Breaking pin devices

Set pressure is the pressure at which the device begins to relieve, e.g., lift pressure of a spring-actuated relief valve, bursting pressure of a rupture disk, or breaking pressure of a breaking pin device. 

Pressure-relief devices include direct spring-loaded and pilot-operated relief valves that close or reseat if the vessel pressure is brought back into a safe condition, as well as non-reclosing devices such as rupture disks and breaking-pin devices. 

Two types of non-redosing pressure-relief devices are used rupture disks and breaking-pin devices. 

Breaking-pin devices have a similar construction to spring-loaded relief valves, except the valve disk is held against the seat by a pin that is designed to buckle or break when the set pressure is reached, as illustrated in Figure 13.46. Once the valve has opened, the pin must be replaced before the valve can be reset. 

Both rupture disks and breaking-pin devices are sensitive to temperature. The manufacturer should always be consulted for applications that are not at ambient conditions. Since non-reclosing pressure-relief devices can be used only once, the set pressure is determined by testing a sample of the devices out of each manufactured batch. Pressure-relief valve test methods are specified in AS ME PTC 25-2001. 

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. 

Breaking pin device in combination with pressure relief valve... 

Fig. 7-18. Breaking pin device in combination with pressure relief valve (Type CG-7) for cargo tanks.

Pressure-relief-device requirements are defined in Subsec. A. Set point and maximum pressure during relief are defined according to the service, the cause of overpressure, and the number of relief devices. Safety, safety relief, relief valves, rupture disk, breaking pin, and rules on tolerances for the reheving point are given. 

The diaphragm is not a pressure-protective device the breaking pin serves that function. The process-side diaphragm and another one mounted at the top of the valve are there to prevent corrosion by exposure to process gas or the atmosphere. When the set pressure is exceeded, the pin breaks and the valve opens. The upper diaphragm then breaks, and chlorine escapes. When the pressure returns to a safe value, the valve closes and then functions as a standard spring-loaded relief valve until the breaking pin and diaphragms can be replaced. 

Should the breaking pin fracture, the relief valve instantly pops fully open and, after tank pressure is relieved and returns to a safe working pressure, the relief valve will reseat and function as a conventional spring-loaded relief valve until it is convenient to replace the breaking pin portion of the device. 

Agglomerate breaking and liquid feeding device shown in broken line. Where no liquid feeding is necessary, a pin-type agglomerate breaking device is used. Tumblers of this type are available plain or with any of the above features. 

If the ultimate in protection is required, a membrane of metal less than 0.1 mm thick is left across the nozzle face and provides visible tamper-evidence. Sometimes a special double-ended cap is used, incorporating an integral piercing device. The tube is pierced by removing the cap, reversing it and screwing it back onto the tube until the inverted cone pierces the membrane. If the product is of the unit dose type a membrane tube is used without a cap or threaded portion, e.g. taper or torpedo ended tubes. In this case piercing of the nozzle must be carried out with a pin or similar device. Alternatively a break-off style tip can be used. 

The piston-and-cylinder device shown here contains an ideal gas at 20 bar and 25 C. The piston has a mass of 300 kg and a cross-sectional area of 0.05 m . The initial volume of the gas in the cylinder is 0.03 m . the piston is initially held in place by a pin, and the external pressure on the piston and cylinder is 1 bar. The pin suddenly breaks, and the piston moves 0.6 m farther up the cylinder, where it is stopped by another pin. Assuming that the gas is ideal with a constant-pressure heat capacity of 30 J/(mol K), and that there is no heat transfer between the gas and the cylinder walls or pi.ston. estimate the piston velocity, and the temperature and pressure of the gas just before the pi.ston hits the. second pin. Do this calculation assuming... 

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