[conspire] Watering automation: an edge case cautionary tale

[Paul Zander]

For reasons that are lost in time, in my experience, one has to refer to pipe as "trade size".  I don't expect 1" pipe to have anything that measures as 1".   The dimensions were established by the pipe manufacturer's and became understood by the plumbers.  So fittings for 1" pipe from one company will work with 1" pipe from another.   

My personal guess is that this  started with pipes with a certain inside dimension to carry so much water.  Then fittings were designed to attach the outside of the pipes.  After the fittings became widely used, metallurgy improved.  Pipes could hold the same pressure with thinner walls.  But the fittings generally attach to the outside.  Or maybe this all had to do with the first major makers of pipe not being very careful with exact measurements.
I used 1" as an example.  For most anything in and around a hose 3/4 is quite adequate.  You could go down to 1/2 for some sprinkler circuits.  Or just do everything in 3/4 to keep it simple.

Then there is lumber. Long ago, trees were sawn into timbers that measured 2" x 4".  But the sawing left edges that were rough.  So it was decided to have 2x4's that were sanded smooth.  And that had to be standardized.  For a while the the sanded ones measured 1- 3/4 x 3-3/4 inches.  Oh, and saw technology improved so they didn't really have to sand 1/8" off all of the faces.  About 50 years ago, it was decided that these dimensions were too awkward for the math skills of the typical carpenter.   (Or maybe the lumber industry wanted to get a few more cents from each tree.)  So the standard for so-called 2x4's became 1-1/2 by 3-3/2"

      From: Rick Moen <rick at linuxmafia.com>
 To: conspire at linuxmafia.com 
 Sent: Tuesday, March 21, 2017 5:44 PM
 Subject: Re: [conspire] Watering automation: an edge case cautionary tale
   
Quoting Paul Zander (paulz at ieee.org):

> Yes it would be good to replace the mix of pipes and hoses, but I
> wouldn't recommend galvanized pipe.  Over time, it rusts, fills with
> deposits on the inside and leaks.  It's also a bit awkward to work
> with unless you own a pipe threader. I think ACE used to have one, but
> they are gone.  The time and effort saved using plastic will still be
> a positive even after a couple of "oops" with a shovel in future.  Dig
> trenches about a foot deep and use sch 40 PVC, at least for everything
> beyond a shut off valve.

Yeah, thanks.  You're not the only person who's mentioned Schedule 40
PVC in this regard.  Duncan MacKinnon keeps talking to me in his
accustomed mile-a-minute fashion about things I could do, and about 10%
of the content sinks into my city-boy brain.  Part of the 10% that stuck
was a passage where he said quite a bit about running galvanised pipe
along the fenceline, which he claimed would have many advantages
including durability, and that I could branch off laterals from the
fenceline galvanised pipe to wherever I needed a drip-irrigation run,
and be able to change that at will.

I'm sure he also talked at length about Schedule 40 PVC in one or more
high-speed conversation, but that left only a lingering trace in my
long-term memory, which your mention of same re-stimulated.  Otherwise,
what he said was part of the 90% that went poof after I heard it.


> Don't use the thinner pipe.

My quick readings suggest that this is often Schedule 20 PVC, and you
find a lot of people saying 'Hey, don't use Schedule 20.  Use Schedule
40!'  (The schedule number is a relative number referring to pipe wall
thickness.  Many people get confused and think it refers to pipe width,
but that's a different metric.)

I've actually worked with this stuff at one of my late mother's rental
houses long ago.  Pretty damned easy to work with, if I recall.

What a morass of terminology.  Oy.  


'Nominal Pipe Size (NPS)':  diameter of the hole expressed as a
'non-dimensional number'.  Oy again.  'Non-dimensional' as in relative
to other diameters.  Starts at '1/8' and goes up to 92.  

'Schedule':  Another non-dimensional number indicating relative
wall thickness for that size of pipe.  

'Outer Diameter (OD)':  Means what one thinks it means.  (Except you end up
having to deal with weird-ass decimal fractions of inches.)

In order to find out what all this actually amounts to, you need to
consult a table, like
https://en.wikipedia.org/wiki/Nominal_Pipe_Size#NPS_tables_for_selected_sizes .

'For a given NPS, the OD stays fixed and the wall thickness increases
with schedule.'  Ah, that clarifies it a bit.


I really want to fire this reality and hire a metric one.


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