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3 Expansion
Tanks
•WHY USE THEM
•TYPES
•LOCATION
•SIZING

4 Expansion
Tanks
•WHY USE THEM?

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Effect of Temperature Change
Low Temperature Condition
Air Charge
System Fluid
High Temperature Condition
Air Charge
System Fluid
Water is incompressible
It expands when heated
System
If the volume of the system cannot change, pressure will increase
System

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Types of Tanks
•Standard Compression Tank
• Diaphragm Tank
• Bladder Tank

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Expansion Tank Types
Gas
Water
System
Compression Tank
Charging
Connection
System
Charging
Connection
Gas
Gas
Bladder
Diaphragm
Water
System
Diaphragm
Tank
Bladder
Tank
(Larger Systems)

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Standard Compression Tank
System Connection

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Standard Tank Fitting
Air • Purpose: Separates air bubbles from the system liquid at the boiler.
• Prevents free air from spreading into the system.
• Still found in older, larger volume boilers.
Air
Water

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Boiler
P
NOTE: No auto air vents!
Or, valved off if used

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Diaphragm Tank
System Connection
Air Charge
What happens if air charge is lost?

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Air Charge
Bladder Tank
System Connection
Replaceable bladder

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Effect of the “net expansion”
Absorbs the net thermal expansion, V
1
– V
2
, keeps the system within the “allowable pressure rise” band.
Cold Warming Design
Temperature
1
P
1
V
2
P
2
V

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Compression or Diaphragm
Tanks?
Compression
• Water and air in contact
• May be larger, heavier
• Require tank fittings
• Rarely require repair
• Low initial cost
• Difficult initial set up
• Seismic Considerations
Diaphragm/Bladder
• Impermeable barrier
• Probably smaller
• Require vents and thermal loop
• Repair difficult or impossible
• Higher initial cost

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Location:
At the POINT OF NO PRESSURE CHANGE

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Closed Loop System

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Closed Loop System

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Closed Loop System
12 PSI
Point of no pressure change
12 PSI

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Closed Loop System
12 PSI
Point of no pressure change
Pump
14 PSID
12 PSI

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Closed Loop System
12 PSI
Point of no pressure change
Pump decreases pressure here to -2 PSI
12 PSI
14 PSID across system

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Closed Loop System
12 PSI
Point of no pressure change
Pump
14 PSID
12 PSI
Pump increases pressure here to 26 PSI

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Closed Loop System
12 PSI
Point of no pressure change
Pump
14 PSID
19 PSI
12 PSI
5 PSI

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Closed Loop System
12 PSI Air Charge
12 PSI
12 PSI

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System Components
Cold Water
Supply
Reducing
Valve
High Capacity Air Vent
To Pump
Suction
By-Pass with
Globe Valve
Rolairtrol
Air Separator
Blowdown
From System
Bladder Tank

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Expansion Tanks
System
Tank
Drain

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Expansion Tank Sizing
• Required Data:
– Total System Water Content (Volume)
– Average Design Water Temperature
– Minimum Fill Pressure
– Maximum Operating Pressure (usually 10% below relief valve )

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Expansion Tank Sizing
Example #1:
1200 Gallon System
12 PSI Fill
180 F Temperature
75 PSI Relief Valve
5 Gallons in Boiler

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Expansion Tank Sizing
Example #1:
• Required Data:
– Total System Water Content (Volume)
• 1205 Gallons
– Average Design Water Temperature
• 50 o F heated to 180 o F
– Minimum Fill Pressure
• 12 PSI Fill
– Maximum Operating Pressure (usually 10% below relief valve )
• 65 PSI

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Expansion Tank Sizing
Calculation
Volume x (Net Water Expansion Factor) = Gallons
Expanded
Gallons Expanded / (Acceptance Factor) = Total Gallons
Gallons Expanded = Acceptance Volume
Total Gallons = Total Tank Volume

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Expansion Tank Sizing
50F heated to 180 F
Calculation
1205 X 0.02757= 33.22
gals expanded
33.22
gals expanded
/ 0.665 = 49.95 gals
12psi fill and 65psi maximum operating pressure

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Expansion Tank Sizing
Calculation
1205 X .02757 = 33.22 Acceptance Volume
33.22 / .665 = 49.95 Total Tank Volume

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