API MPMS 6.2 pdf download Manual of Petroleum Measurement Standards Chapter 6—Metering Assemblies Section 2—Loading Rack Metering Systems 4.5.3 Check Valves Check valves are required to prevent backflow, siphoning with low tank head, and cross contamination of product during blending applications. When choosing the proper check valve, consider pressure drop and slamming of the flapper, which can cause damage when...