What needs to be done or what is wrong...

[DD716TED]

I have a "frost Free" exterior faucet installed at my house.... All of a sudden I noticed a small puddle of water below it on the concrete whenever I had it turned on and connected to a sprinkler or water timer... At first I thought the hose gasket was bad but replaced it with no change... Then I noticed that the water was leaking from the top of the valve where the anti-siphon (I think) cap is located....It only leaks when the water is on as when the valve is off, no leaks what so ever... Ideas as to what is causing this and can it be fixed without replacing the entire valve? The picture shows the valve and where it is leaking...

.

[akaothermick]

That's the built in vacuum breaker, see if you can unscrew the cap, could just be dirt on the seal, normally those things are around $15 so if its an issue just replace it with a new one, your local codes probably require the vacuum breaker style, if you have a well, then you are the only one that draws up dirty water if the hose is left in dirty water and the water pressure drops, your choice of non vac or vac break then.

[DD716TED]

I removed the cap and looked everything over.. I then reinstalled the cap which was somewhat loose before I removed it and tightened it down.. No more leaks... I was just cautious about doing something to the valve that might require a total replacement.. It is located as far from the crawl space entrance as could be and would be difficult to remove and replace... Thanks again for the info.....