Is steam theory like water

Snowmelt

I’m only asking, are you going to affect the final result if you take a three inch pipe and cut it to two inch.

Jamie Hall

More or less... doesn't really mind contractions. But doesn't care for expansions.

JUGHNE

I think it is all dependent on pressure drop.
But for steam you have maybe 2 psi to deal with, with water we are talking 50-60 psi. You could lose some at that pressure and not notice it.
But to me with steam that much drop because of that much 2" pipe seems like it would be noticed in performance. Just a WAG on my part.

Snowmelt

Also what the hell is the second pic it looks like some sort of zone valve for steam?

Jamie Hall

Snowmelt said:

Also what the hell is the second pic it looks like some sort of zone valve for steam?

Probably is. Some systems did have powered zone valves off thermostats. They work. Sort of. If they are full port. Otherwise they are just plain trouble.

Snowmelt

The art school did have 2 thermostat, one doing the gym other doing some of the rooms.

Tinman

I see zone valves on large steam systems quite regularly now, mostly in very old churches and multi-family buildings.

JUGHNE

On the piping with the zone valves, is the condensate return pumped?

Snowmelt

One zone is just for the gym, other is for about 8 rooms. That might explain the 280,000 btu. 140,000 for the gym 140,000 for the rest of the place. There is 2 zone valves so the answer would be yes, one of the zone valves is for the gym and is using a condensation pump.

Snowmelt

The top pic is a 2 inch zone valve the bottom pic is a 3 inch zone valve. It appears some one replaced the three inch pipe with two inch copper and stuck a 2 inch zone valve there.

ChrisJ

> @Jamie Hall said:
> More or less... doesn't really mind contractions. But doesn't care for expansions.

Why not? A radiator is a huge expansion.

Jamie Hall

ChrisJ said:

> @Jamie Hall said:

> More or less... doesn't really mind contractions. But doesn't care for expansions.



Why not? A radiator is a huge expansion.

And the steam does exactly what saturated steam does when it expands. It condenses. Thing is, that's great in a radiator -- but not in a steam main. Saturated steam is funny stuff...

Snowmelt

JAmie now I’m confused, if pipes are bigger 3 inch instead of 2 inch it will condense. I thought smaller pipe will condense or have more velocity, or both. Let’s use this for example 280,000 btu in a 2 pipe vs 3 inch pipe.

ChrisJ

It condenses because it's cooled by the radiator. As it expands the pressure drops which if anything keeps it a vapor longer.

Jamie Hall

Oh dear. I hate entropy. I hate enthalpy. I hate saturated steam.

The problem, of course, is that saturated steam is a long long way from an ideal gas.

OK. Let's start with the contraction. What will happen at a contraction is the steam will compress. The velocity will increase slightly and the pressure will drop slightly -- but the temperature will increase slightly. Now, however, if we encounter an expansion, the gas (steam) will try to expand. In doing so, the temperature will drop, When the temperature drops, if the steam is saturated -- that is, in equilibrium between liquid and vapour phases -- it will condense. Not all of it. But some (depends on the expansion ratio). Now in a radiator, the remaining steam condenses on the cool surfaces of the radiator -- which is just what we want it to do. In a steam main, though, it will condense onto the walls of the pipe. Which we don't want it to do.

In extreme cases the result can be that practically no steam makes it past the expansion, which can really be tiresome.