check valve for condensate return pump and water level

slater

I am looking for a recommendation for a check valve to use between a Hoffman condensate return pump and steam boiler. Originally there was a swing check valve but when water got high on the return side it would equalize with the boiler and cause boiler to be overfilled. I tried an apollo spring check valve but they do not recommend using on lines with pumps. It caused LOUD vibrations within check valve. This has been recommended by several distributers. On systems with heartford loop gravity return setups how high do you see water levels get when a system sits idle and all condensate finally makes its way back?

Pumpguy

Condensate pumps typically use a metal-to-metal bronze swing check valve.

Is your boiler boiler a fairly recent replacement? If yes, it may not have enough water storage capacity to fill the entire system with steam. This is a common problem when old large water storage capacity boilers are replaced smaller modern ones.

If this is the case, you will have a starve-then-flood situation where the boiler takes on make up water to get the entire system filled with steam. Then when the system shuts down, the system is overfilled with condensate which then spills out the overflow. Next time the boiler starts, the vicious cycle starts all over again.

If this is the case, then the only solution is a separate boiler feed pump(s) and tank package. The size of the BF tank will depend on the steaming capacity of the boiler and how much steaming time you want the package to provide. Typical recommendations are 10 - 20 minutes steaming time.

If this is not the case, then you might take a look at your low water make-up valve. If this is an automatic type, it might be leaking and overfilling the boiler during off times.

Something else to take a look at is the equalizer line between the steam header and return line. If this is not working, condensing steam will hold condensate until the system eventually equalizes. See attached file.

I'm not a boiler guy, so others may chime in with other suggestions.

ratio

I'm up against the same problem here. I ended up replacing the failing check valve with a brass swing check from off the shelf at Lowes, & it worked the first season, but it seems to be leaking through now.

I'm probably going to end up with a feed pump, as I end up feeding quite a bit of water before the condensate starts coming back on a cold start, but I need to think about it some more.

Jamie Hall

Is this a residential application? If so...

It is my opinion that it is rare to the point of being extremely unusual for even a very large residential system with a properly sized boiler of the modern sort to require a condensate return pump of any kind.

Consider that 3" pipe has a capacity of around a third of a gallon per foot of pipe. Now if that is filled with steam at any reasonable pressure, that equates to .0002 gallons of water. So suppose we have a steam system with 200 feet of 3 inch main, and we further suppose that the radiators have ten times the volume of the piping. Doing the math, that equates to less than half a gallon of water boiled off to fill the entire system.

Not a big deal with a boiler...

However, that is not to say that there aren't systems where there are condensate return problems!

Things to check:

Correct near boiler piping, especially the header and equalizer to the top of the Hartford loop. Problems with the header can result in the boiler happily burping half its water out. Problems with the equalizer can result in the water backing out of the boiler into the returns.

Really crudded up wet returns slowing condensate return.

Incorrect static water level (too low) resulting in segments of what should be wet return pipe, but which is now dry being dry until the boiler fires, at which point even a small rise in pressure can back the water into these lengths of pipe. This usually causes other problems as well. This is usually caused by someone replacing a big old fashioned boiler with a new, shorter one with a lower water level, and not matching the water levels by putting the new boiler up on blocks.

Now if this is a large industrial facility, or a campus or something, then yes, you may need pumps. See below...

In answer to the specific water level question by the OP, I would regard it as a sign of a problem if the water level were more than a couple of inches lower at cutout pressure than it was cold.

Now if you do need to introduce the complication of a pump into your set up for some other reason, it must be a boiler feed pump, not a condensate return pump. The fundamental difference is in control: the boiler feed pump is controlled by the water level in the boiler itself, and operates only to maintain that level. You do NOT want a condensate return pump which will operate to empty a condensate receiver tank based on the level in that tank -- that is a sure way to wind up with an overfilled boiler.

But what if your system is so large, or so laid out that some of the condensate can't return to the vicinity of the boiler by gravity? There you do need condensate return pumps from those receivers -- but they don't go direct to the boiler. They should go instead to a secondary receiver, which feeds that boiler feed pump.

slater

PumpguyPumpguy Posts: 134Member ✭✭

November 28



Condensate pumps typically use a metal-to-metal bronze swing check valve.

Is your boiler boiler a fairly recent replacement? If yes, it may not have enough water storage capacity to fill the entire system with steam. This is a common problem when old large water storage capacity boilers are replaced smaller modern ones.

If this is the case, you will have a starve-then-flood situation where the boiler takes on make up water to get the entire system filled with steam. Then when the system shuts down, the system is overfilled with condensate which then spills out the overflow. Next time the boiler starts, the vicious cycle starts all over again.

This describes the issue I am having with the boiler. The condensate pump does have a bronze swing check valve. The watchman condensate receiver had a vent/overflow pipe but they had it so tall that water was filling the risers probably 10" above the boiler when the water equalized. I lowered the vent so that the water goes no further than the very top of sight glass.

I was doing a blow down on everything and discovered that the Hoffman model 55 F&T trap does not appear to be processing the water fast enough. I opened the cover on the swing check valve and there is water flowing slowly. There was probably at least 3 gal of water backed up. I took the face off and cleaned the inside but it is still not keeping up. The face with internals was replaced new this summer. Does anyone have any recommendations for a different trap that will allow the water to return faster. This is a 2pipe system and the vents are on the returns.

Sorry I forgot about the quote function on the post and can not seem to change it.

nicholas bonham-carter

these problems are why we try to do without any sort of condensate/feed tank on a steam system, and go with gravity return.
When a boiler is rated for X steam square feet, it should not only be able to supply enough heat for the radiation, but also supply enough steam volume to fill all the pipes and radiators.
The exceptions to gravity return are as Jaimie has noted few, and far between.
A non-powered reservoir tank can be used to supplement any lack of water in the boiler capacity.--NBC

slater

nicholas bonham-carter said:

these problems are why we try to do without any sort of condensate/feed tank on a steam system, and go with gravity return.
When a boiler is rated for X steam square feet, it should not only be able to supply enough heat for the radiation, but also supply enough steam volume to fill all the pipes and radiators.
The exceptions to gravity return are as Jaimie has noted few, and far between.
A non-powered reservoir tank can be used to supplement any lack of water in the boiler capacity.--NBC

nicholas bonham-carter said:

these problems are why we try to do without any sort of condensate/feed tank on a steam system, and go with gravity return.
When a boiler is rated for X steam square feet, it should not only be able to supply enough heat for the radiation, but also supply enough steam volume to fill all the pipes and radiators.
The exceptions to gravity return are as Jaimie has noted few, and far between.
A non-powered reservoir tank can be used to supplement any lack of water in the boiler capacity.--NBC

This summer I fixed the near boiler piping and used both steam taps and piped it 100% to factory install specs. It was piped with one riser with no cleanout straight into the main. It had the condensate pump already and I took it out and made it a gravity return with a heartford loop. All the A &B dimensions where at minimum so I thought It would work. when I tested it kept kicking off on low water so my thought was that's why the condensate tank was added so there was reserve water. I then took out the heartford loop and added back in the condensate tank. I don't think I am loosing anything by having it In there because it holds the water level within 7/8" while system is running other than a mechanical part that can fail. I think I have maybe narrowed it down to the Hoffman 55 F&T trap it had not had anything done to it in over 20yrs. I cleaned the housing and bought new face with internals. Now it appears water is not going through trap fast enough to refill tank. probably was not before either and may be why condensate tank was added. I need to figure out a better option to replace the f&T trap that can handle more water. If this trap would have handled the condensate better the gravity system may have worked.

slater

Here are some pictures of the new boiler piping.

slater

Jamie Hall said:

Is this a residential application? If so...

It is my opinion that it is rare to the point of being extremely unusual for even a very large residential system with a properly sized boiler of the modern sort to require a condensate return pump of any kind.

Consider that 3" pipe has a capacity of around a third of a gallon per foot of pipe. Now if that is filled with steam at any reasonable pressure, that equates to .0002 gallons of water. So suppose we have a steam system with 200 feet of 3 inch main, and we further suppose that the radiators have ten times the volume of the piping. Doing the math, that equates to less than half a gallon of water boiled off to fill the entire system.

Not a big deal with a boiler...

However, that is not to say that there aren't systems where there are condensate return problems!

Things to check:

Correct near boiler piping, especially the header and equalizer to the top of the Hartford loop. Problems with the header can result in the boiler happily burping half its water out. Problems with the equalizer can result in the water backing out of the boiler into the returns.

Really crudded up wet returns slowing condensate return.

Incorrect static water level (too low) resulting in segments of what should be wet return pipe, but which is now dry being dry until the boiler fires, at which point even a small rise in pressure can back the water into these lengths of pipe. This usually causes other problems as well. This is usually caused by someone replacing a big old fashioned boiler with a new, shorter one with a lower water level, and not matching the water levels by putting the new boiler up on blocks.

Now if this is a large industrial facility, or a campus or something, then yes, you may need pumps. See below...

In answer to the specific water level question by the OP, I would regard it as a sign of a problem if the water level were more than a couple of inches lower at cutout pressure than it was cold.

Now if you do need to introduce the complication of a pump into your set up for some other reason, it must be a boiler feed pump, not a condensate return pump. The fundamental difference is in control: the boiler feed pump is controlled by the water level in the boiler itself, and operates only to maintain that level. You do NOT want a condensate return pump which will operate to empty a condensate receiver tank based on the level in that tank -- that is a sure way to wind up with an overfilled boiler.

But what if your system is so large, or so laid out that some of the condensate can't return to the vicinity of the boiler by gravity? There you do need condensate return pumps from those receivers -- but they don't go direct to the boiler. They should go instead to a secondary receiver, which feeds that boiler feed pump.

This is a residential application and the near boiler piping has been redone to manufacture specs. I also cross referenced Dan Holohans book lost art of steam heating and found there specs to be right on. The system has a Hoffman specialty watchman series wc condensate return pump controlled by a Mcdonnell & Miller NO42s low-water cut-off/pump controller. Boiler has a separate low water cut-off and auto water feeder. This is a two pipe system with dry returns that could very well be crudded up being over 100 yrs old. I lowered the vent/overflow on the condensate pump which stopped then boiler from flooding but water goes out overflow instead. The last issue seems to be the Hoffman 55 F&T trap not allowing water to pass fast enough to refill condensate tank while system has been running awhile. This causes low water condition and low water feeder add water which would not be needed if F&T trap would process the condensate faster. Called Bell & Gossett rep and Hoffman 55 with 3/4 inlet has a .253 orifice. They said I would have to go to a new H series F&T trap with1-1/4 inlets to get a larger orifice that is .312. Just not sure this is the best option.

Jamie Hall

You may need that larger orifice. You may not.

What you do need is to make sure that the pump -- call it whatever you like -- that pumps water into the boiler is controlled by the water level in the boiler and nothing else. Further, that automatic water feeder should not go into the boiler, nor be controlled by the boiler water level. It should be controlled by low water levels in the condensate receiver tank.

Then just make sure that your tank is big enough that it never ever overflows (but don't make it too high -- the water level in the tank must never get above about six inches below the water level in the boiler).

slater

Jamie Hall said:

You may need that larger orifice. You may not.

What you do need is to make sure that the pump -- call it whatever you like -- that pumps water into the boiler is controlled by the water level in the boiler and nothing else. Further, that automatic water feeder should not go into the boiler, nor be controlled by the boiler water level. It should be controlled by low water levels in the condensate receiver tank.

Then just make sure that your tank is big enough that it never ever overflows (but don't make it too high -- the water level in the tank must never get above about six inches below the water level in the boiler).

The McDonnell miller 42s is plumbed in to boiler and activates condensate pump solely off of water level in boiler. When water level in boiler gets low float drops closes switch sends power to condensate pump to pump water into boiler. condensate pump has its own float switch that will not allow pump to turn on if receiver tank is empty. The boiler has a Mcdonnell Miller ps 800 series 24v probe low water cut-off with a wf series 24v water feeder. I am not sure why it would be a problem adding water to boiler when condensate receiver is already dry or the water demand would have been fulfilled by it already. I also have a concern with putting oxygenated water in receiver that has not had a chance of the boiler burning out the oxygen. Seems there would be more corrosion in the piping since everything is black pipe. I would like to see a bigger receiver but that is $1400 and its not my money so I'm trying to make this work if at all possible. I'll post updated pictures in a few days when I get back in town.

Steamhead

slater said:

I think I have maybe narrowed it down to the Hoffman 55 F&T trap it had not had anything done to it in over 20yrs.

Where is this trap located?

slater

Steamhead said:

slater said:

I think I have maybe narrowed it down to the Hoffman 55 F&T trap it had not had anything done to it in over 20yrs.

Where is this trap located?
The trap is located at the end of the steam main. I'll add pictures so you can see the setup. The trap with issue is the one in front in picture. I also added picture of Mcdonnell Miller 42s discussed in an earlier comment.