What a Hunter PGV anti-siphon valve does

A Hunter PGV anti-siphon valve is an irrigation control valve with an atmospheric vacuum breaker built into the body. The vacuum breaker sits above grade between the supply line and the zone outlet. It stops the zone pipe from siphoning irrigation water back into the potable supply when supply pressure drops. On a code path that accepts atmospheric vacuum breakers for residential irrigation, the anti-siphon valve replaces a separate backflow device. One fitting on the wall does both jobs.

Hunter's PGV anti-siphon line comes in two variants: the PGV-100 and the PGV-101. The mechanical difference between them is a single component: flow control.

The only material difference: flow control

Both the PGV-100 and the PGV-101 use the same valve body, the same diaphragm, the same 24V solenoid, and the same atmospheric vacuum breaker assembly. The single mechanical difference is a flow-control stem on top of the PGV-101.

Flow control is a stainless steel screw that rides on the valve seat. Turn it down and it throttles how far the diaphragm lifts off the seat when the solenoid energizes, which reduces downstream pressure and flow at the valve outlet. Turn it back out and the valve runs wide open. The PGV-100 omits the stem. Its diaphragm lifts to full travel every cycle, so downstream pressure equals supply pressure minus the valve's small fixed pressure loss.

When the PGV-101 (flow control) earns its place

Flow control is a pressure-tuning lever at the head of the zone. Three install profiles want it:

• Long lateral runs where head-of-zone pressure runs well above nozzle spec. Static supply pressure of 70+ PSI is common on municipal lines in the Southeast and Southwest. Spray nozzles specified at 30 PSI mist visibly at that supply pressure. Throttling the valve down to 35 to 40 PSI at the outlet ends the misting at the source, before any per-head regulation is in play.
• Mixed-head zones where the closest sprinkler over-pressurizes. A single zone with three heads near the valve and three at the far end runs the near heads at near-supply pressure and the far heads close to spec. Flow control trims the whole zone toward the spec range so the near heads stop misting without starving the far heads.
• Multi-valve manifolds where you want per-zone pressure tuning at the valves. Cheaper than installing a downstream pressure regulator at each zone. Faster to adjust seasonally as supply pressure shifts.

When the PGV-100 (no flow control) is enough

Short residential runs on a single-head-type zone don't need pressure tuning at the valve. If supply pressure sits in the 30 to 60 PSI band and every sprinkler in the zone is the same family, the nozzles handle the pressure themselves. Pressure-regulated spray bodies like Hunter's PRS30 and PRS40 Pro-Spray bodies make a flow-control valve redundant on that install. Each head regulates its own outlet pressure, so trimming at the valve buys nothing.

Code path and what an anti-siphon valve covers

The PGV anti-siphon body carries an integral atmospheric vacuum breaker (AVB). Where local code accepts an AVB as the backflow assembly for residential irrigation, the anti-siphon valve is the whole device. Installs that require a pressure vacuum breaker (PVB) or reduced pressure zone (RPZ) assembly need a dedicated backflow preventer upstream of the zone manifold. The PGV-100 or PGV-101 alone won't satisfy that code path. Check the local jurisdiction before you spec, especially on commercial installs and cross-connection-controlled water districts.