Paasche AB Turbo troubleshooting

suviljan

Young Tutorling
Dear airbrush gurus,

I purchased some time ago Paasche AB Turbo on eBay. Let's put this tactly and say I have seen less temperamental and more reliable boat engines. I have managed it to make it work with inks and Vallejo Airbrush Acrylics, but there is one big issue.

The turbine works erratically. I have used 1.5 bar as the intake pressure, and the turbine doesn't take on spinning until jerking the finger lever back and forth. And if I stop spraying for a while, after a minute the turbine may start or maybe not. I have checked the needle, and it is okay. I have loosened the bearing screws on the top and bottom of the turbine housing, so it should not be an issue.

Can you please help me? What is wrong with the turbine? Or is it back to the trusty old Iwata HP-C ?

- Suzy, IPMS Finland member Fi-889 -
 
There is a screw to adjust the amount of air being directed toward the turbine. Air gets split, some headed toward the turbine, some to the air blast jet at the needle - you need to establish a good balance. You need to make sure that you have adequate airflow hitting the turbine, Then you need to make sure that the bearings are not only loose, but also adjusted properly - if they are too loose the turbine will wobble, and stick in the bearings. If the bottom bearing is too high or too low, it will cause binding of the turbine. Try tuning the turbine without a needle in the brush. If it stars binding when you add the needle, well, then you know it's the needle... they are a pain in the arse to get just right. Once you do, you will know, and you will now why you wet through the trouble. The vast majority don't have the patience, hence the brushes demise..
 
Hi Dave,

I have had to open the turbine adjustment needle almost fully open to have the turbine to spin. Could it be that the screw which connects the needle cam to the finger lever is too tight?

I have attempted to adjust the top and bottom bearing screws of the turbine housing, and they definitely do have an effect on the spin. I will continue the fight today and tell you more about the results.
 
Today's results:

I opened the turbine housing and adjusted the lower bearing so that the nozzle hits the turbine wheel maximally. The needle camshaft screw wasn't the culprit - it moves along the small eccentric on the turbine shaft.

I then took off the needle and tried the airbrush without the needle. It appears the turbine is extremely sensitive to the airflow adjustment screw (on the left side of the shaft, just next to the turbine housing, and I need to open the screw almost fully to get an even spin. Is this normal?

I put the needle on. The needle is OK, as it doesn't compromise the function any way.

How much should I adjust the screw on the blastpipe?
 
I then took off the needle and tried the airbrush without the needle. It appears the turbine is extremely sensitive to the airflow adjustment screw (on the left side of the shaft, just next to the turbine housing, and I need to open the screw almost fully to get an even spin. Is this normal?
The turbine should spin even at small openings of the air screw. It should start out slow, and then gain speed as you open the screw. There are a few instruction sheets available in the documents section - you might want to double check all the adjustments on the brush according to the instruction sheet. Make sure to also check where you have the screw in the trigger set.
 
Hi Dave,

which pressure should I have? I have 1.5 bar feed pressure on the compressor (I usually use 1 to 1.5 bar on my Iwata). Stould I have more? What coul be wrong if the turbine starts spinning only at the turbo screw almost fully open? Should I use higher feed pressure?
 
pressure should be OK, but won't hurt to bump it up another half bar... I would guess at the bearing(s) not being adjusted properly, as the turbine should spin quite freely.
 
Interesting read, I hope you get it sorted.

I love to tinker! I hate having things that do not run or work and often spend way more keeping something old running and repairing things rather than buying new.

Its much more satisfying and good for the planet, atleast thats what I tell myself!

I imagine this will be a rewarding repair if you succeed and can take advantage of its ability to accurately tune paint and air feed. I hear they achieve the finest lines of any airbrush!
 
I twisted the knob to 3 bar. It seems the hose compressor joint of the Paasche hose leaks. I then loosened the lower bearing screw on the airbrush housing. The turbine started - at first, with slow spinning speed, and it gathered revolutions. It sounded like a dentist drill. I think I let the turbo screw be as it is. It is almost wholly open, but at least the turbine spins. Any idea why mine has to be that much open? Is there so great a pressure loss somewhere?

My Iwata works perfectly well with the Iwata hose at 1 to 1.5 bar pressure. Seems I need to twist the knob with the Paasche Turbo a little bit higher.

I then adjusted the paint cup and tried Tamiya lacquers thinned with acetone. Whoa! I could get line approximately 0.8 mm wide - not yet the hairline as promised with the Paasche Turbo fluff, but narrow enough to do Wellenmuster camouflage for 1/144 German aircraft.
 
It is a mistake to compare working pressures between two different types and brands of airbrushes - apples and oranges kind of thing. The air valves are different, the air passages through the brush are different, etc... All that matters is that you can get it to work the way you want it to. There is nothing easy about learning a Paasche AB Turbo. If I'm gonna be honest, I will say I am impressed you got Tamiya to spray from it at all, so job well done there!
 
It seems I just have to use the Paasche Turbo with significantly higher pressure than the Iwata HP-C (or the Iwata clones).

Do you think it would be a good idea to insert a drop of lubricant on the turbine bearings? Could it be possible that there could be a foreign obstacle in the airway? Or a simple leak (and an ensuing air pressure drop).

Anyway, when I bought that gadget, I was well aware it is capricious and tricky, but so far the results seem encouraging. One of my modelmaking friends has successfully done MRP lacquers and Xtracolor enamels with Paasche Turbo.
 
I know a tech that used to repair them through a retail outlet, and they used Petroleum Jelly (Vasaline) as a lube for the turbine bearings. I use poly-urea grease, myself.
 
I will go on adjusting and fiddling around. Seems I have gotten at least something right ;) I will try lubricating the bearings - I noticed they were completely dry. I will report you how it goes - it is late now here where I live.
 
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Today I put a pinch of Klöver Vaseline on both the top and bottom bearing of the turbine. Whoa! It began to spin immediately and without issues. I was able to screw the turbo screw inwards two whole turns, and the turbo still spun.

I call the turbine now adjusted. I will try tomorrow with both lacquers and acrylics - seems by the earlier results that the needle and blastpipe setting needs only minor fiddling. I will also ask my friend on how he did with modelmaking enamels).
 
Today's Turbo Fight:

I get now the turbo spinning at 2 bar pressure. It accelerates to full speed at five seconds, and the turbo screw can then be turned tight for one round and it still keeps spinning. It appears it spins best when the trigger is ahead and needle least out.

I tried today Ammo by Mig Acrylics (1 drop paint and 1 drop Vallejo Flow Improver). I was able to get 0.5 mm wide constent pattern, but it is very sensitive to the position of the paint cup. It seems it is now time for fine-tuning.

Tamiya Lacquer (1 drop paint + 1 drop acetone) went also fine - I got rather thin line, but not yet the hair-thin line. My friend insisted enamels should do just fine, but they need to be thinned down a lot.
 
Today's Turbo Fight:

I have now found the good airflow pressure (2 bar) and blastpipe, paint cup position and turbo screw setting. I tried today Tamiya Lacquer 1:1 with acetone, and WHEEEEEE! I managed to get consistent extremely thin line - approximately 0.1 mm wide.

It seems I have found the correct settings, and now the "smoke ring" camouflage seen on WWII Italian aircraft, would succeed in 1/144 scale. I got a suggestion of 20% Humbrol enamel + 80% mineral spirits - that should also do the thing.

Wowsers! An awful fight, but this must be the finest piece of airbrushing hardware there is.
 
Good to hear. I have 2, one from '40, one '80. I have a bunch of parts inbound and will be diving deep into rebuilds and adjustments.

In the past, messing around with them, it's really a balancing act. Once you get it going well, you don't want to touch anything, but change a needle bend and you'll redo everything.

Different greases have different results in performance as well. I've tried wheel bearing grease, ceramic, clock oil and moly. I just picked up some poly urea based on Dave's recommendation to use when everything is replaced.

Both of mine (both very cheap, under $50 each) have a frozen upper bearing, so I can only adjust from the lower. I can bring up the lower bearing on the 80 and run it well without the upper cover. Theres a bit of vibration in the wheel, but it spins freely.

The '40 shaft bearing is toast, the top part is flat, instead of a tapered point like the later ones, it has a small spindle that is broken, so I've always operated it without contact on the top. Fortunately the shaft bearing thread are the same between models, even though the turbines are completely different in material and design (unfortunately Paasche only sells them as an assembly so I had to pony up $34 each for a pair). The cam is a bit different so I need to use an '80 model walking arm i the '40 but it works fine. That brush design is a bit different, instead of the turbine cover, theres a brass arm that holds the bearing.

I generally run my brushes around 20 PSI or lower, as low as 5-8 in some cases but the I dial it up to 35 for the turbos. I treat them like the other air hogs on my collection.
 
Dear airbrush gurus,

I purchased some time ago Paasche AB Turbo on eBay. Let's put this tactly and say I have seen less temperamental and more reliable boat engines. I have managed it to make it work with inks and Vallejo Airbrush Acrylics, but there is one big issue.

The turbine works erratically. I have used 1.5 bar as the intake pressure, and the turbine doesn't take on spinning until jerking the finger lever back and forth. And if I stop spraying for a while, after a minute the turbine may start or maybe not. I have checked the needle, and it is okay. I have loosened the bearing screws on the top and bottom of the turbine housing, so it should not be an issue.

Can you please help me? What is wrong with the turbine? Or is it back to the trusty old Iwata HP-C ?

- Suzy, IPMS Finland member Fi-889 -
Hi Suviljan, both of my turbos are from the 1990s. I have them both from new. I have rebuilt one of them a couple of times, including replacing the bearings. It is my experience with both of mine, that the bottom tungsten bearing should be screwed in all the way, and then backed out one quarter of a turn. The top bearing should be adjusted so that it just binds up the turbine, and then backed off so it runs freely - one eighth of a turn will likely be close to the correct tension. Vaselene not only serves to protect the tungsten bearings, but also keeps the internals of the turbine housing from drying out. For a while I was missing the point in using a silicon grease. However, in my experience, vaselene does exactly what it is supposed to do. Please let me know how you go.
 
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