I'm copying a question and the answer that might be useful regarding the Watson Smith type 140:
Question:
"We have number of the above I/P's used in our gas network. It has come to my attention that instead of using compressed air as a supply we are using methane gas we transport through the network. My question is would this invalidate the certification,
"
Our answer:
"Yes, the type 140 is suitable for methane as process gas and it includes a feature called "captured bleed" which allows you to pipe the vent of the converter away to a safe place.
Please see the instruction manual (page 7) for further details."
Regards
Fred