Types of Expansion Tanks

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By Taco, Inc.

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Types of Expansion Tanks

  1. 1. Types of Expansion tanks <ul><li>Open </li></ul><ul><li>Closed Tanks </li></ul><ul><ul><li>Plain Steel </li></ul></ul><ul><ul><li>Bladder/Diaphragm (Captive Air) </li></ul></ul>
  2. 2. Open Expansion Tank <ul><li>Water in system in contact with the atmosphere. </li></ul><ul><li>Corrosion problems likely. </li></ul><ul><li>Cannot eliminate air in system. </li></ul><ul><li>Cannot control system pressure. </li></ul><ul><li>Infrequently used today. </li></ul>
  3. 3. Plain Steel Expansion Tank <ul><li>Tank must contain air to provide a “cushion” for expansion and contraction of system fluid. </li></ul><ul><ul><li>Air cannot be eliminated, but is “controlled”. </li></ul></ul><ul><ul><li>Air can be reabsorbed into water. </li></ul></ul><ul><ul><li>Air is left in system to cause problems. </li></ul></ul><ul><li>Air in tank in direct contact with water and tank. </li></ul><ul><ul><li>Potential tank corrosion problems. </li></ul></ul><ul><li>Tank size is larger. </li></ul><ul><li>Possible lower installed costs. </li></ul><ul><li>Higher operating and maintenance costs. </li></ul>
  4. 4. Plain Steel Expansion Tank
  5. 5. Plain Steel Expansion Tank
  6. 6. Bladder Expansion Tank (Full Acceptance Volume) <ul><li>Air for expansion and contraction “cushion” is separated from system fluid by rubber bladder (air is captive). </li></ul><ul><ul><li>Air can be eliminated and system performance improved. </li></ul></ul><ul><li>System water contained inside bladder. </li></ul><ul><ul><li>Tank corrosion problems significantly reduced. </li></ul></ul><ul><li>Reduced tank size over plain steel tank using precharged tank. </li></ul><ul><li>Full acceptance volume minimizes risk of bladder rupture from loss of air charge. </li></ul><ul><li>Lower operating and maintenance costs. </li></ul>
  7. 7. Bladder Expansion Tank (Full Acceptance Volume)
  8. 8. Bladder (Captive Air) Expansion Tank
  9. 9. Bladder Expansion Tank (Partial Acceptance Volume) <ul><li>Air for expansion and contraction “cushion” is separated from system fluid by rubber bladder (air is “captive). </li></ul><ul><ul><li>Air can be eliminated and system performance improved. </li></ul></ul><ul><li>System water contained inside bladder. </li></ul><ul><ul><li>Tank corrosion problems significantly reduced. </li></ul></ul><ul><li>Reduced tank size over plain steel tank using precharged tank. </li></ul><ul><li>Lower operating and maintenance costs. </li></ul>
  10. 10. Bladder Expansion Tank (Partial Acceptance Volume)
  11. 11. Diaphragm Expansion Tank (Partial Acceptance Volume) <ul><li>Air for expansion and contraction “cushion” is separated from system fluid by horizontal rubber diaphragm (air is “captive”). </li></ul><ul><ul><li>Air can be eliminated and system performance improved. </li></ul></ul><ul><ul><li>Tank corrosion problems reduced. </li></ul></ul><ul><li>Reduced tank size over plain steel tank using precharged tank. </li></ul><ul><li>Uses lower cost, but non replaceable, diaphragm. </li></ul><ul><li>Lower operating and maintenance costs. </li></ul>
  12. 12. Diaphragm Expansion Tank (Partial Acceptance Volume)
  13. 13. Bladder/Diaphragm Expansion Tank Sizing <ul><li>Expansion Tank Sizing </li></ul><ul><ul><li>V t =V s (υ 2 /υ 1 )-1)-3αΔt </li></ul></ul><ul><li> P a / P f - P a / P o </li></ul><ul><ul><li>Where </li></ul></ul><ul><ul><ul><li>V t = Expansion tank volume (gal.) </li></ul></ul></ul><ul><ul><ul><li>V s = System volume (gal.) </li></ul></ul></ul><ul><ul><ul><li>υ 1 = specific volume of water at lower temperature ( 0 F) </li></ul></ul></ul><ul><ul><ul><li>υ 2 = specific volume of water at higher temperature ( 0 F) </li></ul></ul></ul><ul><ul><ul><li>Δt = Design operating temperature difference ( 0 F) </li></ul></ul></ul><ul><ul><ul><li>α = Coefficient of liner expansion of pipe material (in/in- 0 F) </li></ul></ul></ul><ul><ul><ul><li>P a = Tank fill pressure (psia) </li></ul></ul></ul><ul><ul><ul><ul><ul><li>For plain steel tank, P a = atmospheric pressure </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>For captive air tank, P a = fill valve setting </li></ul></ul></ul></ul></ul><ul><ul><ul><li>P f = Minimum system operating pressure (fill valve setting, psia) </li></ul></ul></ul><ul><ul><ul><li>P o = Maximum system operating pressure (relief valve setting +/- static height difference, psia) </li></ul></ul></ul>
  14. 14. Bladder/Diaphragm Expansion Tank Sizing <ul><li>Diaphragm/Bladder tank sizing. </li></ul><ul><ul><li>V t = V s (υ 2 /υ 1 )-1)-3αΔt </li></ul></ul><ul><li> P a / P f - P a / P o </li></ul><ul><ul><li>By precharging the tank P a = P f </li></ul></ul><ul><ul><li>Therefore V t =V s (υ 2 /υ 1 )-1)-3αΔt </li></ul></ul><ul><li> 1 - P f / P o </li></ul><ul><li>Captive air tank will be smaller because: </li></ul><ul><ul><li>Tank is precharged to the minimum operating pressure of the system (fill valve setting). </li></ul></ul><ul><ul><li>The air charge is separated from the system fluid by the diaphragm/bladder and increased pressure does not result in a larger volume of air going into solution. </li></ul></ul>
  15. 15. Captive Air vs. Plain Steel Expansion Tank Sizing <ul><li>Captive Air vs. Plain Steel Expansion Tank Size </li></ul>

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