Cold water inlet valve?

[skydve76]

Hello: DIYer here. Installed my own sprinkler system 5 years ago is pretty much my resume.

Please educate me. On the top of the water heater, where the cold water line goes in, is there some sort of automatic valve that shuts off the cold water into the tank once it is full? There is a manual turn valve on top, thats not what Im referring to. If so is this automatic valve replaceable?

Issue:
Recently started pulsating when using cold water, especially the sprinklers, If I close the manual cold water valve on top of the heater, the pulsing stops. This tells me it must be inside the heater, its literally the first thing after the water line in the house. Oddly, while water still being used, if I reopen it the pulsing does not come back until later. Not sure how long it takes to come back.

Thought about just leaving the manual valve half close to try that but I know that's not a solution.

Im assuming there is a valve in there that has gotten weak (spring valve?). I may try to flush the heater and see if the dip tube is clogged or something weird going on there.

Please educate and advise!! Its an old A.o Smith (state select) 6 50 nbrt. Probably the cheapest 50 gal you can buy. Gas powered.

 

[WorthFlorida]

Sprinkler zone valves do close fairly fast and you'll usually hear a thud sound when the last zone valve closes. Controllers when changing to the next zone valve during a run program, the next valve will open before the current one closes to prevent the water from being slammed shut, except the last one.

What is on your water heater could be a master valve for the irrigation system or to a water leak detection system? Any wires connected to it? Nothing inside the WH can cause this. If this valve actually shuts the water off with a full tank (?) the water expansion on heating has no where to go, pressure builds up and as suspect internally a spring went out of calibration or broke.

 

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[Fitter30]

Take a pic of the valve