New water hammer on old boiler

Bravajo

Hoping someone can help. I have a Weil-MClain SGO-4 that we installed 20 years ago. It is running a single pipe steam system with in-wall convectors. It has run well and QUIETLY for the past 20 years until this heating season.

The whole system, but in particular one radiator, is banging like crazy whenever the heat comes up. It is both violent and persistent. As far as I can tell it does this until the air vent closes in the farthest radiator and then it quiets for the remainder of that heat cycle.

I changed some air vents and the main line vents thinking that could be the problem but no dice. I have noticed the sight glass water dips lower than normal when making steam than it had before but returns to normal height after the boiler shuts off.

A few recent changes; 1) the burner had some ignition problem causing soot and fouling and my service company came and cleaned the combustion chamber and performed annual maintenance. 2) in October I had the hot water coil that sits inside the boiler replaced due to corrosion.

It seems like a high pressure problem but my boiler's steam pressure gauge is broken/frozen so I am replacing that today to diagnose if my pressuretrol is malfunctioning or clogged. The switch in the pressuretrol definitely cuts the burner when tripped but I am not sure what pressure it is tripping at.

The only other thing I can come up with in my research is skimming but I am afraid of breaking something when removing the 1 1/2" cast iron plug that's been in place for 20 years.

Am I on the right track? Any other suggestions? What is overfiring?

ethicalpaul

The two causes that I would suspect are:

1. They added some water treatment to your boiler without telling you and now the boiler is surging and the boiler water is getting thrown into your mains during the firing cycle (could also be caused by oil introduced by parts replacement)

2. Something changed in your venting and/or pressure control systems that is causing high boiler pressure during firing and the boiler is pushing its water out the "back" into the condensate return and up to the mains that way. You mentioned this possibility and a new low pressure gauge can rule this out/confirm it.

Just for fun, can we see a photo of your boiler and its near piping, taken from about 10 feet away showing from the floor up to the ceiling?

Skimming can't hurt, they might have introduced some oil into the boiler with the coil change. If we see the picture maybe there's an alternate skim point other than the presumably stubborn plug.

JUGHNE

Has the control pigtail been cleaned all the way back to the boiler connection/opening?

Bravajo

Thanks guys for the comments/ideas. I have attached two pictures here so you'll have more context.

A couple of notes; 1) I am replacing the PSI gauge and removing and cleaning the pigtail this evening. 2) The pigtail is tapped into the top of the LWCO housing.

Question, is that big plug in the center of the boiler that is above the burner the skim port?

ethicalpaul

Yes, that would be a good place to skim from. Nice and high, and a large port. I would keep it that size, run an elbow and then a nipple and a full-port valve all heading horizontally to the right to clear all your front panel stuff.

Your boiler piping looks good, so i'm sure you'll be able to get it back to operating silently and nicely.

You might need a big cheater on that plug. On the bright side, it appears to stand proud of the boiler jacket so you may be able to get a nice big wrench on it.

Nice pin btw

Bravajo

ethicalpaul said:

Nice pin btw

Thanks!

Bravajo

I replaced the pressure gauge and watched it for a heating cycle.

It looks like the pressuretrol is cutting out at 3 psi and cutting back in at 2 psi. Sounds a little bit high from what I have been reading. I imagine if I could set it any lower the boiler would cycle a lot more. I am not sure if that is something I should focus on.

This heating cycle did not create a bunch of water hammer which is also a bit strange. I did lower the water in the sight glass a bit before it ran to the line marked on the boiler jacket.

ethicalpaul

Lowering the water level could definitely reduce boiler water carryover into the main, which could definitely reduce hammer.

3psi is indeed too high. Lower the pressuretrol if you can but beware lowering it so much that the spring separates internally.

The pressuretrols seemingly always are calibrated too high from the factory but you should be able to get it to cut out at 2psi

Yes it will cycle more but that's preferable to running 3psi. Those higher pressures are just wasted fuel anyway.

You said you replaced your main venting? Are they working well?

Bravajo

ethicalpaul said:

You said you replaced your main venting? Are they working well?

They seem to be. They are hoffmans and they are releasing the air and closing properly on steam. Might be a little slower than ideal. Any other way to diagnose them?

I was able to take the pressuretrol down a bit to the bottom of the travel. I'll track the low pressure gauge and see if we achieved a cut-out at 2psi.

EBEBRATT-Ed

@Bravajo

The water in you bucket looks a bit nasty. I would drain the boiler, then refill it then boil the boiler out with TSP and then skim the hell out of it.

If you can't get the big plug out try one of the (3/4"?) plugs to the right. It won't skim as well but if you trickle the water in slow enough it will work

ethicalpaul

The main vents sound ok per your description. Does pressure start rising some time after the main vents close?

how long after steam production starts does it take for pressure to start rising?

Bravajo

EBEBRATT-Ed said:

@Bravajo

The water in you bucket looks a bit nasty. I would drain the boiler, then refill it then boil the boiler out with TSP and then skim the hell out of it.

If you can't get the big plug out try one of the (3/4"?) plugs to the right. It won't skim as well but if you trickle the water in slow enough it will work

Thanks for the feedback. The bucket had some sediment at the bottom before flushing the LWCO but generally flushing the LWCO is a bit nasty like that.

I'll work on the TSP and skim as soon as I get the monster plug out.

Bravajo

ethicalpaul said:

The main vents sound ok per your description. Does pressure start rising some time after the main vents close?

how long after steam production starts does it take for pressure to start rising?

Pressure didn't start rising until quite a bit after the main vents closed. I assume that is the time required for the steam to rise up all the piping and through the radiators to close the air vents.

I would say no less than 10 mins after the main vents closed the pressure rose but I will time it next time.

BobC

The oil on the coil may have introduced enough oils to induce the banging. Drain and refill the boiler a couple of times and see if that quiets it down, if it does the filthy water is the problem.

The quiet will only last a cycle or two before coming back and then you'll have to go on to tsp and skimming. On a boiler that old it may take a big impact wrench to get that plug out.

Bob

ethicalpaul

Pressure didn't start rising until quite a bit after the main vents closed. I assume that is the time required for the steam to rise up all the piping and through the radiators to close the air vents.

I would say no less than 10 mins after the main vents closed the pressure rose but I will time it next time.

Yes, sounds good. I wanted to make sure the pressure wasn't building immediately which would indicate your main venting wasn't...venting.

Bravajo

ethicalpaul said:

Yes, sounds good. I wanted to make sure the pressure wasn't building immediately which would indicate your main venting wasn't...venting.

I was checking my two main runs in the basement, they are the same length. The rear run came-up to temp much quicker than the front run due to the venting capacity of the different vents. I am replacing the front main vent with the same as the rear one so they vent at the same rate.

Bravajo

A general follow-up: The biggest change that I made was lowering the water level in the boiler by about an inch on the sight glass. I previously (many years) ran it at the higher level but with the new found water hammer thought lowering it might help.

I also lowered the pressuretrol to its lowest setting but it had a very small impact on max pressure (maybe 1/2 PSI).

Between these two changes the hammer has been reduced by 75%. Not completely gone, but close.

I think this coming week I'll skim the boiler and/or TSP. I suspect that cutting oil introduced when retapping some of the studs for the hot water coil may be the culprit.

STEAM DOCTOR

@Bravajo. Did service company increase the firing rate of the boiler. In a certain sense,  just cleaning out the soot will effectively change the steaming rate. More of the heat from the fire will end up inside the boiler water. 

Bravajo

STEAM DOCTOR said:

@Bravajo. Did service company increase the firing rate of the boiler. In a certain sense,  just cleaning out the soot will effectively change the steaming rate. More of the heat from the fire will end up inside the boiler water. 

they did brush out the boiler and clean-up the flue. It was fouled from the improper combustion which led to the service call.

They didn't mention increasing the firing rate but they did spend more time than normal on the tune-up. I was wondering the same thing; if they made the flame hotter and it is generating too much steam, too quickly.

I am pretty friendly with the owner over there. I can ask him. Is there any way to gauge the firing rate?

tomsloancamp

I’m curious where is the location of your radiator that has the issues? If it were caused by oil (mixing with condensation to cause banging), would you
have banging elsewhere like the mains? 

nicholas bonham-carter

Search for “clocking the gas meter” on here.—NBC

Bravajo

tomsloancamp said:

I’m curious where is the location of your radiator that has the issues? If it were caused by oil (mixing with condensation to cause banging), would you
have banging elsewhere like the mains? 

The most prevalent radiator was the one furthest from the burner. it was the one with the loudest and longest duration.

Other radiators and mains and risers were also hammering but either for a shorter duration or less noisy.

Bravajo

nicholas bonham-carter said:

Search for “clocking the gas meter” on here.—NBC

would this apply to an oil burner or just natural gas?

EBEBRATT-Ed

@Bravajo

Clocking the meter is only for gas. Lowering the water level reduced the water hammer......that's your clue to the fix which is skimming. Not that there couldn't be another issue like a sagging pipe. Sometimes (most of the time with my luck) problems are additive. If you have a problem you look for 1 fix and it takes 3 to fix it

TSP use 1 lb of TSP/50 gallons of boiler water...so the SGO-4 holds 12.5 gallons so 1/4lb of TSP

Bravajo

@EBEBRATT-Ed Thanks!!

I think it is a skimming issue with some other things combining in. I don't think I have a sagging pipe.

Time to get the big cheater bar.