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Steam check valve hammering
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!