I have zero pressure regulators on all my pumps at one of my washes. They work okay for awhile, but tend to go bad frequently. Most likely the soap kills them like it does many other things. Last fall I got fed up with replacing them so often, so now I use an air pump with them to inject the soap and wax into them instead of letting it draw from the tank with suction. Is it the best setup? Nope, but it sure works like a champ! I could get rid of the regulators altogether, but then I'd have to increase my air pump pressure from 20psi to something higher.
I'm not an expert, I just piddle with the equipment until I get it to do what I want. In this case, I wanted a lot of soap to get on the vehicle so the customer gets what they came for!