I ordered the O-rings and the white backup rings. That online store is great except for their communication skills. They don't answer the phone nor emails. What I did is measure the O-rings and white rings and then went on their site and ordered several sizes around what I thought they should be. They shipped all of them. I haven't sorted things out yet to figure out which is which.
You may want to try one of these:
The General Pump YBRV5325 relief valve is a brass body regulator that prevents drastic unexpected increases in pressure within your car wash water system.
www.kleen-ritecorp.com
They are designed different than the grease fitting versions. The O-rings in the grease versions rub up and down against the brass throat causing the scarring or scratches in the soft brass. In the above version the O-rings are mounted in the brass (they don't move) and the stainless bullet is the thing that goes up and down with the O-rings rubbing against the stainless (no marring or scratches).
I've got both installed on my razors and the above versions haven't leaked yet.