ASME MFC-8M:2001 pdf free download

ASME MFC-8M:2001 pdf free download

Primary elemcnts in gas service with (he secondary mounted below (he primary will require provision for accumulation and removal of liquids before the liquids rise above the secondary device pressure taps (See Fig. C8). For condensing vapors with he secondary above the primary, see Fig. C9, A clean fluid can be used to purge the system to keep dirt out or to ensure the contents of the system (See Fig. ClO).
Pre-fi lied physical harrier diaphragm seals called remote seals or chemical seals are used in certain applications. Dcilcction of the diaphragm requires some small force that must be considered in the calibration process. Errors are reduced with larger diaphragms and good design. It is recommended that the impulse lines or capillary tubes to remote seals be of identical length and be arranged to reduce the exposure to ditTerent temperatures.
Maintenance of special systems may be labor intensive and require care and knowledge. The recommended installations require less maintenance to continue accurate measurement
7.1 Pressure Taps
The pressure taps must accurately sense the pressure of interest (see MI:C’.3M. The holes through the pipe wall, or through orilice flanges lutist be smooth and have no protniding internal burrs resulting from drilling or welding. Pressure tap connections shall be at right angles to the centerline of the pipe. The hole bored through the pipe wall is to be no larger than required to avoid plugging. Industry practice is to accept the boring provided in standard orifice flanges. Typical values are l/4 in. for pipes 11/2 in. and smaller: 4i in. for 2 in. pipe: and ‘/ in. for pipes 3 in. and larger. Research laboratories and aerospace applications with ery clean fluids prefer smaller holes because larger holes may interkre with fluid how near the pipe wall. In very dirty services, flush diaphragm seals have been used. To ensure measurement sensitivity, diaphragms are typically a nominal W) mm or 1(X) mm (3 in. or 4 in.) in diameter.
7.2 Impulse Line Size
The required diameter of the impulse line depends on the service conditions. Lines smaller than 6 mm will not easily allow gas bubbles to flow up and out of a liquid system, nor allow liquid drops to flow down. In smaller sizes and with liquids.