Hydrostatic Testing and Refill Service

What This Service Covers

Hydrostatic testing and refill is the periodic testing of the pressure vessels used in gas fire suppression systems, at the intervals required by applicable pressure vessel regulations, followed by refilling cylinders that pass with suppression agent and returning them to service. Over the years, cylinders can lose pressure integrity to internal and external corrosion, material fatigue, or impact damage — which is why testing them at defined intervals is both a legal requirement and a fundamental safety measure.

This service also covers refilling passed cylinders in-house at GYS’s own facility, under proper quality-control processes.

How the Process Works

The process begins with cylinders being safely removed from the system and prepared for testing; necessary precautions are planned in advance so the protected area is not left unprotected while the system is temporarily out of service. Cylinders first undergo a visual and surface inspection, checking for signs of corrosion, deformation, or mechanical damage. The hydrostatic pressure test follows: the cylinder is subjected to a water pressure at a set multiple of its working pressure, measuring whether the material withstands it without permanent deformation.

Based on the test result, the cylinder is either approved or condemned for safety reasons. Cylinders that pass are refilled at GYS’s own facility with the appropriate agent, to the correct weight and pressure values. Finally, refilled cylinders are labeled and documented as legally required and coordinated for reinstallation on site.

Correct Agent and Approved Filling

A cylinder must be filled with the agent the system is listed/approved for, at the fill quantity and pressure specified by the system manufacturer. Agent of unknown origin, a wrong fill quantity or an incorrect nitrogen superpressure can prevent the system from reaching its design concentration. After filling, the cylinder weight and pressure are therefore recorded and checked against the label data.

Why It Matters

An untested or overdue cylinder carries serious risk, both because it’s uncertain whether it can safely hold fill pressure and because a pressure loss would prevent the system from delivering its full suppression capacity. Periodic hydrostatic testing catches this risk in advance, under controlled conditions, preventing an unexpected failure in the field.

Performing the refill in-house also keeps fill quality and agent purity under control from start to finish, helping preserve the system’s performance at the same level as its original installation.

This service is one step in the life cycle of a gas fire suppression system project, from survey to maintenance; every step and agent option is on our home page.