Cleaning HVLP gun between spray coats...

I am spraying water-based poly which needs about 2 hours between coats (according to the can).

I am wondering how thoroughly I need to clean the gun between coats -- balancing efficiency vs. the need to keep the gun clear of any hardened poly (especially since water-based dries fast).

Would it be sufficient to spray water through the gun after each coat (I bought an extra 20oz paint cup that I can fill with water) and then just wipe off any obvious excess poly from the gun itself and the nozzle?

Or do I need to do more of a full cleaning/dissassembly of the gun between coats? If so what would you recommend?

Also, my rationale for buying an extra cup is that I could keep the excess poly in the cup between coats rather than repeatedly refilling the cup and then pouring it back with each coat... Is this OK, or is it recommended to fully empty and clean the cup between coats...

Personally, I would clean it. I have tried just about every way possible to get around it, but two hours is too long to have the gun/ material exposed. Cleaning the fluid passages and rinsing with water will get you only so far with a gun.

A couple of other notes - labor is expensive, material isn't. If I am going to shoot a project, or cabinets, or anything else, I never save any material for more than a few minutes in the cup. Some of the lightening fast lacquers and conversion finishes I will keep in the gun, and put the whole gun/cup assembly in a 5 gallon bucket with a sealing lid since I know I will be spraying again in 15 minutes.

And if you are shooting a finish that you need to wait (to me, more than 30 minutes) to recoat, only load what you need in the gun, and pour out the remaining finish into your proper waste barrel and clean the gun after you make a pass. Don't ever "wipe" the nozzle, air horn, or any other part. On better guns the airstream around the fluid discharge area will have holes that are literally few thousandths in diameter, and the smallest bit of debris wiped across them can easily clog them. That will affect your spray pattern and finish, and can be incredibly hard to clean if material sets up inside that air stream hole.

Depending on the material, you may not have to clean the cup. Remove the gun, fill your cup to a bit more than half, then seal with one of these:

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are the best, but I have also used poly lids that fit nut cans (free) and some other odds and ends of poly lids that sealed tightly. If you really want to save some time, put a cup liner in your cup before using, and just charge your second cup with water and a bit of detergent to use as cleaner.

The only way to a really good finish from a gun is to keep it as spotless as possible. That means keeping it as clean as possible. So as little fun as it is, I would clean between each coating if I had to wait two hours.

Robert