The Plumber Problem • Hacker News Board

Re: The Plumber Problem

#251

Post by pavel_lishin » Sun, Aug 20, 2023, 8:57 PM UTC

brightlancer wrote: post #190

pavel_lishin wrote: post #60

Earlier quoted context omitted.

An alternative explanation is that the machines aren't using the humans for anything ; they're just devoted to the most ethical treatment of these billions of people who believe themselves to be at war, and the only way to capture them and keep them sane is to hook them up to virtual reality and keep them complacent. Every human is a prisoner of war, in the finest possible cell.

Neo and almost everyone else was born in the Matrix; they weren't captured in war.

Sure. Because to prevent their prisoners of war from reproducing would be genocide.

They're effectively in a giant prison; within the prison, they're free to do whatever they want. They just can't leave.

Re: The Plumber Problem

#252

Post by pbhjpbhj » Mon, Aug 21, 2023, 6:25 PM UTC

deadbunny wrote: post #44

pbhjpbhj wrote: post #14

Earlier quoted context omitted.

Do horse drawn vehicles make 3 grooves (I assume that's what you were alluding to)? I'd expect it would just be a wide band of pretty bare ground with two grooves inset from the edges?

I would assume the 3rd groove is from the horse.

Yes, but I wouldn't expect it to be a groove. Human hips mean when walking single-file we make a grooved path, particularly in harder terrain as we'll narrow our gait to reduce environmental resistance to travel. Sheep produce very similar paths. But horses are wider at the hip yet have a similarly wide foot .. so I'd expect more of a swathe (wider path, ie not a groove) of damage, with sufficient horses.

I grew up in a small village where a significant proportion of people ride, gaps in hedgerows where a number of horses have just passed through (eg a hunt) produce a wide band of hoofprints. But, I've never seen a route mainly used by horsedrawn carts.

Most of our bridleways look like slightly wider footpaths, but they're primarily used by pedestrians or bicycles and horse traffic is still relative little.

Anyway, ...

Re: The Plumber Problem

#253

Post by iamthemonster » Tue, Aug 22, 2023, 1:15 AM UTC

almostnormal wrote: post #227

iamthemonster wrote: post #81

I witnessed the converse of this in the recent Mario Brothers movie. There is a scene where steam piping is about to overpressure and it shows a pressure safety valve lifting. Well that pressure safety valve is an accurately drawn ASME I BPVC open-bonnet PSV with test lever. The open bonnet is to expose the spring to air so it is kept cool and therefore has the correct force downwards on the seat. If you specify a cl…

> If you specify a closed-bonnet PSV (like the vast majority of PSVs) for steam service then the whole valve body can get up to the steam temperature, including the spring, and it doesn't lift until a much higher pressure than your bench test indicates. That was surprising. With a quick search about temperature and springs I found 3 items: 1 Spring constant descreases with temperature, not much at small increases but…

Yes definitely - the vendors of the PSVs will calculate for you a special compensation factor that allows you to test the PSV at normal room temperature, but still have it open at its set pressure when it is at a higher operating temperature.

They call it the "cold differential set pressure".

You can calculate your own cold differential set pressure just as a cross-check against the vendor's calculation to make sure there are no misunderstandings but ultimately you should just use the vendor's value.

In the case of steam, because it is obviously non-toxic and non-flammable you can just let it go to atmosphere in an emergency, so the best thing is just to let the spring of the PSV be exposed to atmosphere rather than some variable operating temperature.