Randy:
I suspect that "rule of thumb" goes back to Johnathan Swift and "Gulliver's
Travels". In one of the journeys, Gulliver was being measured by the King's
tailor for a suit. He carefully measured his thumb. Questioned, he gave his
rule:
Twice around the thumb is equal to once around the wrist.
Twice around the wrist is once around the neck.
Twice around the neck is once around the head.
Twice around the head is once around the chest.....
And so, he had the client completely sized with only one measurement!
I'm sure that a lot of us have used these laws of homogenity!
George McKinney
I suspect there are many books in effect talking about "rules of thumb" (I think another one having to do with piping is from American Society of Civil Engineers (ASCE), see abstract for "Pipeline Rules of Thumb Handbook - Fifth Edition" at https://www.asce.org/bookstore/book.cfm?book=4182). As this book is in its fifth printing, this perhaps means it has either been some popular, or revisions are necessary or desirable as some of the "rules" may change?
As far as where this phrase came from, I do not know but I think that the thumb has probably been a rather convenient unit of measurement for thousands of years. In our measurement system, I believe the width of a thumb is roughly about one inch, and thumbs are also held up for some reason out in front of some folks faces (photographers or videographers?), I guess in some fashion to sort of relatively "size up" situations. I have always had the impression rule of thumb sort of means that some of these (rules) may be sort of rough (measurements or calculations etc.), or sort of derived more from experience than rigorous scientific knowledge or determinations/research, but like you I will await certainly more expert lexicography.
Randy Conner
-----Original Message-----
From: PipingDesign@yahoogroups.com
[mailto:PipingDesign@yahoogroups.com]On Behalf Of Jijoy
Sent: Thursday, July 21, 2005 1:05 AM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] Selection of flange
Dear Elie,
Thanks for the rules of thumb.
Are there any piping rules of thumb ?
Thanks for your answer
Cheers
It sounded like the vessel already has a flange; if so, why couldn't you get the information on the flange.
Do you know the ANSI rating of the flange or the MAOP of the vessel?
Is the vessel carbon steel?
Is the fluid caustic?
My rules of thumb are:
For cast iron flange, I use flat face with spiral wound gasket
For carbon steel, ANSI 150-300- or 600 LB (MAOP of 285-740-&1440 psig), I
use raise face with spiral wound gasket
For carbon steel, ANSI 900 and higher, I definitely will use RTJ flange
Anyone knows where the expression "rules of thumb" came from?
Cheers,
JP <jijoy@mis.co.ae> wrote:
Dear all,
Could anyone of u answer the following query :
There is a nozzle in a Vessel (which is a closed drain sump). I have to
select a flange for the nozzle and the piping to follow.
How will I select the type of flange whether ring, RF etc..
The nozzles sizes are 2", 4", 6", 8". Based on the selection of flange I
will also have to order the bolts.
The bolt sizes can be obtaibed fron B16.5.
Can anyone tell me how to selectthe type of flange to be used.
Thanks in advance
Jijoy
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