Steam check valve hammering

TeeSee

Need some advice regarding a two-pipe steam system in a residential two-story Colonial in New England.

Arrived at this home with the steam system hammering the house off its’ foundation. The homeowner could not give me an exact time this started happening, but it had been going on for years. Going through the system, I discovered steam and water pouring out of the steam condensate pump vent and the check valve slamming hard after the pump cycled. Second, the check valve was leaking causing the pump to cycle even when the boiler was cold.

I came back 21 days later to find the VXT I just reset had passed 389 gallons since my first visit! So, new F & T trap innards and a new Hoffman #8 cleared up the steam and water pouring out of the vent pipe. All new Hoffman #4s cleared up the humid basement. Cleaning the mud out of the horizontal pigtail explained why the boiler never cycled. Piped it vertically and now we are running at .5 to 1.5 psi. What a difference…the system is now quiet except for that evil check valve at the condensate pump.

The condensate pump has a 1-inch discharge to the Hartford Loop with a ¾-inch check valve right at the Loop. See attached picture. I thought I would move a new 1-inch check valve to the base of the pump to solve the hammering the check valve produces when the condensate is hot. The check valve does not hammer when the condensate is cold or warm….only 180+ hot. It only hammers for about 30 seconds to a minute after the pump sends water back to the Hartford Loop, then to the boiler. Even moving the check valve to the base of the pump still causes hammering.

I tried this first in an effort to keep costs down, but I figure I need to repipe the pump discharge line to the floor, then up to the Hartford Loop. Right now, as seen in the picture, it comes horizontally out of the Loop, then a few swing joints, over to the receiver, then down to the discharge on the pump. I know the water line is above the Loop and check valve so theoretically both are immersed in water and should keep the steam out of the discharge piping. Now I’m thinking I have flash steam occurring at the Loop because who ever piped the discharge did not go immediately to the floor with a close nipple and elbow at the Loop tee. This would explain the broken check valve. Unfortunately, I cannot prove if the old check valve hammered because it was broken. Also, the new check valve I installed back at the Hartford Loop has a 90-degree seat…the one I took out has a 45-degree seat. Does that matter?

I would appreciate advice from anyone who has run into a similar situation or if someone can confirm my suspicions regarding the horizontal mess of piping from the pump to the Hartford Loop. Being so close to the finish line is aggravating with just one more hurdle to go. Thank you for your help!

Jamie Hall

Puzzles...

After some thought...



I guess my first question would be -- why is there a condensate receiver and pump at all?  In most cases with a residential system, the returns should be fast enough to manage by gravity without needing a reservoir or the extra headroom which such a setup provides.  Have you looked into that?  It occurs to me that it may have been a kludged response to some other problem with the system -- such as excessive pressure or bad traps.



If it turns out that the thing really is necessary for some reason, then the next question is to really be sure that it is the check valve which is rattling, and not a genuine water hammer at the Hartford loop.  That can be a little tricky to figure out.  If it is the check valve, though, you might try substituting a spring type valve; they sometimes close more reliably than a swing check.

TeeSee

Returns

I dismissed the returns because they are less than 30" to the water line and confirmed the need for the condensate pump. Unfortunately, I do not have the exact measurement of the B dimension in my file anymore. I did adjust the pressuretrol to its lowest setting of .5 - diff 1 to meet the B dimension max pressure to inches rule of thumb. This house has always had a condensate pump due to its' low basement ceilings and I am told this is the third boiler and possibly the third or fourth condensate pump since the 1970's. 

I was thinking of a spring check too, but the cost and gamble of installng it with the same failure makes me second guess that avenue. I was wondering if the check valve with a 45 degree seat would do the trick, but again, another gamble.  I'm suspicious of the condensate pump discharge piping connection at the Hartford Loop being the problem. Just looking for someone to confirm this idea. I know something is wrong here because that original 45 degree swing check was worn out and leaking...must have been taking a beating.

Jamie Hall

Argh...

Got to admit I'd have to call someone considerably brighter than I am on this one... sorry!  Where in New England are you?  Maybe one of the guys under Find a Contractor in your state?

JUGHNE

Throttle discharge from pump

Just a guess from reading; if the discharge into the Hartford is throttled down by a plug cock or ball valve maybe the water won't hit the steam.  Pages 171-172. TLAOSH.

nicholas bonham-carter

Check valve

What is the height of the main above the waterline?

If all of the radiator traps are functioning, along with the crossovers, and the pressure is limited to 6 ounces with a vaporstat, then you could go with gravity. Most likely, if the house is of a certain age, the original installation would have been all gravity, so why not return it to its original configuration.

Make some changes in the returns, to bypass the condensate tank, and pump, and see if there isn't some improvement, with a vaporstat.--NBC

nicholas bonham-carter

Moving this post

Probably more steam pros will see this thread if it is moved over to the steam section.--NBC

TeeSee

Ideas

I cannot validate the expense of re-piping the system. The system was running good until just a few years back. New information suggests the system started hammering a bit when the latest condensate pump was installed.

I like the idea of the boiler cock. I'm thinking if I re-pipe the discharge from the condensate pump, I will include this to increase my outflow pressure and slow my makeup water into the Hartford Loop.

I appreciate everyones ideas on this problem. I'm taking NBC's advise and posting it on the steam thread...see you there.

TeeSee

Ideas

I cannot validate the expense of re-piping the system. The system was running good until just a few years back. New information suggests the system started hammering a bit when the latest condensate pump was installed.

I like the idea of the boiler cock. I'm thinking if I re-pipe the discharge from the condensate pump, I will include this to increase my outflow pressure and slow my makeup water into the Hartford Loop.

I appreciate everyones ideas on this problem. I'm taking NBC's advise and posting it on the steam thread...see you there.