Sprinkler pipework acceptance: the hydrostatic and air tests explained

Fire protection · 24 Oct 2026

New sprinkler pipework is hidden behind ceilings within weeks. The acceptance pressure tests are the last good chance to find a weak joint before it is out of reach. NFPA 13 (Standard for the Installation of Sprinkler Systems) sets these tests. This article summarises them in our own words, based on the 2022 edition.

Why test at all

A sprinkler system may sit idle for years. It then has to hold pressure the day a fire happens.

The acceptance tests prove three things:

• joints, fittings and hangers are sound;
• there is no leak path at normal and surge pressures;
• the installer's workmanship meets the standard before it is covered.

The hydrostatic test

Under NFPA 13 (2022 edition), new system piping is hydrostatically tested at 200 psi (about 14 bar). The pressure must hold without loss for 2 hours.

Higher test pressures can apply to systems with high working pressures. Check the exact rule in the edition your authority enforces.

How it is normally run

1. Fill slowly. Vent air at the high points. Trapped air compresses and hides leaks.
2. Isolate what should not be tested. Some devices are not rated for the test pressure. Follow the manufacturer's instructions.
3. Raise the pressure with a calibrated gauge. Use a gauge at the low point, with a range suited to the test pressure.
4. Hold for the full period. Inspect all visible joints during the hold.
5. Record and sign. Record the start and end pressure, the times, the gauge ID and the witnesses.

"Without loss" means exactly that. A small drop is a failure, not a tolerance. The usual causes are a leaking joint, a passing valve, or air still in the system.

Temperature matters

Water expands and contracts with temperature. A pipe in morning sun can gain pressure, and a cooling pipe can lose it. Plan tests so the temperature is stable, and note the conditions on the test record.

The air leakage test for dry systems

Dry pipe and double-interlock preaction systems are tested twice:

• the hydrostatic test above;
• an air pressure leakage test.

Under NFPA 13 (2022 edition), the air test is run at 40 psi (about 2.8 bar) for 24 hours. Any leakage that causes a loss of more than 1.5 psi over the 24 hours must be found and corrected.

The air test does not replace the hydrostatic test. In freezing conditions, an interim air test may be allowed until water testing is possible. The water test must still be done later.

Who should witness

Agree in advance who will witness and sign:

• the contractor's representative;
• the owner's engineer;
• the authority having jurisdiction (AHJ), if it requires attendance.

Use the test certificate form required by the local authority, and keep a copy in the building's fire protection file.

Common reasons for a re-test

• Air left in the system. Pressure "drifts" as air dissolves or moves.
• Gauge problems. The gauge is uncalibrated, or its range is too wide to read small changes.
• Partial isolation. A closed valve hides part of the system from the test.
• Test run too early. Some joining methods need curing time before pressure testing.
• Temperature swing. The test runs across a hot afternoon or a cold night.
• Missing records. No signed record means no proof, even if the test passed.

A short checklist for the test file

• Drawing showing the test boundaries
• Gauge serial number and calibration certificate
• Start and end times, and start and end pressures
• Ambient conditions noted
• Leaks found, repairs made and the re-test result
• Signatures of witnesses
• Separate air test record for dry or preaction systems

Summary

Test at the right pressure, for the full time, with air removed and a calibrated gauge. Record it properly. For dry and preaction systems, add the 24-hour air test. These steps take little time compared with opening a finished ceiling to find a leak.

General guidance only. The authority having jurisdiction and the official text govern.