Sprayer valve maintenance

I have a field sprayer with Teejet AA144 valves that is driving me bonkers. 

 

The valves are solenoid operated and the plungers rust up internally with the slightest bit of moisture around.  I end up having skips and under-sprays whenever a valve acts up.  Sometimes, they will open only partially resulting in an under-spray, which is very hard to catch.

 

When they stick, I have to take it apart and clean it with steel wool.

 

I have tried using WD40 silicone lubricant after cleaning, but that does not seem to cure the problem. 

 

I'm in the process of replacing a 3-gang unit right now and want to avoid a future problem.

 

Does anybody have any suggestions that might help?

 

Thanks

 

Ralph

 

Sprayer valve maintenance