Anti-siphon valves are important for garden hose bibs. Whether you use drip systems or garden hose sprayers, they prevent contamination to your potable water. If this is the source of your hammering, then I would replace it with a standard hose bib and attach an anti-siphon valve to it. If that doesn't resolve the hammering, then you probably need a small expansion tank on the same line to absorb the hammering which can damage pipe joints over time. If you've never done any plumbing yourself, I suggest getting a plumber or a handyman to replace the hose bib. It's easy to break off the threaded joint if you don't support the pipe in the wall as you unscrew the valve.