auto feed system - necessary?

elfie

if you have a large commercial boiler, is there a need for an auto feed tank?  what are risks if you have one and it doesn't work.



lots of residential steam boilers dont have an auto feed system



seems there may be a problem is you dont have an auto feed system 



what happens if there is a leak without an auto feed system and the low water cutoff device does not work?  could this lead to a dry fire situation?

RJ_4

combination

Many cities require redundant low water cutoffs on commercial boilers one of them being a lwco feed valve combination.  ex. ( mcdonnell miller # 51 ).  Yes a boiler could dry fire if any lwco is neglected.  Mc Miller recommends blowing down the lwco weekly.   I found when doing boiler P/M 's that if customer could do it themselves every 2 wks that was good.  I would clean or replace the strainer basket every 3 months and completely clean entire unit yearly especially the bowl float assy.

will smith_4

can you clarify

What do you mean by an auto feed tank?

If yours is a system with a vacuum return/feed pump, you'd ideally need a receiver along with it. The feed pump on the vacuum tank will pump condensate out as soon as it's float switch rises-if it just goes straight to the boiler, I can pretty much guarantee you'll end up with a flooded boiler, because that float doesn't care what's going on in the boiler. If it pumps into a receiver, the pump/s on it will be controlled by the boiler's controller-and will only feed when needed.

If a tank/pump isn't working, your controls should bring in fresh water to make up-and also shut off the burner if that fails.  Depending on your code, you may have two LWCOs for added safety. It's always possible both could fail. If you EVER can't see water in the gage glass, shut off the water feed, shut off power to the boiler, and call for service. If you feed water to a boiler that was in a low water condition and still firing, the results could be catastrophic.

Some pics would help us identify exactly what you've got.

 

Dave in QCA

Feed water tank?

Elfie, if you have not already purchased "The Lost Art of Steam Heating", you should.  It will be very valuable to you and I think will help give you a basic understanding of a steam system and its components.  Read all of Chapter 11 on condensate and feedwater tanks and pumps.   Once you have read that, you should read the whole book.  When you're finished, read it again.  Then read it once more just for good measure.  You need to get a better handle on the basics.  I am quite alarmed by your lack of understanding of your system as indicated by the questions you ask.  As the old adage goes, "There is no such thing as a stupid question."  But, I'll add to that, "except for a question that is asked when you already know the answer but are hoping someone will give you wrong answer that might justify a bad plan of action."

.......As you know, the feedwater tank collects the condensate from the system.  The feedwater pump returns it to the boiler on call from water from the boiler.  If the feedwater tank water level gets too low, fresh makeup water is added to the tank.



If this unit is not working, how is the water going to get back to the boiler?



If the feedwater pump runs while the tank is dry, it will ruin the seals in the pump.  If the boiler is not able to get water, the LWCO will shut off the burner.  If the LWCO fails, the boiler will dry fire.   If the boiler dry fires, it could get so hot that it starts the building on fire, it could explode of water suddenly returns for some reason.  Either one of the above situations could kill people.



Residential gravity return systems are different. The condensate returns to the boiler without a pump.  Residential systems may have an auto feed setup for adding makeup water to the system.  Some don't.  But, the boiler is fine as long as no condensate is lost and as long as someone routinely checks the water gauge.

jumper

redunancy

Redundant low water shut offs is a good idea. Inexpensive insurance. So is an alarm.

elfie

Dave in QCA

thanks for the feedback



some I work with are not concerned about the safety steam boiler ops  if the LWCO devices are not working and the autofeed system is not working.



when i speak to some so called steam experts, they say that human safety is not much of a concern for low pressure boilers due to high pressure limit shut off and pressure relief valve controls.



your comments convey a more serious risk when a dry fire situation occurs.  i respect the views.



further, i hope to get 'lost art of steam boilers' book - the author is amazing.



 further, i was seeking clarification on safety issues when a dry fire situation occurs.  we have a commercial boiler firm and when the annual service contract was canceled to save money, they didnt come back and say  'hey, you guys are crazy if you dont clean the lwco devices and test key safety controls on system'.  the feeling was that if its NG, its ok to skip a yr.  maybe for a hot water boiler it might be ok, but not for a steam boiler.



i was hoping for info that would help me to convince parties of the need to do service. 

thanks for your comments and support

Madcap_Magician

Safety first...

I'm a boiler operator in MN where we take this kind of thing very seriously.



If that boiler dry fires or if you even suspect it has been dry fired it needs to be shut down immediately and inspected before it's put back into service. If you find that the LWCO and autofeed systems are not working properly and the boiler has been firing you need to shut that boiler down. Unless of course it's under the continuous supervision by a boiler operator until the autofeed and or LWCO is fixed.



Your former service company is not going to say anything. They probably assume you have either hired someone else or are competent enough to service the boiler yourself.



If your boiler is dry firing and some goon adds water it will flash to steam. Water expands 1600 times when it turns to steam. The pressure controls and safety valves on the boiler are not going to do anything in that situation. At that point you'll be getting a new boiler system, new management, and some new co-workers to replace the ones maimed by hot water and flying steel. Sorry for being graphic but this is very serious.



Couple questions for you. What state are you in? Can the boiler feed water to itself and maintain a proper water level automatically without the day tank? How large is this boiler system (horsepower, BTU ratings, or sq ft. of heating surface)?

ChrisJ

explosion

Madcap, I believe this was due to a damaged LWCO.



http://youtu.be/1WoA2mxtSHU