I'd say a generalized definition is the first isolation valve in a branch or system. Could be a sub-header off the main steam line or the first isolation valve for pressure/instrumentation tubing.

MPP-LTD,
The answer is "Yes" to all the above.
It is used by different companies for whatever, wherever and however they (the company as a whole or some individual in the company) choose. They just need to define it.

It is important to understand that the term "Root" valve is a function, NOT a valve Type, It is any valve type used for "That" purpose, normally consistent with all other valve types from that commodity's Piping Material Line Class Specification.

Sometimes its possible to do all the right things and still get bad results

MPP-LTD

I've been working now in oil and gas systems for over 30 years and never heard anyone ever refer to a valve as a "root" valve, but your logic makes sense and like pennpiper says (and he has more experience than me in plant design) it could be different things to different people.

I would struggle to say this is a "common term" though.....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

I, too, have never heard the term 'root valve' in a 40 year career. Maybe it is used for snipe hunting.

https://en.wikipedia.org/wiki/Snipe_hunt

Is it maybe a regional thing? I'm on the east coast and it's a pretty common term in industry.

Thanks for all the feedback, we are putting together SOPs and some procedure writers use this word. I have mistakenly thought it was term only for Instrument Isolation valves. The term makes more sense as first isolation valve of any branch, given that a root is like the bottom / start of a tree or plant. Anyway I fairly unimportant question but it was something that was annoying me for a while! Thanks.

A root valve is a pretty common term for me as well. I live along the gulf coast and most of my career has been in the oil and gas field.

But yes, "root valve" is just a term used as to indicate the first isolation valve following a take-off from a larger header. For me, the term has been used for vents, drains, and instrumentation. I have also heard the term used for equipment isolation valves as well, although I'm not sure if that is as common or if it is just something I hear where I am.

PIP PNC00005 "Design of ASME B31.3 Metallic Piping Systems" states:

3.3.3.6 Small Piping Root Valves


3.8.7 Utility Stations

"Thinking is the hardest work there is, which is probably the reason why so few engage in it."

-Henry Ford

Google search indicates that root valves are a special type of valve with multiple ports used for instrument isolation and mounting gauges. So a simple ball valve used for instrument or branch isolation would not be a root valve.

https://www.google.com/search?q=root+valve&cli...

I started my reply before seeing DGrayPPD's post, just to be clear.

Not contradicting anyone, but in my experience a root valve is, as pennpiper wrote, a functional descriptor, synonymous with a master valve, which is the first one in a series of two, the latter being the martyr valve, the idea being that the master valve is normally open and is only closed occasionally as the service permits to confirm its operability, with the martyr valve normally used to perform controlling, throttling or isolating functions. As such it is the martyr valve that takes a beating, hence the name, with the master serving to provide a reliable isolating point for the martyr valve's replacement.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]