How to drain and winterize a Hunter sprinkler system

Below freezing, water trapped in irrigation pipes does what water always does: expands by about 9% and splits whatever holds it. The damage doesn't show up until spring start-up, and by then you're replacing cracked PVC, a split backflow preventer, a brass shut-off valve, and a handful of zone valves and nozzle bodies. Winterizing the system before the first hard freeze is one afternoon of work; not winterizing it is a four-figure repair.

This guide covers the two methods homeowners use to clear water from a Hunter sprinkler system before winter:

• Manual drain. Gravity does the work, using the drain valves built into the system. Works only when the system was designed for it (auto or manual drain valves present, sloped lines).
• Compressed-air blow-out. An air compressor pushes water out through the heads, zone by zone. The universal method, but requires a large enough compressor and strict PSI discipline to avoid wrecking nozzles, seals, and pipes.

The guide also covers the two things every system needs regardless of method: protecting the backflow preventer (the most freeze-sensitive component above grade) and setting the controller so the system doesn't try to run during the freeze.

Before you start, identify what Hunter components you have. The procedure is the same across the Hunter rotor + spray family (PGP, I-20, MP Rotator, Pro-Spray, PRS30, PRS40); the controller step varies by model (X-Core, Pro-HC, HCC, X2 — see the Hunter brand page).

Decide your method (manual drain vs blow-out)

Three questions pick the method for you:

1. Does your system have drain valves on every zone? Look for small brass or plastic valves at the lowest point of each zone line, downstream of the zone valve. If yes, manual drain is on the table. If your installer didn't include drain valves (most retrofit jobs and many DIY installs), you don't have the option — go straight to blow-out.
2. Is the system installed with slope on every line? Manual drain is gravity-only. On a perfectly flat run, a drain valve at the low end drains the section it can reach and leaves an unknown volume of water in the rest. If you're not sure whether the lines have slope, blow out instead — the air clears the line either way.
3. Do you have a compressor in the 80–100 CFM range? A typical garage compressor (5–10 CFM) cannot push enough volume to clear an irrigation zone — it'll pressurize the line without moving water. Rent a tow-behind compressor from a hardware store or hire a pro. PSI is not the spec to chase here; CFM is. A small high-pressure compressor will overpressure the system without clearing it.

How the answers map:

• Drain valves present + sloped lines + mild climate (occasional light freeze): manual drain is sufficient.
• Drain valves present + sloped lines + hard freeze climate: manual drain first, then a follow-up blow-out for the residual water gravity can't move.
• No drain valves or flat lines or hard freeze climate: compressed-air blow-out only.

When in doubt, blow out. Manual drain underperforms in conditions homeowners often misread.

Method 1 — Manual drain

The manual drain method works the system from the supply side downward. Sequence matters: shutting the water off before opening the drains gives gravity a clean path; opening drains first just makes a puddle.

What you need

• The location of your main shut-off valve (typically at the meter or a basement isolation valve upstream of the backflow preventer).
• A list of every drain valve in the system. Walk the system before the first freeze and note locations — the time to find them is not in the dark with a freezing wind.
• Winter plugs for any open pipe end you create during the process — sized to the pipe diameter. Mixed-size sets (#6 through #12) cover most residential systems; see the Sprinkler Winterization category for the full range plus insulated backflow bags and drain valves.

The sequence

1. Shut off the main water supply to the irrigation system. This is the upstream isolation valve, not the backflow's downstream shut-off.
2. Set the controller to rain mode (the "Off" position on X-Core; "Suspend Watering" on Pro-HC and HCC via Hydrawise; "System Off" on X2). The controller can stay powered — see below.
3. Open every manual drain valve, starting at the highest-elevation zone and working down. Water exits each drain as you open it; the system drains by gravity.
4. If you have auto drain valves (they open automatically when zone pressure drops below ~10 PSI), simply opening the main shut-off relieves pressure and they discharge on their own. Verify each one drained.
5. Open every zone at the controller for 1–2 minutes (one zone at a time) to clear standing water from the lateral lines. The water exits through the heads.
6. Drain the backflow preventer per the next section — this is a separate procedure.
7. Cap any open pipe ends you created (drain valve unions, test cocks) with appropriately-sized winter plugs.

Verify the drain worked

The first sign of a partial drain is a zone that still produces water when you open its heads by hand 30 minutes after the sequence. If a zone still has water in it, the lateral has no slope at that location, or a drain valve is blocked. Do not declare the system winterized. Either follow up with a blow-out for that zone, or accept the freeze risk knowingly.

Method 2 — Compressed-air blow-out

The blow-out method works on any system regardless of slope or drain-valve presence, which is why it's the standard. The trade-off is risk: pushing air through irrigation components at the wrong PSI cracks heads, melts nozzle seals, and ruptures pipes. The numbers below are not suggestions — they're Hunter's published limits and the difference between a winterized system and a broken one.

Hunter's published PSI limits

Per Hunter Industries' winterization guidance:

• Never exceed 80 PSI at the compressor regulator, regardless of pipe material or head type.
• PVC piping (rigid white pipe): 80 PSI maximum.
• Polyethylene piping (flexible black pipe): 50 PSI maximum.
• If you don't know what your laterals are made of, treat the whole system as polyethylene and cap at 50 PSI. Polyethylene is the more freeze-tolerant material but the more PSI-sensitive one for blow-out — the lower limit always wins.

The blow-out pressure should also stay below the maximum operating pressure of the lowest-rated component on the zone. If your zone has a 50 PSI-rated drip regulator on it, that's your ceiling, not the 80 PSI pipe rating.

Compressor sizing

The spec is CFM (cubic feet per minute), not PSI. Hunter recommends an 80–100 CFM compressor for any mainline of 2" or less — typical residential. That is a tow-behind rental compressor, not a garage 5-gallon. A small compressor that hits 80 PSI on the gauge but only delivers 5 CFM cannot move enough air through the zone to push the water out; the line pressurizes, the heads pop up dry, and the water stays in the pipe.

Rent the right compressor or hire it out. The "I'll just use what I have" instinct is what cracks pipes here.

What you need

• An 80–100 CFM compressor with a regulator that can be capped at 50 or 80 PSI.
• A threaded NPT-to-air-coupler fitting sized to your system's blow-out port. Most systems have a 3/4" or 1" male NPT port downstream of the backflow preventer; if yours doesn't, your installer will know where the air injection point is. A standard brass NPT-to-air-coupler from a hardware store is the right fitting — not a quick-coupling valve.
• ANSI-approved eye protection. Hunter is explicit: compressed air during blow-out can launch debris from a head with enough force to cause serious eye injury. Do not skip this.

The procedure

1. Shut off the main water supply upstream of the backflow preventer.
2. Open a downstream test cock or hose bib to drain residual mainline pressure. The line should be at 0 PSI before you connect the compressor.
3. Connect the compressor to the blow-out fitting downstream of the backflow. Never connect upstream of the backflow — air will rupture the backflow's check assemblies.
4. Cap the regulator at 50 PSI (polyethylene) or 80 PSI (verified PVC). Confirm the regulator setting before opening the compressor valve. There is no recovery from over-pressure — heads and seals fail instantly.
5. Activate one zone at the controller — the zone farthest from the compressor first. The far zone is the longest path; clearing it first ensures air keeps moving toward the compressor connection as you work through closer zones, rather than pushing water back into already-blown zones.
6. Slowly open the compressor valve. Air enters the line, displaces water, and exits through the active zone's heads. You'll see water spray for the first 30–60 seconds, then a mist, then air only.
7. Run each zone for ~2 minutes (Hunter's guidance — "approximately two minutes or more per station"), or until no water exits the heads, whichever is longer. Do not run a single zone for more than ~2 minutes continuously — air friction inside a dry zone heats up plastic components and can warp gears.
8. Advance to the next-closest zone at the controller. Do NOT shut the compressor off between zones — keep air flowing.
9. Repeat for every zone, working from farthest to closest. After the last (closest) zone is clear, shut off the compressor first, then close the controller.
10. Do a second pass on any zone that still pushed water on the first pass. Residual water in a low spot needs a second go to fully clear.

What NOT to do

• Never blow air without a zone open. Air with nowhere to go pressurizes the mainline and rips the weakest fitting. The active zone is the relief valve for the air.
• Never exceed Hunter's PSI limit for your pipe material. 80 PSI on polyethylene is a guaranteed split. There is no upside to pushing past the limit.
• Never run a single zone dry for more than ~2 minutes. Frictional heat in a dry rotor or valve warps gears, deforms seats, and shortens life.
• Never connect the compressor upstream of the backflow preventer. The backflow's checks are not built to seal against air pressure from the wrong direction; you'll destroy the device.
• Never stand directly over an irrigation head while it's blowing out. Hunter's safety guidance: "Do not stand over any irrigation components (pipes, sprinklers, and valves) during air blow out." Debris ejected at 50–80 PSI is dangerous.

Backflow preventer — the most freeze-sensitive component above grade

The backflow preventer sits above grade between the water supply and the irrigation system, exposed to ambient air. It is the single most likely component to split in a freeze, and the most expensive non-controller component to replace. Treat it as a separate procedure regardless of which clearing method you used.

By backflow type

• Pressure Vacuum Breaker (PVB) — the most common residential type. Close both shut-off ball valves (one on either side of the device). Open both test cocks to drain water out of the body. Leave the test cocks slightly cracked through winter; leave the ball valves at 45° (half-open) so any residual water has expansion room.
• Reduced Pressure Zone (RPZ) — required in some jurisdictions. Same shut-off + test-cock procedure as the PVB. RPZs have an extra relief valve that drains automatically when pressure drops; verify it discharged.
• Double Check Assembly — close both shut-offs, open test cocks, drain. Same 45° rule on the ball valves.

Insulation

Wrap the device in an insulated backflow bag sized to your device. The small BFA1HBBG insulated backflow bag ($20.99) fits most 3/4" and 1" residential PVBs and double-checks. For larger residential or light-commercial devices, the 24" × 24" insulated bag ($58.99) is the next size up. Insulation alone does not stop a hard freeze on an undrained device — drain first, insulate second.

If you're replacing a freeze-failed backflow this season, Febco's T765HBV PVB (FEB-58-1135) is the in-stock model with a built-in freeze sensor for systems that need to detect impending freeze automatically — a one-time upgrade that catches the case where someone forgets to winterize.

Set the controller for winter

The controller does not need to be removed or unplugged for winter. Leave it powered so the internal battery doesn't drain and the programming survives. What you change is the run schedule.

By Hunter model

• X-Core (HUN-58-0053, -0054, -0056, -1193) — turn the dial to "Off". Programs remain stored; nothing runs. The seasonal-adjust dial is for percentage scaling during the season, not for full shut-down — "Off" is the winter setting.
• X2 with Wi-Fi Module (HUN-58-1841) — set "System Off" in the Hydrawise app. Programs remain.
• Pro-HC PHC-1200 and HCC (HUN-58-1760) — use Hydrawise's "Suspend Watering" feature with an explicit start and end date (e.g. Nov 1 to Mar 31). The controller resumes automatically on the end date, which avoids the spring-start mistake of forgetting to turn it back on.

Rain/freeze sensor adjuncts

A wireless rain/freeze sensor (e.g. the Rain Bird WR2RFC-48) wired to the controller's sensor terminals provides a second layer of automation: if a shoulder-season freeze hits while the system is still active, the sensor cuts irrigation until temperatures recover. Useful where shoulder seasons are unpredictable; not a substitute for the winterization procedure itself.

Spring start-up checklist

1. Inspect the backflow preventer for cracks. If you see hairline cracks or wetness at the test cocks, replace before pressurizing.
2. Close all test cocks and return both ball valves to fully open. Remove the insulation bag.
3. Slowly open the main supply — half-turn at a time. Sudden pressurization can rupture even a healthy line.
4. Manually run each zone for 1–2 minutes. Watch every head: stuck, clogged, or damaged heads show themselves immediately.
5. Return the controller from Off / Suspended back to its program.

Products referenced in this guide

• Insulated Backflow Bag (small) — fits most 3/4" and 1" residential PVBs.
• 24" × 24" Insulated Backflow Bag — for larger residential and light-commercial backflow devices.
• Hunter Pro-HC PHC-1200 — 12-station Wi-Fi controller with Hydrawise "Suspend Watering" mode for winter.
• Rain Bird WR2RFC-48 Wireless Rain/Freeze Sensor — adjunct freeze cut-off for the shoulder seasons.
• Drain valves, manual isolation valves, and winter plugs (#6–#12 sizes) — see the Sprinkler Winterization category.

Keep going

If you're working through the rest of your seasonal maintenance:

• Sprinkler Winterization category — every winter plug, insulated backflow bag, and drain valve in one place.
• Backflow Preventers category — replacement PVBs, RPZs, double-check assemblies (Febco, Apollo, Lasco).
• Controllers category — Hunter X-Core, Pro-HC, HCC, X2 models and Wi-Fi modules.
• Hunter brand page — every Hunter sprinkler, rotor, nozzle, and controller stocked on Total Sprinkler.