Hello all. Just want to make sure I understand my expansion tank. I redid my storage piping earlier and at the same time installed a new tank. B&G HFT-40V. I am having some high pressure issues with the new setup. I am getting over 30PSI at high temps. I installed the tank where the SETON w-90 originally had a small tank. Between the fill valve and a T fitting in the return loop to the system pump. There is a ball valve between the tank and pump along with a small drain setup between the tank and shutoff valve. Originally I brought the system up to temp (165) while draining the tank slowly as the pressure was rising. Kept the system PSI to 12. Then I shut off the fill valve supply. After the system cools to around 140 the pressure will drop to 0. Slightly open the fill valve for a few seconds and the pressure will rise to 12. Heat up the system again to 160 and run for a day. Try to heat system to 180 and the psi will rise to 30. I then turn off the ball valve between the pump and tank to drain some water. I only get out about 2-3 gallons before the tank is empty. I can then reopen the ball valve and the PSI will return to 12-15. I would think the tank should be holding around 10-11 gallons when the system has the high pressure. I have been through this procedure several times and still only drain 2-3 gallons when the psi is reading 30.
expansion tank volume
- Thread starter grumpy chief
- Start date
-
Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.
We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.
We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.
- Status
maple1
Minister of Fire
I couldn't follow what you are doing there exactly or how the tank is tied in, but the general procedure (concisely) is:
-Check the air pressure in the tank ('precharge') before you hook the tank up to the system. Typical is 12psi. (I replaced my expansion tank this fall, it came overcharged by 3-4 psi according to the guage I had. I helped replace one on my fathers system just yesterday, it came with no air pressure in it).
-Hook the tank up to the system when the system is cold, keep tank valved off.
-Set your system (water) pressure to desired - typically 12 psi cold.
-Open valve to expansion tank, heat system.
-Check the air pressure in the tank ('precharge') before you hook the tank up to the system. Typical is 12psi. (I replaced my expansion tank this fall, it came overcharged by 3-4 psi according to the guage I had. I helped replace one on my fathers system just yesterday, it came with no air pressure in it).
-Hook the tank up to the system when the system is cold, keep tank valved off.
-Set your system (water) pressure to desired - typically 12 psi cold.
-Open valve to expansion tank, heat system.
Are you sure the tank is sized correctly? Here is an easy to use sizer program.
Also where is the tank tied into the piping? It should be on the inlet side of the pump.
http://westank.com/calculator/
Also where is the tank tied into the piping? It should be on the inlet side of the pump.
http://westank.com/calculator/
stee6043
Minister of Fire
Thanks for the replies, been busy last couple days. 1000 gallons storage. Calculator program shows I am at minimum size as long as storage temp is not allowed to go below 140. Should be bigger but still within range. Main question, simply put (I hope). When system pressure has raised from 12 to 30 and the tank is shut off from main loop, then drained, shouldn't about 10 gallons drain out when the capacity is stated as 11 gallons. 40 gal tank. Tank precharge is 12. Tied in with t fitting about 3 feet before the pump inlet. 5 feet from t fitting to exp tank.
maple1
Minister of Fire
Are you sure about the precharge? Did you measure it with an accurate guage, and with no water pressure on it?
I also think you need more expansion, not near enough there I don't believe. Too late in the day to do calcs...
I also think you need more expansion, not near enough there I don't believe. Too late in the day to do calcs...
stee6043
Minister of Fire
Did you copy the correct model expansion tank? B&G HFT-40V?
According to the brochure that tank has 11.3 gallons of acceptance. Holy crap...you'll never get there. I ran a little overboard with 120 gallons of acceptance on my system but you're still way, way undersized with the amount of water you have in your system.
I can see what you're trying to do by establishing a target min-pressure at 140 degrees with the intent of creating enough headroom to get to your upper limit. You're basically trying to re-zero at 140. I really don't think you're ever going to get there with a tank that small, even with your bleed/reset strategy. What program did you use to tell you that tank is okay to use? With 1,000 gallons of storage plus your boiler and piping you're off on your acceptance volume by a factor of 5X+/- depending on who you listen to.
My two cents only but I'd run that thing without storage until you can get another (larger) tank in there.
According to the brochure that tank has 11.3 gallons of acceptance. Holy crap...you'll never get there. I ran a little overboard with 120 gallons of acceptance on my system but you're still way, way undersized with the amount of water you have in your system.
I can see what you're trying to do by establishing a target min-pressure at 140 degrees with the intent of creating enough headroom to get to your upper limit. You're basically trying to re-zero at 140. I really don't think you're ever going to get there with a tank that small, even with your bleed/reset strategy. What program did you use to tell you that tank is okay to use? With 1,000 gallons of storage plus your boiler and piping you're off on your acceptance volume by a factor of 5X+/- depending on who you listen to.
My two cents only but I'd run that thing without storage until you can get another (larger) tank in there.
Probably used the calculator wrong, Yes it is the hft-40. Yes the PSI was 12 while empty and isolated. You are correct that I tried the zero reset at 140. Before I re-plumbed my storage in Oct I had a homemade expansion tank above the boiler. Used a 30 gal water heater and had a clear 1 in PEX going from the bottom heater element fitting to the top element fitting. Never seemed to get more than 3-4 inch change in water level from low to high temps. Ordered the hft-40 to try and clean up the install. Can reinstall the converted water heater. Still don't know why I was only getting 2-3 gallons out after isolating tank and draining. Thanks for all your responses. Did drain out some air from the precharge though in case the gage is off.
- Status
Similar threads
