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[tsrc8204]

Dear all,

From the P&I diagrams, I found some RVs or TSV that the body size was always 3/4" X1", why? thanks for calify.

tsrc.

[ankur2061]

tsrc,

TSVs or TERVs(Thermal Expansion Relief Valves) as some call it need not necessarily be 3/4" X 1" for all cases. They could be 1'X1" or even 1"X2" and which i have seen.

However, it seems the underlying question seems to be that "why are they normally small in size".

Well, to understand that you must understand the thermal expansion relief scenario. Section 5.14, "Hydraulic Expansion" of API STD 521 very precisely explains the phenomena of hydraulic expansion (increase in liquid volume) due to increase in temperature.

In this standard it is also explained that the relief valve (TSV) is provided to relieve the excess pressure generated due to volumetric expansion. If a calculation is performed to determine the relief flow rate, it has been generally found that the relieving flow rate is very low. In view of such a low flow rate, a standardized size of 3/4" X 1" has been proposed by major relief valve manufacturers and endorsed by the process industry.

However, as a caution, if you are dealing with long pipelines with large diameters and running 100% liquid full and/or large vessels/heat exchangers running 100% liquid full then the 3/4" X 1" size may not apply and bigger sizes may be required.

All in all, a thermal expansion relief device may require some analysis to determine its sizing.

Please do study API STD 521 to get a clear picture of what the thermal (hydraulic) expansion phenomena means.

Regards,
Ankur.