Cylinders are made of different kinds of materials. Generally, cast iron is used for cylinder operating pressures up to 1,000 to 1,200 psig, nodular iron or cast steel for operating pressure in the 1,000 to 2,500-psig range, and forged steel for pressures greater than 2,500 psig
Like all pressure vessels, the cylinder has a maximum allowable working pressure (MAWP). The maximum allowable working pressure of the cylinder determines the setting of the relief valve that is downstream of the cylinder. The MAWP of the cylinder should be a minimum of 10% or 50 psi greater than its operating pressure.