The valves are ridel 204 , now called the 205. Sorry I thought I had put that in the original question. The diaphrams are secured by the 8 screw pattern, all zones flow excellently when activated. If anything, I might have too much pressure, definitely not a low pressure or flow problem. The owner of Sprinkler supplies for less .com was very helpful, previously, in telling me , with the new solenoids on the old style valve I needed to remove the white plastic ring around the plunger, which got my system, at least functioning. The only problem that seems to be remaining is the bleed screws. I have to loosen two of them until I hear the valve start flowing, at which point they leak a little, but that starts the zone . Then the zone works great, but on the one zone I have to go back and loosen the bleed screw again and wait till I hear the valve seal shut. If I tighten the bleed screw during operation of the most annoying zone, it will immediately shut off again.