McMenon Averaging Pitot Tubes

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The McMenon Averaging Pitot Tube (MAPT) is a multiport self-averaging flow meter with a design based on the classical pitot tube concept of fluid flow measurement, which can be installed into a variety of industries. The flow meter produces an averaged differential pressure (DP) signal proportional to the square of the flow rate. The DP output is normally piped to a Differential Pressure transmitter in order to generate an electrical signal proportional to the flow rate.

For certain applications, the DP transmitter can be mounted directly on to the flow meter via an integral valve manifold.

Each one is designed to span the process pipe diameter and comprises four basic components — an outer impact tube, internal averaging tube, a low pressure chamber and a head with HP and LP impulse connections.

The outer impact tube has several pressure-sensing holes facing upstream which are positioned at equal annular points in accordance with a log-linear distribution. The ‘total pressures’ developed at each upstream hole by sum of the impact of the flowing medium and the static pressure are firstly averaged within the outer impact tube and then to a second order (and more accurately) averaged within the internal averaging tube.

This pressure is represented at the head as the high-pressure component of the DP output. The low-pressure component is generated from a single sensing hole located on the downstream side of the outer impact tube, measuring static pressure. For bidirectional flow measurement, it can be supplied with the same number of downstream ports as upstream.

The MAPT is an improvement on the round sensor design due to the unique profiled flats which are positioned around the downstream hole in order to define the separation point at which the flow lines separate as the fluid passes around the outer impact tube. This feature creates a stable pressure area at the downstream pressure sensing hole thereby maintaining a more constant flow coefficient at high velocities enabling a wide range of flow measurement (turndown).