OH NOOO! Quincy failure

One of my Quincys wouldn't supply air. Typical problem with Quincys is the high-pressure side exhaust valve gets carboned up and the valve disk
won't seat right. We did cut the instances of the failure by switching to synthetic oil. We had been using Rotella non-detergent and the valves would carbon up three to four times a year. With synthetic they carbon up once every two years.
There's a clipboard hanging on the compressor rack and we log all maintenance and failures, one page will log many years. We change the oil twice a year; it probably should be more often. To clean the valve takes about half an hour, a quick disassemble and brushing of the parts with a wire wheel and the disk will seat right for another two years.
The other three valves don't get hot enough to scorch the oil. I'm definitely not complaining about the Quincys, they are the best compressors made but I wonder if there is a cheap cure to what I consider a design flaw.
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Tom Gardner wrote:

Add some cooling to the compressor head? Even copper pipe, a small pump, radiator & fan would help. There are small radiators made for laser systems on Ebay, that will hold a couple 5" muffin fans.
--
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"Michael A. Terrell" wrote:

Figure out what temps that valve is seeing (IR thermometer may help), compare to the carbonizing temp for the synthetic oil and add cooling to get it under the critical temp.
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Also, check if the intercooler fins are plugged with crap/wood/oil crud from your (Tom's) shop and do not do their job. This would cause temps higher than desirable.
i
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wrote:

....and also has a noise shield or weather shield been built around the compressor which will end up locking heat in.
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Tom, the oil is the source of carbon. I am thinking that perhaps you need to work on the seals and such, to cut down on the amount of oil that goes into the compressed air.
i

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When we change oil, it's never low and the water in the tank and coming from the cooler aren't milky. But I'm sure some oil gets past the rings and such. I don't know what it should be though, it's been 20 years since the last major rebuild on that pump. The other two are about the same.
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What about your intercooler lines, are the fins plugged up?
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On 12/7/2011 7:02 PM, Ignoramus5603 wrote:

Nope, all's clean. This part of the shop is about the best. Haven't you seen Quincys carbon up? This one runs at about a 5o% duty cycle and the switch is set at 85 and psi. If pressure drops below 80 psi number two Quincy kicks in. We have a third Quincy ready to go if there is a massive failure of some sort and a 10hp Hydrovane if all else fails. Another Quincy pump in in the machine shop awaiting an overhaul but it never seems to be a pressing issue. As you can tell, air is very important to almost every operation and a number of machines have air as their only energy source.
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Tom Gardner wrote:
This one runs at about a 5o% duty cycle and

Why are you running a two-stage compressor at 85 PSI? That doesn't make sense! These pumps are designed to deliver somewhere between 120 and 175 PSI to the tank, and the first stage produces close to 80 PSI. So, the 2nd stage is pretty well wasted the way you have it set up.
I think you'd do better with all single-stage compressors if you only want a line pressure of 85 PSI.
Jon
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On 12/8/2011 11:25 AM, Jon Elson wrote: ...

That's what regulators are for...
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On 12/08/2011 12:11 PM, dpb wrote:

Well, yes, a lot of people use 2-stage compressors to fill a tank at 175 PSI and then regulate down to 90 PSI or so. But, that is not efficient. If Tom's compressor is running 50% duty cycle, it probably makes some difference to make it efficient.
Jon
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Tawm, Tawm, Tawm...! If most of the machines are Air operated only, and your draw during the day is fairly constant and a known volume...
Why the HELL are you still running regular start-stop piston air compressors all day? Are You Mad?? I don't want to see the Demand Charges on your power bill as these big motors are cutting in and out.
At the Very Least you should have Unloaders installed and run the primary machine in Constant Run Unloader Mode all day, and you can rotate that duty between the three Quincies you have real easy.
And if Machine #2 starts more than twice an hour, it needs to be in Constant Run, too. Motors don't like short-cycling.
You'd be a lot better off for a factory with a known constant daily air load at around 100 PSI by going to a Screw Compressor. They have VFD's and run in their own version of Unloader Mode - they throttle the compressor to the needs of the shop, and will fully unload when everything shuts down for Lunch. One start surge in the morning, then it runs for the day.
Figure out whether you need a 10 or 25 or 50 HP unit, and then haunt the regional auctions till you see one that's the right voltage and someone screws up and gives it away. Grab two if they're insane. Haul it home.
--<< Bruce >>--
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Yes, but not as badly.

Sounds like you need a rotary screw compressor. I sell them on various occasions for very cheap prices.
i
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On 12/8/2011 9:19 PM, Ignoramus12911 wrote:

I do run the Hydrovane full time every so often but people don't like the constant whirr.
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Tom Gardner wrote:

Move it to the restrooms. Then they won't spend a lot of time in there. ;-)
--
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If it doesn't have one, maybe add an oil-cooler circuit.
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This maintenance issue is another reason why 2-stage air compressors really aren't worth the additional cost (or better at delivering compressed air), compared to a single-stage multi-cylinder air compressor.
The second stage of a 2-stage pump is essentially just wasting power as the smaller bore bumps up the pressure of the larger/intake bore.
In a single-stage 2 cylinder pump, both bores create a more consistent air flow, not like the hiccup or stutter effect of a 2-stage.
The oil carbon residue (even though minimized by synthetic oil) is a result of the elevated heat generated from the second stage, and only a routine maintenance schedule is likely to avoid performance issues.
This is proven by the relatively low pressure cut-off settings on the unit mentioned.. the second stage is still generating elevated temperatures even though the demand on the unit is low. If a single-stage pump was operating at this minimal performance level (80 psi is hardly work for a quality air pump), it would require far less repairs (presuming pumps of similar quality and routine oil changes).
Any oil types that I'm familiar with will all create solid residues when heated to a particular temperature, at that temperature point is best avoided. Unless there is an additive to change the oil's characteristics without modifying the lubrication properties, it's just the way they are, IME.
--
WB
.........


"Tom Gardner" <mars@tacks> wrote in message
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The efficiency of a single stage falls off around 120 - 150 PSI due to the mechanically (or economically) necessary cylinder head clearance that limits compression ratio.
jsw
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It seems to me that 120-130 psi would still be plenty of overhead for the stated cut-off of 80 psi.
For the purposes of a home shop, where volume is sometimes the primary requirement, 130 psi shut-off is completely adequate with a suitably sized tank and a reasonable pump displacement.
When a working pressure near or over 150 psi is actually needed, a 2-stage is neccessary.
Most equipment is designed to operate at up to 90 psi and 150 is a considerable amount of overhead for a properly sized unit. Yeah.. I use the high side of a regulated air line for an impact wrench sometimes.
While the second stage of a 2-stage pump is bumping up the pressure of the first/intake bore.. in a single stage pump, the second piston is delivering air to the tank the same as the first.. resulting in a greater displaced volume delivered to the tank.
At a point, both systems become inefficient, especially if the unit isn't adequately sized for the usual demand.
One high-volume piece of equipment that's often mentioned is a sandblaster or blasting cabinet. Using a higher pressure for blasting sheetmetal parts often results in a severely warped workpiece due to the metal expanding. Lowering the air pressure will prevent expanded metal.
If a good sized air compressor can't keep up with a blasting gun, it's better to reduce the orifice size of the tips.. the pressure can remain reasonable, the air compressor can keep up and the media is used more effectively.
--
WB
.........


"Jim Wilkins" < snipped-for-privacy@gmail.com> wrote in message
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