User Guide

BULLETIN 10-9 / Page 15
When a Sporlan TEV is properly selected and applied, the
factory superheat setting will usually provide an operating
superheat in the range of 8 to 12°F. A precise determination
of the valve’s operating superheat from a factory setting is
not possible since factory settings are determined on the
basis of static superheat, and opening superheat of the valve
is influenced by several design factors within the system.
Once the TEV has been placed on the system and set to
the desired operating superheat, however, the valve’s static
superheat can be measured on a test fixture permitting the
desired setting to be duplicated for production runs.
All Sporlan TEVs have reserve capacity in addition to the
capacity shown in the rating tables in Bulletin 10-10. This
reserve capacity should not be considered when selecting a
valve and, in most cases, will not be utilized if the valve is
properly selected and applied. Reserve capacity, however,
is an important and necessary characteristic of any well
designed TEV. Reserve capacity enables the valve to adjust
for a temporary increase in load, periods of low condensing
pressure, and moderate amounts of flash gas in the liquid line.
Valve Setting
All Sporlan TEVs will produce rated capacity at the stan-
dard factory setting. If the valve adjusting stem is turned
clockwise, the additional spring pressure created will
increase static superheat and decrease the valve’s capacity
to a limited degree. Turning the adjusting stem counter-
clockwise will decrease static superheat and increase the
valve’s capacity to a limited degree. Figure 14 illustrates the
effect setting has on valve capacity.
Referring to Gradient Curve A in Figure 14, Capacity C2 is
achieved with a static superheat setting of A and an operat-
ing superheat of C. Turning the adjusting stem clockwise
will increase the static superheat and shift the curve to
the right. This new curve, identified as Gradient Curve B,
shows that valve capacity will decrease to capacity C1 at
the same operating superheat C. Capacity C2 can only be
achieved at the expense of a higher operating superheat
designated as D.
On an operating system where a given valve capacity is
required, any valve adjustment will merely change the
superheat at which the valve is operating.
Evaporator Temperature
The pressure-temperature curves for all refrigerants have
a flatter slope at lower temperatures. Figure 15 illustrates
a P-T curve using R-22 as an example. The P-T curve for a
thermostatic charge will also be flatter at lower tempera-
tures. As a result, a given bulb temperature change causes
a smaller bulb pressure change at lower evaporator tem-
peratures. A given change in superheat will result in less
pressure difference across the valve diaphragm at lower
evaporating temperature causing a reduction in valve open-
ing and valve capacity.
Subcooling
Subcooling is defined as the difference between the refriger-
ant liquid temperature and its saturation temperature. For
example, the amount of subcooling of R-22 liquid at 85°F and
196 psig is calculated as follows:
saturation temperature of R-22 liquid at 196 psig =
100°F subcooling = 100°F - 85°F = 15°F
Adequate subcooling of the refrigerant liquid is necessary
to prevent the formation of liquid line vapor due to pres-
sure losses in the liquid line. Vapor in the liquid line, even
in small quantities, will measurably reduce valve capacity.
Several methods by which liquid line vapor can be prevented
in spite of relatively high liquid line pressure losses are
explained in Bulletin 10-11.
Pressure - psig
Temperature - °F
Refrigerant - 22
Pressure - Temperature
70
10 20 40
30
50
∆ P = 7.1 psi
∆ P = 5.0 psi
5°F
5°F
30
tnaregirfeR
a431,21 25 psi
705,205,A404,22 35 psi
A014 45 psi
)ainommA(717 40 psi
*Average Pressure Drop Across Distributor
Superheat
Valve Capacity
0
B
A & B Static Superheat
C & D Operating Superheat
Capacity C2
Full Open
Capacity
Capacity C1
A
C
D
Gradient Curve - A
Gradient Curve - B
Figure 14
Figure 15
tnaregirfeR
teeF–tfiLlacitreV
02 04 06 08 001
isp–ssoLerusserPcitatS
12 11 22 33 44 55
A404,22 01 02 30 39 49
205,a431 01 02 03 04 50
A014 9 71 62 43 43
705 8 71 52 43 42
)ainommA(717 5 01 51 02 25
Table 8
Table 9
*See Sporlan Bulletin 20-10 for pressure drop data as related to percent loading.