Troubleshooting "Hiccups" with an Air-Assisted Airless Gun

Woodweb comes to the rescue again, diagnosing a finisher's spraygun malfunction and saving him a bundle of cash. April 10, 2008

I've got two Kremlin sprayers. One of them is older than the other. The older one has a much heavier gun than the other. The older gun is leaving a strange pattern. When the pump cycles, the gun stops spraying for a split second, leaving a space with no lacquer. It also sprays a much finer mist just before this happens. I have taken the pump apart and everything seems normal. Can anyone shed some light on this problem?

Forum Responses
(Finishing Forum)
From contributor J:
We call them hiccups; it usually means I have to add oil to the piston pump.

From contributor T:
You may have some debris caught in either the upper or lower ball of the pump. As the pump cycles, it loses pressure on one side because the ball cannot seat properly, thus the gap of material being dispensed. As the material ceases to dispense from the tip, the atomizing air over-particalizes the spray patterns, resulting in the fine light mist you described. Once the cycle of the piston reverses, it catches up and starts to spray normally again until the next stroke.

To test this and see which, if either, ball is failing to seat, you can perform a stall test. Trigger the gun while watching the direction of travel of the piston. Stop triggering the gun with the piston in the up direction of the stroke. Wait 60 seconds or so... The piston should not move or creep in the up direction without the trigger being pulled. If it moves at all, the upper ball is the culprit. Repeat the test, stopping the piston in the down position. If it creeps with the trigger closed, it is the lower ball failing to seat.

The only three other (less likely) reasons I can think to see a wink in the fan pattern is: (1) a clogged filter between the pump and the gun. Obviously check all filters for obstruction. (2) Using non-stainless steel hoses with water based or acid catalyzed materials. This would cause an obstruction (water or acid can cause the copper ions to leave the brass fittings used on non-stainless hoses and form a hard mass in the fitting) to develop in the fitting of the hose, eventually cutting off flow though the hose. This would resemble the effect of a clogged filter as well. (3) Putting the Teflon packing in the pump section in upside down, not allowing for the seal to engage in the upward stroke. Make sure the seal is facing with the wide part in the upward direction.

From the original questioner:

Thanks - I'll try the test and see what happens!

From contributor C:
Contributor T, your advice about testing the up and down cycle of the pump has saved me somewhere between 100 and 1000 smackeroos, as that was the over the phone quote my local Kremlin dealer gave me. It turned out the downstroke was the culprit and removing the cage with the bottom ball and thoroughly cleaning it solved my problem. I have had priming problems with that ball before, but never a skipping fan, so I trusted my dealer when he said I needed a rebuild. If you want me to send you that money it would be fair to me, as fixing it took less time than packing it for shipment. I was not the original poster of this problem, I just had the same problem. I hope the questioner has equal success. Thanks a few hundred times.

From contributor T:
You made my day! I am glad to be of help...

From contributor O:
That post from contributor C made my evening, and I don't even *have* a Kremlin gun.