The definition of a T/P valve is a valve that has a separate chamber for the pressure balance element and a separate chamber for the thermostatic element. Recently, Leonard and Powers have introduced shower valves claiming to be T/P valves. By looking at the cutaways you can see that neither Leonard nor Powers meet this criterion.
Engineering vs. Marketing
In talking with specifying engineers, we need to make certain that there is a distinction between engineering and marketing. The marketing side of the equation is that those valves did pass the ASSE 1016 test for the T/P valves, but is it truly a T/P valve based on the definition of T/P valves. We could easily have our Series 3000 shower valve tested to the T/P test and have it pass, but that would infringe on the definition of a true T/P valve.
The engineering argument comes down to one question, “How is Leonard and Powers equalizing the hot and cold water pressures prior to mixing in the thermostatic chamber?” The engineering of the Lawler valve is very simple to see and explain to the specifying engineer.