The web's mother lode of free irrigation information!

Irrigation Product Listings & Reviews

Hunter ASV Series Anti-Siphon Valve

Hunter ASV Anti-Siphon Valve
Hunter ASV Anti-Siphon Valve


The ASV is Hunter's anti-siphon valve, intended for residential and light commercial use. An anti-siphon valve is a valve that has a built-in backflow preventer.



Anti-siphon valves are primarily used for residential irrigation systems. The Hunter ASV is essentially their SRV valve with a anti-siphon vent added. Like the SRV, the flow control on this valve is a bit difficult to use, a screwdriver is helpful. Construction of the valve is PVC. The PVC body is black, which helps with UV resistance, but this valve should still be protected from direct sunlight. The Hunter ASV is a good quality valve for a small residential irrigation system.

Important Installation Rules:

These rules apply to any brand or model anti-siphon valve!

The bottom of the anti-siphon valve MUST be 6 inches higher than any of the drip emitters or sprinkler heads it operates. That means that it must be installed above ground. Do not install any anti-siphon valve below ground level or where it might be submerged under water (ie; it can't be underground in a box.) If the yard has a slope, I suggest installing the anti-siphon valves at the highest point in the yard. Run a mainline from your water source to the high point in the yard. Then install the anti-siphon valves above ground at that high spot. From the anti-siphon valve run pipe to the sprinklers or emitters. Note that if the sprinklers or emitters are higher than the anti-siphon valve, the backflow preventer part of the valve will not work! Water will run out of the vents on the anti-siphon valve if there are sprinklers or emitters higher than it. If more than a tablespoon of water spills out of the anti-siphon valve vent, it almost always means the valve is not properly installed.

The anti-siphon valve must be the last valve on the pipe before the sprinkler heads or emitters. Don't install any other valve, manual or automatic, on the downstream side of the anti-siphon valve. This applies to all brands and models, not just Hunter. I can't count how many times I have heard store salesmen, or even contractors who should know the installation rules, tell customers that they can use a single anti-siphon valve as a backflow preventer and install several, cheap globe valves after it to control the sprinklers. THEY ARE WRONG! The backflow preventer device that is part of the anti-siphon valve will NOT stop the backflow if another valve is installed after it. When you use anti-siphon valves to control your irrigation all of the automatic valves must be anti-siphon valves, and all of them must be installed 6 inches higher than the sprinklers or emitters that they control. For a better explanation of why you need a backflow preventer and how it works, see the backflow preventer page.

Manufacturer's Performance Data:

Valve Pressure Loss in PSI for ASV Valves
Flow 1 GPM 5 GPM 10 GPM 15 GPM 20 GPM 25 GPM 30 GPM
3/4" size valve 1.0 PSI 2.0 PSI 2.0 PSI 3.0 PSI 6.0 PSI    
1" size valve 1.0 PSI 2.0 PSI 2.0 PSI 3.0 PSI 6.0 PSI 6.0 PSI 9.0 PSI

Note: Pay close attention to pressure losses. Select valve size based on pressure loss. Often the pipe size to the valve will be larger than the valve size. For example, the 1" size valve can handle 30 GPM, however a 1" size pipe will not hold that much. You would need to use a 1 1/4" or possibly even a 1 1/2" pipe. To connect the larger pipe to the 1" valve you need to use a reducing fitting. Do not use the 3/4" valve for flows over 20 GPM.