Fusible metal device

The fusible metal device melts when high temperature (160-212°F) is reached. This will also allow all the contents of the cylinder to escape. 

Acetylene cylinders are fitted with safety devices to release the acetylene ia the event of fire. Cylinders manufactured ia the United States are equipped with safety devices which contain a fusible metal that melts at 100°C. In large cylinders the safety devices are ia the form of a replaceable, threaded steel plug with a core of fusible metal. Small cylinders (0.28 and 1.12 m 10 and 40 fT, respectively) may have the fusible metal ia passages ia the cylinder valve. 

LB = lens blocking W = work holding RS = radiation shielding FSD = fusible safety device PC = proof casting SMF = sheet metal forming ... 

Type CG-2 and CG-3 (fusible plugs), A fusible plug is a thermally operated pressure relief device that affords protection against excessive pressure developed by exposure to excessive heat. Once sufficient heat melts the fusible metal, the contents of the cylinder will be vented. The CG-2 fusible metal has a nominal melt temperature of 165°F (73.9°C) the CG-3 fusible metal has a nominal melt temperature of 212T(100X). 

Fig. 8-3 illustrates typical ftisible plug bodies with recommended design considerations. Fig. 8-4 illustrates ftisible metal cast directly into a cylinder valve body. Fig. 8-5 illustrates a separate device threaded into a cylinder valve body. Sufficient heat to melt the fusible metal is necessary for proper functioning of this type of device. Therefore, the location of such devices is an important consideration. 

Caution No attempt should be made to repair used fusible plug devices because of the possibility of the wrong fusible metal being used, the absence of a qualified repair procedure, and the possibility of destroying the bond... 

Limitations Since the fusible plug is a thermally operated device, it is designed to function only when the fusible metal melts out. Hence, it does not protect against overpressure from improper charging practices. 

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. 

The CG-4 combination device has fusible metal with a nominal melt temperature of 165°F (73.9°C). The CG-5 combination device has fusible metal with a nominal melt temperature of212°F(100°C). 

In this type of device, the rupture disk portion (CG-1) is directly exposed to the internal cylinder pressure and is directly upstream of the fusible metal. In general, the same components that make up the CG-1 device are used. The discharge ports, downstream side of the rupture disk holder, are filled or partially filled with fusible metal. (See Figs. 8-6 and 8-7.) The rup-... 

Limitation CG-4 and CG-5 combination devices function only in the presence of both predetermined heat and pressure. Sufficient heat must be present first to melt the fusible metal. Therefore, this device does not offer protection against overpressure from improper charging practices. 

Type CG-9. This is a high-pressure fusible plug for use at cylinder service pressures above 500 psig (3450 kPa) using a fusible alloy with a yield temperature not over 224°F (107°C). The nominal yield temperature is 217°F (103°C). (See Fig. 8-13.) Because of its high resistance to fusible metal extrusion, the device has been used extensively on vehicular compressed natural gas fuel cylinders where it provides protection of partially charged cylinders in fires. 

Each pressure relief device assembly must be examined to ensure it is free of visual indications of abuse, damage, extrusion of fusible metal and that it appears intact. Each device must be the appropriate type and pressure rating for the gas and cylinder as prescribed in DOT and TC regulations and CGA S-1.1, Pressure Relief Device Standards-Part 1-Cylinders for Compressed Gases [1, 2, 23]. 

Never tamper with pressure relief devices in valves or cylinders. Keep sparks and flames away from acetylene cylinders and under no circumstances allow a torch flame to come in contact with the fusible metal pressure relief devices, which melt at approximately 212°F (100°C). Should the valve outlet of an acetylene cylinder become clogged by ice, thaw with warm, but not boiling water. 

Fusible plugs can be installed on the cylinder as independent devices, or fusible metal can be cast directly into a suitable orifice in the cylinder valve body. In some cases, a fusible plug may be installed as a separate device into the cylinder valve body. 

Sufficient heat to melt the fusible metal is necessary for proper functioning of this type of device. Therefore, the location of such devices is an important consideration. 

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). 

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]... 

AV-9 Handling Acetylene Cylinders in Fire Situations, Provides guidance and practical information on procedures to use when acetylene cylinders are involved in a fire. Includes description of acetylene cylinder construction and potential sources of ignitable leaks from fusible metal pressure relief devices, valve components, etc. (approx. 20 minutes)... 

Any of these devices will provide protection against a cylinder bursting from excessive temperature, except in the case where an intense flame impinging on the sidewall of a cylinder may weaken the metal at that point and cause a local failure before the heat or pressure cause the safety relief device to operate. Devices 3 and 4 may not provide protection in cases where a liquefied gas cylinder has been overfilled and exposed to a high temperature that is below the fusible metal s melting point. Because of this, extreme care should be used when filling liquefied gas cylinders and filling should never be attempted by the user. Never tamper or attempt to remove or block a cylinder s pressure relief devices since this could cause an extremely hazardous condition. 

Fusible metal. These devices melt at about 71 to 100°C (160 to 212°F) and allow the entire contents of the cylinder to escape. 

Frangible disk/fusible metal. This device functions only after sufficient heat has melted the fusible disk, after which excessive pressure will burst the frangible disk. The entire contents of the cylinder will then escape. 

The first two safety devices, which employ fusible metal, will not always prevent a cylinder failure if the cylinder is overfilled and... 

Heat detectors are activated by either melting a fusible material, changes in electrical current induced by heat loads on bi-metallic metals, destruction of the device itself by the heat, or by sensing a rate of ambient temperature rise. 

Fusible Link - A release device activated by the heat effects of a fire. It usually consists of two pieces of metal joined by a low melting point solder. Fusible links are manufactured at various temperature ratings and are subject to varying normal maximum tension. When installed and the fixed temperature is reached, the solder melts and the two metal parts separate, initiating desired actions. 

Rose s metal A fusible alloy containing 50% bismuth, 25-28% lead, and tin. Its low melting point (about 100°C) leads to its use in fire-protection devices. 

FUSIBLE PLUG - Plug or fitting made with a metal of a known low melting temperature. Used as safety device to release pressures in case of fire. 

Heat is the most obvious choice of a characteristic by which a fire can be automatically recognized. In the section on fire suppression systems, the fusible links in the sprinkler heads represented one type of heat detector. Alloys have been developed that will have reproducible melting points. When the temperature at the detector site exceeds the melting point of the alloy, contacts are allowed to move so that the device can either make or break a circuit, just as with a manual alarm system. There are plastics which can perform in the same manner. Fixed temperature systems are very stable and not prone to false alarms, but are relatively slow to respond. There are several other versions of these fixed temperature detectors, including bimetalhc strips, where the differential rate of expansion of two different metals causes the strip to flex or bend to either make or break the contact. Others depend upon the thermal erqransion of hquids. 

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