Was the problem attributable to the new one being metric or the old one being imperial. If it was pipe fittings, more likely the old one being NTP and the new one being BSP
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
Pat,
The old one was imperial 1-3/8" the new one was 30 mm. This is where the body of the valve screws together. The good news was that the pipe sizes were still the same .
B.E.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
I'd be careful with those pipe threads. That 'metric' valve probably has BSPT threads which are almost the same as NPT threads, and with smaller sizes used for low-pressure liquid applications, you might get away with using them interchangeably. But if it's high-pressure or gas or the pipe is larger than 2", don't even think of trying it.
The tooth angle for NPT is 60° while BSPT is 55°. And there are differences in the thread-form as well.
Out of interest, how many people opining have actually used both systems 'in anger'?
I have to admit that while I've used Imperial/American customary more at work (at least linear measures & lbs), while almost all my education (except the aerospace design course taught by an American prof) was metric, in terms of hard core calculations most have been done in SI.
My experience is sort of the opposite of yours, KENAT. All education and first 15 years of work in US, then the rest in Australia. There was a familiarisation period, and I still convert some things in my head, but I much prefer SI.
I was educated in imperial in Aus pre metric then about 5 to 10 years of mostly imperial in daily life before the transition was into full swing.
In school, all science was done in metric, but drafting was done in imperial.
I work on cars, and that always involved both as initially I worked on VW and GM cars, then GM cars came with mixed systems and I also started on Japanese cars which although metric are on some items, a slightly different metric to Europe.
I have done some machine work and built things. Using drills taps and dies gets interesting. Disadvantage is two complete sets of cutting tools, but the advantage is you are more likely to have the ideal size for a particular spot. For instance, 1/4" UNC is a bad size re thread strength and bolt strength at the root dia but 6mm is better proportioned.
BSP vs NTP is more problematic as for some sizes great care has to be taken to differentiate, but a mismatch will assemble reasonably OK but will leak and be weak.
I have also used a lathe and mill where the calibrations are in imperial, but the drawing and micrometers are in metric. You learn to convert on the run and get a feel, but it is slow until you learn to think in an ambidextrous manner. It is always more prone to error.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
Kenat,
As you know I was raised in the UK and used imperial systems until the changeover. I also worked for an engineering company in the UK that exported systems to Russia. All of the drawings were drawn dual dimension and the tolerance stackups had to work in both sets of dimensions. There were little things like the banning of 1/4" bolts on the job, because we knew that the russians would stick a 6mm bolt in the hole if they lost one of ours and in some cases that smaller bolt would be marginal on strength.
After I came to the States, I worked for a company repairing German fiberglass sailplanes. All of those dimensions were metric to DIN specs or LN so you were working mm, centimeters. or meters on american equipment calibrated in inches or thousanths therof.
Great fun.
Now the latest, I just finished a package of drawings for a company (in inches) who sent them to a fabrication company who promptly asked if they could have them in metric. The good news there was that all I had to do, was change the units on my cad program. Then go back and check the tolerance stack ups.
B.E.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
I was educated in metric units (although I was taught imperial at primary school).
In my time spent on the shop floor (alternator/starter manufacturing), the drawings were all in metric, but the machine operators all spoke in imperial, so it was very mixed. I could convert between microns and thou' without thinking for a while.
This letter and a reply appeared in the PEGG (Alberta Engineering Association newspaper) in 2002. Sorry that it is a bit long, but I think it is interesting.(Authors names deleted).
Re: Earth's Warmth Tapped to Heat Aquatic Centre,
The PEGG, March 2002
Once again, I read a confused article with mixed units of measurement. From the article: "72,000 lineal feet of three-quarter-inch underground piping..."; "at 11 feet, nine feet and seven feet below the surface"; "moderate at about 7C from about two metres to nearly 300 metres"; "three 30-ton geothermal heat pumps."
First, mixing units in a single story is profoundly sloppy writing. Second, imperial measurements are utterly archaic and have absolutely no place in our official organ.
The purpose of this publication is to serve Alberta's engineering and geoscience communities, and these communities use SI. We have no need for any imperial measurements, and it is intolerable that the editorial staff insists on imposing imperial units on us because they are unwilling to expend a little effort to provide SI equivalents.
Ignorance of the metric system is pathetic and unacceptable. Canada switched over to SI in the 1970s. I'm afraid I cannot accept any argument against switching to SI; The PEGG and its editorial staff simply must catch up to the rest of the world.
I am embarrassed to imagine what professionals from other jurisdictions must think of Alberta's engineers from reading articles such as this.
Reply:
Re: Stop Mixing Measurement Systems, Readers' Forum, The PEGG, April 2002.
XXXX XXXXX, P.Eng., bashes mixing different systems of measurement and the very use of the imperial system. While he makes some valid points, I cannot accept his overly agitated tone and misplaced passion. This matter is certainly not as hot as he sees it.
The imperial system is archaic, yes; but it has served the mankind for centuries and for that alone, it deserves some respect. We are not the first nor the last people here; we are living in an environment created by previous generations, and these generations mostly used the imperial system.
To me, when dealing with existing facilities, 20 feet makes a lot more sense than 6,096 mm, 40 p.s.f. sounds more natural than 1.9 kPa; and when I drive on Icefields Parkway and see a sign saying that vehicles over 4,550 kg are prohibited on this road, I can't help laughing. Those who mindlessly converted 10,000 pounds to the metric system forgot that 10,000 is a round number, and is appropriate here, whereas after seeing the 4,550, one can only
ask: "How on earth did they manage to calculate it with such precision?" It is just one of the myriad examples around us when common sense is sacrificed to a political campaign.
I was born and trained as engineer in Russia, and till age 33 I never knew what a foot and a pound was; still, it didn't make me a genius to figure that out when I started practicing in Canada. I often use mixed units in the same formula in my calculations, and it's OK as long as you are careful with the conversion factors. But the same holds true when you use any system of measurement; not to confuse meters with millimeters, kN/mm2 with MPa, and so on.
And this problem is not unique to Canada. In early 1980s when the Soviet Union signed the SI convention, there was an attempt, in the weather forecasts, to call the atmospheric pressure in hectopascals. Guess what? In three months it was all rolled back to millimeters of mercury.
Custom and tradition are real factors, not to be taken lightly.
Mr. Moorman says that he "cannot accept any argument against switching to SI." Probably so; but who cares? Good designs, as well as bad designs, can be prepared using any system of measurement.
Finaly, any new graduate who hopes to compete in an international engineering marketplace knowing only one system of units is in for a rude awakening and a fast education.
Without mixed use of units, we'd never have had the great line from The Young Ones, where cool Mike is chatting up a lady:
"I know what you're thinking baby and if I were to tell you, you'd think I was talking centimetres."
One problem with metric units is that 100 km/h isn't fast, 200 km/h is too fast. There's no equivalent of the "ton" that was so important to teenages on their bikes.
I learned English units in school, and eventually, metric. In college, we worked in English and metric units. The company I work for transitioned to metric when we adopted 3D CAD.
I firmly believe that journalists should repeat the numbers and units they are quoted. I suppose an engineering magazine should be held to a higher standard, but conversions do lead to mistakes. This is particularly true when the numbers and units are coming from some techie whose job you are not qualified to do. No one here is a universal genius.
I worked in a marine exhaust shop that built custom stuff in inch units, for installation in yachts all over the world, with customers providing boat measurements or drawings in both systems.
We did a lot of scaling of drawings back and forth. The worst problem I had was a fabricator/designer who infected a fair number of drawings with conversions using 25mm to the inch.
Before fabrication proceeded, we insisted on actual measurements of the boat, even if we'd been working with the plans, not because of any difficulty with conversions, but because the whole concept of interchangeable parts has not yet reached the boatbuilding industry.
Same problem with building capital machinery. Never trust the architectural drawings of the building where the equipment is going to be installed. Send someone there with a steel tape and quadrille pad and don't start making your installation drawings until those 'as-builts' are setting next to you.
Not that it'll save you from stupidity, like the time AFTER we got the 'as-builts' the customer decided to upgrade his fire-sprinkler system without letting us know and when we went to erect one of the main peices of equipment (these machines were as large as a small house), we discovered that the new service mains entered the building and passed right through an upper corner of the steel framework. Fortunately there were no moving parts in the area and all we needed to do was cope around the plumbing, but the customer got dinged for an extra day or two of labor and material costs.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
I remember back in 1977 when I was in K-Mart store getting school supplies for my senior high school year. At the time, I knew I was headed off to engineering school the next fall, so this conversation is one that I remember.
It was unseasonably cold, about 10 C or so. The woman ahead of me was complaining to the cashier that it was the Canadian government's fault for implementing the metric system, since Celsius degrees are colder than Fahrenheit degrees. (i.e., 10 vs 50).
So, by that line of reasoning, and with due regard to the increasing concerns over global warming, perhaps we all *should* convert to SI units, thereby saving the planet.
I should summarize this in a technical discussion paper to present to a managerial team of MBAs in order for us to move forward with this proposal.
I always thought the conversion factor between centigrade and Celsius was 1:1. Isn't it in fact just a language thing anyway. ie same word in different languages or is it something like hood vs bonnet or trunk vs boot.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
Thinking back to my physics days at school, I believe Centigrade is a 100 point linear scale between water's freezing and boiling points (or any two arbitrary temperatures), whereas Celsius was absolute and related to Kelvin by 273.15. Or something like that ... an A-Level question designed to catch out students.
