Walter,
I have a ball valve in line to the drive plate. It's great for a positive shutoff when moving equipment in and out of buildings and vans, and when you stand the machine up to chaNnge a pad. It also gives you more control of how quickly you put down solution. Up until I bought the Mytee Wave tank, I was pulling a bent piece of brass connected to the solution valve.
The Mytee floor machines have a mountainbike brake lever style solution lever that is easy to pull and modulate. If yours solution feed lever is brass, you might want to build up the diameter of the area with rubber or plastic tubing...many times before I had the Mytee solution tank and machine my "trigger" finger would go to sleep from compression on a small area of it.