Air Compressor............ Again......

OK, I bought a compressor on January 1st 2005, it has done OK service, but this was before I really understood what a good compressor is, this one is NOT a "Good" compressor.

In >> THIS << thread I outlined a problem I was having with this compressor. I thought the problem was fixed, but is is not.

I thought I had fixed the problem, but it did not work, stuff gets between the valve seat and the rubber valve that is supposed to seal it, so it leaks, just a bit , but enough that the compressor does not really work right.

You can see the part in question below.


The rubber valve has become hard, I did sand it smooth, but the rubber is still hard, so I came up with the idea to glue on a softer new piece of rubber, I did this, the rubber is about 1/16" thick, it should have worked but the problem is still this junk that gets all over the valve, it looks like rust or something from the tank

I really want to buy a new compressor, the last one I'll buy for a very long time, the budget is tight, as we are getting ready to send our eldest daughter to Canada for high school. Right now, I'd just like to fix the compressor I have, and then start looking for a good used unit, they are out there now, as a lot of places here are going bankrupt, and a lot of these larger compressors run 3-phase motors, so they are out of reach of a lot of guys. I have three phase power in the building, because of the elevator and I have it wired into the Dungeon

Back to fixing the compressor I have.

The valve works like this, the compressed air comes from the pump to the valve, passes through and goes into the tank, the valve is a one way type, held down by a spring, when the pump is not pumping, the valve keeps the compressed air in the tank. There is also a bleed for the pump, this is the black nylon tube you see in the pics. When the pump shuts down, the pump stops pumping, the valve closes, but there is still pressure line from the pump to the valve. You don't want any pressure on the pump, because when it goes to start again, the pressure could be too high and the motor could not be able to turn the pump from a stop. The control unit triggers the valve on the bleed line, this lets any pressure in the line between the pump and the valve out, you know, that "pssssssssss" you hear when the compressor reaches it's preset pressure and shuts down.

What happen now is compressor shuts down and the control unit triggers the bleed line, and the "psssssss" goes on and on and on, until the preset point is reached and the compressor comes on again......

The problem is the junk from inside the tank(?) or the pump(?) gets between the valve seat and the rubber valve, and it leaks.

I've taken it apart and cleaned it way too many times so now I'm looking for a solution.

A new valve, something more mechanical would seem to be answer......

I just had a thought while writing this..... where is the junk coming from that is fouling the valve?

The pump takes in air through the air cleaners, and compresses it...... right?

The air the is going into the tank, must be full of this junk, I'm now thinking it can't be from the tank, the air flow is going into the tank......

Maybe I'm looking at this in the wrong way, maybe the air cleaners are falling apart, or.... But where is all the junk coming from?

Maybe I'll have to tear down the pumps, maybe the rings are gone and the junk is oil, or......?

Huh...... strange what happens when you try to coherently put your thought down.....

Oh well, what do you think of that hypothesis?

The junk that is fouling the valve cannot becoming from the tank (can it?) it must becoming from the intake side, the pump etc....

More to look into

The 'gunk' may be the compressed and overheated crankcase oil from your compressor.

The oil is getting pumped past the piston rings on the piston's downstroke. This can happen if the crankcase vent is plugged, or if the rings are badly worn - or if the wrong oil was used.

Jim DeLaney said:

The 'gunk' may be the compressed and overheated crankcase oil from your compressor.

The oil is getting pumped past the piston rings on the piston's downstroke. This can happen if the crankcase vent is plugged, or if the rings are badly worn - or if the wrong oil was used.

Click to expand...

Thanks Jim.

The oil is the right stuff, I changed it about a year ago, and bought the right stuff, but I did notice that the compressor takes a LOT longer to reach it's preset pressure shut off point, so maybe the rings are bad.

They are simple pumps, I guess I'll be taking mine apart and see what I can see....... Oh well, there goes my Sunday

I forgot to ask in the first post, what Cubic Feet per Minute (CFM) do you guys consider a minimum for a compressor?

I think I read somewhere here that a sander would take 8 CFM.

I recently passed up on a decent Hitachi Bebicon compressor (a gold standard over here) that was 2.2Kw (about 3 Hp) and 265 liters per minute or about 9.35 CFM. It was three phase, not a problem, with a 21 UDS Gallon tank. One thing that I thought was good was the pump was fairly slow speed, designed to turn at only 730 rpm (I think that is slow) it sold for about $400.

If I go used, that is the kind of deal I want to catch.

So, what kind of CFM do you think I need to run air tools?

Cheers

Stuart it's always something isn't it , hope you get it going for the compressor is an important part of my woodworking too ........

stu,
for a one man shop who actually uses air, like a vacuum pump (venturi type)
sanders, diegrinders etc... look for either a two lung single stage pump with 3-1/2" bores or a four lung two-stage pump...either should displace 11+ cfm at 90psi.
talk to a local compressor dealer and ask what they stock parts for so you`ll know brands to look for.
in the last few years rotary-vane pumps have come unto their own and are becomming more affordable for small shops...the good thing about these units is that you can produce 20+cfm from a pump not much bigger than a portable compressor.....but they do whine.

Stuart Ablett said:

Thanks Jim.
The oil is the right stuff, I changed it about a year ago, and bought the right stuff, but I did notice that the compressor takes a LOT longer to reach it's preset pressure shut off point, so maybe the rings are bad...

Click to expand...

Stu,
before you start tearing it down, check the crankcase vent. If it's plugged, then every downstroke of the piston will pressurize the crankcase, potentially forcing oil past the rings.

If the vent is open, then, yeah, it might be worn rings.

tod evans said:

stu,
for a one man shop who actually uses air, like a vacuum pump (venturi type)
sanders, diegrinders etc... look for either a two lung single stage pump with 3-1/2" bores or a four lung two-stage pump...either should displace 11+ cfm at 90psi.
talk to a local compressor dealer and ask what they stock parts for so you`ll know brands to look for.
in the last few years rotary-vane pumps have come unto their own and are becomming more affordable for small shops...the good thing about these units is that you can produce 20+cfm from a pump not much bigger than a portable compressor.....but they do whine.

Click to expand...

Tod, thanks for the info.

The compressor I have now is 4.3 cfm, I've found some good used units that have a LOT more CFM than that.

Here is one, 7.3 Hp, and 21.2 CFM

It is about $700 right now, no bids and one day left, I won't be buying it, but that is the kind of unit I'm seeing for sale here. If I clear out a spot on the Dungeon Annex, and then set it up there, and run the pipes back into the Dungeon, I would be golden, an auto drain thing added and all I've have to do is change the oil now and then.

The other road I could go is this type of unit.....

This type of unit has a couple of neat features, one is the box it is built into is sound proofed, so it is quiet, and keeping the unit in the box keeps everything nice and clean too.
it is a 5 Hp unit, and does 15.5 CFM, it too is about $700 right now.

Jim DeLaney said:

Stu,
before you start tearing it down, check the crankcase vent. If it's plugged, then every downstroke of the piston will pressurize the crankcase, potentially forcing oil past the rings.

If the vent is open, then, yeah, it might be worn rings.

Click to expand...

Thanks Jim, I did check that, it was fine, and the oil level was also spot on the site glass too.

Funny, the air vent is really simple on this compressor.........

...... they are just using a marble in a plastic part, seems to work

And here is the oil......

..... the floaties are from the workshop, the sludge in the bottom is minimal, and the oil is still fairly clean. I also cleaned out the crankcase of the pump, it has only a bit of sludge in the bottom.

I do have some good news and some bad news. The good news is, I know what the problem is, the bad news is......... I know what the problem is....

I tore the pump off the tank and took it apart.........

The right and left heads...... gee, wonder where all the rusty junk was coming from


The valves, or reeds are really in rough shape.

The pistons......

They have some junk on top, this one, the right one is the worst, but this just mostly wiped off, as the aluminum did not rust.


A close look at the rings show they are in OK shape, there is no "blowby" and the wear on the rings looks fine to my eye, the piston skirts are also fine.


Looking at the bores of the cylinders also show they are good shape.

I think the air filters are not working well enough, I guess I'll have to improve them.

cont...........

Once I cleaned off the junk, the heads and the cylinders needed some work, so I got out my glass plate that I use to lap my hand planes, and I set to work.........


The heads and the cylinder tops all ended up looking similar to this, I think this will be an improvement.


The valves, or reeds on the right cylinder were the worst this is the best I could get them, I think this will be an improvement over how they were, but is it good enough? I don't know. The left cylinder ones cleaned up nicely.


I got it mostly back together, I have to fit the cross over pipe, and go buy some new oil, but I'll do that tomorrow, time for bed now.

I hope this fixes it for now, I will have to improve on the air filters, but that should not be hard, the holes are threaded with 1/2" pipe thread, so I can make something up if I have to, find a filter from something else and make a housing, or maybe just buy a good filter from Hitachi or something.

Cheers!

most compressors have npt threads for the air intake.....it`s a simple matter to rig pipe to a "filter box" that could use an off the shelf k&n..........
reed valves are cheap......and yes the jugs and rings look good from here
the heads could use a good cleaning though.
as far as the pics of new to you pumps......both are not familiar to me but the 3-lunger looks kinda like an ir design?

[edit]
as i was typin` you were postin` about fixin` the problem..........sorry about being redundant.

No problem at all Tod.

I might just have an old motorcycle K&N filter kicking around, if I did not toss it About 4" in diameter and 8" long, it would work great...... If I can find it

I need a washer, a compression washer, it goes on that valve thing that is getting dirty, the one I have is aluminum and it don't squish anymore, it won't seal well. What the heck do you call them things

Stu, Seems I type too slow, Lol.

Looks like you have it figured out. I would "deglaze" the cylinders some (in a crosshatch pattern) with some fine emory paper.

Also, make sure those rings are expanding to a larger diameter than the piston so as to apply even pressure against the cylinder walls, which makes the seal. If the rings have heated enough, they will lose temper and no pressure will be against the cylinder, causing slow pumping and oil blowby. You may have to replace the rings.

Looks like you did a good job on the heads and reed valves.

I think (MNSHO), you are pulling pretty moist air into the compressor and it is condensing inside the cylinders.

As far as a replacement filter/s, an automotive air filter element will work nicely. You can build a well sealed filter box/silencer (use interior baffles to cut down on intake noise) and you should be good to go for a long time. I would mount the filter box off the compressor too, like on the wall, or somewhere, and plumb it with a piece of wire reinforced, or ribbed vacuum hose.

This is what I would do, but you are the resident engineer there, so have at it.

Aloha, Tony

One thought... good rebuild job so far, by the way... if you do build up an air filter rig for it, pay attention to the inside of the pipe as you're putting it together. If it ain't clean inside, crap can get into the cylinders from the dirty insides of the air cleaner & mess up your day. Deburr the pipe ends, even, and wash 'em out. I've seen some ugly STUFF inside brand-new pipes & nipples & fittings.

Yep, sometimes the guys that cut the threads, don't bother to clean up after

Well, I got it fixed, sort of

All back together and running again, but it is supposed to pull 0.79 Mpa (115psi) peak, but shuts off at 0.59 Mpa (85.5psi) which it does, but the first time I ran it, it shut off at 85psi, but not on the pressure switch, but on the thermal overload on the motor

I let a little air out and then tried it again, and it seems to stop at the right point. I don't have any leaks I can find with the soapy water and the bleed valve works right too, one spurt of air and then nothing, just like it is supposed to.

I guess the compressor is fixed, but some of it is a bit bodged, I could NOT for the life of me find a crush washer the right size (ID 30mm, OD 36mm and 2mm thick). I ended up using a bunch of teflon tape and some pipe dope, it is not leaking, but I'll have to find a crush washer at some point

I also have not worked out the air cleaner, I'll have to do that soon.

Thanks for the help, now I need to sell this thing CHEAP and get a better unit.

Cheers!

That ring gasket around that brass check valve? If you're REALLY CAREFUL, you can cut one out of stock gasket material with a VERY SHARP knife. A piece of boxboard would work well, too. Shellac it for the seal. Lay it over the opening to cut the center out, then tighten down the plug & trim the outside.

Thanks Tim, I know I could make one myself, but it is a 50 cent part........ if I could find one The bodged set up I did is holding air, no leaks, so I'll leave it for now.

I am sure that the fix I put on the compressor is not 100%, the thing is supposed to pump to 8 kgf/cm2 (115 psi) and turn it self back on when the pressure drops to 6 kgf/cm2 (85 psi) but it will only pump to about 6.5 kgf/cm2 ( 93 psi) before the thermal overload on the motor shuts things down. I've adjusted the controller so it now shuts down at 6 kgf/cm2 and kicks back on at 4.5 kgf/cm2

I'm sure that the one reed valve is the cause, it is very pitted and cannot be making a good seal, I got the head and the tops of the cylinders nice and flat, almost no pitting, so they should seal, but that one reed valve, well one bad reed valve would be all it needs to not work at 100%

I might just have to try to make one, I was thinking a cheap set of feeler gauges should have the right thickness and size piece of steel in it, good luck finding it other wise.

Cheers!

Can't get a repair kit? I got one for mine a few years ago. Went to a compressor repair shop. They sold me the kit. It had reeds, seals, gaskets. etc. About $14.

Carol Reed said:

Can't get a repair kit? I got one for mine a few years ago. Went to a compressor repair shop. They sold me the kit. It had reeds, seals, gaskets. etc. About $14.

Click to expand...

I wish I could, this is a Chiwanese unit, the compressor repair shops here are all brand shops,Toshiba repairs Toshiba, Hitachi, repairs Hitachi etc, well, at least the ones I've found

Stuart Ablett said:

Thanks Tim, I know I could make one myself, but it is a 50 cent part........ if I could find one The bodged set up I did is holding air, no leaks, so I'll leave it for now.

I am sure that the fix I put on the compressor is not 100%, the thing is supposed to pump to 8 kgf/cm2 (115 psi) and turn it self back on when the pressure drops to 6 kgf/cm2 (85 psi) but it will only pump to about 6.5 kgf/cm2 ( 93 psi) before the thermal overload on the motor shuts things down. I've adjusted the controller so it now shuts down at 6 kgf/cm2 and kicks back on at 4.5 kgf/cm2

I'm sure that the one reed valve is the cause, it is very pitted and cannot be making a good seal, I got the head and the tops of the cylinders nice and flat, almost no pitting, so they should seal, but that one reed valve, well one bad reed valve would be all it needs to not work at 100%

I might just have to try to make one, I was thinking a cheap set of feeler gauges should have the right thickness and size piece of steel in it, good luck finding it other wise.

Cheers!

Click to expand...

You've got a plenty-big cooling fan for that motor? Typically, a big fan is built into the compressor pulley & the motor is right in the same airstream as the compressor's cylinders. You may need to bump up the motor if it's getting adequate cooling now.

How fast does it get up to 6 from the turn-on point of 4.5? How big's the tank?