Brand new Vaporstat doesn't seem to work - pigtail question

GBC_illinois

109A_5 said:

Hello @GBC_illinois,
With the Pressuretrol you may be able to calibrate it now. There is a small set screw under the microswitch on the linkage going to the diaphragm. I think it uses a 0.050" hex key (Allen wrench). There has been other posts on this subject.

Thank you, I was about to toss it! I have moved my dysfunctional 4psi Vaporstat to its former position in the control tree, because that Vaporstat seems to work acceptably if I set it to 1.25psi or greater. As a "backup" controller, a 1.25psi limit is better for my sub-1psi system than whatever the lowest pressure the pressuretrol is likely to maintain.

mattmia2

With the rapid cycling of the condensate pump, it sounds like it is working to put water back in to the boiler that was thrown out as liquid water rather than replacing water that left as steam, condensed in the system and returned as water.

GBC_illinois

EdTheHeaterMan said:

Water has weight and that may be the reason for the difference.
I have looked at different posts and have found this to be a problem. There is a water seal that is designed to protect the controls and gauges from the high temperature of the steam. This is usually accomplished by a pigtail that is filled with water to keep the steam from the gauges and controls. In your case it is the "control tree" with a series of 90° fittings to create a trap for said water to accumulate.

Some of the old timers and dead men have actually used an air gap to protect the gauge from steam. If you have an 18" vertical pipe off the top of the boiler with no vent. There is air trapped in that vertical pipe so no steam will get to the gauge. I'll see if I can find the article

@EdTheHeaterMan now that I've done some precision bench testing on both my controls and my gauges, I've come to believe you are right about the weight of the water in the control tree / pigtail affecting the gauges and controls; it's not a huge difference with my setup, but measurable.

My 32" WC gauge seems to read pressure accurately on a bench test, but on my control tree it reads approximately 1oz less than my manometer, which is connected to the drain of my boiler sightglass. I am inclined to believe the manometer provides the true reading of boiler pressure, so it makes sense that the gauge would read 1oz less due to the water weight. Since my vaporstat is connected in the same method to the same tree with the same amount of water, I imagine it receives the same pressure reading as the gauge. Thought you might like to have another datapoint!

GBC_illinois

109A_5 said:

Hello @Fdarby82,
You may need to vent better so the steam moves better. It maybe lethargic and just makes pressure quickly. If the steam is not readily moving away from the Boiler it is building pressure.

@109A_5 (or anyone who has thoughts), RE: "Might need to vent better" -- I have a question. First some background...

This is a 1920 building, and as far as I can tell the mains are condensate lines are mostly original. It's 2-pipe, and none of the radiators have air vents or steam traps, only thermostatic valves to control the temperature. Steam flows freely back into the condensate lines, when the boiler is on long enough to heat the rads. This might waste money, but it does also heat the basement, which is otherwise unheated, so I'm not planning to change this setup as installing 59 radiator steam traps would be a huge expense and cause us extra maintenance in future. The near-boiler piping was replaced in 2011, so I don't know what that original piping looked like. It's clear to me this system was designed to operate at vapor pressures, far less than 1psi. I've been experimenting with pressures since the new vaporstat arrived, and I've found 10oz seems to be sufficient to get all the rads hot quickly; below that pressure is questionable.

So, venting: The system currently has only two air vents in the entirety of the building: one of these guys (pictured at bottom) at the very end of each condensate return, right before it drops down through a F&T steam trap into the condensate tank. Note that there are NOT vents on either of the steam mains. Both of our air vents hiss quite a lot when the boiler is starting up, for about 10-15 minutes, until the air seems to be out of the system. They do not seem to let steam out, because after the boiler has been on for a while, they are silent.

The question I have been wondering about is: Should we also have a vent on the end of each steam main? If so, why weren't they originally put in (as I think the folks who designed the original system did so thoughtfully)? Since there are no radiator steam traps, in theory any air in the system at startup will be pushed through the mains, through the radiators, and back into the condensate lines, where the two vents will remove it. I would think that the air at startup would cause quite a bit of friction in pushing all the way through 250 feet of pipe (including the radiators) to finally exit out the end of the condensate vent. Would vents on the end of the steam mains expedite this air-removal process to get the radiators hot faster after boiler startup?

EdTheHeaterMan

@GBC_illinois said

@EdTheHeaterMan now that I've done some precision bench testing on both my controls and my gauges, I've come to believe you are right about the weight of the water in the control tree / pigtail affecting the gauges and controls; it's not a huge difference with my setup, but measurable.

The conversion factor is 1" water column = 0.57803666923766 ounces per sq. inch pressure
or 1 ounce per sq. inch pressure = 1.7299940526590531 inches water column.

So if water is involved in the pigtail in order to keep the steam from the measuring device (gauge or control) and water is used as a way to measure pressure. It goes to reason, that pressure acting on water will have an effect on the pressure reading. When dealing with 2 or 3 PSI or greater, the less than 1/2 PSI difference created by raising the water in the gauge column 1 fraction of an inch higher than on the steam side of the pigtail does not make that much of a difference. When you are dealing with a few ounces of steam pressure, and you are looking for exact measurements (which is an exercise in futility in my mind) then those water column differences must be accounted for.

109A_5

Hello @GBC_illinois,
I would not suggest adding 59 vents to your system. That system, as originally built may have run predominantly in a vacuum. You may be interested in how @pmj runs his system I believe his EDR is about half of yours and is also a two pipe system.

With a vacuum there it less air to push out of the system so the steam can get where it needs to get to faster. You may want to increase the existing venting so the air can be purged out faster which means the radiators get steam faster reducing fuel costs. This may reduce the pressure during the part of the cycle until the vent(s) close. Once the vents close the pressure will rise so at some point the boiler can be shut off and maybe a delayed restart would help the overall fuel economy.

From another post, I think @clammy believes your system has been knucklehead and you agree so your challenge is to minimize the knucklehead-ness, which you have been doing.

To me the condensate pumping is an issue too. Since it has damaged the boiler AND reduces the steaming when the boiler is running. You can have a just tank to store extra water to maintain a decent water level when steam and condensate is out in the system, no pump. Maybe the volume of the pump can be reduced (change the pump) to a rate closer to the actual condensate return volume to minimize the impact of pumping cold water into the boiler. With no pump the condensate just trickles back to the boiler at a more reasonable rate. Also with the existing pump maybe the water level differential or hysteresis can be reduced so that the amount of water pumped at each instance is less. However that would increase the cycles of the relay that controls the pump. I would consider a Solid State Relay instead of a mechanical one, since you have had relay problems too.

Another idea is a separate timer limiting the run time (or duty cycle) of the existing pump. And should the separate timer fail 'stuck on' the original pump controller will still be in overall control.

Being that it is a Coop I don't know how much creative latitude you have with this system.

GBC_illinois

109A_5 said:

Hello @GBC_illinois,
I would not suggest adding 59 vents to your system. That system, as originally built may have run predominantly in a vacuum. You may be interested in how @pmj runs his system I believe his EDR is about half of yours and is also a two pipe system.

With a vacuum there it less air to push out of the system so the steam can get where it needs to get to faster. You may want to increase the existing venting so the air can be purged out faster which means the radiators get steam faster reducing fuel costs. This may reduce the pressure during the part of the cycle until the vent(s) close. Once the vents close the pressure will rise so at some point the boiler can be shut off and maybe a delayed restart would help the overall fuel economy.

From another post, I think @clammy believes your system has been knucklehead and you agree so your challenge is to minimize the knucklehead-ness, which you have been doing.

To me the condensate pumping is an issue too. Since it has damaged the boiler AND reduces the steaming when the boiler is running. You can have a just tank to store extra water to maintain a decent water level when steam and condensate is out in the system, no pump. Maybe the volume of the pump can be reduced (change the pump) to a rate closer to the actual condensate return volume to minimize the impact of pumping cold water into the boiler. With no pump the condensate just trickles back to the boiler at a more reasonable rate. Also with the existing pump maybe the water level differential or hysteresis can be reduced so that the amount of water pumped at each instance is less. However that would increase the cycles of the relay that controls the pump. I would consider a Solid State Relay instead of a mechanical one, since you have had relay problems too.

Another idea is a separate timer limiting the run time (or duty cycle) of the existing pump. And should the separate timer fail 'stuck on' the original pump controller will still be in overall control.

Being that it is a Coop I don't know how much creative latitude you have with this system.

I wouldn't want to add vents to the radiators, my thought was to add them to the steam mains, just one at the end of each, for a total of 2. There are existing unused connections from the steam main which are plugged, so it wouldn't be very much work to try it. I realize this wouldn't get the last bit of air out of the end of the mains before the radiators, but wouldn't it get most of the air out, making less friction to get the first steam to the rads after the boiler starts firing?

The vacuum condition that is created in my system is limited to just about 20 minutes after the boiler shuts off; it returns to atmospheric pressure as the condensate finishes returning, so it is at atmosphere when the boiler fires again. A Gorton vent like this one https://www.supplyhouse.com/Gorton-G2-Gorton-No-2-Straight-Air-Eliminator-3524000-p says that it is for 1-pipe steam, but wouldn't it also benefit 2-pipe steam at the end of the steam main, for a system that starts at atmospheric pressure like mine?

I will check out posts from @PMJ

RE: Pump: I am keen on getting rid of this pump. I've carefully measured the condensate return rate and the total volume of condensate out in the pipes during the boiler cycles, and my data shows that the condensate returns quickly enough in my building that having a separate condensate collection and return system is not necessary at all. So my plan is to eventually return this to gravity feed, but I'm probably not going to spend much money on incremental fixes until then. I have spoken with @The Steam Whisperer and he's given me some ideas about how to do that. Unfortunately it will probably be a while before we have funds for it.

RE: Coop -- it is a shared building, but no one else takes an interest in the boiler, and since my changes eliminated our terrible water hammer, the other shareholders only weigh in if changes are particularly expensive.

GBC_illinois

@109A_5 also, the reason my system only stays in vacuum briefly after the boiler shuts off appears to be the same air vents that are on the condensate mains -- the one I took a picture of in my last post. They hiss after the boiler shuts off, and using a cigarette lighter adjacent to the air port, I was able to identify that the air was being sucked back in at that time.

109A_5

Hello @GBC_illinois,

GBC_illinois said:

I wouldn't want to add vents to the radiators, my thought was to add them to the steam mains, just one at the end of each, for a total of 2. There are existing unused connections from the steam main which are plugged, so it wouldn't be very much work to try it. I realize this wouldn't get the last bit of air out of the end of the mains before the radiators, but wouldn't it get most of the air out, making less friction to get the first steam to the rads after the boiler starts firing?

The vacuum condition that is created in my system is limited to just about 20 minutes after the boiler shuts off; it returns to atmospheric pressure as the condensate finishes returning, so it is at atmosphere when the boiler fires again. A Gorton vent like this one https://www.supplyhouse.com/Gorton-G2-Gorton-No-2-Straight-Air-Eliminator-3524000-p says that it is for 1-pipe steam, but wouldn't it also benefit 2-pipe steam at the end of the steam main, for a system that starts at atmospheric pressure like mine?

Sure vent the Mains, I just thought it may be easier to do it where the vents already exist. The faster you remove the air (or let it out) the faster the steam can move and at a lower pressure.

You may see the correlation between the condensate ceasing and the vacuum diminishing. I think it is just coincidental. I would try this experiment; At the completion of a normal heating cycle, temporary shut off the boiler so it can't restart, and with electrical or duct tape tape over the holes in all the vents (condensate tank too) and see how long the vacuum lasts. With normally 20 minutes of vacuum it seems your system is fairly tight and may be perfect for @PMJ's control strategies.

I think with @PMJ system he lets the air out and never lets it back in. Minimal air for the steam to push against promotes best performance and economy and he loves the confort. Besides the normal thermostat he monitors the farthest radiator pipe from the boiler for the presents of steam with a thermal switch and then limits the boilers run time with a timer. If he has any Presuretrols or Vaporstat they are just for safety and not cycle control.

Vacuum also lowers the boiling point so less fuel to make steam.

I bet the other other shareholders are glad you have an interest, less they have to deal with.

GBC_illinois

109A_5 said:

Sure vent the Mains, I just thought it may be easier to do it where the vents already exist. The faster you remove the air (or let it out) the faster the steam can move and at a lower pressure.

You may see the correlation between the condensate ceasing and the vacuum diminishing. I think it is just coincidental. I would try this experiment; At the completion of a normal heating cycle, temporary shut off the boiler so it can't restart, and with electrical or duct tape tape over the holes in all the vents (condensate tank too) and see how long the vacuum lasts. With normally 20 minutes of vacuum it seems your system is fairly tight and may be perfect for @PMJ's control strategies.

I'm going to try this experiment as you prescribe, thank you. I've tried a similar experiment where I taped off the two air vents only, but forgot about the condensate tank vents. There's also a vacuum breaker installed in an odd location between the condensate pump and the boiler, which I only noticed recently. I don't know if that even does anything (I don't ever hear it), but I'll try taping it off too. If I could keep my system in a vacuum between cycles, that seems far superior to pushing the air out every time.

109A_5

Hello @GBC_illinois,

Back to this for a moment. Be advised I am NOT a Psychics professor.

See drawing; If all the pipes were 3/4" and the boiler is at 16 Oz. I would think the pressure of the 5 pipes would be 16 / 5 = 3.2 Oz. However with the 5 pipes the cross sectional area of 1/4" pipe (is a lot less) so I would think the pressure would be greater than 3.2 Oz. but maybe less than 16 Oz. The ratio of cross section areas would have to be calculated with the different pipe sizes. Maybe it is better stated that the PSI (Pounds per Square Inch) is the same if the surface area on either side of the water is the same but I bet it is not in your case.

I have seen other situations that the distribution pipe is not the water trap and in your case 5 pigtails would be needed. Again I only see about 0.25 WC or 0.1445 Oz. difference with my pigtail. I'm assuming this due to bias of gravity with the water in the pigtail. The pigtail has the same pipe size on each side.

GBC_illinois

109A_5 said:

Hello @GBC_illinois,
See drawing; If all the pipes were 3/4" and the boiler is at 16 Oz. I would think the pressure of the 5 pipes would be 16 / 5 = 3.2 Oz. However with the 5 pipes the cross sectional area of 1/4" pipe (is a lot less) so I would think the pressure would be greater than 3.2 Oz. but maybe less than 16 Oz. The ratio of cross section areas would have to be calculated with the different pipe sizes. Maybe it is better stated that the PSI (Pounds per Square Inch) is the same if the surface area on either side of the water is the same but I bet it is not in your case.

I have seen other situations that the distribution pipe is not the water trap and in your case 5 pigtails would be needed. Again I only see about 0.25 WC or 0.1445 Oz. difference with my pigtail. I'm assuming this due to bias of gravity with the water in the pigtail. The pigtail has the same pipe size on each side.

This is a great diagram, it pretty accurately represents my control tree. I don't know the science well enough here though to dig into it, and as of now I have solved the problem with my Vaporstat -- it was just a bad part. The new Vaporstat may be an oz or two off of what my manometer reads, but it's close enough for me to consider that issue closed.

As for the vacuum test you prescribed, I just tried it, and was shocked at the results. With the condensate tank vents plugged as well as the condensate air vents, the system got deep into vacuum -- over 1psi of vacuum before I removed the plugs, because I was nervous about what those vacuum pressures could do to my new Vaporstat. I heard its diaphragm pop as it got down that low, and now it appears to behave slightly differently than it did before, allowing slightly higher pressures. Not enough for me to worry about it, still seems fine.

Another issue arose when I ran this test: with that much vacuum, my F&T steam traps at the end of the mains and condensate lines weren't able to pass condensate, or did so very slowly. The flow rate of condensate at the end of the boiler cycle is easily audible, and it unmistakably slowed to a trickle. I suppose this would not be an issue if I return to gravity feed, because I could then remove the traps, but with the current setup emptying into a vented condensate tank, I don't see how I can get rid of the traps. So, it appears that as long as I have the F&T traps and a boiler feed tank/pump, maintaining vacuum won't be a realistic option. Does that sound accurate, given the results of this test?

Also, can a Vaporstat normally operate when exposed to such a severe vacuum? If I do return to gravity feed as I intend and let this vacuum occur at the end of the cycle, I would still need a pressure controller than can function to keep the boiler at 10oz.

Thanks for all your help!

GBC_illinois

@109A_5 here's a pic of my steam trap setup, you can see them at the end of the piping behind the tank.

109A_5

Hello @GBC_illinois,
To me major changes to the system probably should be done off season unless it is an emergency.

I do not have a good overall visualization of @PMJ's system, like if he has multiple Mains and multiple condensate returns, F&T traps etc. I believe his control strategy is based upon the heat load of the farthest radiator from the boiler and a timer limiting boiler run time. I would assume he has a Presuretrol for a backup safety control. I would think he would not need a Vaporstat with his control strategy and since the system is usually below atmospheric pressure and the Vaporstat uses atmospheric pressure as the reference for system pressure on the back side of it's diaphragm. The Vaporstat should tolerate a vacuum since I think steam boiler systems commonly go into a vacuum when the boiler shuts down and the radiators are still condensing. However the newer production units may not be as robust as older ones were.

Depending on how handy you are with pipe wrenches the F&T traps could have a bypass valve installed and the same with the condensate tank / pump. So more controlled testing could be done to determine what final direction you want to go with. To pay a contractor to do this may be a costly experiment. You could also put a temporary valve under the Vaporstat to protect it during tests.

In the mean time while waiting for the off season additional venting may help and the cost for the vents may be recouped in fuel savings and it gives you time to learn and understand what @PMJ has done and if it is good for your system.

Personally I want to introduce more significant vacuum to my system but I only have a one pipe system and running new additional pipes to each radiator I would have rip the house apart to get to the upstairs radiators. I do have some ideas to explore. I believe this system originally utilized vacuum more than now since when it was new I'm assuming all the radiators vents were DOLE 2B vents which are vacuum vents. A few have been changed over the years and are no longer vacuum vents. As near as I can tell DOLE 2B vacuum vents are no longer available.

PMJ

@GBC_illinois ,

These systems were all designed originally to run at very low and constant pressures....single digit ounces. This was quite straight forward originally with constant fire. Intermittent fire causes rapid and dramatic pressure changes which in my opinion makes trying to control the boiler to produce even heat with a pressure device problematic to say the least. The whole process should be operating well below the operating range of any standard pressure device. I consider my vaporstat a safety device only.

I have only one opening to the atmosphere in my two pipe system with a solenoid valve on it. It closes when the burner goes off, no air is allowed back in and the entire system sinks into 5-6inches Hg of natural vacuum. The next burn fills that vacuum with steam, and when the internal pressure reaches atmospheric the valve opens and the small amount of air that leaked in with the burner off is pushed out at the end of the burn. The max positive pressure is 2oz for the pushing out. So the dramatic change in pressure from +2oz to - 6 inches Hg that occurs every cycle is no issue because it is not used to control the firing of the boiler. My opinion is that it makes no sense whatever to attempt to control the firing of a boiler with a pressure device when the maximum steam pressure ever intended for the system is single digit ounces.

I use a temperature switch at the most remote radiator in my system to control each firing such that a consistent fill amount is reached every time, one that I know from experience will heat on design day if the system cycles continuously. In my system that means radiators not even 1/2 full. I shut the boiler off when that fill amount is reached, and the next firing(if a call for heat is still in progress) is initiated a timed amount after that same sensor opens, indicating that a sufficient amount of the heat from the previous burn is already in the living space. So the pace of the boiler is controlled by the conditions - that is how fast steam is condensing in the radiators - and that depends obviously on the outside conditions. So the burn times and the wait times in between adjust themselves to the actual demand. As conditions get colder, vacuum between burns deepens because steam is condensing faster which causes burn times to be longer and wait times in between shorter.

In my opinion having a boiler big enough to heat a structure on design day run flat out to thermostat satisfaction or attempting to control it with a pressure device makes no sense whatsoever. Neither device will react to stop the run of the boiler until long after the time a stop was actually needed. The boiler's output must be spread out more evenly by another method to get a result one could call even heat.

I'm happy to discuss any time.

GBC_illinois

PMJ said:

@GBC_illinois ,

These systems were all designed originally to run at very low and constant pressures....single digit ounces. This was quite straight forward originally with constant fire. Intermittent fire causes rapid and dramatic pressure changes which in my opinion makes trying to control the boiler to produce even heat with a pressure device problematic to say the least. The whole process should be operating well below the operating range of any standard pressure device. I consider my vaporstat a safety device only.

I have only one opening to the atmosphere in my two pipe system with a solenoid valve on it. It closes when the burner goes off, no air is allowed back in and the entire system sinks into 5-6inches Hg of natural vacuum. The next burn fills that vacuum with steam, and when the internal pressure reaches atmospheric the valve opens and the small amount of air that leaked in with the burner off is pushed out at the end of the burn. The max positive pressure is 2oz for the pushing out. So the dramatic change in pressure from +2oz to - 6 inches Hg that occurs every cycle is no issue because it is not used to control the firing of the boiler. My opinion is that it makes no sense whatever to attempt to control the firing of a boiler with a pressure device when the maximum steam pressure ever intended for the system is single digit ounces.

I use a temperature switch at the most remote radiator in my system to control each firing such that a consistent fill amount is reached every time, one that I know from experience will heat on design day if the system cycles continuously. In my system that means radiators not even 1/2 full. I shut the boiler off when that fill amount is reached, and the next firing(if a call for heat is still in progress) is initiated a timed amount after that same sensor opens, indicating that a sufficient amount of the heat from the previous burn is already in the living space. So the pace of the boiler is controlled by the conditions - that is how fast steam is condensing in the radiators - and that depends obviously on the outside conditions. So the burn times and the wait times in between adjust themselves to the actual demand. As conditions get colder, vacuum between burns deepens because steam is condensing faster which causes burn times to be longer and wait times in between shorter.

In my opinion having a boiler big enough to heat a structure on design day run flat out to thermostat satisfaction or attempting to control it with a pressure device makes no sense whatsoever. Neither device will react to stop the run of the boiler until long after the time a stop was actually needed. The boiler's output must be spread out more evenly by another method to get a result one could call even heat.

I'm happy to discuss any time.

You clearly have your system figured out to a T. I think there are definite learnings I can take from your setup, but I'm going to message you privately about it.

mattmia2

Is that an enormous side outlet boiler with only one outlet used?

Jamie Hall

I haven;t really been following this one... so a few remarks, which may be redundant. The control tree arrangement you have should work fine. The only thing which may seem a little odd is that if its connection to the boiler is below the boiler water line, there will be a slight offset in the pressure it is seeing -- but it is related to the depth below the water line, and is thus fairly constant. Shouldn't be an issue.

The relatively quick rise to a few ounces is not really a problem either -- provided that then the pressure stays more or less constant until all the radiators are full. If that is true, fine -- but if it isn't, you need more main venting.

Now the condensate tank and feed. First, a disclaimer: I dislike them. But sometimes they are a necessary evil. It isn't really clear from the various posts, but the pump which transfers water from the condensate tank must be controlled by the water level in the boiler and nothing else. This is really important. If yours isn't set up that way, you should be able to work with your upper level LWCO (you do have two, don't you?) and possibly a time delay relay to control the pump. There needs to be a reliable check valve on the line, of course.

The water level in the tank, then, must be controlled by either a float valve or float switch and electrical valve to add water only if the tank gets low. There is a possibility that, with this arrangement and slow returns, the tank may overflow. Undesirable -- but not a problem, provided the tank has an overflow at or below the low operating water level in the boiler. The overflow must be big enough to accept the full flow of the makeup water line. This will keep your tank from overfilling your boiler.

Now this matter of steam in the returns. No. The system will never work well and efficiently if you get any steam or pressure from any source in the dry returns. First, they must have copious venting -- more even than the steam mains (some older systems even simply had an open pipe!). Second, there must be some means on every radiator to ensure that steam cannot leave the radiator -- only air or condensate. There are two ways to do that: steam traps on the radiator outlets, or tight pressure control and orifices or calibrated valves on the inlets. You do say that you have no traps on any of the radiators -- which makes me wonder if the outlet elbows may be, or may have been, one of the many other ingenious contraptions which served somewhat the same function -- but always in conjunction with low pressure. Worth looking at to see.

To go back a little to that condensate receiver. Since you have one, you also have to have a F&T trap on every single condensate drip from the steam mains to the wet returns. No exceptions. And they must be working. Otherwise you will get steam in the wet returns -- and from there into the dry returns and the condensate receiver. Both of those happenings will also cause the system to run poorly. The condensate receiver must be vented, of course -- but that is NOT a substitute for vents on both the steam mains and the dry returns.

109A_5

mattmia2 said:

Is that an enormous side outlet boiler with only one outlet used?

GBC_illinois

Jamie Hall said:

I haven;t really been following this one... so a few remarks, which may be redundant. The control tree arrangement you have should work fine. The only thing which may seem a little odd is that if its connection to the boiler is below the boiler water line, there will be a slight offset in the pressure it is seeing -- but it is related to the depth below the water line, and is thus fairly constant. Shouldn't be an issue.

The relatively quick rise to a few ounces is not really a problem either -- provided that then the pressure stays more or less constant until all the radiators are full. If that is true, fine -- but if it isn't, you need more main venting.

Now the condensate tank and feed. First, a disclaimer: I dislike them. But sometimes they are a necessary evil. It isn't really clear from the various posts, but the pump which transfers water from the condensate tank must be controlled by the water level in the boiler and nothing else. This is really important. If yours isn't set up that way, you should be able to work with your upper level LWCO (you do have two, don't you?) and possibly a time delay relay to control the pump. There needs to be a reliable check valve on the line, of course.

The water level in the tank, then, must be controlled by either a float valve or float switch and electrical valve to add water only if the tank gets low. There is a possibility that, with this arrangement and slow returns, the tank may overflow. Undesirable -- but not a problem, provided the tank has an overflow at or below the low operating water level in the boiler. The overflow must be big enough to accept the full flow of the makeup water line. This will keep your tank from overfilling your boiler.

I appreciate your detailed analysis!

RE: Pressure rise rate -- it is not very consistent in the rise, partially due to the on-off of the condensate pump, filling it with new cooler water every minute. But, to your point, I do think I need more venting. This is my next priority for my system, to increase the venting.

RE: Condensate pump: I dislike it too, and will replace it with gravity feed when I have the opportunity. I am relatively certain it will work fine without the condensate tank/pump from my measurements. The pump is controlled on boiler water level, not tank water level. And the tank has an internal float which controls the makeup water valve. It used to overflow when the boiler was set at 7psi, but now that it runs at 10-11oz, the tank no longer overflows when the condensate comes back. Either way, I hate it and look forward to getting rid of it.

Jamie Hall said:

Now this matter of steam in the returns. No. The system will never work well and efficiently if you get any steam or pressure from any source in the dry returns. First, they must have copious venting -- more even than the steam mains (some older systems even simply had an open pipe!). Second, there must be some means on every radiator to ensure that steam cannot leave the radiator -- only air or condensate. There are two ways to do that: steam traps on the radiator outlets, or tight pressure control and orifices or calibrated valves on the inlets. You do say that you have no traps on any of the radiators -- which makes me wonder if the outlet elbows may be, or may have been, one of the many other ingenious contraptions which served somewhat the same function -- but always in conjunction with low pressure. Worth looking at to see.

To go back a little to that condensate receiver. Since you have one, you also have to have a F&T trap on every single condensate drip from the steam mains to the wet returns. No exceptions. And they must be working. Otherwise you will get steam in the wet returns -- and from there into the dry returns and the condensate receiver. Both of those happenings will also cause the system to run poorly. The condensate receiver must be vented, of course -- but that is NOT a substitute for vents on both the steam mains and the dry returns.

RE: Steam in the returns: We do have Thermostatic valves (Danfoss RA 2000) on each radiator intake to control the temperature in each coop unit, but we absolutely do not have traps on the returns. Not even the elbow orifice traps you are talking about. I've disassembled some return elbows to verify, and the condensate pipes from the radiator get hot. It may not be conventionally proper to go without radiator traps, but all I can say is that it works for us. Many of the 15 individual owners of the coop are not wild about letting me or anyone else access their units, but they WILL complain about heat problems -- and when people complain about not enough heat, they usually say "make the boiler run more often", even if the issue may be a radiator malfunction -- so everyone in the building spends more on heat because this resident with a malfunctioning radiator don't want to deal with having it inspected or serviced. By going without radiator steam traps, there is one less maintenance variable to worry about there. The thermostatic rad valves do wear out, but those are easier for the other owners to understand when they go bad, and they can even replace them themselves. So, with our trap-free setup, maintenance of the entire system is quite simple. And it heats the basement with our hot condensate lines as another added benefit. If we were to install traps, this would be a herculean effort, with 59 radiators, requiring cooperation from every resident, and by my guess, about $20,000 including labor. Unless there was an immediate, obvious benefit in comfort or cost savings, I would get raked across the coals for wasting that money. And imagine if people started screaming because the basement was suddenly cold...

Another thing about that is that our boiler cycles on and off with an indoor thermostat, and those cycles are usually short. So, at our low pressures of <11oz, pressure does not really build in the condensate lines. The cycles are usually just about long enough to heat the rads fully and not much else.

RE: Condensate receiver and traps: We do have F&T traps on every line returning to the condensate tank, and they work fine. I look forward to getting rid of those when I return to gravity feed and get rid of the tank though.

mattmia2

You need to have orifice plates sized to the radiator in the supply of the radiator if you are using TRVs. The steam in the returns will keep other radiators from heating. Once they are there you shouldn't have to touch them again as long as they are reinstalled if a TRV valve body is replaced.