Strainers All Positive Displacement flow meters should be protected with a strainer on meter inlet side. The strainer need not have a great deal of filtering capacity (other strainers should be used for this purpose), as it is intended only to catch the occasional particle on which the flow meter might jam. Strainer Shown   If no air eliminator is required, any simple strainer will do. When air elimination is necessary, then FPP strainers are required - with appropriate air elimination components to fit the system. On diesel fuel high capacity strainers should be used if the velocity exceeds 7 f/s (210 cm/s).