Vortex Flow Meter Installation Guide
The two most important installation considerations for vortex meters are upstream and downstream straight length requirements, and the need to keep all wetted parts "flooded". We discuss both these installation considerations below.
Why are flow meter straight lengths important?
Like most flow devices, a Vortex flow meter requires a well developed and symmetrical flow velocity profile, free from any distortions or swirls if it is to give good accuracy and repeatability. To achieve good accuracy and repeatability it is standard practice to place the meter some distance from sources of turbulence. Common sources of turbulence include pumps, valves, changes in line direction (i.e. bends), changes in line size etc.
How are flow meter straight lengths defined?
Most manufacturers provide the user with minimum distances for their particular products. These distances, referred to as straight lengths, are indicated in Pipe Diameters (D). For example, 10 D means place the flow meter ten times the pipe's internal diameter away from the source of turbulence. Because turbulence both upstream and downstream can reduce accuracy, manufacturers provide straight length requirements for both upstream and downstream of the meter.
Vortex Meter Straight Length Requirements
Different manufacturers claim differing requirements, with fewer straight lengths being marketed as an advantage for the end user. As a general rule of thumb straight lengths should be about the same as that required for an orifice installation with a beta ratio of 0.7 - see the table below:
If you are compensating for pressure and temperature then allow 3 to 4 pipe diameters between the meter and downstream pressure taps, and thermowell insertion lengths should be as small as good practice allows and be located 5 to 6 D downstream of the meter.
Installing a Vortex Meter
Obtaining the necessary straight lengths can be difficult, especially in compact plants. Therefore it is worth remembering that Vortex meters can be installed vertically, horizontally, or at any angle, as long as they are kept flooded. So if installing vertically try to have upward flow.
The following pages on Control and Instrumentation.com give more detail on flow measurement basics:
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For those who want to read further about the theory of flow measurement and the differing types of flow instrumentation, then the following books from Amazon will be of interest: