Liquid Thermal Relief Valve
Sizing
By
AKINYELE, O.I
Sizing & Set Pressure
For liquid relief, the capacity requirement is usually small, specifying an
oversized device (NPS ¾ x NPS 1) is usual practice.
If there is doubt about the adequacy of the selected size, calculation is
required according to API 521. (see case study)
TRV set pressure must be carefully selected such that it is not above the
maximum pressure permitted by the weakest component in the protected
system. However, it should be set high enough to open only under
hydraulic expansion condition
National Engineering and Technical Company Ltd.
Wed July 26, 2017
2
Sizing Criteria
• Offsite lines greater than 10,000 ft (3,048 m) – FRS-DU-5057-D.2
Assume 330 BTU/hr/ft2 (1041 W/m2) solar heat input to the line shadow.
That is,
Heat input (Q) = 330 BTU/hr/ft2 x line length (ft) x line outside diameter (ft)
Heat input (Q) = 1,041 W/m2 x line length (m) x line outside diameter (m)
• Heat Exchangers with design duties above 5 MMBTU/hr (1,465 kW)
National Engineering and Technology Company Ltd.
Wed July 26, 2017
3
Case Study
National Engineering and Technology Company Ltd.
Wed July 26, 2017
4