old Curtis compressor question?

[kenfain]

I have an old Curtis compressor. Model C9685-28755. I love how this thing is made. Old school design. Centrifugal unloader n such. I'm hearing an unnatural noise in the top end. A kind of strange knock. Not a regular knock. But irregular, intermittent. Also doesn't sound like a solid knock. Not a tap or nothing. More like a "burble "for lack of a better term. I'm sure my description leaves a lot of questions. But that's all I can think of to describe it. Seems like a few people on this forum, have a more than average knowledge of very specific compressor problems. So I'm hoping maybe I can get help pinning this thing down. The machine works flawlessly, otherwise. The noise seems to definitely be coming from the very top. Only thing up there are valves right? Any help would be appreciated.

 

[kenfain]

Really? Nobody? Not even a guess?

 

[Jim Johnstone]

Check the valves to make sure they aren't getting stuck and clacking around or fluttering.

Sent from my SGH-I727R using Tapatalk 2

 

[Grounded Ken]

I would start by making sure all the valves are tight. When is the noise happening?

 

[kenfain]

Happens from right after start up. It's intermittent, but consistent. If that makes sense. I suppose what I mean is it doesn't go away after it warms up. In fact it seems to get slightly more noisy, louder. Only slightly. I'm suspecting a valve problem. But it also has an unloader on top. I was hoping someone would know what's involved with breaking into this thing. I mean,will it come apart at my speed or will springs or ball bearings come flying out? Plus it has several different types of nuts on top. I know the small ones take the head off. But the big ones are like a nut in a nut.is one for inspection, one for access? My concern is it's possibly got an adjustment, that I could knock outta whack. Don't have any kind of manual for this thing. Just lots of questions. Not the least of which is torque values for re-assembly. Thoughts?

 

[Grounded Ken]

If you have the external centrifugal (the weights behind the flywheel), this could be part of the problem. Give me a call tomorrow 1-800-845-0125, I have a lot of Curtis info.

 

[crewchief]

You just unbolt the valve covers and pull the valves out. I do this almost weekly. Your best option is to send it out for a rebuild if you are unsure. These are tough compressors that can handle a good bit.

 

[kenfain]

Yeah,I might have too try that. The manual on most compressors say to inspect the valves every so often. I called Curtis. Talked to one of the tech guys. He talked me thru the process. I was at work at the time. So I couldn't make full use of the advice. But In my defense, I have to say. He took about fifteen minutes explaining how to take out a single valve. Didn't expect it to be that involved. Afterwards asking him in summary. Was it easy, and just sounding complicated? Should I just wade on in? He said it was fairly involved. Of course depending on experience and or mechanical abilities. His advice was if it ain't broke ,and it makes all the air it's supposed to. In the amount of time it's supposed to (he did the math for the proper time 0 psi to cutout. ) Then leave it alone. Course that was before the noise got this bad. Anyway he basically talked me out of it. However things have changed. I think I'm goin in. Just trying to find out how to go about it. And as was suggested earlier. Might not be valves at all. Might be the unloader. I'm goin in, but I don't want to rush in unprepared.

 

[pcmeiners]

Sounds like the check valve or the valves need to be cleaned or overhauled, possible unloader issue.

Just had to completely dis-assembly my D96 pump due to Sandy flooding. Pretty straight forward, easy.

Download the D96 parts diagram pdf to show how the parts go back should you forget.
As to the valves, the toughest part is removing the covers. Takes a bit of force ( actually a *****), as in a pipe on a monkey wrench, reassemble with Never Seize, torque to spec. ( guess it would have cost Curtis $.01 more to put never-seize or equal on the cast threads)

My valves were a bit rusted so I wire wheeled the parts, luckily the important sealing surfaces were OK; each valve comprises of only a few parts. Each valve is slightly different then the others so mixing up parts is not a big issue, but separate and clean individual valve parts separately. I went over the sealing surfaces with oiled wet/dry 2000 grit paper. I oiled each valve assembly before reinstalling. Make sure you introduce no grit into the head, which requires you to clean everything a few times before re-installing. Personally, since you would be basically doing only the valves, if it is not the check valve, I would remove the cylinder head, so as to not introduce foreign matter into the cylinders while removing the valve assemblies; most likely the head gasket will remain intact as mine did.

As to the check valve, if that is the issue, could be broken sealing disk or spring, just purchase another if that is the case. Ebay has them.

If you need seals/gaskets, I purchased a gasket set frrom OEM Air Compressor Corp. for $29.00 which has the copper seals located in the valve assemblies, along with all other pump gaskets.

http://www.oemair.com/Home/tabid/219/Default.aspx

 

[kenfain]

Sounds good to me. Grounded Ken,gave pretty much the same diagnosis. And also a couple of manuals. Thanks to Grounded Ken and all the pros who do this stuff all day. Then coach us through all our technical needs in their spare time. You guys help out more than you probly realize. Building the experience, and the confidence to do it yourself. Not have to pay someone. PRICELESS!! Thank you. Hey I'm gonna read this here manual. Then I'm goin in! Wish me luck.

 

[dwp99]

I also have a Curtis compressor with the centrifugal unloader. 1948 vintage. Keep us posted with pictures on your progress.

 

[kenfain]

To be totally honest. All I have for a computer, is this tiny little phone. I'd love to post pics, but I don't have a clue how it might be done. If it's even possible. If someone knows a way. Please share. Bear in mind I know less about computers, than compressors. And that's not much.

 

[Grounded Ken]

I thought about a bit more, check the unloader plunger, it may be bouncing off the valve plate intermittently make the lub-lub sound, might be a broken or weak unloader spring.

 

[kenfain]

Thanks Ken! Received all the info you sent. Just what I was wanting. Yes it looks like I'll have to start with the unloader. As it's right in the way, getting to the valves. One question comes to mind. If the spring is not broken, which would be obvious. But weak, how would I know? Having no frame of reference. Will there be obvious signs, such as scuff marks from extended travel of whatever the spring holds? I know to look for bent, broken or excessive wear. Anything else? I will of course clean all surfaces prior to re-assembly. But I'd really like to have that aha!..there the problem, moment. I really don't like, taking apart something not working. Finding nothing wrong. Putting it back together.now it works. Feel kinda cheated ya know? Course that's better than the the alternative ....

 

[Grounded Ken]

The spring you want to check is down by the crankshaft on the lever mechanism.
When the machine stops it pull a pin upward to relieve pressure on the head. As it (the compressor) starts, the centrifugal weights actuates the lever arm pushing the pin down closing the reliefs in the head. If there is any wear in the lever mech. this can alow the pin to bounce. This pin is inbetween the valves in the head. Check all linkage for wear or slop. It's been a while since I've dealt with one of these units. There are no parts available for the linkage, from Curtis or the aftermarket that I know of. But if the linkage is too far gone there is a way to unhook and unload in a different way.

 

[kenfain]

I've removed and cleaned the low pressure in and out valves. Also removed and cleaned the pin and spring for the unloader. I don't know about the tolerance of this thing. Seems snug enough. No slop. Spring seems ok. The only thing I've seen that seems off, is on the output. There are 3 small springs. One was shorter than the other 2. I replaced it with a similar spring of the same length and diameter. (I'll have to remember to replace it with the right one later ). Otherwise ,work continues. Thanks all.

 

[kenfain]

Just an update. I've cleaned and polished all valves and seats. The spring issue has been resolved. Everything assembled. Pumping air like crazy! Although it was quite a struggle, getting the high pressure side apart. Had to use wd40 let it sit overnight. Still had to use a cheater. Done, but the noise is still there. The search continues.I think I should check the wrist pin. Seems easy enough to access. Any thoughts. Do I have to drain the oil? Is there a gasket? Why can't I just pop off a side, have a quick look?

 

[kams1973]

You've gone this far, so you may as well remove the side covers and pull the conrod caps for a visual inspection. In addition, you will be able to check the ring for the pump's positive ring fed lubrication. If everything checks out, remove the bolts for the cylinders and pull them with the pistons. Then remove the pistons, inspect the rings and wrist pins. If all checks out, reassemble. Making a new gasket should be a snap.

 

[pcmeiners]

If you proceed to delve deeper...

Pulling the cylinder body is a piece of cake, light force the pistons come out. There is a paper gasket between the cylinder body and the crank case. When you pull up on the cylinder body, once you get a couple inches of clearance, place a heavy rag in the gap on both sides so the pistons do not hit the crankcase, once freed. To reinstall, no piston ring compressor is needed, the is a bevel on the piston bores, so all you need do is oil the cylinder wall and squeeze the rings a bit with your fingers, as you push gently. The pistons go in a certain direction, so refer to the parts diagram, also remember to space the piston rings gaps properly. Curtis has PDF as to the torque for all the bolts.
If you decide to go that far, I would clean out the crankcase thoroughly. Mine had bits of metal from the sand casting in the sump (aside from fine sand from hurricane SANDY ). Before I closed mine up, I threw a super magnet in the sump. You will need to drain the oil and you will need to make gaskets or buy them.

I see you enjoy the largest valve cover removal, I had loads of fun getting mine off.

 

[kenfain]

If I had it to do over again. I'd use larger tools.

 

[mcd]

I had similar symptoms on a D97 I just picked up.
It has unloaders that are operated by air pressure, but I'll wager the internal parts and functionality are the same.

I'll post the operating principal on the D97 unloader and hope it might help someone who might be doing a little head scratching:

These appear to be very stout units, with some serious durability, there are lots of little parts, so take lots of pics at disassembly.

I noticed there wasn’t the familiar release of air after the compressor cycled, and was concerned the unloader was malfunctioning.

I disassembled the thing to figure out how it works.

The system uses 2 diaphragm actuators, located on the cylinder head, one over the intake port of the low pressure cylinder, and the other over the intake valve of the high pressure cylinder.

When pressurized, these diaphragms actuate rods that hold the check-valves open. Kind of like a compression release on motorcycles of my youth.

The diaphragms are connected to a 3-port solenoid that controls air pressure.
Solenoid port connections:
1: To Diaphragms
2: To Pressure storage tank
3: Vent to atmosphere (small inconspicuous hole on lower side of solenoid valve.

When the compressor has reached its high pressure shutoff, the solenoid is also turned off, which allows tank pressure to flow to the diaphragms causing them to push the intake valves open. There will be no external or audible release of air in this process, just the slight movement of the actuator rods to hold the intake check-valves open. (you will be able to see the external springs compress during actuation).

When the compressor starts, the held open valves ensure the motor faces no head pressure, and can easily come up to speed.

At the same time as the motor is energized, the solenoid is also energized, and begins to bleed air from the diaphragms to the atmosphere.
There is a restriction in the atmosphere bleed, which is calibrated to allow sufficient time for the motor to reach speed prior to facing head pressure.

Now that I understand how it works, diagnosing issues is easy.

A lot of parts for sure, but a functionality that is elegant.

And one easily connected to the relay outputs of a VFD with a slow ramp. I’m running a 10hp 220v 3ph motor on single phase with a Fuji 15kw VFD.

Found some broken springs and a corroded check valve in mine, so off to order parts tomorrow.

I am hoping the burbling and intermittent knocking from mine was caused by the broken springs on the valves. Finger crossed.

NOTE: even with the broken springs, this thing made a TON of air and was very quiet !!

Cheers,
Chris