Expansion tank failures
Expansion tank failures
(OP)
All,
We've had repeated expansion tank bladder failures in our facility and I need some advice as to where to look for problems. It is a large volume tank (57 gallon, 215 L) on a hot water hydronic system. It is sitting on the floor and connected on the down stream of the hot water boiler and upstream of the pump. It is connected to the bottom drain of the air separator and after the 2nd failure we installed a braided 3/4" hose rather than the 1" line it had originally. It sees 20-30 psi at 200 degrees F. It is rated for 125 psi at 240 F max. It was precharded to 25 psi on the air side. The boiler's relief valve is set at 45 PSI. We've had 4 failures in the last 3 years. This last one lasted 5 months. The bladder looks like a giant hot water bottle and the tears always occur at the "neck". No sharp edges in the tank. The tears appear like the material is stretched to a failing point. One last item, the factory has no answers. It does not appear that the seams are coming undone. Anyone had similar experiences? Any ideas?
We've had repeated expansion tank bladder failures in our facility and I need some advice as to where to look for problems. It is a large volume tank (57 gallon, 215 L) on a hot water hydronic system. It is sitting on the floor and connected on the down stream of the hot water boiler and upstream of the pump. It is connected to the bottom drain of the air separator and after the 2nd failure we installed a braided 3/4" hose rather than the 1" line it had originally. It sees 20-30 psi at 200 degrees F. It is rated for 125 psi at 240 F max. It was precharded to 25 psi on the air side. The boiler's relief valve is set at 45 PSI. We've had 4 failures in the last 3 years. This last one lasted 5 months. The bladder looks like a giant hot water bottle and the tears always occur at the "neck". No sharp edges in the tank. The tears appear like the material is stretched to a failing point. One last item, the factory has no answers. It does not appear that the seams are coming undone. Anyone had similar experiences? Any ideas?





RE: Expansion tank failures
RE: Expansion tank failures
RE: Expansion tank failures
Cheers
Mark Hutton
RE: Expansion tank failures
RE: Expansion tank failures
RE: Expansion tank failures
1) Review your system pressure calc's. Ensure you take into consideration the vertical height of your system (in feet), convert to psi, then add 5 psi to ensure a minimum pressure at the highest point of the system.
2) Check to make sure no one has opened a bypass valve accross the make-up water pressure regulator (if you have one) or that the glycol make-up tank pressure switch/regulator isn't overpressurizing your system. Just becuase the boiler pressure relief valve is set for 45 psi doesn't mean it's actually working (they tend to stick if not excersized occassionally).
3) Change the expansion tank to a "full acceptance" type so the bladder can expand into the full tank volume. It sounds like you have a "limited acceptance" tank, which will not allow the bladder as much expansion.
Good luck.
RE: Expansion tank failures
Jabba
RE: Expansion tank failures
Definitely redo your pressure calcs as russmech suggests.
Did you go out and see your manufcaturer's other installations similar to yours?
Atlas
RE: Expansion tank failures
When the water heats up, it will expand and increase the pressure. The PRV will shut down when the pressure exceeds its set point.The expansion tank bladder will then expand to accomodate the expansion. If the tank is properly sized the operating pressure will be between the fill pressure and the proper relief valve setpoint. The relief valve should be set such that at no point in the piping, allowing for the pump heads, static head and expansion pressure will the piping be subjected to its limit pressure. Usually this is the 125 psig for the expansion tank bladder limitwhile the piping limit is 150 psig. For for safety allowance the RV is set at around 100 psig. If the expansion tank is undersized or if higher pressure (above design PRV setpoint) makeup water is introduced or if the relief valve setting is instead too high the expansion tank bladder may be overstressed.
RE: Expansion tank failures
RE: Expansion tank failures
Thanks for the input. Last week I started checking the size of the tank compared to the system volume. Using one manufacture's work sheet I calculated the size I would need. I've gotten one estimate for a replacement as the present tank came in low, in capacity. I'd like to use this forum as a sounding board, If I may. I have a total system volume of 1642 gallons. What size would I need in a full acceptance tank? Is this the problem? I failed to include the following: There are 2 boilers and they were not installed at the same time, years apart. Aparently the same is true of the some of the heating system. Oh and the present tank's capacity is 57 gallons. I came up with a tank with 140 gallons. I could have added another smaller tank to make up th difference, but the difference in cost was not considerable.
Thoughts?
Thanks,
Teto
RE: Expansion tank failures
Another question: In the worksheet I used, 5 parameters were required. Total system volume, minimum system temperature, maximum system temperature, minimum system pressure at tank and maximum system pressure at tank. All were straight forward. However, what value would be used for minimum system temperature? I found myself considering either makeup water temperature (55 F to 75 F) or the lowest possible temperature (say 100 F), perhaps due to a system failure shutdown.
Any thoughts,
Thanks
Teto
RE: Expansion tank failures
Try to send your concerns to Amtrol, they have very knowlegeable reps in the expansion tank business. I would stay away from any TACO product.
http://www.amtrol.com/
Atlas