Page 214 - Valve Selection Handbook

Pressure Relief Valves 201

tional behavior of the valve has to be assessed, the plant operating pres-
sure has to be raised further by about 5% or 10%.
To overcome the need for overpressurizing the plant, portable verifica-
tion devices such as those shown in Figure 5-34 have been developed
that permit initial and periodic in-situ testing of pressure relief valves
without interfering with normal plant operation. These devices simulate
overpressure by introducing a measurable lifting force on the valve stem
that may be produced either mechanically, hydraulically, or pneumatical-
ly as in the device shown in 5-34. There is no need for controlling the
system pressure. The duration of the actual tests is short and measured in
seconds rather than minutes. The values that may be verified are:

• Set pressure
• Popping pressure
• Blowdown of reseated valve
• Valve lift
• Spring rate

Figure 5-34. Portable Device for the In-Situ Verification of Valve Operating Data
without Interfering with Plant Operation. (Courtesy of Sempell A.G.)