ASME PTe 25-2001

to the increase or decrease in pressure. It is normallyused for incompressible fluids.

safety relief valve: a pressure relief valve character­ized by rapid opening or closing or by gradualopening or closing, generally proportional to theincrease or decrease in pressure. It can be used forcompressible or incompressible fluids.

2.3.2 Nonreclosing Pressure Relief Device. Apressure relief device designed to actuate and remainopen after operation. A manual resetting means maybe provided.

design types:(a) rupture disk device: a device that contains a

disk which ruptures when the static differential pres­sure between the upstream and downstream side ofthe disk reaches a predetermined value. A rupturedisk device includes a rupture disk and may includerupture disk holder.

(b) breaking pin device: a device actuated bystatic differential or static inlet pressure and designedto function by the breakage of a load-carrying sectionof a pin which supports a pressure-containingmember.

(c) buckling pin device: a device actuated bystatic differential or static inlet pressure and designedto function by the buckling of an aXially-loadedcompressive pin which supports a pressure-con­taining member.

(d) shear pin device: a device actuated by staticdifferential or static inlet pressure and designed tofunction by the shearing of a load-carrying memberwhich supports a pressure containing-member.

(e) fusible plug device: a device designed tofunction by the yielding or melting of a plug, at apredetermined temperature, which supports a pres­sure-containing member or contains pressure byitself.

(f) frangible disk device: see rupture disk device.(gJ bursting disk device: see rupture disk device.(h) direct spring-loaded device: a device actuated

by static differential pressure or static inlet pressurein which the disk is held closed by a spring. Uponactuation, the disk is held open by a latching mech­anism.

(i) pilol-operated device: a device in which thedisk is held closed by system pressure and theholding pressure is controlled by a pilot actuatedby system pressure. The pilot may consist of oneof the devices listed above.

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PRESSURE RElIEF DEVICES

design features: nonreclosing pressure relief de­vices may include one or more of the follOWingdesign features.

(a) low lift device: a device in which the actualdischarge area is dependent on the lift of the disk.

(b) full lift device: a device in which the actualdischarge area is independent of the lift of the disk.

(c) reduced bore device: a device in which theflow path area below the seat is less than the flowpath area of the inlet to the device.

(d) full bore device: a device in which the flowpath area below the seat is equal to the flow patharea of the inlet to the device.

2.4 PARTS Of PRESSURE RELIEF DEVICES

adjusting ring: a ring assembled to the nozzle orguide of a direct spring valve, used to control theopening characteristics andlor the reseat pressure.

adjustment screw: a screw used to adjust the setpressure or the reseat pressure of a reclosing pressurerelief device.

backllow preventer: a part or feature of a pilot­operated pressure relief valve used to prevent thevalve from opening and flOWing backwards whenthe pressure at the valve outlet is greater than thepressure at the valve inlet.

bellows: a flexible pressure-containing componentof a balance direct spring valve used to preventchanges in set pressure when the valve is subjectedto a superimposed back pressure, or to preventcorrosion between the disk holder and guide.

blowdown ring: see adjusting ring.

body: a pressure-retaining or containing memberof a pressure relief device that supports the partsof the valve assembly and has provision(s) for con­necting to the primary and/or secondary pressuresource(s).

bonnet: a component of a direct spring valve orof a pilot in a pilot-operated valve that supports thespring. It mayor may not be pressure containing.

breaking pin: the load-carrying element of a break­ing pin nonreclosing pressure relief device.

breaking pin housing: a pressure-retaining compo­nent that supports the breaking pin in a nonreclosingpressure relief device.