Blowing Out an Irrigation System Using a Spigot

Yes, use a spigot only if it is a hose-bib or other dedicated blowout connection on the irrigation mainline after the backflow preventer; an ordinary outdoor faucet is not automatically safe for this job. Winterize before temperatures consistently fall below 32°F (0°C), because water trapped in pipes, valves, and backflow equipment can freeze and crack components. The spigot is only the connection point: you still need a compressor with enough air volume, a pressure regulator, and a safe air path.

What a Spigot Connection Means for Irrigation Blowouts

A sprinkler-system blowout pushes compressed air through the irrigation mainline and then through one zone at a time, forcing water out through the sprinkler heads or drip outlets. The mainline is the supply pipe that runs from the water source and backflow device to the zone valves.

For Hunter irrigation systems, the compressor may connect to the mainline through a quick coupler, hose bib, or another designated connection after the backflow device. A hose bib is often shaped like an ordinary spigot, but its location and plumbing path matter more than its threads.

A usable spigot must send air toward the zone valves without sending it through the backflow preventer or a pump. Compressed air can damage those components.

How to Blow Out an Irrigation System Through a Spigot

Use this decision table before connecting a compressor.

Connection you found	Use it for blowout?	Why
Hose bib or quick coupler downstream of the backflow device and connected to the irrigation mainline	Yes	Air enters the sprinkler piping in the correct direction.
Exterior house faucet tied to household plumbing	No	It may not connect to the irrigation mainline and can route air into indoor plumbing.
Connection upstream of the backflow preventer	No	Air would be forced through the backflow device.
Connection that requires air to pass through an irrigation pump	No	Pumps should be drained separately, not blown through.
No downstream connection exists	Not yet	Install a proper blowout fitting or hire an irrigation professional.

Step 1: Shut Off Water and Prepare the System

Turn off the irrigation system’s water supply at its shutoff valve.
Drain accessible water from the system using its normal drain points, if present.
Complete this work before temperatures consistently fall below 32°F (0°C). Sullair’s portable-compressor winterization guidance uses that freezing point as the deadline for a seasonal blowout.
Set the irrigation controller so you can manually run one zone at a time. Do not let it run a regular watering schedule while you are winterizing.
Close any manual drain valve that would otherwise vent the compressed air during the blowout.

Manual and automatic drain valves can remove some water, but they are not a substitute for a proper compressed-air blowout where freeze protection is needed.

Step 2: Protect the Backflow Device, Pump, and Sensors

Find the backflow preventer, usually located near the irrigation water shutoff.
Confirm that the spigot or hose-bib connection is on the downstream side, the side leading away from the water supply and toward the zone valves.
Close the backflow isolation valves before introducing air.
Remove any flow sensor before injecting compressed air, then seal the open pipe connection. Blowout air can damage flow sensors.

Step 3: Match the Compressor and Regulator to the System

A spigot solves the connection problem, not the compressor-capacity problem.

The important compressor rating is CFM, or cubic feet per minute, not just PSI. A small consumer compressor may reach a high pressure but still lack enough air volume to clear a sprinkler zone thoroughly.

For Hunter irrigation systems, a common sizing method is:

Largest zone GPM ÷ 7.5 = compressor CFM needed

For example, a largest zone flowing 15 gallons per minute needs about 2 CFM at the irrigation connection using that formula. Determine the GPM for the largest zone, not the total GPM for every zone combined.

Set the pressure regulator before opening the compressor valve:

Hunter limits blowout pressure to no more than 50 psi for polyethylene pipe and 80 psi for PVC pipe.
Keep pressure below the maximum operating-pressure rating of the lowest-rated component in that zone. A valve, drip fitting, nozzle, or other part may have a lower rating than the pipe.
Do not compensate for inadequate CFM by filling the compressor tank and dumping a high-pressure blast into the mainline.
A Sullair 185 Series compressor has a 100 psi outlet.

If you do not know the pipe material, zone flow rate, or pressure rating of the system’s weakest component, hiring a certified irrigation professional is the safer choice.

Step 4: Connect the Compressor and Blow Out Each Zone

Attach the compressor hose to the downstream blowout spigot, hose bib, or quick coupler.
Make sure the connection is secure and keep people away from sprinkler heads and exposed fittings.
Turn on one irrigation zone at the controller.
Start the compressor and slowly open its air valve to introduce air gradually.
Watch the sprinkler discharge while that zone runs. With Sullair portable-compressor equipment, a zone typically takes about two to three minutes, but the discharge is the real stopping point: move on when water changes from mist to air.
Shut off that zone and run the next zone. Continue until every zone has been run twice in short cycles and cleared.

Opening multiple zones can create excessive air velocity and friction, which can heat and damage pipes or fittings. Do not leave the compressor unattended.

Sprinkler heads that remain raised while air continues to move through the zone are a useful sign that the compressor is delivering adequate air volume. Heads that drop immediately or produce only weak, brief bursts may indicate too little CFM, a closed valve, or a restricted connection.

Step 5: Finish the Backflow Device and Shut Down Safely

Turn off the compressor and disconnect it from the blowout spigot.
Release any remaining air pressure from the irrigation system.
Drain the backflow device separately. Open and close its isolation valves several times to help trapped water escape.
Leave the backflow isolation valves at a 45-degree angle, approximately half open, and open the test cocks so water cannot remain trapped in the upper portions of the device.
Drain the irrigation pump separately if your system has one.
Do not leave manual drain valves open after the blowout.
Turn the irrigation controller off for the winter and make sure the irrigation water supply remains off.

These finishing steps matter because the backflow assembly and pump can still hold water even after the underground zones have been cleared.

When an Outdoor Faucet Is Not a Safe Blowout Spigot

A standard faucet mounted on the side of the house is usually part of the domestic plumbing system. Even if it has the same garden-hose threads as a blowout hose bib, it may be upstream of the backflow preventer or completely separate from the sprinkler mainline.

Forcing air into the wrong faucet can pressurize plumbing that was never meant to receive compressor air.

No Downstream Blowout Fitting

If the system has no hose bib, quick coupler, or capped fitting after the backflow device, do not improvise by using the nearest faucet. A proper downstream blowout fitting needs to be added to the irrigation mainline.

A Spigot Located Before the Backflow Device

Air entering a spigot ahead of the backflow preventer would have to travel through the device before reaching the irrigation zones.

That can damage internal backflow parts and may leave water trapped where it can freeze. Use a connection after the backflow device.

Blowing Out Drip Irrigation Lines

Drip zones can be blown out through the same type of downstream mainline connection, but they need extra care because drip tubing, emitters, filters, and fittings may have lower pressure ratings than rigid PVC pipe.

Run each drip zone individually from the irrigation controller. Set the regulator below the maximum operating pressure of the lowest-rated component in that zone, which may be a drip fitting or emitter rather than the supply pipe. Watch for water leaving accessible drip outlets or flush ends, and stop the zone when the visible discharge changes from water mist to air.

Do not blow air through a pump, backflow preventer, or flow sensor to reach the drip lines. If you cannot identify the drip zone’s pressure rating or cannot observe its discharge, professional winterization is the safer option.

How to Confirm the Irrigation System Is Winterized

Before walking away, use this short check:

Every sprinkler and drip zone was cleared.
Each visible zone changed from water discharge to mostly air before you moved on.
The compressor was disconnected and system air pressure was released.
The backflow device was drained and left in its winter position.
Any pump was drained separately.
Flow sensors are protected.
Manual drain valves are not left open.
The irrigation water supply and controller are off.

A blowout reduces freeze risk; it does not make damaged fittings, bad valves, or buried leaks disappear. In spring, inspect the backflow device and visible connections before slowly restoring water pressure.

Frequently Asked Questions

Can I use a small pancake compressor to blow out my irrigation system?

Only if it can supply the required CFM continuously. Use the largest zone’s flow rate divided by 7.5 to estimate needed CFM, and do not make up for low CFM by releasing a fully charged tank in a high-pressure surge. Many small compressors can reach the needed PSI but cannot move enough air volume to clear a zone reliably.

How do I find the drip irrigation blowout valve?

Look for a hose bib, quick coupler, or capped fitting on the irrigation mainline after the backflow preventer and before the zone valves. The correct fitting sends air toward the drip valves and tubing without routing it through the backflow device or pump. If the only visible spigot is on the house wall or upstream of the backflow preventer, it is not the right connection.

Can I run a sprinkler system off a regular spigot?

A regular spigot can supply a small hose-end sprinkler setup, but that is different from a permanently installed irrigation system. A built-in system needs adequate water flow, proper backflow protection, and plumbing that meets local requirements. Do not assume that a faucet used for watering can also serve as the system’s safe compressor connection.

Do I need to blow out a system that has automatic drains?

Usually, yes, in areas that freeze. Automatic and manual drains may leave water in low spots, valves, backflow devices, and other components. Compressed-air winterization clears water from the zones, while the backflow device and pump still need separate draining.

When should I schedule irrigation winterization?

Schedule it before temperatures consistently fall below 32°F (0°C). Do not wait for a hard freeze warning, especially if the system includes exposed backflow plumbing, drip equipment, or shallow supply lines. If you cannot confirm the air path, compressor CFM, and pressure limits, arrange professional winterization before freezing weather arrives.