steam pressure valves

Eastman

Does anybody ever put a pressure reducing valve on a residential steam boiler? ...to keep the pressure in the boiler higher and possibly improve the boil?

STEAM DOCTOR

What are you trying to accomplish? You will flood the building. Steam systems are open (more so if it's one pipe). Higher pressure will ruin the boil. The higher the pressure, the higher the temp needed to bring to boil.

Eastman

By "flood the building" do you mean water will be pushed out of the boiler?

Jamie Hall

Eastman said:

By "flood the building" do you mean water will be pushed out of the boiler?

Among other evils. There is absolutely no reason to run a heating system over 2 psi (that's what, if memory serves, the Empire State Building in New York runs at). In fact, most residential systems run at less -- many, vapour systems, at much less (like -- half a pound or less).

All that increasing the boiler pressure will accomplish (assuming that you have the correct reducing fittings and pumps) is that it takes more heat to bring the water up to the boiling point -- which is higher.

If you wanted to do it for some reason, you would not only need a pressure reducing valve on the steam mains, but also you would need a condensate receiver and boiler feed pump on the condensate returns.

Eastman

A couple years ago or so I saw a video of a boiler with transparent piping. At higher pressure there was a lot less water carrier out with the steam.

Eastman

Yeah, I just watched it again. At higher pressure there's like no water being ejected out of the boiler.

Abracadabra

Eastman said:

Yeah, I just watched it again. At higher pressure there's like no water being ejected out of the boiler.

It gets pushed back out of the return. A properly piped header/equalizer should not throw water into the mains.

Eastman

You're talking about the weil mclain video?

Fred

If you restrict the amount of pressure going out through the mains, that pressure is going to push water out somewhere and that somewhere is the wet return. Increasing the steam pressure in the boiler and restricting it at the mains is not something you want to do. The pressure should be no more than 1.5 PSI to a max of 2 PSI on a steam boiler, period. If it is throwing water out into the mains, either it isn't piped correctly or the boiler needs skimming.

Eastman

I realize we would need to pump the water back in.

I don't know guys --the video is pretty convincing.

Jamie Hall

A properly installed and piped boiler, with the correct riser and header sizes and connections -- which is a big if, as we all know -- will not put any significant water into the mains.

Change the piping, and I am quite sure that one can get a lot of water into the mains at any pressure one cares to run at.

It's a lot easier to do the near boiler piping correctly than it is to monkey around with pressure reducing valves and boiler feed pumps... cheaper, too. More reliable. What's not to like?

Eastman

I guess the question is: is the weil-mclain video a demonstration of a boiler that is incorrectly piped?

Jamie Hall

Not having seen the video, I can't comment on that. That said, a boiler may put a fair amount of water into the header, even if it correctly piped -- although bigger risers will reduce that or even eliminate it. What a correctly piped header and equalizer will do, however, is let all the water -- like, really, all of the water -- which does make it into the header go right back into the boiler where it belongs.

Going a little farther afield here. Many old time boilers had huge steam chests at the top of the boiler -- a lot of space and height open above the boiling water. They could and did get away with somewhat simpler piping. Other, larger heating boilers (like the one which was originally in the building I care for) had a very large steam drum above the boiler and separate from it, which separated any water coming up from the steam, and returned the water to the boiler through the equalizer and sent the steam off to the heating system. Virtually all power boilers -- which operate at far higher pressure (sometimes as much as 1500 psi!) -- also use a steam drum arrangement which separates the water from the steam.

A properly piped header is, really, nothing more than a variation on a steam drum!

vaporvac

Do we care if there's water in the header so long as it returns to the boiler through the equalizer? Isn't that why the "best" practice involves tall risers and an up-sized header with adequate spacing between the header, the riser to the mains and equalizer take-off? The real goal is quick and even distribution of steam throughout the system, and that is accomplished with low pressures, the lower the better with vacuum best of all.
Perhaps you could post the video for us to see, @Eastman

ChrisJ

I see where Eastman is coming from.

The lower the pressure in the boiler, the larger the bubbles. Not sure if you could run the boiler at a higher pressure (5-10PSI) and run the system at a nice low pressure and even if you could, I don't know if you'd gain anything.

What we really want, and need are boilers with a larger area to accumulate steam in and larger tappings.


WM's video to me, is a boiler that is piped bare minimum and perhaps even with dirty water. I doubt my boiler ever throws that kind of water out unless the water is really really dirty.

Eastman

@ChrisJ

Hi ChrisJ. I thought the video was really surprising. The rep giving the presentation seemed kinda surprised and said something to the effect like "it should calm down once the system starts to pressurize."

@vaporvac See if this link works for the video:https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=video&cd=20&cad=rja&uact=8&ved=0CEkQtwIwCTgKahUKEwiQzLS_j5vJAhUIbj4KHe_aBsg&url=https://www.youtube.com/watch?v=1loCscHGiRo&usg=AFQjCNEiGwREmfPvb1zWl_jypIcWibrA6g

jumper

I remember somebody installing a hot water boiler in a steam heated building. Opened and repaired wall before he realized his mistake. What options then? Some way of expanding heated water to steam and pumping condensate back into boiler? Or a hot water to steam generator? I chose not to get involved.

ChrisJ

Imagine how much better that header would work under those conditions if it was an inch bigger and if the equalizer was a few sizes bigger.

ChrisJ

Hatterasguy said:

He confused you.

Right after he made that statement, he closed the "King valve" and stopped the steam delivery to "the building".

Of course, without any flow, you observe a perfectly calm boiler.

Watch what happens when he opens the "King Valve" when the boiler reaches 5 psi.

I was going mainly off of these videos. I've watched all of the parts many times over the years.

https://youtu.be/-bGkiq9QDXc

ChrisJ

And this seems like exactly what's going on in the WM video.


https://youtu.be/8Lmagejlc1s

Eastman

Yeah, ChisJ gets what I'm after. The boil is better with a little pressure.

@Hatterasguy Ignore the flash steam production.

Eastman

So that Spirax Sarco video #5 says we should avoid low pressure in the boiler.

Perhaps near boiler piping should have a constriction at the connection to the mains? But keep everything else wide open?

ChrisJ

Eastman said:

So that Spirax Sarco video #5 says we should avoid low pressure in the boiler.

Perhaps near boiler piping should have a constriction at the connection to the mains? But keep everything else wide open?

For those boilers designed for pressure, yes.
Our boilers aren't designed to supply 3.5 + BAR (50+ PSI).

KC_Jones

My question is what about the wasted energy to do this? So do you maintain the boiler at pressure all winter? Or do you cycle it like it does now on the thermostat? If the first that seems like a ton of wasted energy. If the second what happens when the burner shuts off? The temp drops the pressure drops and again wasted energy. I am having a hard times seeing any advantage at all over what is currently done. The reason it boils violently at low pressure is there is very little if any resistance to the steam escaping, adding or building pressure increases this resistance. The basic reason the boiling point increases with pressure. So essentially you think it's better to resist the steam escaping than allowing it to move freely. That seems counter intuitive to what is trying to be accomplished which is the free movement of steam.

Eastman

The counter-intuitiveness is what interests me.

No, I'm not suggesting keeping the boiler under pressure all winter --just during a burn cycle. I have a hard time imagining the cycling losses would be significantly different than what is common now. However, I can definitely imagine a significantly better transfer of heat if the boil is improved quite a bit.

Jamie Hall

Several minor points...

first, the heat transfer from the flame to the water is a function of the temperature difference (and the presence of any boundary layers on either side, which can be minimized by ensuring turbulent flow -- and the more violent the turbulence, the better). Greater temperature difference, greater heat transfer. Further, the rise in pressure raises the boiling point -- at 15 psig, for instance, it is about 250 Fahrenheit.

Thus, from that standpoint, a boiler operating at higher pressure will have lower inherent efficiency, unless there is a feedwater heater operating off the exhaust gas stream.

Second, you have a significant increase in complexity. Pressure reducing valves -- particularly ones which drop to very low gauge pressures and hold them there under varying flow and upstream pressures -- are touchy gadgets. Boiler feed water controls and pumps also add considerable mechanical complexity.

And cost.

As against providing proper steam and water separation by means of a properly designed steam drum or header arrangement.

I just don't see the point at all. I'm not arguing that a smoother boiler (smaller bubbles) can't be achieved at higher pressures, and that this is aesthetically pleasing. I'm arguing that that does nothing to improve the efficiency and operation of the unit over what can be achieved with proper piping design, and that it adds considerable operation and mechanical complexity with is best avoided.

Mark N

Don't confuse power boilers with heating boilers. Eastman do you have a copy of TLAOSH? Read chapter 4, especially page 44 on the right hand side with the paragraph that starts with "Consider Modern Boiler G from the above chart for example." it is explained.

Eastman

Is there a specific difference you wish to highlight? I don't have the book.

Mark N

I would suggest you get it, it's a great read. Home heating boilers always start at 0 psig and have to be able to produce dry steam at 0 psig. If it can't do that you will have water hammer,spitting vents, water level problems, surging, and uneven heat.

Jamie Hall

Mark N said:

Don't confuse power boilers with heating boilers. Eastman do you have a copy of TLAOSH? Read chapter 4, especially page 44 on the right hand side with the paragraph that starts with "Consider Modern Boiler G from the above chart for example." it is explained.

You mean me? I don't -- I'm just familiar with both of them (and, for that matter, locomotive boilers -- which are yet again a different sort of thing!). There are, however, some things which are common to all three -- and perhaps the most important is the necessity to produce dry steam. If you think that water hammer in a steam system is a bore, you should contemplate a turbine which has had small slug of water try to go through it... (note the word "try" )

Mark N

Sorry, Jamie not you I was answering Eastman.

Eastman

What is the concern from TLAOSH?