It took me about 30 seconds to find this thread( so quick, right?)https://shop.truckmountforums.com products carries all the parts very reasonably.
I figured that it's important to bring it back, not only for members starting to get their feet wet, but for everyone else to refresh their memory. As I was looking for this particular thread with yours @Jim Davisson comprehensive coverage, I like to point out that I found many of the threads with a similar topic just this year alone, not going back to year 2013.
So, for those, who own injection sprayer ( Hydro force) or other systems( and who doesn't), please go back to posts #4, #5, oh what Am I saying read it all and bookmark it, you never know when you gonna need it.
Happy learning, everyone!
$20 for member, who can guess ( + , - 1) how many injector valves do I have in my garage. Even I don't know at this moment, but I'll get to counting tomorrow.