I use pump sprayers for alot of tasks. Applying homemade weed killer, de-icer for multiple vehicles, various cleaners for A/C's, etc. Thus I can't have too many pump sprayers around
Since I need 2-3 different cleaners for different coils, I found it easier to have separate sprayers set up rather than one sprayer and constantly be rinsing and switching between cleaners. Many problems can be traced to clogged nozzles and leaking check valves. I've accumulated various brands of sprayers - and lo and behold they don't all take the same check valve diaphragms. Though they look the same there are minor differences in thickness, curvatures, and materials that don't interchange between brands or handle all chemicals the same. I think I've used black, brown, gray, red, white, and blue rubber check valves.
After much research I figured out which ones I needed and called the websites and had 5 of each sent to me. Cost a bit - at $1.50 each (or more) plus some shipping it adds up fast. But now if I'm on a job right in the middle of spraying and the thing quits, I have spare valves in the truck. I figured I'd post my findings here in one place - maybe it'll help you guys out. I'll dig my parts bin out and my sprayers and get the info posted (probably time to change out the check valves anyway!)
One thing I can say is all the manufacturers recommend (actually, they expect) that you rinse the sprayer out and let it dry after each use! If not, the diaphragms tend to break down and dissolve. It's a pain but it'll make them last alot longer.
I'm gonna try and dig out my sources, so you can buy the check valves individually. Though many companies are only making the diaphragms available in a kit, which is more expensive.