Page 173 - Valve Selection Handbook

160 Valve Selection Handbook

An overview of the ASME Code safety valve rules by M. D. Bernstein 1
2
and R. G. Friend may be found in Reference 44. A reprint of a summary of
the ASME Safety Valve Rules taken from this reference publication may be
found in Appendix A of this book.

TERMINOLOGY

Pressure Relief Valves

Pressure relief device: A device designed to open in response to exces-
sive internal normal or subnormal fluid pressure, and sized to prevent the
fluid pressure from exceeding a specified normal or subnormal limit. The
device may be either of the type that closes after the pressure excursion
has receded or of the non-reclosing type.

Pressure relief valve: A pressure relief device that recloses automatically
after the pressure excursion has receded.

Direct-loaded pressure relief valve: A pressure relief valve in which the
fluid pressure acting on the disc in the opening direction is opposed by a
direct mechanical-loading device such as a weight or a spring.

Safety valve: A direct-loaded pressure relief valve that is intended main-
ly for gas, vapor, or boiler and steam applications and characterized by
pop-opening action.

Relief valve: A direct-loaded pressure relief valve intended mainly for
liquid service.

Safety relief valve: A direct-loaded pressure relief valve that may be
used either in gas or vapor service or in liquid service. The valve will
open in gas or vapor service with a pop action, and in liquid service in
proportion to the rise in overpressure though not necessarily linearly.

Conventional safety relief valve: A pressure relief valve in which the
loading device is enclosed in a pressure-tight bonnet that is vented to the
valve outlet.

1
Foster Wheeler Energy Corporation, Perryville Corporate Park, Clinton, NJ 08809.
2
Crosby Valve & Gage Company, Wrentham, MA 02093.