Originally Posted by Wet_Boots
It's easy to forget that pressure and force are two different things.
One example of a valve that absolutely depends on the diaphragm being the spring force is the Greenlawn angle valve
, with its thick urethane diaphragm. Also, the infamous Toro Flo-Pro valve began its unhappy existence without a diaphragm spring, only to see one a few years later.
We see a lot of the GL valves here, as I think they are actually made here in Colorado if I remember correctly. The diaphragms do weaken over time, just like any of them. But they are stiffer than most, and rarely do I see a GL valve weeping due to a damaged diaphragm.
Of course I hate the Toro Flo-Pro, and see way too many of them. I went to one home that was having issues, and I took apart the valve. Noticed there was no spring above the diaphragm, so I found a spare, and put it in. Still issues with the valve not closing. Fought with it for 20 minutes (would have replaced it if it would have been convenient, but it is NOT an easy replacement due to location) and finally took the spring back out. Would not close again, so I replaced the solenoid, and right away it closed. That was my first experience with that valve not having a spring, and it wasted some of my time that morning, but now I know.