Flushing the sludge out of the bottom of a steam boiler.

Don1450

Dan H. talks about adding King valves to the main risers and the returns to isolate steam boilers. He says that you can use them to run the pressure up to 10 PSI and then open the lowest flush valve to remove normal sludge build up. If these are not present in the system then can the sludge still be effectively removed by simple draining??? How often should it be done if you are doing it without the benefit of higher pressure??? What about the added oxygen once you refill? Won't that just cause more rust? Lastly, can you simply increase the pressure of the boiler (temporarily) to achieve high pressure for flushing?

I feel that this is a very confusing topic and I would love to here a definitive answer.

Fred

You don't want to raise the pressure in the system if you can not isolate the boiler. Increasing the pressure to 10PSI or anywhere near that could damage your main vents and your radiiator vents and possibly even open up some leaks. Normally, if the boiler has been in use for a while and is not a new install, just opening the drain valve once a month, during the heating season and draining water until it get clean should suffice. If the boiler has been neglected for a number of years, and you believe there is a significant amount of sludge build up in the boiler, you can shut the boiler down, let it cool, drain it and go in through the skim port, with a wand and clean it that way, with the drain valve open as you are cleaning it. Once cleaned close the drain and the skim port and refill the boiler to its normal water level and fire it up. Bring it to a boil to cook off any excess oxygen from the fresh water.

Adding fresh water on a regular basis is not a good thing but we all have to add water when we blow down our boilers or when some of the water evaporates, or when we do maintenance. It's the nature of the beast. On those occassions, it's necessary and expected and as long as the water is boiled after those activities it has minimal affect on the boiler. Adding water daily, or worse yet, after each heating cycle because of leaks in the system is where you get into trouble.

Unless your boiler is unusually filthy, using the draining valve during a heating cycle (being very careful not to burn yourself) should be suffecient.

Don1450

Thanks. I think I get it now. My boiler was newly installed a few days ago and I tried to do all of my research and direct the installers as to piping changes. I had them follow all of the do's that I collected here and from other online sources, but unfortunately I did not see any info on the isolation valves for boiler blow down until after everything was completed. Your suggestion that I just make sure to drain once a month from here on out sounds like it'll prevent any build up of sludge. More importantly, your advise to immediately boil the water to remove oxygen rectifies what seemed like a contradiction (i.e. drain often, but don't fill often).

Thanks again, you've made things much clearer.

Fred

So this is a new boiler. Hopefully you caught all the details for the near boiler piping and that won't be an issue. Over this Heating season, probably starting in the next week or two, you are going to see the water in the sight glass start to bounce like crazy and it may even push the water level low enough that, if you have an auto water feeder, it may add water and be over filled when the boiler is not heating. Know that that just means you need to skim the boiler to get the oils off of the surface of the boiler water. Of course that means you will be adding water during those skims but, that too is part of the process. It may take several (2, 3, 4 maybe more) skims to get all of the oils out but you will see improvement with each skim. When the water bounce in the glass is around 1/2 to 3/4 inch, you're good. I assume they installed a skim port and full port valve for you. Skimming is a simple but time consuming process and we can give you instructions or guide you to threads on this sight for how it's done if you don't already know.

Don1450

That would be great if you could help with skim instructions. The installers did put in a valve at the skim port and they skimmed it a couple of times at the start up. They'll be back one more time to skim, but I would like to know the procedure and do it a few more times even if its over kill.

nicholas bonham-carter

Do a search here for skimming methods , such as this one:--NBC

Peerless suggests boiling some washing soda during the initial cleaning phase, and then skimming slowly for a few hours. I like the "cold water displacement" method, wherein slowly adding cold water will displace the hot washing soda water and push it out the skimming port. When the water out of the port is tap water cold, you can be pretty sure all the old dirty water is gone.

Fred

I always skim mine right after a heating cycle (maybe 1 or 2 minutes after the boiler has shut down to make sure there is no remaining steam).
1. Turn the power off to the boiler so that it can't come on during the skim process.
2. shut the valve to the auto water feeder off if you have one.
3. Open the skim port valve
4. put a bucket under it and, using the manual water valve ( or water feeder bypass valve) open it and feed water into the boiler until it starts to flow out of the Skim port.
5. Turn the water valve down until the water coming out of the skim port is just a trickle (smaller than the circumference of a pencil, maybe half that circumference)
6. Let it run that way for four to five hours flowing into the bucket. Two buckets work best so that you can empty one while the other collects water. ( Once I have the water adjusted to where I want it, I hook up a garden hose and let it run into a floor drain. That way, I can leave it and do other things for several hours and come back to it. I have even left it skim overnight if the weather permits)
7. After the skim is done, close the skim port, close the manual water valve and use the drain valve on the boiler to lower the water level in the boiler back to its normal level.
8. Turn the power back on as well as the Auto water feeder valve (if you are accustomed to having it on)
Call it a day! If after a week or two, if you see the water in the sight glass is unstable again, repeat the process. Depending on how much piping was changed/replaced, it may take a few weeks for all the oils to return to the boiler.

Don1450

Wow this sounds easy! Since my system is new and I had a lot of new pipe installed do you recommend adding TSP to the boiler and running it for a while before the skimming. If so please advise me as to the details of this.

rrwitherspoon

Do all boilers have skimming port? Where would it be located on boiler? Burnham IN7

Fred

All of them have tappings where a skim port should be installed. Many times installers don't put them in. It should be above the water line and be about 1-1/2 inches in diameter. Burnham uses a 3/4 inch port on some of their boilers but still above the water line. You should see a pipe sticking out of the side or front of the boiler with a full port valve and plug on it or just a cap on the end of the pipe. If the installer skimmed it when he installed the boiler, it should be there (If he actually did a skim). If you don't see that pipe, look for a knock-out in the cabinet panel, above the water line. It is behind that. Look in your owner's manual. it should show thee location.

Fred

Don1450 said:

Wow this sounds easy! Since my system is new and I had a lot of new pipe installed do you recommend adding TSP to the boiler and running it for a while before the skimming. If so please advise me as to the details of this.

TSP is used during the initial cleaning but not for skimming. You don't want the oils diluted or dispersed throughout the water. you want it to stay on the surface where it can slide out of the skim port.

Don1450

Do I do the initial cleaning now before I begin the skimming process or after several skims?

Either way, what is the initial skimming procedure?

Any suggestions would help. Thanks.

Fred

Is this a brand new boiler? The initial cleaning should have been done at that time and the instructions for that is outlined in your owners/installation manual. I outlined the steps for skimming above. Repeated below:

Fred said:

I always skim mine right after a heating cycle (maybe 1 or 2 minutes after the boiler has shut down to make sure there is no remaining steam).
1. Turn the power off to the boiler so that it can't come on during the skim process.
2. shut the valve to the auto water feeder off if you have one.
3. Open the skim port valve
4. put a bucket under it and, using the manual water valve ( or water feeder bypass valve) open it and feed water into the boiler until it starts to flow out of the Skim port.
5. Turn the water valve down until the water coming out of the skim port is just a trickle (smaller than the circumference of a pencil, maybe half that circumference)
6. Let it run that way for four to five hours flowing into the bucket. Two buckets work best so that you can empty one while the other collects water. ( Once I have the water adjusted to where I want it, I hook up a garden hose and let it run into a floor drain. That way, I can leave it and do other things for several hours and come back to it. I have even left it skim overnight if the weather permits)
7. After the skim is done, close the skim port, close the manual water valve and use the drain valve on the boiler to lower the water level in the boiler back to its normal level.
8. Turn the power back on as well as the Auto water feeder valve (if you are accustomed to having it on)
Call it a day! If after a week or two, if you see the water in the sight glass is unstable again, repeat the process. Depending on how much piping was changed/replaced, it may take a few weeks for all the oils to return to the boiler.

Don1450

Thanks Fred for all of your help. The boiler install just happened yesterday and the installers finish up around midnight. We still have to clean and skim, but they, like myself are learning a lot about steam as we go. The install came out great and all of the piping is right to the specifications that are in the manual and online in many places. Since they aren't steam experts I just wanted to get as much clarity about this next phase before we actually begin, which should be within the next few days. I'll check the manual as you suggested.

Thanks again for all of your great advice.