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VERTICAL MOUNTING
SIZE EACH
SECTION FOR
80 EQUIVALENT FT.
SIZE DOWN
MIN 15 DIAMETER
MIN 10 DIAMETER
NOTE: For satisfactory expansion valve control, good thermal
contact between the bulb and suction line is essential. The bulb
should be securely fastened with the two bulb straps, supplied
with each expansion valve, to a clean straight section of the suc-
tion line.
NOTE: On multiple evaporator installations, the piping should be
arranged so that the flow from any valve cannot affect the bulb of
another. Approved piping practices, including the proper use of
traps, ensures individual control for each valve without the influ-
ence of refrigerant and oil flow from other evaporators.
EXTERNAL EQUALIZER CONNECTION
Thermostatic expansion valves with an external equalizer connec-
tion will not work unless the connection is made to the suction
line. The connection should be made at a point close to and direct-
ly downstream of the sensing bulb where the pressure can be prop-
erly sensed. The connection should not be located where a trap is
in the suction line between the sensing bulb and the equalizer con-
nection. If the connection is made on a horizontal section of the
suction line, the connection should be made at the top of the tube.
Equalizer connections on vertical risers should be at least 10 pipe
diameters above the start of the riser.
Most TXVs used on larger evaporators are externally equalized.
This line only provides pressure feed back to the TXV and does
not allow refrigerant flow into the TXV. System pressures will not
equalize through this line. Figure 108 shows good mounting
locations.
If any evaporator pressure or temperature control valves are locat-
ed in the suction line at or near the evaporator outlet, the equalizer
must be connected on the evaporator side of these valves.
OIL RETURN CONNECTION
If the evaporator coil is supplied with an oil return connection at
the bottom of the suction header, this small connection must be
teed in ahead of the first mixing elbow and before the TXV bulb
as shown in Fig. 108. The oil return line should be kept small in
diameter; a 1/4-in. line will suffice in most cases. It is not neces-
sary, when the compressor is below the evaporator, that the riser at
the evaporator extends at least as high as the top level of the evap-
(Preferred Method)
HEADER
COIL
MIN 8 DIAMETER
Fig. 108 — Refrigerant Piping Detail
2 ELBOWS
DROP BELOW
TXV BULB
REMOTE BULB ON SMALL SUCTION LINE
(LESS THAN 7/8 IN.)
orator; after the 15-diameter riser has been provided, the suction
line may elbow down immediately.
Piping loops serve to control oil accumulation in idle coil sections
and prevent off cycle drain back. When the compressor is located
below the evaporator the suction header should be extended above
the highest point of the evaporator circuit before dropping to the
compressor.
EXPANSION VALVE ADJUSTMENT
Each Sporlan TXV is thoroughly tested and set at the factory be-
fore shipment. The factory superheat setting will be correct and no
further adjustment is required for the majority of applications.
How to Determine Superheat Correctly
1. Measure the temperature of the suction line at the bulb
location.
2. Obtain the suction pressure that exists in the suction line
at the bulb location by either of the following methods:
a. If the valve is externally equalized, a gage in the
external equalizer line will indicate the desired
pressure directly and accurately.
b. Read the gage pressure at the suction valve of the
compressor. Add the estimated pressure drop through
the suction line between bulb location and compressor
suction valve to the pressure. The sum of the gage
reading and the estimated pressure drop will equal the
approximate suction line pressure at the bulb.
3. Convert the pressure obtained in Step 2a or 2b above to
saturated evaporator temperature by using a temperature-
pressure chart.
4. Subtract the two temperatures obtained in Steps 1 and 3
— the difference is superheat.
How to Change the Superheat Setting
The valve should be set with the system as near as possible to de-
sign conditions. To reduce the superheat, turn the adjusting stem
counterclockwise. To increase the superheat, turn the adjusting
stem clockwise. When adjusting the valve, make no more than
one turn of the stem at a time and observe the change in superheat
closely to prevent over-shooting the desired setting. As much as
140
HORIZONTAL MOUNTING
EXTERNAL
EQUALIZER
LINE
OIL
RETURN
CONNECTION
BULB MOUNTING
(SEE DETAIL A)
DETAIL A
a39-3971
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