back on. Used a small 3/16” socket on a 1/4” driver handle to push it on with.
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There is a large fiber washer in the top of the valve.
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When the air is being pumped, it pushes the check valve in the bottom of the valve open, which in turn pushes that large fiber washer in the top of the valve down and closed. That prevents air from escaping out the vent hole. And forces the air being pumped down the center tube in the valve fitting.

When the pump stops pumping and the check valve closes, that movement also pushes the large fiber washer on top up and unseals the access to the vent hole. Compressed air trapped in the line from the head can now vent and release the head pressure.

When the compressor is running, if you listen close where the check valve is going into the tank, you can hear a small psst, psst, psst, psst of air leaking in time with the pistons. It is very faint.

Installed the 2nd brass piece that is part of the body and converts it to a compression fitting. Just put together snug with the hex flats lined up.
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Started it into tank by hand, then used a 13/16” deep socket to screw it back into the tank.


Used new copper pipe and new compression fittings I had here to make a new line from the valve to the top of the compressor head.
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Worked as it should when I powered it up.

Turned off at 120 psi. And the unloader let the head pressure off quickly.

Let off some air pressure and it kicked back on at 90 psi. No motor struggle.
Tried that 5 times and it seemed to be working.
Drained off the air, opened drain petcock, and left it.

Tried it again twice the next day and it is working right.
Next afternoon I used it for about 2 hours out in front of the shop and it did not fail.
So maybe it will hold for awhile.

I think I figured out how this kind of check valve/unloader works now. I have not worked with one like this before.

Motor shuts off, pump stops pumping, and has equal pressure on both sides of the check valve. Spring action pulls the check valve lightly closed. Upper part of valve unseals the air vent. Air pressure on pump side of valve bleeds off the head pressure. Pressure in tank is greater now on tank side and that pressure pushes against the rubber check valve and it seals hard so air does not leak back into the pump side. Pump side has 0 pressure on it so now motor can turn pump easily to start building pressure up again.
This check valve action also happens between the pressure strokes of the pump pistons.
Each time a piston finishes a stroke, the spring pulls the check valve closed until the 2nd piston creates pressure and opens it again. You can hear that air leaking out the hole in the side of the brass fitting in time to the pump strokes.

Seems to me it lets off the head pressure faster now than it use to when it was working.
Also noticed (I think) it seemed to take longer to fill from zero to 120 psi. Not much longer but a little.
Maybe that replacement spring being a little stiffer makes that difference.

Those broken and worn parts bother me. So I think I will order a new valve anyway.
Don’t want it to quit working in a month on the day I need it the most. That is when things usually happen.
Found one on Ebay for $24.95 with free shipping.

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I’ll put the old one away for a spare should I need it.

Just thought I would put this out there. It bugged me the answer to the problem on these was always replace the check valve / unloader.
Seemed to me there had to be a way to clean them or fix them. Too bad they do not make a cheaper rebuild kit for these.

It worked for me. If anyone else wants to try it, do so at your own risk.
Please use common sense if you decide to work on one like this. Your experience may vary from mine. And I shall not be held accountable for any damages you may have.

Sent from my DELL WS650 Desktop PC, by tappity tap tap'n on the keyboard. And which not even once have I dropped down the hole in the outhouse.
Utility before aesthetics.

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Murray LT Model: 425618x48B, 18hp B&S, 42" deck, 2004, Hydro trany., foot control. My Mower
Murray RER, Model 30550H, 1999, 10 hp Tecumseh, 30” cut, single blade. My trimmer.
Murray, Noma Model: 633124X8, 12hp Tecumseh OHSK120, 33", 1997, Walk behind snow blower.
MTD Snowblower Model: 317E150-129, 139cc / 21”, 1996 My “Power Shovel”.

Last edited by Newsman; 03-24-2017 at 08:33 AM.
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