Combination rupture disk/fusible plug

Type CG-4 and CG-S (combination rupture disk/fusible plug). A combination rupture disk/fusible plug pressure relief device requires both temperature and pressure in that order for it to operate and therefore provides for maximum retention of the cylinder contents. Sufficient heat is required to first melt out the fusible metal, after which the device will afford the same protection as the CG-1 rupture disk device. 

Fig. 7-6. Combination rupture disk/fusible plug device (Type CG-4 or CG-5) factory-assembled as a complete unit.

Pressure relief devices authorized for use on argon cylinders are the Type CG-1 rupture disk, CG-4 and CG-5 combination rupture disk/fusible plug devices, and the CG-7 pressure relief valve. Refer to CGA S-1.1, Pressure Relief Device Standards—Part I— Cylinders for Compressed Gases, for further information. [4]... 

As previously stated, the valve must be equipped with a Type CG-1 pressure relief device equipped with a rupture disk. A backed pressure relief device, that is, a combination rupture disk/fusible plug device, must not be used on a carbon dioxide cylinder valve. 

Carbon tetrafluoride is authorized for shipment in DOT specified cylinders as identified in 49 CFR 173.302 and equivalent Canadian regulations. [1] and [2] Authorized pressure relief devices include the Type CG-1 rupture disk, the Type CG-4 or CG-5 combination rupture disk/fusible plug device, or the Type CG-7 pressure relief valve. [3] The rupture disk must have a bursting pressure not exceeding the minimum prescribed test pressure of the cylinder. 

Cylinders must be equipped with a CG-4 type pressure relief device. This device must be in both ends of the cylinder when the cylinder is over 30 inches (76 cm) in length. This type of device is a combination rupture disk/ fusible plug, utilizing a fusible alloy with a yield temperature not over I70°F (76.7°C). 

Authorized pressure relief devices for use on silane cylinders are the IVpe CG-4 combination rupture disk/fusible plug device wherein the fusible metal has a nominal yield temperature of 165° F (74 °C). Consult CGA S-1.1, Pressure Relief Device Standards— Part 1—Cylinders for Compressed Gases, for further information and requirements. [11]... 

The most common cylinder valve used for dichlorosilane is a stainless steel diaphragm valve with a Connection CGA 678 outlet. The cylinder valve body has a combination CG-4 type pressure relief device consisting of a fusible metal plug, melting about 165°F (74°C), which is protected from the cylinder contents by a frangible metal disk, i.e. a rupture disk, rated at 250 psig (1724 kPa). 

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