12
SS-APG008H-EN
Expansion Valves
Expansion valves meter refrigerant into the evaporator
under controlled conditions. If there is too much refrigerant,
the refrigerant will not completely vaporize and the
remaining liquid will slug the compressor. If there is too little
refrigerant, the system won’t make capacity and there may
not be enough cooling for the compressor.
Note:
Expansion valves are pre-installed on the TWE
product and the superheat has been set properly.
When using air handling units beside the TWE,
, lists expansion valves. Each evaporator distributor
requires a dedicated expansion valve in order to maintain
proper coil distribution. The expansion valve should be
selected to match the capacity of the coil that the distributor
feeds.
Example 1: 10-ton coil (one refrigerant circuit) with two
equal distributors
10 / 2 = 5
Each TXV should be selected for 5 tons. However, care
should be taken to ensure the condensing unit is capable of
operating at these conditions.
Example 2: 10-ton coil (one refrigerant circuit) with two
distributors and a 60/40 coil split
10 x .6 = 6 and 10 x .4 = 4
One TXV should be sized for 6 tons, and one TXV should
be sized for 4 tons. However, care should be taken to
ensure the condensing unit is capable of operating at these
conditions.
If the coil or distributors have a difference of only one circuit
tube, the difference should be ignored.
The proper balance for feeding refrigerant for a TTA/TWA
system is to provide 18°F of superheat— the difference
between the saturated and actual refrigerant temperature
leaving the evaporator. Expansion valve superheat is
preset from the factory, but it isn’t set to 18°F. Use the turns
listed in
to adjust them to the correct 18°F
superheat.
Table 1.
Expansion valves
Sporlan
Standard off-the-shelf nominal valve settings (90 PSIG air test setting)
Field adjust for 18°F
Valve
Superheat, °F
CW turns available
CCW turns available
Superheat change per turn
ERZE
(a)
or RCZE
12
4.5
4.5
2.4°F
2 1/2 CW
OZE
3.4°F
1 3/4 CW
(a)
May also be called BBIZE
