DeVilbiss Model PAFTV Runs constant, cannot exceed 90PSI in Tank

by JP
(Danbury CT USA)

Exploded pump/part view

Exploded pump/part view

Exploded pump/part view
Their version of a part manual

DeVilbiss Model PAFTV 660 V-3 1STG Oiless 6HP/60Gal 240Vlt.


Set for 120PSI cut off & 60 PSI cut in. Mainly used for running air tools and clearing/blowing with various nozzles.

Was working fine, the just cut in at 60 one day, and began running constantly and will not exceed 90PSI into tank.

Holds pressure fine, no leaks heard or sen anyplace, including with soapy water spray test for bubbles.

The manufacturers manulas & web site & links are useless.

Your other page addressing this issue is the best source I have found so far, and I believe that my issue may well be one of the ones you mention.

My question is, do you have or know of any diagrams that exist, that I can access to try to narrow down the problems you mentioned?

Perhaps something that shows the typical direction of air-flow thru the pump & into the tank? Possibly with labels as to the parts/locations you have mentioned in the previous respone page for this problem?

Any direction you can point me in to try to narrow what I am looking for would be greatly appreciated by me and I am sure many others.

Thanks, Joe

__________________
Bill says....

Joe, no, I don't have them, but I'm hoping for you that some of our other site visitors may have the info for you.

Cheers,

Bill

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May 30, 2011
For Inranraaj Re: Servo piston-unloader valve
by: JP

I am guessing that you replied to my posting before my reply to Bill's first answer made it to the page, and I got Bill's reply before your" made it to the page. As I said to Bill, I know next to nothing about compressors & my main mechanical experience is all automobile related. I don't know if you can see the details of the explodes parts pics I included in my original post, or not. But if you can, perhaps you could let me know which parts you are speaking about by the number on the exploded views. If you cannot, and would not mind emailing me direct at
joepeterson56@yahoo.com, I can email you the parts views as the original PDF files I got from the DeVilbiss web site. I really would appreciate it, especially if it saves me from tearing it down needlessly and costing me $$ for new gaskets I may not need to begin with.
Thanks, JP

"Does this compressor has a servo piston, normally will be located in the unloader valve.Check on sticky servo valve or damaged of the tension spring.You can service the servo valve and while the compressor running, do shut off the oulet ball valve and see what is the servo piston reading at the pressure gauge.If its show 90PSI,adjust the servo valve by mean of adjusting screw.I feel its more likely a servo valve jammed or sticky valve."

May 30, 2011
DeVilbiss Model PAFTV Runs constant, cannot exceed 90PSI in Tank
by: Inranraaj

Does this compressor has a servo piston, normally will be located in the unloader valve.Check on sticky servo valve or damaged of the tension spring.You can service the servo valve and while the compressor running, do shut off the oulet ball valve and see what is the servo piston reading at the pressure gauge.If its show 90PSI,adjust the servo valve by mean of adjusting screw.I feel its more likely a servo valve jammed or sticky valve.

May 30, 2011
Thanks for the reply bill
by: JP

Do you think The right track tho, that it is one of the causes you mentioned? There is only one gasket on each pump, so I guess I could pull them, but unless it is a super obvious gasket failure, not sure how I would know by looking at them, knowing nothing about these thigs. All my experience has been with car engines, but I would imagine it should be similar. I did forget to mention that a number of years ago, this thing did blow up the connecting rod/pump valve assemblies for no aparent reason & I had to mail order and replace those. They use way too many plastic parts in these pumps to suit me. I was also thinking maybe the plastic caps & or Orings that seal those could be dried/cracked.

Guess maybe I should just do a tear down/rebuild on it unless I hear back from another reader here within a few days. Not sure if I will still be able to get all the parts for it though, & hate to think what a new one would cost me these days. Never realized just how much I use this thing until it has been down for 2 weeks!

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devilbiss 4hp 20 gal

by buddy
(cameron, nc.usa)

this air compressor is roughly 15 yrs old....never had a problem with it. few days a go, i turned it on and it wouldnt build over 60 lbs of pressure. got a new pressure switch....still will not work.....and its not the voltage . i have it plugged straight to 120....what else could be the problem.....sucking air good....not huffing at all.....

__________________
Bill says...

Hi Buddy. It could be the vale leading to the tank, but I think it's more likely that you've got an internal gasket failure, and the compressed air is just cycling inside the compressor once it reaches the pressure level to open the gasket leak.

Cheers,

Bill

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I have a devilbis compressor that turns on and off when building pressure

by jacques Dufour
(Montreal, Canada)

Hi
When I start my compressor it goes from 1 to 50 psi without problem, than it stops for 15 seconds and restart for 15 seconds increasing from 50 to 60 psi.
than it stops for 10 seconds and restart for 10 seconds increasing from 60 to 70 psi., stops for 10 seconds and restart for 10 seconds increasing from 70 to 80 psi. and so on, till it gets to the allowed pressure(110psi).
For all these steps the pressure contactor remains on till it gets to the final pressure ant than turn off.
I changed the valve for another one without any improvements.
If I unplugg the tube going to the tank( valve) and let the compressor run without pressure ; it won't stop.
If I block the hose with my thumb; it will start cycling on and off...

Any suggestion

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Flow restriction from Devilbiss PRO 4000 to 60 gal tank.

by Terry Cole
(SOUTHERN CALIFORNIA)

Mounting of the V-Twin was not an issue, but the plumbing to the tank requires some modifications

Mounting of the V-Twin was not an issue, but the plumbing to the tank requires some modifications

Mounting of the V-Twin was not an issue, but the plumbing to the tank requires some modifications
Here's how I adapted the new pump outlet to the existing 3/8
The limiting factor is that the tank has a 1/2

Replaced the frozen tandem, single phase pump on my Devilbiss PRO 4000 5-horsepower, 60-gallon compressor with a V-twin pump I bought new from Harbor Freight (described as being designed for a 5-horsepower motor).

Besides the necessary mounting modifications and determining the correct pulley sizes to get the desired pump speed relative to the five-horse GE motor, I had to adapt the hard line from the pump to the tank.

The original line size of the tandem pump was 3/8" tube, attached to a 1/2" pipe in-tank check valve.

The V-twin uses a 3/4" tube crossover from the cylinders and a 3/4" tube as an exit to the tank.

I originally tried to adapt these parts and while the compressor would spin nicely with an empty tank up to about 70-psi, once at that point the motor loads and eventually triggers the automatic motor shutoff.

Likewise, if I reset the motor and try to fire it up, it wavers, starts then slows down and again triggers the overload circuit or pops my fuse at the panel.

Obviously, I discovered that going from 3/4" tube to 3/8" tube is too much of a restriction and is causing the pump to hit a wall with regards to flow.

My question is this: Will going from the 3/4" tube down to a 1/2" tube be a sufficient derestriction? Unfortunately, the tank bung is 1/2" NTP. That will allow me to get a 1/2" NPT TO 1/2" tube check valve. Otherwise, my only alternative besides getting another pump is to drill and tap the tank bung, which will be almost as expensive (cost of drill and tap) as a smaller tandem pump. This appears to be a problem that many might encounter when replacing a factory pump with a less-expensive aftermarket one. Any suggestions will certainly be appreciated.

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Aug 30, 2014
Terry Cole did you ever get it working >?
by: Anonymous

wondering if by Terry Cole
from (SOUTHERN CALIFORNIA) ever got his compressor pump swap on his 60gal tank working I have the same twin pump and was going to do the same thing I just need to no if you worked the bugs out before I spend any more time and money for something that wont work ? thanks

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