Metco FMR unit conversion

[TintinMilou]

I would like to convert FMR units in SCFH.
Metco DJ console flow meters show:

Air: SCFH=15.80x%
O2: SCFH=14.44x%

Are these equations OK ?

And for Hydrogen ??

Thank you

[Gordon]

Hi TintinMilou

to the Surface Engineering Forum.

If you have a copy of the Metco Diamond Jet Process Manual, there should be a section towards the back giving flow rate conversion tables for some fuels, oxygen and air.

Your equations seem ok if you are operating specifically at a pressure of 75 psi for air and 150 psi for oxygen only. (info from original Diamond Jet Process Manual)

air - SCFH = FMR . 15.795 . square root(P + 14.7/14.7)
oxygen - SCFH = FMR . 4.314 . square root(P + 14.7/14.7)

I would have thought Sulzer Metco would have flow rate conversion tables for hydrogen. My old manuals don't include hydrogen (propylene fuel only), later manuals might. We also need to be careful that we are talking about the exact same type of flow meter. If you can not obtain conversion tables you could do the maths https://www.gordonengland.co.uk/conversion/gformula.htm
if you know the calibration details of the flow meter tube (gas type/molecular weight, pressure and temperature).

[TintinMilou]

Thank you very much Gordon !!!

[RGS]

Hi Gordon,

Does back pressure from the torch effect your conversion formulas?

Thanks,
Rick

Edit: Nevermind, I figured it out.

[Gordon]

Hi Rick (RGS)

to the Surface Engineering Forum.

For those that may not of figured it out:

Under normal operating conditions using flow meter tubes with the flow adjustor/throttle on the output side (usual set-up), back pressure from the gun should have little effect on the reading, as the flow meter tube should be under steady pressure as set from the gas supply regulators.

The only exception I know is for the Metco 3M/7M plasma hydrogen flow meter which has the adjustor on the input side (I think this was for safety reasons). This set-up does effect the reading as the tube pressure is dictated by the back pressure and not so much by the regulated input. In this case the conversion formulas are not accurate as pressure becomes an unknown factor.

[J!m]

Hydrogen flows for Plasma secondary gas for the 7MC are dictated by nozzle bore diameter more than anything else. Bill Rusch had some excel sheets that I used to have, which indicated this. Supply pressure had no effect of the actual flow.

But it reality, we set flow to obtain a certain voltage/power so it really is a "reference only" as far as I'm concerned.