Vortex Meter PLC Compensation Formula

Hello everyone

A while back I had a post about some constant values that were used to perform a calculation using a DP orifice plate set up.

Here is a new one reguarding a Vortex Flow Meter set up to the following calibration:
Process Temp 421.8 F
Pressure 314.69 PSIA
Process Density .679 lb/ft3
K-Factor 300.95
Density Ratio 12.625
This is for 300# saturated steam.

The formula that is in the PLC is described as a compensated steam flow compute instruction and is as follows:

(.357 * (Degrees F + 460) * lb/hr)/PSIA
or
(.357 * Degrees R * lb/hr)/PSIA

What I would like to know is where does the .357 come from?

It should be noted that the process here normally runs around 295 PSIG. In another part of the process that has the flow meters set up the same as above the typical process pressure is around 240 PSIG and the .357 listed above is replaced with a .177 and in yet another part of the process the typical pressure is set to 220 PSIG and the .357 is replaced with .155.

It seems that the lower the process pressure the lower the mystery value. I just do not have a clue where this number comes from.

If anyone has seen this before or has any ideas please let me know.

I cannot say for sure, but since your looking at the flow of saturated steam, I would say it is the specific volume of steam at different pressures. I would think that would have to be part of the calculation. Although I have to say that .177 at 220 psi, doesn't quite sound right. I was thinking .177 is the specific volume of steam at around 160 psi. Then again, I have never really had to work with those calculations.