Blow Down - how important to do?

elfie

have a 12 section commercial steam boiler



how important is it to do low water cutoff blow downs and main tank blow downs?



can this all be done annually when the boiler is cleaned?  are there any safety or life of boiler concerns by only doing it once per yr?



thanks.

Dave in QCA

MOST Important!

Regular blowdown of your LWCO is probably the most important thing that you MUST do in the operation of a steam boiler.  Most agree that it should be done once per week.  Ideally, it should be done when the boiler is firing so that you can verify that it functions correctly and shuts the burner off. 



In many cases, the LWCO is also the water feeder.  What happens if you don't blow it down?  The float chamber becomes filled with sediment and sludge, over time completely filling in the space under the float.  So, what happens is that the float isn't floating in water anymore, it is setting on a bowl of mud.   When this happenes, the float cannot drop.  That means, that it cannot add water, and it cannot shut the burner off either.  Then, you have a situation called dry firing.  The boiler runs until all of the water is gone.  The building is  not getting any heat, so the boiler just keeps running.  The water feeder and lwco can't function, because the float is setting on that mud.  This is a guaranteed way to crack the boiler, damage much of the other boiler controls and components because of excess heat, cause a fire in the boiler room, and even burn the building down!!!



This is no joking matter.  This is basic steam boiler operation!  Someone needs to be on TOP of this!



Regarding blow down from the main tank.... I'm not sure what you mean.  If you mean from the bottom of the boiler, yes it also needs to be done on a weekly or monthly basis to keep the sediment from accumulating in the bottom of the boiler. 



Blowdowns should be done when the boiler will fire within the hour and bring the boiler back up to boiling temperature so that any O2 in the make-up water will be driven off.

elfie

lwco devices - is an auto water feed device here?

here is pic by steam boiler of the lwco devices



no sure which does what

Dave in QCA

LWCO devices

  It is impossible to say with 100% certainty, because you never know how someone may have wired these up, or how someone else may have altered them... but, this is what it should be.



The LWCO closest to the boiler looks like it is at a slightly higher elevation.  It should be the primary feedwater control, via a feed water pump, and LWCO.  The float is designed to have to different trip levels in the mechanism.  Highest position, nothing - as float drops, activates feedwater pump.  If float drops further, shuts off burner.  The three valves on the side, arranged vertically are called try-cocks.  They are a back up to your site glass.  If the site glass for some reason broke, you would have to shut off the valves above and below the site glass.  The Try cocks give you another methor of checking water level.  The bottom valve should squirt water, the top vavle should squirt steam (if there is pressure), the middle valve may do either, depending on the exact level, which may fluctuate an inch or two.



The LWCO to the right is a single function device, it is a back up. It is at a slightly lower elevation.  If the primary LWCO failed for some reason, and the water level dropped further, this secondary LWCO would shut off the burner.



These should be blown down preferably while the boiler is firing and has is steaming. 

elfie

LWCO device controls condensate return from cond tank?

so the device on left most likely controls activation of pump by condensate tank to allow water to return back to boiler?



and/or does the condensate tank also automatically pump water back to boiler (via float control inside the condensate tank)? - in this case the makeup water line is connected to the condensate tank



maybe its a dual purpose sorta thing.



if the LWCO devices are clogged and dont work does that potentially mean that pump for returning condensate water from the tank may not be activated which could mean the boiler water level would go lower and lower potentially leading to a dry fire situation?

Dave in QCA

Feedwater

A feed-water pump and tank, and condensate receiver tank and pump are not the same thing.  Where is the freshwater added on your system?



Who has operated and maintained this boiler in the past?  Who installed it, how long ago.   These resources should be able to give you reliable instruction on how to operate the boiler.  It sounds like you do not have a good understanding of it, and I believe that it is a dangerous path for you to rely on information from this website to give you that basic education.  We can try.  We can help. We can help you solve problems, but we can't be in the boiler room with you so that we can see the WHOLE set up.  This is a bit complex, in fact, VERY complex.



Every answer that is given on this site comes with an implied, "It all depends" caveat.  It all depends on what else is there, how the system is put together, how it is wired, modified, etc.   Many many factors that we cannot see, and cannot know without the benefit of actually seeing the details of the system



You need to get a professional in there.



While, it is in my nature to try me best to help anyone out.  I am getting concerned that my long distance advice may be depended upon too much, and that since I cannot see the whole system and how it is put together, my advice may be wrong, or at best, incomplete.  



Therefore, I am stepping away from giving further advice.  Please get a professional in there or at least someone that can lead you through the basics of the proper operation of your boiler.   The fact that you asked whether it would be OK to blow down the LWCO once a year indicates that you need to acquire quite a bit of basic education on the operation of your boiler and steam system.  You need to do it before serious damage occurs because of your actions or inaction.

elfie

makeup water line is connected to boiler feed tank

interested in gaining knowledge about how the boiler feed tank returns water to a steam boiler (ie.it appears that condensate/makeup water is returned to boiler based on boiler needs as controlled by a pump controller located by boiler)



and then if the LWCO device acting as a pump controller gets clogged due to not doing a blow down, how risky is this in creating a potential dry fire situation (ie. the pump controller would not return condensate to boiler and this will eventually reduce the water level)



i know its very bad to not do a blow down, I am interested to know consequences of not doing it and thereby learning more about the system



i am learning about systems, not operating systems.

Jamie Hall

Safety circuits...

If the boiler feed pump doesn't run -- for any reason, for example because the feed pump controller wasn't blown down and the float hung up -- then the potential exists for a dry fire situation.  In your situation, it looks as though you had a secondary LWCO which should (emphasis SHOULD) shut off the boiler if the primary one -- the one related to the pump controller -- doesn't work, or the feed pump doesn't run for any other reason.



Belt and braces.  You very much want to check that primary controller -- in your situation, for two things: first, as it is blown down and the float drops, the pump should turn on.  If you blow it down further (you should, once in a while at least) the burner should stop.



You also want to check that secondary controller at least once in a while to make sure that it opens, too, when the water level drops.  This pretty well requirs a continuity test across its terminals -- such as an ohmmeter or somesuch.  That secondary one should have a manual reset -- not automatic -- and, should it ever trip, you want to find out why it tripped before you reset it.