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Expansion tanks

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Expansion Tanks

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Expansion

Tanks

•WHY USE THEM

•TYPES

•LOCATION

•SIZING

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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

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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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