Brochure

Parker Hannifin Corporation
Climate & Industrial Controls Group
Cleveland, OH
Catalog CIC-2003-1/US
Thermostatic and Constant Pressure (Automatic) Expansion Valves
166
Valve Selection Procedure Thermostatic Expansion Valves
Valve Selection Procedure
1. Determine application information.
It is important to obtain specific system information
in order to choose the correct valve for a particular
application. Listing this information will aid in making
choices such as capacity, charge, and fitting configura-
tion which will result in the best possible valve choice
for the application.
• System refrigerant. Determine what refrigerant will
be used in the system.
• Evaporator load or system capacity. Determine
the design system capacity.
• Evaporator operating temperature/pressure.
Determine the design evaporator temperature and
pressure.
Evaporator temperature is usually speci-
fied, or can be calculated by subtracting the “TD”
temperature from the desired environment control
temperature. Evaporator pressure can be deter-
mined by looking up the associated saturation
pressure for the known evaporator temperature in
a refrigerant table.
• Evaporator pressure drop, distributor pressure
drop. Determine any pressure drop which will occur
after the refrigerant exits the valve, such as distribu-
tor pressure drop and evaporator pressure drop.
• Condenser operating pressure/liquid tempera-
ture. Determine the condenser pressure and liquid
temperature. The liquid temperature can be deter-
mined directly or by subtracting a desired subcooling
amount from the condenser design temperature.
When determining the liquid pressure, consider any
factors which may affect the pressure entering the
valve; such as friction losses, vertical lift, and pres-
sure drop across system components such as
dryers, sight glasses, and other valves.
2. Determine the required nominal capacity and
charge for the valve.
A.Evaporator temperature
B. Pressure Drop
C. Design System Tonnage
D. Valve Type
Refrigerant
20 ft. 6 m 40 ft. 12 m 60 ft. 18 m
R-12 11 0.75 23 1.6 33 2.3
R-22 10 0.69 20 1.4 30 2.1
R-502 10 0.69 21 1.4 31 2.1
R-134a 10 0.69 20 1.4 30 2.1
R-404A 8.5 0.59 17 1.2 25 1.7
Vertical Lift Pressure Drop
• Connection configuration (fitting types, sizes,
orientations.) Determine what style connections are
best suited for the application, SAE flare or ODF
copper.
• Valve adjustment requirements (adjustable,
non-adjustable.) Determine whether or not field
adjustment is required.
• Bypass bleed requirements. Determine if the
system requires equalization of high and low side
pressures due to compressor starting limitations.
Contact the factory if this is necessary.
Liquid Line Temp. 70°F 80°F 90°F 100°F 110°F 120°F 130°F 140°F
Multiplier R-22 1.21 1.11 1.07 1.00 0.93 0.87 0.81 0.71
Selection of nominal capacity
• Find the correct capacity table. Refer to capacity
table section and find the correct page for the
system refrigerant in either English or metric units.
• Find the correct evaporator temperature section
for the application based on the design evaporator
temperature.
• Determine the pressure drop available across
the expansion valve. Deduct the evaporator
pressure from the condenser pressure, then deduct
pressure losses due to distributors, vertical lift,
strainers, other valves, dryers in liquid line, and any
significant friction losses in the evaporator and
condenser refrigerant lines.
• Find correct pressure drop column.
• Find a capacity selection in that column which
most closely matches the desired system capacity.
The usable capacity published in the table repre-
sents the valve’s nominal capacity at a specific
condition. The system design capacity at that same
condition should be at least 50% of, but not more
than 10% over the selected valve’s capacity.
• Determine the correct type and capacity valve.
Read across to the leftmost columns which describe
the model(s) and nominal capacity which will be
best for the application.
• Correct table capacity for liquid line (subcooling)
temperature. Subcooling will normally increase
both system and valve capacities. Subcooling will
also increase the density of the liquid refrigerant,
increase the enthalpy difference across the evapora-
tor and prevent flash gas at the metering device.
Flash gas severely reduces the refrigerant flow
through the valve orifice, decreasing valve capacity
and increasing operating superheat. Correct the
system design capacity for liquid line temperature
with the liquid temperature correction table located
on that page.