2 pipe steam banging

sinbad

I am a plumbing and heating contractor in upstate NY. I occasionally get roped into working on steam systems.

My engineer friend has a house in Pittsburg  with steam heat and the pipes bang loud when its cold outside.



He got me to go to Pittsburg this weekend to see if I could figure out how to fix the problems.



The house is 3 stories plus the basement.  There are 4 radiators on the 1st floor, 4 on the 2nd floor and 3 on the 3rd floor. no radiators in the basement.  Each radiator is approximately 2 ft long, 9" wide and are not cast iron, but look like fin tube radiators( like for a car). Each has 1/4" black ironpipe nipples sticking up on the top side with elbows for the air vents.  The vents are not in great shape.



I suggested we change all air vents to new dole 1a's and replace the 2 hoffman #75 main vents in the basement.  Then I figured when it gets real cold soon, we can set the rad. air vent dials to the different settings to balance the system at that time.



I would like to know if I'm doing this right or not.  Any and all suggestions would be greatly appreciated.



I live @ 6 hours away from Pittsburg,  so This is my farthest service call.  LOL.

So I can't be driving back and forth very much.  That would be very expensive for my friend, but I'd make out like a bandit  !!!



Thanks for the help



Big Dean0

lchmb

first

Is this something new? Has something changed or been changed? Can you get pic's of the close boiler piping to see if there are issues there? Is this a new system or old? Then of course I would suggest you go to the shop to look at some of the great books on steam

http://www.heatinghelp.com/products/Steam-Heating-Books/25/73/A-Pocketful-of-Steam-Problems-With-Solutions 

Here's a good start (and good reading)...

Jamie Hall

Get the books, but wait, there's more...

Ichmb is right -- get hold of the books.  You won't become and instant steam expert, but with patience and some thoughts you'll be well on your way.  And we could use a steam expert or two in western upstate New York!



That said, if it bangs -- really bangs -- what is happening is that somewhere (or somewheres!) water is not able to drain freely and gets caught up in the steam flow, which cheerfully propels the slug of water at speed into the next elbow, T, valve, or what have you down the line.  Causing water hammer.



The cures for this are many and varied, as are the causes.  But while you are waiting for the books -- which go into all this in detail -- in two pipe steam by far the most common cause is a steam line with inadequate pitch, or even sometimes reverse pitch.  All the steam runouts (with rare -- very rare -- exceptions) to the radiators must pitch back towards the steam main, and must exit the steam main from the top, or at the worst from 45 degrees off the top either way.  Almost any other setup is asking for trouble.  The next most common cause is a pipe which has sagged -- often a steam main but sometimes a long runout -- so that there is a low spot in it which can trap water (whang).  There are other causes... think like steam and water: when the steam condenses in the main or runout which it will, every time the system starts, where can the water drain to?  It's got to go somewhere...



Later in the cycle, banging can also be caused by wet steam -- make sure the boiler is piped correctly.



You mention air vents on the radiators.  There should be no need for vents on the radiation in two pipe steam: the steam should enter at a high point, and the condensate (and air) should exit, almost always through a trap, at a low point.  Can you clarify if this really is two pipe and, if so, what the piping on the radiation is like?  Traps?  Inlet and outlet locations?  Valves?  And why are there vents?



Pictures always help...

Steamhead

2-pipe with air vents?

Unless this is an OLD, OLD system, those fin-tube convector air vents don't belong there.



I have a feeling this might be a Trane or other setup where the air goes down the return lines to a central vent in the basement. When this works as designed, you don't need vents at each convector.



Are there traps on the convector return connections? Look up in the basement ceiling, they may be there. Do the return lines in the basement run overhead, and end at a vent in the boiler room?



Have your friend take some pictures of some convectors, the piping underneath them, and the piping around the boiler. Let's take a look at this.

nicholas bonham-carter

Banging 2-pipe system

Probably those 2 Hoffman 75's will not be enough for such a tall system, with long pipes, and much air to vent. What is the operating pressure? Too much can render vents temporally, or permanently inoperative (when polished up, the hoffmans make attractive paperweights,)

Can your friend isolate the location of water-hammer :boiler proper, close system piping, supplies, returns, or radiator .themselves? Often the hammering location will have to be felt with gloves on, rather than simply heard. --NBC