Positive displacement (PD) meters measure volumetric flow directly by continuously separating (isolating) a flow stream…
External Housing PD Meters
PD meters are usually built with inlet and outlet connections from ¼ inch to 16 inches in diameter and are designed to handle pressures to 1440 psi (600 pounds ANSI) and flow rates to 12,500 BPH. Typical housing materials are carbon steel, cast iron, ductile iron, aluminum, bronze, or stainless steel. Consult the manufacturer for help in selecting the proper material.
PD meters may be of single- or double-case construction. The advantages of doublecase construction are that (1) piping stress is not transmitted to the measurement element; (2) the measuring element can be easily removed for service or inline flushing on startup; and (3) the differential pressure across the measuring element walls is minimal, thus eliminating the possibility of dimensional changes in the measuring element due to system pressure variations. Small meters of materials other than carbon steel are normally single-case. Meters over 6 inches almost always use carbon steel double-case construction.
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