Is a 3 gallon air compressor enough to blow out sprinklers?

Quick Answer

A 3 gallon air compressor may be enough to blow out sprinklers, depending on the size of your sprinkler system. Smaller systems with just a few zones may be blown out by a 3 gallon compressor. However, larger systems with many zones will likely require a larger compressor such as 5-10 gallons. Factors like pipe size, length, and number of heads will determine the CFM requirements to properly blow out the system.

What Size Air Compressor for Sprinkler Blowout

The size of air compressor needed for blowing out sprinklers depends on the CFM (cubic feet per minute) requirements of your system. Here are some general guidelines:

System Size	Air Compressor Size
Small (1-4 zones)	3-5 gallon
Medium (5-10 zones)	5-10 gallon
Large (10+ zones)	10+ gallon

A small sprinkler system with just a few zones may only require 15-30 CFM to properly blow out. In this case, a 3-5 gallon air compressor that delivers 2.5-4 CFM per gallon would be sufficient.

However, larger systems with many zones, long pipes, and dozens of sprinkler heads may require 50 CFM or more. A 10 gallon compressor delivering 4 CFM per gallon would be a safer bet for ensuring you can provide enough airflow.

The CFM rating is more important than tank size. While a large tank provides more reserve air, the compressor must also be able to deliver adequate airflow (CFM) to quickly blow out all the pipes.

Calculating CFM Requirements

To determine the actual CFM you need, you’ll need to calculate the volume of air in your pipes. This requires measuring the pipe diameters and lengths.

Use this formula:

CFM = Volume (cubic feet) / Time (minutes)

Where Volume = (Pipe area in square inches) x (Pipe length in feet) / 144

As an example:
– 1″ pipe with 300′ total pipe length
– Area of 1″ pipe = 0.785 sq in
– Volume = (0.785 sq in) x (300 ft) / 144 = 1.65 cubic ft
– Blowout time: 5 minutes
– CFM = Volume / Time = 1.65 cu ft / 5 min = 0.33 CFM

So for 300′ of 1″ pipe, you’d need an air compressor that can deliver at least 0.33 CFM per zone. Scale up accordingly for multiple zones.

Add up the CFM for each pipe/zone to determine the total CFM required for blowout. Compare this to the CFM rating of the air compressor.

Factors Determining Air Compressor Size

Here are some key factors that determine whether a 3 gallon air compressor is sufficient for blowing out your sprinkler system:

Number of zones

More zones means more piping that needs to be cleared of water. A system with only 1-3 zones has less CFM demand than a system with 8+ zones.

Pipe size

Larger diameter pipes have greater air volume than smaller pipes. For example, 2″ pipe holds 4x the volume of 1″ pipe. More airflow is needed to clear larger pipes.

Total pipe length

Longer pipe runs require blowing out more water volume and therefore more CFM. A system with 500′ of piping needs more air than one with 200′.

Number of heads

Each sprinkler head contains stagnant water that needs to be forced out. More heads means more water to blow out.

PSI rating

Higher compressor PSI enables blowing water out with more force. Minimum PSI of 60-80 is recommended for sprinkler blowouts.

Fittings and elbows

More fittings and elbows increase resistance and air volume needed. Complex systems require more air.

Benefits of a Larger Air Compressor

While a 3 gallon air compressor may work for smaller systems, going with a larger 5-10 gallon compressor has some advantages:

More power and airflow

A larger compressor has higher CFM capability to force out more water quickly. This minimizes blowout time.

Handles complex systems

With more zones, heads, and longer pipes, a larger compressor is less likely to be undersized.

Reservoir provides longer running

The larger tank enables more continuous runtime before needing to stop to refill the tank.

Less wear on the compressor

A compressor running near full capacity wears out faster than one lightly loaded. A bigger unit runs less to do the same job.

Room for future expansion

If you add zones later, a larger compressor will still have the capacity to handle the increased demand.

More consistent airflow

Larger compressors maintain steadier airflow and pressure. Smaller ones tend to cycle on/off more.

Backup capacity

A bigger compressor allows you to also use air tools like impact wrenches. Gives you reserve capacity.

Investment in durability

Larger units feature heavier duty components that hold up better over time. A wise investment if you’ll use it yearly.

Tips for Using a Small Air Compressor

Here are some tips to get the most out of a 3-5 gallon air compressor when blowing out sprinklers:

Blow out one zone at a time

This prevents airflow from being divided across multiple zones making blowout less effective.

Use drain valves for each zone

Open drain valves while blowing out a zone to let water escape freely without building up pressure.

Allow tank to fully recharge between zones

Don’t start the next zone until tank pressure is at max PSI again.

Start blowout at the lowest points

Blow out downhill zones first so water drains out easier from higher elevations.

Remove sprinkler heads if possible

Eliminates head backpressure so pipes clear faster.

Use a larger diameter mainline

This reduces airflow resistance between compressor and valves.

Keep runs as short as possible

The shorter the pipe length, the lower CFM required for blowout.

Use galvanized nipple/fittings

Prevents corrosion which could restrict airflow over time.

Have a helper monitor zone valves

They can open/close as needed to keep air focused on one zone.

Conclusion

For small sprinkler systems, a 3 gallon air compressor may suffice for doing an adequate blowout. However, larger systems will benefit from the extra power and capacity of a 5-10 gallon unit. Calculating your pipe CFM needs and matching them to compressor output is the best way to ensure proper sizing. A compressor that’s too small will struggle to get the job done quickly. Investing in a larger unit provides power to spare, quicker blowouts, and room to expand the system later if needed. Careful work sequencing and piping optimization can help a small air compressor be more effective. But when in doubt, go bigger on compressor size to guarantee trouble-free winterization of your sprinklers for years to come.