Although it is a little more involved having to dig and cut out a bad valve, I would follow the above advise and just replace the entire valve. I had two Richdel 205SF valves that seemed to be blocked/not opening with enough pressure to operate the sprinklers. I started out by doing the easiest thing which is replacing the solenoid in one of the bad valves with a solenoid from one of the good valves. That didn't help. I then took off the bonnet/top half of one of the bad valves, removed the diaphragm, and replaced it with a diaphragm from one of the good valves. That didn't work either and I ended up messing up a third valve. So I went to Home Depot to look for a new diaphragm but wasn't able to find the exact diaphragm or valve and at the time I didn't know the brand of the valve since it isn't visible from the top. I noticed that the Lawn Genie looked similar so I bought one, took it apart, and tried using its internal parts in one of my bad valves. That almost worked, i.e. the valve would open and close fine with the timer, but there was a slight leak at the valve while in operation. I tried it with and without the O ring around the solenoid port. I tried unscrewing the bonnet and carefully screwing it back in place to make sure it would seat properly. The valve still leaked ever so slightly while in operation. So, I ended up cutting out the bad valves and replacing with new Rainbird valves. I've done two so far and the sprinklers are now working like new. I do have one more valve to replace, but now that I know the brand, and trying to avoid the digging and cutting, I thought I'd look around the net and see if I could find a place that sells Richdel brand valves locally in San Antonio, Texas. Any one knows? And any one have any other suggestions on what else to try for in-the-ground repair?

OK, I've now tried a couple of other valve brands, including a Watermaster with flow control. I get exactly the same result--it works for about 4 cycles, then the spring in the solenoid weakens and the valve no longer shuts off. If I stretch the spring a bit, it starts working again for a few cycles. There are 5 valves, only this one valve always fails after a while. I can swap valves and the problem stays with the line, not the valve. The bad line is the lowest of the sprinkler lines. Could there be a siphoning effect that damages the spring or keeps the valve on even when the solenoid releases?

Go USC, You have the proper idea here and you have read the literature. Yes there is a possibility that the high heads could cause siphoning back to the house or street mains. Yes the burst of water is from the anti-siphon working properly. Yes the installer didn't pay much attention to the regulations(not news). Yes there are other types of anti-siphoning valves but most are not as reliable as the anti-siphon valves and hard to verify they are not working. Sometimes local city/county ordinances spell out the requirements for irrigation systems and alternate valve choices and everything else. Yes your yard would be an unusual case(steep grade changes) by having 5 foot high valves but not unheard of. Your situation would also require higher pressure for the system which may or may not be a good thing. A valve that can be utilized in your situation may be small check valves on the lines to the high irrigation heads( leaves water in the lines) and cuts down on head noise at start up. With all that said, I believe (others may disagree)the height of the tee at the bottom of the irrigation head should be below the anti-siphon valve. My A-S valve is about 24" above the ground as it come off my house hose faucet(aesthetically handicapped) and then goes into a auto-valve manifold in a irrigation control box with the lid about 1 inch above the ground. JMHO Aloha

Aloha, Good news I don't have a drip system. The big black thing is a sediment filter. Go figure they installed it only on one value and not the other not sure why. I have very hard water in my area. Also I don't have a drip system because both values turn on sprinkler heads; however, I might convert my backyard to a drip system in the future because I removed all the grass but still want to water the trees without having to water the lawn. Right now I'm looking to do a quick fix to stop the leaking. I'm going to check outside to see if there is a water value shutoff somewhere in the ground. If there isn't can I install an inline ball type shutoff on each value inlet or will they blow-up being installed on SCH 40 PVC? Can I go higher than 6" inches? I was thinking of going 12" and filling the value cut in the concrete with wood chips. I'm thinking of this design for the values. To be honest I can really care less about the sprinkler system since the lawn is so small. My problem is my water is metered and this is costing be 300 gallons a month. Inlet--->Ball Value--12"-->sediment filter--->Value--->Sprinkler Heads Thanks Bluelogic