Brochure

Catalog CIC-2003-1/US
Parker Hannifin Corporation
Climate & Industrial Controls Group
Cleveland, OH
165
Service
& Check
Valves
Thermostatic and Constant Pressure (Automatic) Expansion Valves
TXVs & AXVs
Thermostatic Expansion ValvesBalanced Port Valves
Balanced Port Valves
Parker balanced port thermostatic expansion valves
can be applied to a broad range of air conditioning and
refrigeration systems. They exhibit exceptional perfor-
mance over a wide variation in load on a specific sys-
tem, or the same valve can be applied to a large range
of application capacities.
Features of the balanced port valve include:
• Fully balanced port design incorporating a patented
power piston.
• Compensates for wide variations in high to low side
pressure.
• Has sufficient capacity to allow for intermittent flash
gas.
• Compensates for wide variations in evaporator load.
• Compensates for changes in liquid line temperatures.
• Compensates for wide variations in pressure drop
across the thermostatic expansion valve.
Operation
Conventional thermostatic expansion valves respond to
four forces (See the illustration at the right):
Force 1 — Thermal bulb pressure times the diaphragm
effective area. This force acts on the top of
the diaphragm which tends to open the valve.
Force 2 — Evaporator pressure times the diaphragm
effective area. This force acts on the under-
side of the diaphragm. It tends to close
the valve. This force is transmitted to the
diaphragm through the valve body with
internally equalized valves and through the
external connection on externally equalized
valves.
Force 3 — Superheat spring force which assists in
closing the valve.
Force 4 — High and low side pressure differential
times the port area. This differential pres-
sure force tends to open the valve.
Balanced port valves respond to forces (F-1), (F-2) and
(F-3) in a manner similar to conventional valves; how-
ever, they take a unique approach to the (F-4) force
created by high and low side pressure differentials across
the ball and valve orifice. (See figure A.) The area of
the Parker Power Piston
®
is equal to the area of the
port diameter. This force is cancelled out as the piston
force and the force across the port are equal and opposite.
As inlet pressure changes, the (F-4) force changes but
always remain equal and opposite and is cancelled out,
therefore, variations in valve system pressures do not have
any effect on the static superheat setting of the valve.
The change in operation superheat is only affected by
operating changes in load requirements. In contrast,
unbalanced (conventional) valves will also change
operating superheat due to the changes in inlet pres-
sure (F-4). This additional superheat change increases
considerably as the port diameter and valve capacity
increase.
Assuming a port diameter of .250 inches and a high
side pressure change of 100 psi, the change in force
of an unbalanced valve would be (100 x .049) or 4.9
pounds. If the effective area of the diaphragm was 1.00
square inch, the change in evaporator pressure would
be 4.0psig. If this example is applied to high side varia-
tions of 100 to 200 psi, and all common refrigerants
are considered at evaporator temperatures from -20°F
to +40°F, it is possible that the superheat change could
vary 3.5°F to 22°F. This superheat change (not inher-
ent in balanced valves) is in variations in load conditions.
Parker thermostatic expansion valves incorporate the
power piston (balanced port), which has been used
successfully for over 30 years. The balanced port
power element assembly incorporates heavy duty dia-
phragm housings and a high strength stainless steel
flat diaphragm to withstand severe high pressures. The
assembly also includes a “buffer” ring for additional
support and subsequent additional endurance. The flat
steel diaphragm provides a smooth stroke without
“snap.” The rugged stainless steel piston assembly
uses a proven Parker “O” Ring packing compound for
refrigerant use. The element is protected from any sys-
tem contaminants by virtue of the piston seal on the
Parker Power Piston. Additionally, this seal prevents
any leakage from the high to low side of the valve.
In the manufacturing process, secondary operations
are made on Parker valves that places the diaphragm
at a specific position relative to neutral (weld point).
This important manufacturing process insures uniform
diaphragm sensitivity. Through this unique manufactur-
ing process, Parker valves essentially minimize the varia-
tion in superheat change to attain a specific capacity.
Forces that Cause Conventional Thermostatic Expansion
Valves Responses