Comparison

Preaction vs Dry Pipe Sprinkler Systems

Dry pipe systems hold air and open on a sprinkler. Preaction systems also need detection first. Compare sequence, freezing and accidental discharge.

Fire Protection · Last reviewed October 17, 2026

Short answer: use a dry pipe system to protect spaces that can freeze. Use a preaction system where an accidental discharge would be very costly, such as data centers, archives and museums. A preaction system adds fire detection and a more complex control, and it may also be used in freezing spaces.

	Dry pipe	Preaction
Pipe contents	Compressed air or nitrogen	Air at low pressure or unpressurized, depending on the type
Operating sequence	A sprinkler opens, the air escapes, the valve trips and water flows to the open sprinkler	Detection opens the valve (single interlock), or detection and an opened sprinkler are both needed (double interlock)
Detection interface	None needed, although supervisory pressure is monitored	A separate detection system (smoke, heat or flame) controls the valve
Water delivery delay	Water must displace the air in the pipe, which takes time	With single interlock, water is in the pipe before heat opens a sprinkler. With double interlock, a delay is possible
Freezing exposure	Suitable, because the pipes hold no water	Suitable, with the same attention to the water in the valve and risers
Accidental discharge	A damaged sprinkler lets air out and can trip the valve	Protected: a damaged sprinkler alone does not release water in a double interlock system
Complexity	Moderate: air supply and maintenance	Higher: detection, releasing panel and valve control
Maintenance	Air pressure, leaks, drains, valve trip tests	All of the dry pipe needs plus the detection and the releasing control tests
Cost	Moderate	Higher

How to choose

Decide what you are protecting and the damage an accidental discharge would cause.
Check for freezing exposure, and the temperatures of the space.
Check the code requirements for the hazard, including limits on water delivery time for dry systems.
Decide which type of preaction (single or double interlock) fits the risk and the response time needed.
Plan the detection, the control panel and the testing and maintenance, with the qualified contractor.

Common mistakes

Using a double interlock system where the water delay is not acceptable for the hazard.
Treating preaction as a dry pipe system without detection testing.
Leaving out air supply supervision on a system that needs it.
Assuming a preaction system removes all risk of leakage. A pipe or joint can still leak.

Related tools and labs

Calculators, labs and simulators are part of the All-Access Pass.

More comparisons

Questions

What is a double interlock?

A preaction system where both a detector signal and an open sprinkler (loss of air pressure) are needed before water enters the pipe. It lowers the chance of an accidental discharge and adds delay.

Can a preaction system be used in a freezing space?

Yes, if it is designed for it. Check the valve and riser protection and the code.

Educational material. Examples use simplified, hypothetical inputs and are not a design, a construction document or professional engineering advice. Confirm requirements with the codes and standards adopted where the work is built and with a licensed engineer.

← All comparisons