Expansion tank quizz
The purpose of adding an expanion vessel to a closed loop system is to "accept" the increase in volume as the fluid is heated and it expands. As the fluid warms, expands, it pushes an amount of that expanded water into the expansion tank/ vessel.
If I had the tank on a closed loop system, started a circulator capable of adding 15 psi to that 15 psi static fill, what would the gauge at the tank show? Would the pressure be the same if the circulator was pumping at or way from the tank?
With this tank precharged to 15 psi, on the air side. What will happen to the pressure, on the air valve, when I put 25 psi water pressure on the tank inlet nipple?
trainer for Caleffi NA
Living the hydronic dream
Comments

You're asking us? You're the guru!
But you sort of cheat on the first question — since you kind of give the answer. The pressure at the tank inlet is responsive only to changes in the volume of fluid in the closed loop system (assuming the pressure doesn't drop so low that the diaphragm or bladder doesn't bottom out). Hence the happy abbreviation "PONPC".
The second question is a little iffy — but assuming that the tank really was precharged to psi, which is 30 psia, when you raise the pressure on the water side — assuming the diaphragm or bladder doesn't do something evil — the prssure on the air side has to rise, too. So it will rise to the 40 psia and the air will compress to three fourths of the original volume (P1*V1 = P2*V2).
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 
The tank is charged to 15 psi. That is a T style 3 port ball valve, so the tank is open to the gauge in this pic.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 

I will keep my closed system with 54+ gallons of water,Internal Air Separator,Airtrol valve,and 15 gallon steel compression tank as the old method of pressure control continues to work well as it was designed to do thanks to gas law, fluid dynamics, thermal dynamics, the dead men and Dan Holohan.
Thanks anyway.
😘
2 
The purpose of adding an expanion vessel to a closed loop system is to "accept" the increase in volume as the fluid is heated and it expands. As the fluid warms, expands, it pushes an amount of that expanded water into the expansion tank/ vessel
.If I had the tank on a closed loop system, started a circulator capable of adding 15 psi to that 15 psi static fill, what would the gauge at the tank show?
15 PSIWould the pressure be the same if the circulator was pumping at or way from the tank?
SAMEWith this tank precharged to 15 psi, on the air side. What will happen to the pressure, on the air valve, when I put 25 psi water pressure on the tank inlet nipple?
It will read the same as the water pressure on the water side (25PSI)because that additional 10 PSI pressure added to the water side wil compress the air as it accepts the increase in water volume.Remember the PONPC paper by Gil Carlison?
You can send my prise to the address you have on file Bob.
Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics1
Categories
 121.3K All Categories
 84K THE MAIN WALL
 2.9K AC, Heat Pumps & Refrigeration
 53 Biomass
 417 Carbon Monoxide Awareness
 40 Chimneys & Flues
 1.7K Domestic Hot Water
 4.7K Gas Heating
 119 Geothermal
 155 IndoorAir Quality
 3K Oil Heating
 56 Pipe Deterioration
 771 Plumbing
 5.4K Radiant Heating
 362 Solar
 14K Strictly Steam
 3K Thermostats and Controls
 51 Water Quality
 38 Industry Classes
 73 Job Opportunities
 17 Recall Announcements