Sizing a vortex meter by the piping line size is poor practice. The line-size vortex meter may not work at all. If the range of flowrates is unknown, first make some approximate measurements (using portable pitot or clamp-on ultrasonic devices). About half of all vortex meter installations require the “necking down” of oversized process piping by concentric reducers and expanders (Figure 4). Even with flow straightening devices installed, the installation will require some straight (relaxation) piping.

The vortex meter requires a well-developed and symmetrical flow velocity profile, free from any distortions or swirls. This necessitates the use of relatively long straight piping upstream and downstream from the meter to condition the flow. Swirl meters, which are similar to vortex meters, contain flow-straightening elements, thus requiring less straight pipe.

The straight length of pipe for the vortex meter must be the same size as the meter and its length should be about the same as required for an orifice installation with a beta ratio of 0.7. Most vortex flowmeter manufacturers recommend a minimum length of 30 pipe diameters downstream of control valves, and three-to-four pipe diameters between the meter and downstream pressure taps. Temperature elements should be small and located five-to-six pipe-diameter lengths downstream.

Flowmeter Piping Requirements for Vortex Meter
Figure 4. Vortex meters must often be smaller than line size. Installations should keep the meter full of liquid at zero flow.
Vortex meters can be installed vertically, horizontally, or at any angle, as long as the pipe is kept full. Installing the meter in a vertical line with upward flow will always keep the pipe full. When the flow is horizontal or downward in a vertical line, keep the downstream piping elevated to trap the fluid. Use check valves to keep the piping full of liquid in the no-flow condition. If the replacement of the meter in a particular piping configuration requires stopping the flow, block and bypass valves can be installed around the meter.

Mating flanges (on Schedule 40 or Schedule 80 mating piping) must have the same diameter and smooth bore as the vortex flowmeter. Use weld-neck flanges rather than reducing flanges. Make sure the inner surface of the mating pipe is free from mill scale, pits, holes, reaming scores, and bumps for a distance of four pipe diameters upstream and two pipe diameters downstream of the meter. The bores of the meter, gaskets, and adjacent piping must be carefully aligned to eliminate any obstructions or steps.

You can avoid excessive pipe vibration by supporting the piping on both sides of the meter, or by rotating the meter so that the sensor is moved out of the plane of the vibration. Process noise due to valve chattering, steam traps, or pumps can result in high readings or nonzero readings under no-flow conditions. Most meter electronics allow for increasing the noise filter settings, but increased noise reduction usually also decreases the low-flow sensitivity of the meter. One option is to relocate the meter to a less noisy part of the process.