MACS Monthly Newsletter - 2020 - SEP4

* Subcooled liquid enters the TXV at Point
1. The TXV reduces system pressure as it
enters the evaporator at point 2 where the
refrigerant starts to "boil" as it absorbs
heat in the evaporator.
* The TXV regulates the refrigerant flow
to the evaporator at a pre-determined superheat level (valve set point) as the refrigerant leaves the evaporator at point 3.
* "Refrigeration Effect" is the enthalpy
change between points 2 and 3. This enthalpy change (BTU/lb.) times the refrigerant mass flow rate (lbs. /hr.) determines
the system capacity (BTU/hr.) or tons.

to temperature results in movement.
Some might ask, how does this power element do
this? Well, the physics behind this movement of the
power element boils down to the charge and the diaphragm. The charge is what is put into the power element. The charge can be just about any gaseous or
liquid compound, but the physical properties of these
compounds is what we really need to understand.
This charge will react by expanding or contracting
in a manner that is consistent with properties of that
charge. In other words, this charge will expand when
heated and contract when chilled. Without this reaction, there would be no movement.
The diaphragm is what separates the upper hous-

Expansion Valve Operation

Dianetti/Milliman

The expansion valve is constructed of many pieces
and parts, but there are two main components that set
every expansion valve apart. There's the sensing half
of the valve and the operating half of the valve.
The sensing half of the valve has a power element
or charge head which is sometimes referred to as the
brain of the valve. This item is designed to sense the
temperature of the refrigerant flowing from the evaporator back to the compressor. This sensing or reacting

Figure 6: Spring loaded ball seat.

Dianetti/Milliman

When discussing expansion valves, refrigerant flow, evaporator temperatures and
pressures, the term "superheat" is a main
topic. In the expansion valve, superheat
is considered static superheat. See the
"Function of Expansion Devices" section
for more details about superheat.

Figure 5: Internal view of the power element.

September 2020

4

MACS Service Reports



MACS Monthly Newsletter - 2020

Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2020

MACS Monthly Newsletter - 2020 - JAN1
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MACS Monthly Newsletter - 2020 - AUG1
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MACS Monthly Newsletter - 2020 - SEP1
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MACS Monthly Newsletter - 2020 - OCT1
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MACS Monthly Newsletter - 2020 - DEC9
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