[conspire] Watering automation: an edge case cautionary tale

[Rick Moen]

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.