Expansion Tank Causing Pipe Banging

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  #1  
Old 10-19-18, 03:18 PM
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Expansion Tank Causing Pipe Banging

Good Afternoon, hope all is well...

Last year, I replaced the expansion tank on my gas fired, hot water system. The Boiler is on ground level and I used my bicycle pump to charge the expansion tank to about 20 PSI (there are a total of three stories in my house--Ground floor plus two additional).

Right about the time I installed the new expansion tank, one of my tenants began complaining about loud banging noises. We just began using the heat here in New York this week and my tenant said the 'banging' noise returned.

I believe the expansion tank is the large 30 pound version (Flexcon HTX 30 4.5 gallons).

Unless you think I should do different, I think I will start by lowering the pressure in the expansion tank to 10 or 12 psi.

Also, I haven't bleed the upstairs radiators so I think I will do that also.

Any ideas will be greatly appreciated.

all the best...
 
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Old 10-19-18, 04:46 PM
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I don't know anything about your system - but I suspect that the expansion tank is way to small. In any case, I can't imagine how reducing the air charge in the tank will help. Have you personally witnessed the banging? Do all the tenants hear it, or just the one? Is the banging heard when the there is a call for heat or when the call is over?
 
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Old 10-19-18, 04:59 PM
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t,
For the limited info provided it is hard to diagnose your problem.

What is your cold boiler temp. In a perfect world you want your expansion tank air pressure to match your cold boiler pressure.

Charging your tank to 20 PSI should not cause your pipes to bang. You should be running at 20 PSI anyway for your system.

What type of radiation due you have. CI rads or baseboard. If you have rads you should have no smaller than a #60 extrol tank. Any cast iron radiation be it rads or CI baseboard requires a minimum of a #60 tank.

When you say banging pipes are they actually banging or is it expansion noises when they initially heat up. Do they just make noise at the beginning or all the way through the cycle.

Does your boiler pressure increase greatly as the water heats. This could a sign of an undersized or defective tank.

Hope this helps a little.
 
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Old 10-19-18, 05:15 PM
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Air must have gotten into the system when the new expansion tank was installed.

When bleeding the system you may have to do it a very little at a time since the system pressure (may differ from the expansion tank pressure) must not be allowed to drop to zero on the third floor which probably means not droppping below about 10 PSI in the basement. Add more water, then bleed a little more, than add more water etc.
 
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Old 10-19-18, 05:56 PM
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When bleeding, get your pressure up tp between 25-28 PSI and maintain that pressure while bleeding. When done drain enough water out to get to your preferred running pressure.

Turn everything back on and test for proper operation.

You maintain a high pressure when bleeding so that when you're done the auto feeder cannot feed any cold water into the system to introduce more air.
 
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Old 10-19-18, 06:30 PM
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If a bladder-type expansion tank is partially inflated on the air side, the air pressure will be equal to the water-side, system pressure. If, hypothetically, the water pressure were higher, the air side would be compressed until equilibrium pressure was reached on both sides.

If the bladder is deflated, then, of course, the two pressures could differ. Likewise, if the bladder's air pressure is inflated above the water pressure, the air bladder will be fully inflated, and, again, the two pressures could differ.
 
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