Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
---
title: Expansion Tanks and Air Separators
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# Environmental and Service Conditions {toc}
−## Equipment shall be selected for the actual service fluid, temperature range, and inhibitor package of the installed system, not for water at nominal conditions. The two most common selection errors - ignoring glycol expansion and ignoring the inhibitor's elastomer compatibility - both originate here. {note}
+## Equipment shall be selected for the actual service fluid, temperature range, and inhibitor package of the installed system, not for water at nominal conditions. The two most common selection errors - ignoring glycol expansion and ignoring the inhibitor's elastomer compatibility - both originate here.
## Service Fluid {toc}
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## On large commercial systems a replaceable-bladder tank is usually the lower life-cycle cost: a diaphragm failure on a non-replaceable tank forces a full tank replacement, including draining and re-isolating that leg, while a bladder is changed out in place. This trade-off should drive the type selection on systems large enough to justify the maintenance access. {note}
+## The expansion tank type shall be specified, with the life-cycle maintenance-access trade-off between replaceable and non-replaceable designs governing the selection on larger systems.
+
```datasheet
label: Expansion Tank Type
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### The tank working-pressure rating shall be selected from a standard rating not less than the maximum system operating pressure at the tank elevation.
−## The rating must clear the worst-case pressure the tank will ever see: the static head from the highest water column above the tank plus the maximum fill-valve set point, with margin to the relief-valve setting. Selecting the next standard rating up is normal practice; selecting exactly at the operating pressure leaves no margin for fill-valve drift. {note}
−
```datasheet
label: Tank Working Pressure Rating
…9 unchanged lines
```
+## The rating must clear the worst-case pressure the tank will ever see: the static head from the highest water column above the tank plus the maximum fill-valve set point, with margin to the relief-valve setting. Selecting the next standard rating up is normal practice; selecting exactly at the operating pressure leaves no margin for fill-valve drift. {note}
+
## Acceptance Volume and Sizing {toc}
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### The tank shell shall be carbon steel conforming to ASTM A516 Grade 70 (SA-516-70) unless a different shell material is required by the service fluid.
−### The shell interior shall be lined with an epoxy or phenolic coating, or the shell shall be stainless steel, where required for compatibility with the system fluid and inhibitor.
−
−### The bladder or diaphragm elastomer shall be selected to suit the maximum operating temperature and the inhibitor package.
−
−## EPDM is the general-purpose air-cell elastomer, serviceable to about 240 °F and standard for hot water systems. Butyl is selected for chilled water and other lower-temperature services. A polypropylene-lined air cell is used where the inhibitor package is aggressive enough to attack standard elastomers. {note}
−
```datasheet
label: Tank Shell Material
…6 unchanged lines
```
+### The shell interior shall be lined with an epoxy or phenolic coating, or the shell shall be stainless steel, where required for compatibility with the system fluid and inhibitor.
+
+### The bladder or diaphragm elastomer shall be selected to suit the maximum operating temperature and the inhibitor package.
+
```datasheet
label: Bladder / Diaphragm Elastomer
…6 unchanged lines
```
+## EPDM is the general-purpose air-cell elastomer, serviceable to about 240 °F and standard for hot water systems. Butyl is selected for chilled water and other lower-temperature services. A polypropylene-lined air cell is used where the inhibitor package is aggressive enough to attack standard elastomers. {note}
+
### Any tank or separator that contacts potable water shall be certified to NSF/ANSI 61.
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## Microbubble separators outperform tangential units at capturing the fine bubbles that come out of solution after the initial fill, because they force water through a coalescing medium rather than relying on velocity-driven separation. Combination air-and-dirt units are increasingly preferred on new work because they remove a separate dirt leg and simplify the mechanical-room layout. {note}
+## The air separator type shall be specified, with microbubble capture performance and consolidation of the dirt-separation function informing the selection for the application.
+
```datasheet
label: Air Separator Type
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### The automatic air vent shall be located in a zone that remains above atmospheric pressure at all operating conditions.
−### A high-capacity manual purge vent should be provided for initial fill to expel the large air volume present at first charge.
−
−## A float-type vent only expels air when the water under it is above atmospheric pressure; placed in a sub-atmospheric zone it does the opposite and ingests air through the float seat. Vent placement is therefore inseparable from the location of the separator relative to the pump. {note}
−
```datasheet
label: Automatic Air Vent
…5 unchanged lines
```
+### A high-capacity manual purge vent should be provided for initial fill to expel the large air volume present at first charge.
+
+## A float-type vent only expels air when the water under it is above atmospheric pressure; placed in a sub-atmospheric zone it does the opposite and ingests air through the float seat. Vent placement is therefore inseparable from the location of the separator relative to the pump. {note}
+
# Location and Air-Elimination Train {toc}
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- One replacement automatic air vent per separator type/size
```