Air compresser's down

jaybee · December 23, 2010, 07:16:00 AM

Two lines to the pressure switch? Should be one plumbed to the base of the switch. That controls your on/off. It would be up from the bottom in your picture and go either to the tank or someplace close to it. It looks like the other line comes down from the top, alongside the switch cover. If I don't miss my guess it'll go to a compression fitting on the switch. That one should go back to that T fitting you showed just off the head.

Someplace downstream from that T should be a check valve. That holds the pressure in the tank while allowing the compressor itself to be depressurized.

What happens with a unit set up like that is that the pressure switch actually does 2 things. One is of course to start the compressor below the lower limit and start it at the upper limit. Plus when the unit reaches upper limit and switches off it opens the end of that small line. That "blows down" the head pressure on the compressor. The check valve is required to maintain pressure in your air system. It produces the same effect as the internal unloaders that Wayne described. You'll hear the pressure release just as the power is removed from the motor.

With this system you have an additional source of possible leakage we haven't discussed. Two, actually. The valve on the pressure switch could start to leak. The check valve could start to leak pressure back toward the compressor. In either case you should be able to find air leaking steadily right around the pressure switch area when the unit is between cycles.

rooster · December 23, 2010, 09:56:40 AM

If I got this right, I need to turn on the compressor and let it build up preasure, then turn it off , and check for air leaking (compresson release) around the ele stw area. This soppost to happen to be ready for a easyer re-start of compressor. If the compression release does happen, it should stop, if not the check valve in the tank may not be seating and leaking. Have I got this right?

wayne petty · December 23, 2010, 12:19:37 PM

is the problem with the big compressor still that it only pumps up to about 30 psi... and continues to run?

this gets back to franks answer... the reed valves are leaking... and need to be lapped to reseal them... after inspecting them...

my thinking is the unloader is not closing.. so compression is not building...

now... if one of the heads is cracked..

/

take that head apart... examine how it works...

i am also taking.. that the air filters are clean... the shop i worked in.. the filter elements were totally clogged... the compressor took forever to build pressure ...

jaybee · December 23, 2010, 01:41:31 PM

Wayne is right that Frank is right (or something like that). When they won't build pressure reed valves are the first subject. Correct on the unloader, though. The pupose is to keep the unit from starting against pressure and you'll want to look for leaks in the whole system. A unit as I've described should have one loud release of air as the power shuts of. A centrifugal unit as Wayne described will do the same thing but a split second later as it coasts down. Either way there shouldn't be a release of air while the unit is running or continuing after blowdown.

rooster · December 23, 2010, 01:54:19 PM

Quote from: "jaybee"Two lines to the pressure switch? Should be one plumbed to the base of the switch. That controls your on/off. It would be up from the bottom in your picture and go either to the tank or someplace close to it. It looks like the other line comes down from the top, alongside the switch cover. If I don't miss my guess it'll go to a compression fitting on the switch. That one should go back to that T fitting you showed just off the head.

Someplace downstream from that T should be a check valve. That holds the pressure in the tank while allowing the compressor itself to be depressurized.

What happens with a unit set up like that is that the pressure switch actually does 2 things. One is of course to start the compressor below the lower limit and start it at the upper limit. Plus when the unit reaches upper limit and switches off it opens the end of that small line. That "blows down" the head pressure on the compressor. The check valve is required to maintain pressure in your air system. It produces the same effect as the internal unloaders that Wayne described. You'll hear the pressure release just as the power is removed from the motor.

With this system you have an additional source of possible leakage we haven't discussed. Two, actually. The valve on the pressure switch could start to leak. The check valve could start to leak pressure back toward the compressor. In either case you should be able to find air leaking steadily right around the pressure switch area when the unit is between cycles.

Its like you said! See pict.

I fired the compressor up, it went to about 25 pds and kept running. Unpluged the compressor and listened for a leak in that area, I heard none!

Wayne:
I have a total of 3 compressors, 2 or mounted to a tanks, the 3rd is on my kitchen table it has a cracked head, its a LaPlant just like the other one. I thought I would remove the cracked head just to see what I dealing with!

When I get this head off I will post.

rooster · December 23, 2010, 05:42:56 PM

I got it apart the reed valves I think are set with a drive rivot. I havent tryed anything yet. Nothing looks rusted or coroded that I can see.

Do the fasteners just get tapped out?

wayne petty · December 25, 2010, 06:57:37 PM

i was going to help you fix your small compressor with this..

http://images.harborfreight.com/hftweb/homebanner/dealcoupons/images/coupon122610.jpg

i don't know how long its good for.. edit i blew it up...expires 12/27 . good instore or online..

back to the subject at hand...

air gets pulled in from the filter side... through the inlet check valve as the piston moves down...

as the piston moves up .. the inlet valve snaps closed and the exhaust valve opens... allowing compressed air into the exhaust chamber.. as the piston reaches the top.. the reed valve on the exhaust side snaps closed..

so.... do you have any way to check them.. i cannot see how they come apart from here...

have you read the gasket.. to see if there is any leaks from the suction side... to the pressure side.. preventing the pressure from building up properly...

something is not sealing.. or holding something open... to prevent pressure from building up...

can you stick your hand over the top of the cylinder and spin the crank... does it seem to have good compression...

i am just hoping that compressor is not one of the low pressure pumps with carbon rings that will only build 30 pounds of pressure.. they were designed for spraying with bleeder type of spray guns... think zolatone spray guns.. and some of the others from the early days of spray equipment..

wayne petty · December 25, 2010, 07:01:13 PM

by the way... is there anything in the upper part of the head... other than ports... in and out?

no check valves there

??

no valve between the chambers down through the top of the head???

got pictures of the upper head.. bottom and top?

?

next test... is to hook up a vacuum gauge to the inlet port... will the pump create vacuum....

enjenjo · December 25, 2010, 11:01:43 PM

I think you will find you have a valve assenbly there that is stuck in the head. Smacking the head, with your hand, against a couple wood blocks set at the edges should pop the valve assembly out. If you look at the right side of the top picture, you can see the bottom of the rivets on the outlet side. I n the parts list, it looks like they only service it as a valve assembly.

wayne petty · December 26, 2010, 02:08:09 AM

i was looking at the retaining straps... i am taking that they are counter sunk below the gasket surface..

i would be that a pin punch could be used on the bottom of the rivets to knock them out... as they cannot come out do to the gasket being above them... does not mean they won't come loose....

you mentioned that you have one with a cracked head...

by the way... i know its late... but... only one of the heads really needs to be messed up for the compressor to not built pressure properly...

the air from one cylinder can leak backwards through a stuck or damaged exhaust check valve into the second cylinder.. and since its leaking in and out.. it will not pull a fresh charge of air in through the intake...

if the other compressor is still powered up.. unscrew the air filter assemblies.. see if you get decent suction on both sides... when you turn the compressor by hand...

since those are aluminum heads.. the surface of the valve seat might be damaged by the reed valves pounding on it..

rooster · December 26, 2010, 08:46:14 PM

Theres nothing in the top of the head, the only parts I see are in that plate. (picts) also the seat appeared to be mushroomed like you mentioned.
I * up the plate when tapping the rivets out, I should have drilled first! (pict). If the reed wears out this one does not show it, and no corrosion.
I removed the air filters and spun the flywheel and got some vac turning it over, there was a noise when I turned the flywheel, it only comes from one cyc, I think what I hear is a pop of the reed valve working, but only on one side.

between the 2 cyclinder is a black plastic plug this is where I added oil when new, looking at this plug there is a hole in each end, I put some spit on top the hole and turned the flywheel and it would suck it in then shout it out. (pict)

Spent most of the day getting the heater back online. Need to find a way to turn up pilot light up.

wayne petty · December 26, 2010, 10:17:12 PM

makes sense the rivets are mushroomed...

drilling them out.. then using a heli coil to restore a smaller thread diameter.. so you can use some button head or pan head allens... must be really strong screws...

do you have some kind of vertical mill.. to restore the valve seat....

or perhaps.. order some new parts from the compressor companies distributers.. if you can get them...

i blew up your last picture.. but could not tell how the recess was formed... where the reed valve fits... was it machined .. or pressed by deforming the aluminum...

perhaps.. if no valve blocks are available... one could use a tiny rod with a TIG machine to build up the seat area.. then mill the recess flat again...

last option... might be to if you have a vertical mill... machine a groove around the seat... glue in with orange silicone.. a silicone O ring.. if you rough it up slightly.. you might even be able to create a valve seat with orange high temp silicone...

this might work... if there was a way to get it really flat..

one could get creative with different alloys of aluminum filler rod..

i wonder.. if one could create new valve blocks with some reed valves from a 2 stroke motorcycle motor... they might not be strong enough to withstand the forces in an air compressor..

last thought... i wonder if both valves are effected.. or just the exhaust valves.. as the exhaust would have much hotter air...

dirt that got through the intake filters could have done this also...

rooster · December 27, 2010, 11:32:17 AM

No! I dont have a milling machine. LOL
The plate is machined. I havent heard anything from that co yet, I do have a good idea what the price of those parts will be. I think its time to move on.

enjenjo: I guess not all compressors are the same that reed is not coming out unless that spring retainer is removed first, there just rivets, struck or mushroomed to hold in place , no threds. It sounds like you have seen a simpler setup, Ricks re-build sounds like it went easy also.
It might be Santa time!

wayne petty · December 27, 2010, 07:56:23 PM

if one side of the pump thats mounted is working....

if you hook at up directly.. it will make pressure....

have you tried at their distributers...

the factory is probably closed for the season...

but the distributers will be open.... they may only sell through distributers...

i seem to recall these were bought from Ebay...

i saw a post .. about a almost complete machine shop.. that had been swamped by katrinas surge... and left to rust in place... on person mentioned.. why not just sand blast the rust off.. slap a coat of paint on .. Ebay it... i hope that you are able to fix it...

i call call the local compressor shops around LA... see what they get for a new set of valve blocks... if i get a break tomorrow... i will give them a call....

rooster · December 29, 2010, 04:01:00 PM

Quote from: wayne pettyif one side of the pump thats mounted is working....

if you hook at up directly.. it will make pressure....

have you tried at their distributers...

the factory is probably closed for the season...

but the distributers will be open.... they may only sell through distributers...

i seem to recall these were bought from Ebay...

[/quote

I isolated one of the cyclinders and it did bring the preasure up to 120 pds and the compressor shut off (havent seen that in a long time) it took some time to do this. There were afew small leaks in my jury rig before the check valve, very small but thay would make bubbles.

I guess I should do the same thing with the otherside just to see how well it does.

I see no distrubuter on the web site, a net search says theres one in Hawaii. There office is closed until Jan 4th!

I got the compressor new off ebay cant remember but I think less than 100.

Now its back to the heater!!

Happy new year!