I have had several questions come up in the last couple of days about where to mount differential pressure transmitters in relation to the pipe mounted flow element. There are three different types of fluids that you will want to measure and they require different mounting methods.
First, is dry gases. The DP transmitter must be mounted vertically above the pipe taps so that all potential liquid or condensation in the line will drain back into the pipe.
Second is liquids. The DP will be mounted vertically below the pipe so that the line will always stay full with liquid.
The third is condensing liquids such as steam. These require that the DP transmitter is mounted below the pipe taps, but they must have a vertical water column that is always filled with the same amount of condensate so that the water pressure on the impulse lines remains consistent. The water column will block the high-temperature steam from cooking your transmitter. If you mount it above the pipe and there is no water present, the 300F+ heat will break your transmitter.
This was a very short and basic introduction to mounting and configuring your DP flow system. For more info and a thorough explanation, please contact me via this site.