Combination rupture disk device/pressure relief valve

Type CG-8, This is a combination device consisting of a rupture disk device followed by and in series with a pressure relief valve. The piping connecting the rupture disk and pressure relief valve is equipped with a sensing device to indicate pressure. The system is designed and constructed so the required relieving capacity is achieved and the operation of the relief valve is not impeded. 

The capacity of the combination of the rupture disk device and the spring loaded safety or safety relief v alve may be established in accordance with the appropriate paragraphs of UG-132, Certification of Capacity of Safety Relief Valves in Combination with Non-reclosing Pressure Relief Devices. 

Rupture disk device in combination with pressure relief valve. Combination rupture disk/pressure relief devices, as illustrated in Fig. 8-18, consist of a conventional reclosing pressure relief valve in series with a rupture disk. The rupture disk is located between the pressure relief valve and the container. The relief valve is... 

Breaking pin device in combination with pressure relief valve. This style of pressure relief device, as illustrated in Fig. 8-19, is very similar to the rupture disk and relief valve combination, except that a breaking pin is used in place of the rupture disk. The breaking pin device is a nonreclosing pressure relief device actuated by inlet static pressure and is designed to function by the breaking of the load carrying section of the pin. 

Rupture disk device in combination with pressure relief valve... 

Fig. 8-18. Rupture disk device (Type CG-1) in combination with pressure relief valve (Type CG-7) for cargo tanks.

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. 

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). 

Pressure relief devices authorized for use on helium cylinders include the CG-1, CG-4, CG-5, and CG-7 type devices. These include rupture disk, combination rupture disk/fus-ible plug, and pressure relief valve type devices. For further information and requirements, see CGA S-1.1, Pressure Relief... 

Rupture Disks A rupture disk is a device designed to function by the bursting of a pressure-retaining disk (Fig. 26-15). This assembly consists of a thin, circular membrane usually made of metal, plastic, or graphite that is firmly clamped in a disk holder. When the process reaches the bursting pressure of the disk, the disk ruptures and releases the pressure. Rupture disks can be installed alone or in combination with other types of devices. Once blown, rupture disks do not reseat thus, the entire contents of the upstream process equipment will be vented. Rupture disks are commonly used in series (upstream) with a relief valve to prevent corrosive fluids from contacting the metal parts of the valve. In addition, this combination is a reclosing system. 

High pressure is perhaps the most important hazard of a gas stored in the cylinder. A typical gas cylinder usually comes filled at a pressure of around 2200-2400 psi (pounds per square inch) (see Special Topic 5.3.1.1 Pressure Units). Upon the sudden release of this pressure the gas can be very dangerous. Of course, as the temperature rises in the laboratory or place where the cylinder is stored, the cylinder pressure also rises, and the greater the pressure the more stress there is on the integrity of the cylinder. To take measures to prevent explosions, manufacturers install a relief valve that is designed to rupture at some prescribed cylinder pressure, temperature, or combination of temperature and pressure. Most of these relief devices open when a disk raptures or melts. Less commonly, a spring-loaded relief valve is installed that can open at some high pressure and reclose when the cylinder pressure is reduced. 

When this combination-type pressure relief device is installed, some regulations require that the space between the rupture disk and relief valve be vented to the atmosphere or monitored to detect any pressure buildup on the downstream side of the rupture disk, which could prevent proper functioning of the rupture disk. 

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