API MPMS 6.2:2004 pdf free download.Manual of Petroleum Measurement Standards Chapter 6—Metering Assemblies Section 2—Loading Rack Metering Systems
4.4 LOAD RACK ACCESSORIES
4.4.1 Strainers A strainer should be installed upstream of the meter, per manufacturer’s recommendations, to trap solid particles that could damage the meter. The strainer shall be checked and cleaned periodically, since an accumulation of solid material in the strainer can restrict flow, creating the potential for prod- uct vaporization just upstream of the meter, and could cause the flow rate to differ from the meterproving flow rate.
4.4.2 Air Eliminators Air eliminators are required in systems where air can be induced into the system. The air eliminator is located upstream of the meter, and its purpose is to dispose of any air in the delivery line before it passes through the meter. If a system is designed so that significant amounts of air, vapor, or both cannot be introduced, an air eliminator is not required.
4.4.3 Vapor Control Regardless of the type of loading that is used—either bot- tom loading or top loading—some vapor will be produced in the truck compartment. The turbulence of the incoming product and the rising liquid level will cause air and vapor to be dispersed either out the top of the truck compartment to the atmosphere or to a vapor-processing system. If the system is equipped with a vapor control system, a check valve shall be installed in the vapor line as mandated by EPA regulations.
4.5 VALVES
4.5.1 Thermal Relief Valves Thermal relief valves are required to prevent over-pressurization of the metering system. Any section of the tank-to-loading-rack supply piping that can be isolated by the closing of control valves, block valves, check valves, etc. shall be protected by thermal relief. The integrity of these valves shall be verified periodically because of their potential to impact measurement. Thermal relief lines should be located to minimize the potential for product bypass around the meter, which can affect measurement accuracy. Installation upstream of the main product meter is acceptable provided the product flow control valve will relieve internally when downstream piping experiences excessive pressure.
4.5.2 Isolation/Secondary Shutoff Valves Inlet/isolation valves are required to shut off flow. Typi- cally, these valves are utilized for maintenance purposes and to minimize the volume of product during drain-down. These valves can be automated and controlled by the secondary overfill protection system. This may reduce the potential for an overflow if the flow control valve fails to fully close when required.
4.5.3 Check Valves Check valves are required to prevent backflow, siphoning with low tank head, and cross contamination of product dur- ing blending applications. When choosing the proper check valve, consider pressure drop and slamming of the flapper, which can cause damage when the valve opens and closes.
4.5.4 Flow Control Valves Flow control valves must be installed downstream of the meter. These valves should provide a smooth opening and closing and be capable of stable flow control. Additionally, quick operation is required to prevent overfill. The manufacturer’s recommended flow control range should not be exceeded. This could result in poor flow con- trol, unsafe shutoff, inaccurate measurement, and premature wear. The flow control valve is typically controlled by an electronic preset to reduce the discharge rate at start-up or before shutdown, to control the delivery rate and to shut off the flow at the conclusion of the delivery. Because most flow control valves depend on differential pressure for proper operation, care should be taken to ensure that operating pressures provide for adequate speed of operation. API MPMS 6.2 pdf download.API MPMS 6.2:2004 pdf free download
