I have an older Apollo HVLP turbine sprayer that uses its original siphon gun. I have been using it for a couple of months to spray pre-cat lacquer and it has worked very well. It has recently started to not want to pull the lacquer out of the can. I took the whole thing apart twice and it all appears to look ok. Now it had degraded to the point where it hardly pulls any liquid out of the can. It just spits a little periodically. The turbine seems to be putting out plenty of air. Does anyone have any recommendations? Can the needle cause this?
From contributor J:
There is a brass fitting on the side of the gun that runs the small pressure tube to the cup. Remove the pressure tube and blow through it to make sure that it is clear. Next, remove the brass fitting at each end of the pressure tube and make sure they are clean and finally make sure the inside of the gun where these fittings screw in is clean. Also, if your gun leaks when tipped your cup gasket is leaking and losing the pressure required to spray properly.
I'm not sure if the older Apollo is exactly the same, but the new one has the air hose running from the side of the gun to the top of the cup lid. Under the cup lid there's a 'duck bill' style check valve that keeps the finish from running up the hose if you tip the gun too far. You may have a check valve in the middle of the air hose between the cup and gun. Usually, the check valve will stop the fluid from getting all the way to the gun body and drying inside the gun. Instead, the dried finish/blockage is at the cup lid or the check valve.
I wouldn't remove the brass fittings, but would pull the air supply hose and make sure air was coming out of the gun fitting and then visually inspect the fitting in the cup lid and clean as required.
The 'duck bill' check valve can be removed and cleaned if it has dried finish in it. If you have the in-line check valve instead, it may be the type than can be disassembled and cleaned or it may be the type that has to be replaced.
Here are a couple pictures of the new gun that show the air supply to the gun and the 'duck bill' check valve under the cup lid.
Try spraying some water to see if the gun stops after a little bit. If it does, place you finger over the nozzle and pull the trigger. You should feel the water bubbling as the atomization air is forced back through the fluid passage and into the cup. Then the gun will spray for a little bit again. That will let you know the cup isn't getting air.