Goin' Up the Country: Milvaco Vapor/MegaSteam Rescue

PMJ

Jamie Hall said:

Just keep in mind in all this, folks, that a vapour system is not necessarily a vacuum system. A vapour system is distinguished by being designed for a very small pressure differential between the steam mains and the dry returns, with radiator flow primarily controlled by calibrated orifices and valves (and, usually, traps -- though not necessarily), crossover traps, and one main venting location at or very near the boiler. In some systems this was just an open pipe to the chimney. In others, which had various devices to ensure that that very small pressure difference was never exceeded, sometimes the vent held against a vacuum, and sometimes not.

Imposing a vacuum on a vapour system will upset the balance and operation of the system, unless the vacuum is applied to both the steam mains and the dry returns so as to maintain the very small pressure difference.

It really isn't this complicated - for sure in two pipe. The mains and the dry returns are always connected to each other through the radiators. It is the collapsing steam which pulls a vacuum on everything. Please remember, vacuum does not mean no air, it just means less air than normal. Vacuum means pressure below atmospheric. There is a difference - especially in how you think about it. The whole system drops below atmospheric and all the relationships inside stay the same. There is no balance upset. I really do know this. If you were to mechanically pull a vacuum from anywhere on the dry return it is no different that a naturally induced one except the pressure can be farther below atmospheric.

AMservices

PMJ said:

Jamie Hall said:

Just keep in mind in all this, folks, that a vapour system is not necessarily a vacuum system. A vapour system is distinguished by being designed for a very small pressure differential between the steam mains and the dry returns, with radiator flow primarily controlled by calibrated orifices and valves (and, usually, traps -- though not necessarily), crossover traps, and one main venting location at or very near the boiler. In some systems this was just an open pipe to the chimney. In others, which had various devices to ensure that that very small pressure difference was never exceeded, sometimes the vent held against a vacuum, and sometimes not.

Imposing a vacuum on a vapour system will upset the balance and operation of the system, unless the vacuum is applied to both the steam mains and the dry returns so as to maintain the very small pressure difference.

It really isn't this complicated - for sure in two pipe. The mains and the dry returns are always connected to each other through the radiators. It is the collapsing steam which pulls a vacuum on everything. Please remember, vacuum does not mean no air, it just means less air than normal. Vacuum means pressure below atmospheric. There is a difference - especially in how you think about it. The whole system drops below atmospheric and all the relationships inside stay the same. There is no balance upset. I really do know this. If you were to mechanically pull a vacuum from anywhere on the dry return it is no different that a naturally induced one except the pressure can be farther below atmospheric.

Also with a with a vacuum pump, you can have a pre purge if the system is cold, and a post purge for as long as the boiler is hot.

PMJ

AMservices said:

PMJ said:

Jamie Hall said:

Just keep in mind in all this, folks, that a vapour system is not necessarily a vacuum system. A vapour system is distinguished by being designed for a very small pressure differential between the steam mains and the dry returns, with radiator flow primarily controlled by calibrated orifices and valves (and, usually, traps -- though not necessarily), crossover traps, and one main venting location at or very near the boiler. In some systems this was just an open pipe to the chimney. In others, which had various devices to ensure that that very small pressure difference was never exceeded, sometimes the vent held against a vacuum, and sometimes not.

Imposing a vacuum on a vapour system will upset the balance and operation of the system, unless the vacuum is applied to both the steam mains and the dry returns so as to maintain the very small pressure difference.

It really isn't this complicated - for sure in two pipe. The mains and the dry returns are always connected to each other through the radiators. It is the collapsing steam which pulls a vacuum on everything. Please remember, vacuum does not mean no air, it just means less air than normal. Vacuum means pressure below atmospheric. There is a difference - especially in how you think about it. The whole system drops below atmospheric and all the relationships inside stay the same. There is no balance upset. I really do know this. If you were to mechanically pull a vacuum from anywhere on the dry return it is no different that a naturally induced one except the pressure can be farther below atmospheric.

Also with a with a vacuum pump, you can have a pre purge if the system is cold, and a post purge for as long as the boiler is hot.

Agreed @AMservices. A pump will provide added enhancements over naturally induced vacuum.

ted_p

ChrisJ said:

AMservices said:

Have you ever worked on a hermetically sealed refrigeration system?  They're kind of air tight.

And there's no reason you could not build a steam system in the same manner

Building a system from scratch with what we have available today is more plausible then trying it with a 100 year old piping.

I can only speak for my system, but in my case the supply valves are the main issue I see. Get rid of them, and my chances of holding a vacuum go way up.

I agree with your take on radiator supply valves, based on my own experience.

Since 2003, I've been looking after 72 unit apartment building, built in the early 40's, heated by a 2-pipe system vacuum system with a Heat-Timer (cycling) outdoor reset control (converted from Vari-Vac ), a Weil-Mclain 1288 Series 1 boiler (9,704 sq ft, net), and 263 cast iron radiators, totaling only 6,226 sq ft of EDR.

The radiators were originally equipped with 3/4" Dunham "Packless" radiator valves (which were designed to hold vacuum). Over the years, it appears that every time that one of the Dunham valves leaked, or jammed, or suffered a broken knob, it got replaced with whatever happened to be cheap at the supply house; so by 2003, over 90% of the packless valves had been replaced with ordinary packed radiator valves. Between 2003 and 2018, we replaced a couple dozen more radiator valves, though only a handful of those were Dunham valves.

The only major component in the system not seriously oversized, was the condensate pump/vacuum producer (venturi type), a Shipco LRV2 (duplex), rated for 5000 EDR, controlled by Square-D Vacuum switches, with the lead pump set to go on at 3" Hg and off at about 8"Hg, and the trailing pump on at 2.5" and off at about 7.5". As long as we fixed every leak we could find, and kept the venturis clean, the vacuum producer could keep-up with the leakage, but just barely. When the boiler wasn't firing, the pumps would typically run for about 40 minutes to get up to 8" Hg and shutdown; but then it took only 2 or 3 minutes for the vacuum to bleed down to 3.5"Hg, and the cycle started over again. Whenever the boiler was firing, both pumps would run constantly, with the vacuum hovering around 3" Hg. I just assumed it was a lot of small leaks in the 60+ year old pipes; and so it went until the beginning of the 2019-2020 heating season.....

During the 2018 and 2019 off-seasons, we replaced the inlet valves on as many of the radiators as we easily could, with Danfoss TRVs. We'd skipped a few, where there wasn't room for the standard valve/operator combination, but by the fall of '19 about 90% of the valves in the building had been changed.

Well, when we started up the system in October 2019, I was pleasantly amazed to find that the vacuum pumps were no longer running all the time.... Now, it only took about 10 minutes for the vacuum to build-up and shut the pumps off, and then they stayed off for about 12 minutes before the vacuum to bled down to the point that the lead-pump restarted!

I was quite pleased, but baffled by this. It wasn't until early this year, during my second reading of "The Lost Art...." , that it dawned on me.... The Dunham "packless" valves, which my system was originally equipped with, were designed to hold vacuum, but the cheap, "packed", replacement valves were not, and were leaking air around the valve stems; and although none of those leaks was large enough to be audible, the aggregate of the air getting in through a couple hundred of them was huge! And I'll quantify "huge" by pointing out that the two, 1HP pumps that my vacuum producer is equipped with, are each rated to remove 6 CFM of air at a 5.5" Hg vacuum.

So now let's talk about the implications of this for naturally induced vacuum systems. If a couple hundred leaking radiator valve stems (each individual leak so small as to be inaudible), can bring a vacuum producer the size of the one I'm working with to it's knees, then how few such leaks would it take to defeat a naturally induced system, which has no ability to expel air once air the system drops into vacuum?

That's why I specifically asked @PMJ about his radiator valves earlier in this thread.

PMJ

ted_p said:

ChrisJ said:

AMservices said:

Have you ever worked on a hermetically sealed refrigeration system?  They're kind of air tight.

And there's no reason you could not build a steam system in the same manner

Building a system from scratch with what we have available today is more plausible then trying it with a 100 year old piping.

I can only speak for my system, but in my case the supply valves are the main issue I see. Get rid of them, and my chances of holding a vacuum go way up.

I agree with your take on radiator supply valves, based on my own experience.

Since 2003, I've been looking after 72 unit apartment building, built in the early 40's, heated by a 2-pipe system vacuum system with a Heat-Timer (cycling) outdoor reset control (converted from Vari-Vac ), a Weil-Mclain 1288 Series 1 boiler (9,704 sq ft, net), and 263 cast iron radiators, totaling only 6,226 sq ft of EDR.

The radiators were originally equipped with 3/4" Dunham "Packless" radiator valves (which were designed to hold vacuum). Over the years, it appears that every time that one of the Dunham valves leaked, or jammed, or suffered a broken knob, it got replaced with whatever happened to be cheap at the supply house; so by 2003, over 90% of the packless valves had been replaced with ordinary packed radiator valves. Between 2003 and 2018, we replaced a couple dozen more radiator valves, though only a handful of those were Dunham valves.

The only major component in the system not seriously oversized, was the condensate pump/vacuum producer (venturi type), a Shipco LRV2 (duplex), rated for 5000 EDR, controlled by Square-D Vacuum switches, with the lead pump set to go on at 3" Hg and off at about 8"Hg, and the trailing pump on at 2.5" and off at about 7.5". As long as we fixed every leak we could find, and kept the venturis clean, the vacuum producer could keep-up with the leakage, but just barely. When the boiler wasn't firing, the pumps would typically run for about 40 minutes to get up to 8" Hg and shutdown; but then it took only 2 or 3 minutes for the vacuum to bleed down to 3.5"Hg, and the cycle started over again. Whenever the boiler was firing, both pumps would run constantly, with the vacuum hovering around 3" Hg. I just assumed it was a lot of small leaks in the 60+ year old pipes; and so it went until the beginning of the 2019-2020 heating season.....

During the 2018 and 2019 off-seasons, we replaced the inlet valves on as many of the radiators as we easily could, with Danfoss TRVs. We'd skipped a few, where there wasn't room for the standard valve/operator combination, but by the fall of '19 about 90% of the valves in the building had been changed.

Well, when we started up the system in October 2019, I was pleasantly amazed to find that the vacuum pumps were no longer running all the time.... Now, it only took about 10 minutes for the vacuum to build-up and shut the pumps off, and then they stayed off for about 12 minutes before the vacuum to bled down to the point that the lead-pump restarted!

I was quite pleased, but baffled by this. It wasn't until early this year, during my second reading of "The Lost Art...." , that it dawned on me.... The Dunham "packless" valves, which my system was originally equipped with, were designed to hold vacuum, but the cheap, "packed", replacement valves were not, and were leaking air around the valve stems; and although none of those leaks was large enough to be audible, the aggregate of the air getting in through a couple hundred of them was huge! And I'll quantify "huge" by pointing out that the two, 1HP pumps that my vacuum producer is equipped with, are each rated to remove 6 CFM of air at a 5.5" Hg vacuum.

So now let's talk about the implications of this for naturally induced vacuum systems. If a couple hundred leaking radiator valve stems (each individual leak so small as to be inaudible), can bring a vacuum producer the size of the one I'm working with to it's knees, then how few such leaks would it take to defeat a naturally induced system, which has no ability to expel air once air the system drops into vacuum?

That's why I specifically asked @PMJ about his radiator valves earlier in this thread.

@ted_p, thanks much for this story. Perhaps you would give us a few details about how the vacuum improves the performance of the system overall.

Just a few comments about natural vacuum in 2 pipe residential:

First, I believe my Mouat system was designed to run very low pressure vapor but not specifically vacuum. I tightened up all the valves that I could hear sucking air. But the real culprit was the large shutoff valve that was over the coal fired boiler and never removed. Below is a picture. I never heard anything there until I attached a compressor and pumped up the system. It is 90 years old also but still tightened up ok.



When my burner shuts off with my system filled as full as I ever fill it will continue to build vacuum for 30-45 minutes and peak at about 6"hg. From there it will gradually fall and totally be gone in about 4 hours. During my normal cycling sequence on an average day new burns will occur after 15-20 minutes off at which time the vacuum level will be between 4-5"hg and still deepening.

I want everyone to know that I have actually spent very little time on leak issues. No time at all in the last 5 years or so. So no one should be thinking this is Mount Everest. I should probably add a pump, but the vacuum I am getting isn't bad and it is totally quiet and effortless. A negotiation with mission control might be required to get permission to add any noise.


Also, by switching the operation deliberately to longer calls and more total cycles, the colder it gets outside I get to a place where there are virtually no starts at all that are not with 5"HG of vacuum present, and all for free. My point here is that taking the most advantage of natural vacuum requires doing a few more cycles which at the same time minimizes the impact of leaks. It was several years into vacuum operation before I tightened up that big valve which doubled my vacuum. But even with it leaking things were significantly improved.

jumper

@ted_p
Does the condensate pump have a vented receiver? If so doesn't air come into the system there? Can't valve stems be sealed with a bit of grease?
My experiences with TRV s on two pipe steam are also positive. I presumed that improvement came from control.