Outdoor faucet leaking from anti siphon valve

When your exterior faucet, or hose bib, leaks, the type of leak indicates the type of repair you need to make. More often than not, the water is coming from the spout, which means you'll have to disassemble the faucet, remove the valve and replace the washer. If the faucet is leaking from around the handle, that's a different problem, but you still have to take apart the faucet. Finally, an outdoor faucet may be leaking from the vacuum breaker, a circular cap on the top of the faucet just behind the handle, and that's the easiest repair of all.

Why Does a Hose Bib Need a Vacuum Cap?

The vacuum cap is circular and about an inch in diameter, and it either slips or screws onto the top of the faucet. The device underneath it is known as a vacuum breaker or an anti-siphon valve. How would a vacuum develop inside a faucet the first place? That can happen for more than one reason.

The supply pipes for most exterior faucets tie into a cold water main that also supplies water to other parts of the house. Suppose demand is unusually high one day. Perhaps you have guests, and two showers are in use at the same time while the washing machine is operating, and someone is running water in the kitchen. The extra demand creates a heavy flow in the main supply pipe, which, in turn, creates suction in the branch pipes that aren't being used, including the exterior faucet.

If the faucet doesn't have an anti-siphon valve and a hose is attached, the vacuum transfers all the way to the nozzle, which may be lying in the mud. It could draw dirt and sediment into the hose through the nozzle, which could end up contaminating the water system. The anti-siphon valve prevents this by closing whenever the water is off and preventing water from flowing backwards.

The Hose Bib Is Leaking From the Top

The vacuum breaker is a simple device that basically consists of a diaphragm and a watertight chamber. When the water is on, water pressure forces the diaphragm down, opening the valve and allowing the water to flow. When the water is off, a spring or the force of atmospheric pressure forces it back against the water inlet, forming a seal that prevents any water from flowing backward. If a vacuum develops in the water line, it only serves to strengthen the seal.

When an outdoor faucet is leaking from the vacuum breaker, it's usually because the diaphragm seal or the spring mechanism has worn out. These are inexpensive parts, so there's no point in trying to repair them, although you probably could if you wanted to. It's much easier to simply replace them, and that's what most people do. Siphoning is a common problem with drip systems, because the drip components are in constant contact with the ground.

How to Service an Anti-Siphon Valve

When water leaks from an anti-siphon valve, it tends to dribble onto the ground, but sometimes it sprays. If so, you'll want to do the repair quickly. Here's how:

1. Turn off the faucet and unscrew the hose to relieve the water pressure.
2. Pry off the cap, using a flat-head screwdriver, or unscrew the cap with a pair of locking pliers. 
3. With the pliers, unscrew the plastic vacuum breaker assembly from the faucet housing. When you remove it, you'll see that it separates into two parts: the diaphragm and the valve housing. It's best to replace both parts. You can usually find a kit that includes both of them. 
4. Screw the new vacuum breaker assembly onto the faucet housing and tighten it with pliers. 
5. Pop the cap back on, or screw it on and tighten it with pliers. 

Some anti-siphon valves come as attachments that you screw onto the faucet spout. When one of these leaks, simply unscrew it and replace it. You can buy a new anti-siphon faucet at a hardware or big box store, and that's also a good place to find screw-on anti-siphon valves. You can also buy these at any hardware store.

What to Do When a Faucet Leaks From the Spout

All outdoor faucets, even frost-free ones, have compression valves, and when one of these wears out, water will leak from the spout. In 99 percent of the cases, the problem is a worn washer at the base of the valve stem. To replace it, you have to remove the valve. Here's how to make the repair:

1. Turn off the water and remove the hose.
2. Unscrew the valve retaining nut, which is just behind or under the handle. This can be more difficult to do than it sounds, and it usually requires a pipe wrench and a lot of muscle. If you aren't getting enough leverage on the wrench, try lengthening the handle with a piece of 1-inch steel pipe.
   
3. Pull out the valve. If you're servicing a frost-free faucet, the valve is on the end of a long rod, so keep pulling until the valve comes out.
4. Unscrew the washer from the end of the valve stem, using a Phillips screwdriver. Replace it with an identical one and tighten the screw to hold it with the screwdriver.
5. Reinsert the valve into the faucet housing and tighten the retaining nut with the wrench.

Water Is Leaking From the Handle

When water is leaking from the handle of a hose bib or frost-free faucet, you can often fix the problem by tightening the retaining nut under or behind the handle, using a pipe wrench or a pair of locking pliers. If that doesn't help, you can replace the packing washer. This requires disassembly of the faucet.

Follow the disassembly procedure you would use if you were replacing the valve stem, but instead of replacing the valve stem washer, you want to remove the packing washer from underneath the retaining nut and replace it with a new one.

If you have an older faucet, you may find packing string instead of a washer. It's getting difficult to find this graphite-coated packing string at hardware stores, but you may get lucky. If so, remove the old packing string and replace it with new material; then replace the nut and tighten it down with a wrench or pliers. If you can't find new packing string, you'll probably have to replace the faucet. It's old, so it's probably time to do that anyway.

When to Replace the Faucet

An outdoor faucet leaking from a vacuum breaker seldom needs to be replaced, nor does one leaking from the spout or handle. Occasionally, however, a faucet may crack, especially if it freezes over in the winter. You can't repair a cracked faucet, so you'll have to replace it.

To replace the faucet, you have to unscrew it from the supply pipe, so make sure to turn off the water first. If you can't find a dedicated valve for the outside faucets, turn off the water for the entire house. Unscrew the faucet, using a wrench and a pipe to increase leverage, if necessary. Wrap plumbing tape around the male threads before you screw the new faucet onto the pipe or into the fitting. Tighten it completely; then turn on the water and check for leaks.

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