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Presure relief with high flow capacity & low cost of ownership: Buckling pin relief valve technology
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In the quest for efficient relief system sizing, it is the goal of the designer to obtain the maximum amount of flow for the smallest financial investment while meeting the often challenging operating requirements of each application. With their full opening characteristics, Rupture Disk Devices provide the best flow option while Pressure Relief Valves offer significantly reduced flow but, with automatic reset, avoid immediate downtime. An alternative option uses ‘buckling pin’ technology to control the set pressure of a high flow, in-line relief valve that equals the performance of the best rupture disk devices.
The buckling pin relief valve (BPRV) owes its high in-line flow capacity to a unique hollow rotating disc. Based upon an offset shaft butterfly valve concept, a pressure differential produces a turning moment on the valve shaft in the direction of flow. This moment is converted to a force in the BPRV external mechanism where it is restrained by a buckling pin under normal service conditions.
At a predetermined pressure relief point, the buckling pin is designed to activate at the corresponding load, allowing the disc to rotate through 90 degrees, full open. This exposes the hollow disc profile to the flow path, providing the maximum flow area for pressure relief.
Set pressure accuracy of a buckling pin activated relief valve is assured by the excellent repeatability of buckling pins made from the same controlled heat of raw material. Euler's Law of 1776 determines that a pin that is held in compression will buckle at a particular load. This buckling point is controlled by three variables:
- Diameter of the pin
- Length of the pin
- Modulus of elasticity (material) of the pin
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Precise control of buckling pin dimensions within each lot results in BPRV accuracy that equals or exceeds that of rupture disk devices. The BPRV takes a centuries old, highly reliable technology, and applies it to a modern engineering application. Buckling pins can be installed in a cartridge form (see picture) allowing a replacement part to be handled conveniently in the manner of an electrical cartridge fuse; this offers the optimum ease and integrity of installation.
Easy reset, typically in the field by the user, is the design basis for the BPRV. This provides a unique combination of high flow capacity, in-line valve technology designed for minimum reset downtime. Reset is by hand and typically takes less than 5 minutes to accomplish even on very large nominal size valves & without the need for specialized tools. The buckling pin which activates the BPRV is housed in an enclosure external to the process. The enclosure protects both the pin and mechanism from environmental conditions.
The application of buckling pin relief valve technology is particularly suited to the following conditions;
- Continuous processes; minimum downtime in the event of activation
- Hazardous service; the operator does not have to remove the BPRV from the piping system for routine replacement pin installation, minimizing the risk of exposure to the process
- Large line size; there is no requirement for special lifting equipment, extensive manpower and the resultant extended downtime to install a spare buckling pin
- Inaccessible locations; the buckling pin replacement part is small and convenient for installation – the option of a buckling pin cartridge further simplifies installation in hard to reach locations
- Remote installations; the small buckling pin replacement part can be easily accommodated in limited stores space
- Frequent operation; the cost of a replacement buckling pin is very modest compared to the cost of larger rupture disks and post discharge relief valve testing
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Buckling pin relief valve technology allows a facility to operate at a high productivity level while increasing safety for operators. Attractive overall cost of ownership combined with certification to international codes and standards (Pressure Equipment Directive, ASME Section VIII) provides the pressure relief system designer with a new and efficient means of compliance with challenging project objectives.
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