sight glass water high, boiler water low

RAW

No I didn't see anything about a Paul system?
And by the way all the loads--2 preheat coils and reheat heat exchanger(there is a domestic water heater also but no load in the wee hours) do have vacuum breakers--new ones at that.

John Goyer

I am dealing with problems with a Peerless cast iron sectional boiler (model LC-09) 40 HP low pressure steam boiler. The boiler is shutting off on low water even though the sight glass is completely full. When the burner cuts off on low water, the water falls back into the sight glass to the "normal" level, or presumably just below it. This boiler is headered with a Hurst boiler of the same capacity. The load is 2 100% outside air handlers, a reheat hot water converter, and a domestic hot water heater. Modifications were made to the system so that all condensate drains from every trap downhill to a in-ground condensate receiver. I could go on with the problems with this system but lets start with some explaination as to why the water in the sight glass is outta sight.

Tim Kelley

Questions

1. Is the sight glass on the same side of the boiler as the low water cut off?
2. Is the top valve on the glass open? If so, is the piping open and unrestricted?
3. How about some photos showing the near boiler piping.
4. Is this a new problem? If so, what has changed in the system, i.e. any piping or control changes?, any load changes?, is the system being set back by the thermostat?
These will give the many knowledgable steamers help to find your problem.
Thanks TK

John Goyer

1. Yes.
2. Yes and the piping is open and unrestricted.
3. Photos now attached. What do people consider "near boiler" piping? Where is the line between "near boiler" and all othe piping?
4. This is not a new problem. The original project was replacing a single high pressure boiler with these 2 low pressure boilers. The system is not set back on a thermostat.

The pressure control is is a simple on/off with high/low fire modulating. The boilers are feed by two independent boiler feedwater pumps. There is a condensate reciever in the building that returns all the condensate. This is not a large facility. The piping system is very small. Other things that occur when the low water/sight glass thing happens are overflowing of the condensate receiver and boiler feedwater tank and elevated (~190 F) feedwater temperature. The feedwater tank is not heated.

John Goyer

back at the top. any thoughts out there?

John Goyer

back at the top. any thoughts out there?

Blackoakbob

Just a couple thoughts....

it would be helpfull if the header was insulated, this would stop a large amount of steam that is wasted just to keep this piping up to operating temperature and a large amount of condensate laying in the piping, probably being lifted into the supply piping and cooling that steam creating a "vaccum" and just sucking the water right out of the boiler, combined with the excessive return water temperature probably flashing as it enters the boiler. Hopefully the feedwater is entering the hartford loop and not being just pumped into the backside somewhere. Do you know if the combination of water capacity of the two new boilers and the condensate pump tank are equal to the capacity of the old boiler. Sometimes replacing a big old boiler with large water capacity and a big steam chest with a new lower water capacity boiler will require the addition of a larger water capacity condensate receiver on the system. Your best bet is to resolve one problem at a time and keep working at it until it starts to react like a steam system. Please let us know how it goes.Best Regards.

Bob W._3

Dan covered something like this in The Lost Art of Steam Heating, probably in the later chapter on controlling the water line. Do you have a copy?

John Goyer

Bob W

No I don't. But I think I will very soon. Thanks for the reply.

John

John Goyer

blackoakbob,

Thanks for the reply. The header was un-insulated in this picture because some work had been done on it. Notice how the stand underneath it have a spacer welded into them. The header was raised to help avoid siphoning. Interesting thought on the water volume of the old boiler. I'll have to look into that. The feedwater does enter into the hartford loop. We've been going at this for 3 years trying to solve one problem at a time. This thing is a moving target. I'll keep this thread updated.

John

Tony Conner_2

Find Your Local...

... Spirax Sarco rep. They at least used to have a video that showed what was going on inside the water space of a running boiler. There were several circumstances in which the water level that showed in the gauge glass was WAY different than the level that was actually IN the boiler. I remember there was a situation in which the low water alarm is ringing-away in the background, yet the gauge glass shows the water level as being just fine, but I don't recall exactly why that was happening. It's an impressive video, even if you're not actually having any problems like this. I've got a copy at home, somewhere, and your problems sounds like a good reason to see if I can find it.

John Goyer

Tony,

I have seen that video. It is very impressive, as you said. We're pretty sure water is getting sucked out of the boiler faster than the feedwater pump can put it back in. I'm guessing the gauge glass, being a much smaller volume compared to the boiler, is showing the high water level because it is seeing a siphoning effect that's pulling the water up into the glass. The problem we're having is finding the reason for the boiler water being pulled out of the boiler. We plan to put HOBO monitoring devices on the feedwater pumps, low water cut-off, and any thing else we can think of and compare that to the data we have available from the demand side to see if we can find a correlation. I'll keep everyone posted and keep those ideas coming.

John

Tony Conner_2

What's...

... the discharge pressure of the feedpump? I see lots of plants with similar problems (the gauge glass thing is weird, though) and often, the feedpump discharge is the same as the operating pressure of the boiler. At any kind of load, there's no pressure differential in the feedwater line to get water into the boiler.

Is there a common pressure transmitter on the header, or does each boiler have it's own? I'll bet each boiler is an independent unit. Are the operating pressures set slightly different on each boiler, so that the second one comes on when the first can't meet the load, then also goes off first when the load drops?

clammy

near boiler piping

Have you check the near boiler pipe sizes to the manafactor suggestion may be your exit velocity is to high and it's siphoning the boiler right out of the boiler ,also have you check the inside of the combustion chamber to make sure that you don't have any flame impingement ? i would check the exiting velocity of the boiler using pipe sizes that where installed there's info about thios in dans steam books just a suiggestion good luck and peace clammy

John Goyer

We recently found that the check valves used in the system were adding tremendous pressure drop so the pumps couldn't keep up because of that. Now pump pressure is running at about 14-16 psig with boiler pressure between 8 and 12 psig. Each boiler has independent pressure control. Simple pressuretrols with boiler on/off, hi/low fire, and hi limit. We've tried running both boilers at the same set points and one at a higher set point than the other as you described with no success.

John Goyer

I just bought Dan's book today. I'll look at this when it comes in. Have a good weekend.

Blackoakbob

Is there alot of noise.....

rattling , popping, etc. when the feed pump runs into the boiler. I had a boiler where the incoming condesate to the hartford loop was too high and made a tremendous amout of noise and it too had a very "active" water line in the gauge glass. So I dropped it to the lowest point suggested by the mfgr and this quieted the incoming water and did calm the gauge glass somewhat. They had been pumping into the waterline in the loop and the "cooler" feedwater was flashing and expanding in there. Best Regards.

blackoakbob_2

What type of check .....

valves are they using as a non-return in the outlet of the boiler to the combined header? I have a concern as to the amount of pressure drop across it and the possible trapping of condensate between the boiler outlet and the check causing water hammer when it opens. I know it's nice to have a non-return valve which prevents the off-line boiler from filling up with condensate but it can be a problem trapping condensate ahead of weighted check valve, or even a swing check, not to mention the pressure drop accross the valve. The water hammer could cause the drip trap on the combined header to fail, ie. a crushed float or collapsed trap vent. Be sure to continue with your very interesting thread. Best Regards.

RAW

Near Boiler Piping

It seems that the two risers off of the boiler are 4" and they tie into a 4" header, that Peerless says should be 6". See pictures that were submitted. That I believe is what Dan refers to as "Near Boiler Piping". Would this be the cause of sucking the water out of the boiler? Would this cause high velocity right at the boiler? Would this installation ever had a chance?

Larry C

Interesting, Do you know what cutoff is shuting burner circuit, I see mm150 and a probe type, is the 150 calling for water on shutoff or you shutting down on probe. Is there an additional cutoff on opposite side of boiler from glass, you may be bending the water line in boiler with all that surging.

You mentioned building used to be h.p., that means piping was much smaller, just a thought

Very important to have the firing rate checked on that Powerflame, does the same problem occur in low fire

Steam Bunny

Might you need a surge column for the Peerless?

I'm just a lurking homeowner and don't have time to think it out or follow the threads- but dug up the following in Dan's section WATER PROBLEMS: THE WATER LINE IS BOUNCING UP AND DOWN IN THE GAUGE GLASS. As it might remotely pertain to your question, here's what he writes: Good luck.


The low-water cutoff needs a surge column.

Do you know about surge columns? It's a Dead Man's piping trick. A surge column can lessen the surging in the gauge glass and the low-water cutoff.
A surge column looks just like a gauge glass, except it's made of pipe, not glass. You build it from two tees, a few nipples, and a short length of steel pipe, which you'll place between the bulls of the two tees. Hook up your low-water cutoff to the runs of the two tees.
The surge column takes up most of the surging, leaving you with a more-stable water line in the low-water cutoff and the gauge glass. A surge column doesn't solve the surging problem, but it can keep the low-water cutoff from bouncing up and down (and on and off) so much.

John Goyer

I think you hit the nail on the head. We finally took our blinders off and realized what was happening. The header will be upsized to a 6" next Wednesday and Thursday. We'll see what happens then.

RAW

Well the change in near boiler piping did not change anything. The size of the header was increased to 6" to try and slow down the exit velocity from the boiler. The second boiler is suspect of carryover also (see attached picture). There is no good way for carryover of water to reenter the equalizer line. Waiting on recommendations from manufacturer. Not sure what effect this has on the second boiler though? We are trying to maintain 9-12psi or as close as possible with purge time and least amount of differental. HELP!!! 4th winter with problems....

RAW

Well the change in near boiler piping did not change anything. The size of the header was increased to 6" to try and slow down the exit velocity from the boiler. The second boiler is suspect of carryover also (see attached picture). There is no good way for carryover of water to reenter the equalizer line. Waiting on recommendations from manufacturer. Not sure what effect this has on the second boiler though? We are trying to maintain 9-12psi or as close as possible with purge time and least amount of differental. HELP!!! 4th winter with problems....

RAW

Well the change in near boiler piping did not change anything. The size of the header was increased to 6" to try and slow down the exit velocity from the boiler. The second boiler is suspect of carryover also (see attached picture). There is no good way for carryover of water to reenter the equalizer line. Waiting on recommendations from manufacturer. Not sure what effect this has on the second boiler though? We are trying to maintain 9-12psi or as close as possible with purge time and least amount of differental. HELP!!! 4th winter with problems....

RAW

Well the change in near boiler piping did not change anything. The size of the header was increased to 6" to try and slow down the exit velocity from the boiler. The second boiler is suspect of carryover also (see attached picture). There is no good way for carryover of water to reenter the equalizer line. Waiting on recommendations from manufacturer. Not sure what effect this has on the second boiler though? We are trying to maintain 9-12psi or as close as possible with purge time and least amount of differental. HELP!!! 4th winter with problems....

RAW

Well the change in near boiler piping did not change anything. The size of the header was increased to 6" to try and slow down the exit velocity from the boiler. The second boiler is suspect of carryover also (see attached picture). There is no good way for carryover of water to reenter the equalizer line. Waiting on recommendations from manufacturer. Not sure what effect this has on the second boiler though? We are trying to maintain 9-12psi or as close as possible with purge time and least amount of differental. HELP!!! 4th winter with problems....

RAW

Well the change in near boiler piping did not change anything. The size of the header was increased to 6" to try and slow down the exit velocity from the boiler. The second boiler is suspect of carryover also (see attached picture). There is no good way for carryover of water to reenter the equalizer line. Waiting on recommendations from manufacturer. Not sure what effect this has on the second boiler though? We are trying to maintain 9-12psi or as close as possible with purge time and least amount of differental. HELP!!! 4th winter with problems....

RAW

Well the change in near boiler piping did not change anything. The size of the header was increased to 6" to try and slow down the exit velocity from the boiler. The second boiler is suspect of carryover also (see attached picture). There is no good way for carryover of water to reenter the equalizer line. Waiting on recommendations from manufacturer. Not sure what effect this has on the second boiler though? We are trying to maintain 9-12psi or as close as possible with purge time and least amount of differental. HELP!!! 4th winter with problems....

RAW

Well the change in near boiler piping did not change anything. The size of the header was increased to 6" to try and slow down the exit velocity from the boiler. The second boiler is suspect of carryover also (see attached picture). There is no good way for carryover of water to reenter the equalizer line. Waiting on recommendations from manufacturer. Not sure what effect this has on the second boiler though? We are trying to maintain 9-12psi or as close as possible with purge time and least amount of differental. HELP!!! 4th winter with problems....

RAW

Another picture for reference.

RAW

Another picture to clarify.

RAW

Another picture to clarify.

RAW

Another picture for clarity

Blackoakbob

Near boiler piping.....

> Another picture for clarity

Blackoakbob

Near boiler piping....

> Another picture for clarity

Blackoakbob

Near boiler piping ....

helps equalize the pressure from top to bottom on the boiler. It's best to make that loop , from the outlet at the top of the boiler, if more than one oulet then all of the outlets should tie together along this loop, then the header should drop down fullsized to a level 2-3 inches below the lowest water level allowed, to that point it may be reduced to the return size and a tee placed to pump in the condesate return water.
Then off the top of this loop, between the last outlet and the drop to the return, the riser to the system header is taken off. This allows the high velocity wet steam leaving the boiler to release the water droplets and allow them to run down the bottom of the loop to the return drop. This gives you drier steam to the header and prevents the loss of heat energy due to wet steam in the header condensing and returning to the condensate tank and wasting energy.
Most manufactuers have a required distance from the normal water line to the bottom of this loop of pipe,ie. 24 -27 inches.
Because the system was high pressure the related piping is smaller than a low pressure system so it is very important to provide dry steam.
I hope looking at some pictures from the mfg and reading this will help it make sense.
Did you ever find a correction for the condensate tank over flowing? Did my suggestion to add a storage tank to hold the condensate 'til the boilers require it make any sense? Please keep us informed. Best Regards

Blackoakbob

I also suggest ...

that you read "drop header in this forum. There is a picture, smaller scale, but the basics are what it's all about. Regards.

Tony Conner_2

The...

...overflowing tanks will likely be due to a combination of condensate returning, and the feedpumps not pulling water out of this tank, and pushing into a boiler that's calling for it. The 190*F water temp in an un-heated feedwater tank would tend to support this.

I'd really look at the feed pumps. I doubt very much that the check valves were the problem. The vast majority of check valve problems stem from them being grossly oversized for the service, and wearing out long before their time. I'd say the pump discharge head is too low, or the pumps have 3-phase motors that are rotating the wrong way. At a guess, I'd say the pump discharge pressure should be something like 20 PSIG to get water into these boilers when they're running at 12.

My brother had a job a few years ago, with exactly these problems. The boiler would trip on low water as soon as the load came up, meanhwile, the feed tank was busy overflowing. Contributing to the problem was that the pump discharge was in "feet", not "PSI". Somebody had figured that 30 feet = 30 PSI. (Uh-oh...) The pump just didn't have enough head to push water into the boiler at anything more than low load. Fortunately, his company didn't design the job, or supply the pumps. The plant owner got to wear that one. Hey, it's just pipe, right...ANYBODY can do it

RAW

This is the second set of pumps

The manufactures rep had us set the discharge at the pump to 19 psi with globe valves to be sure NPSH didn't get low regardless of water temp. We have a high flow, low differental spring loaded Durabala check at both pumps and a swing at each boiler. Pumps are rated 6 gpm and boilers only require right at 3gpm(that is if everything is ok).I've seen the pump curves myself!!!Think I will put an amprobe on them next time water is hot.
We are gonna repipe the 2nd boiler ASAP to try and get some water that may be pulled from that boiler back through the equalizer line (see latest pics). Right now the water is just dragged into the common header (or we believe). Gonna check that in the a.m. and I had a valve put just beyond the trap to check amount of condensate there.

RAW

The tank between the condensate pumps and the feedwater tank was removed 6 months ago. Been there tried that one! I believe the engineers called it a surge tank. We fixed the sectional that first started this forum and now the other boiler has to have the near boiler piping redone (I believe). Then it is on to the mechanical room and the loads if that doesn't take care of it. I tried running pressure lower at one point (3-7) but that seemed not to be enough for the loads (ead dan's take on too much pressure).
I just found the pictures of that drop header and that sparks some thinking.
You say I still need to keep the 24" to the bottom of that drop?