How do you Hydrostatically test Gas Suppression Cylinders?

Hydrostatic testing involves filling gas cylinders with water and placing them into a water filled pressure chambe, usually at 5/3 or 3/2 of their working pressure. This causes the water pressure inside the cylinder to increase and the cylinder to subsequently expand. Cylinder expansion of less than 5% is within the regulations limit and allows for recertification. Compliant cylinders are then dried out, stamped with certification and dated along with their test details. The cylinder is then reconditioned and either a refurbished or new valve is fitted before the cylinder is returned into service.