User Guide

ing the evaporator, which is usually termed hunting or
cycling. The amount of hunting in a system is influenced by
the design of the evaporator coil, suction line piping at the
valve’s sensing bulb location, and the variability of the heat
load on the evaporator. Hunting may cause a reduction in
total system capacity, and a noticeable variation of evapora-
tor pressure on systems having one evaporator. If hunting is
severe, occasional floodback may result.
To help reduce or eliminate valve hunting, many Sporlan
pressure limiting thermostatic charges feature the
FLOWMASTER design introduced by Sporlan in 1948.
This design incorporates a thermal ballast with the charge
to help stabilize valve control.
Originally, it was felt that a highly temperature sensitive
TEV would best be able to reduce hunting. This concept
has proved to be incorrect for the majority of air condition-
ing and heat pump applications and, in fact, it was found
to often aggravate hunting problems. A less temperature
sensitive TEV using specifically designed pressure limiting
thermostatic charges has proven to be the best solution for
these applications.
Type VGA Thermostatic Charge — The VGA charge is
a specially designed pressure limiting charge for R-22 air
conditioning and heat pump applications. The constituents
and thermal ballast used with this thermostatic charge
provide exceptional anti-hunt characteristics, which makes
it the recommended charge for the majority of these applica-
tions. Due to its design, the MOP of the VGA charge is not
as defined as the VCP100 charge, our alternate standard
thermostatic charge for R-22 air conditioning and heat
pump applications. Therefore, if a defined MOP is not
required, the VGA charge may be used in place of the
VCP100 charge.
Maximum operating pressures for standard Sporlan pres-
sure limiting charges are listed in Table 3. The factory air
test pressure represents the valve MOP determined by a
Sporlan air test fixture. The nominal system pressure is the
actual system MOP. If an application requires a pressure
limiting charge with an MOP not shown, contact Sporlan for
assistance.
Due to the design of pressure limiting charges, the valve dia-
phragm and capillary tubing must be kept at a temperature
warmer than the bulb during system operation. Otherwise,
migration of the charge away from the bulb will occur, and
cause loss of valve control.
A properly selected and applied pressure drop type dis-
tributor is effective in preventing charge migration. Figure 7
illustrates how the pressure drop across this type of distribu-
tor keeps the TEV outlet pressure and temperature higher
than the suction gas temperature.
Pressure drop at the refrigerant distributor does not affect
system capacity. The refrigerant distributor simply lowers
the pressure drop across the TEV by a small amount. If the
TEV is properly sized, it will maintain desired superheat
(and system capacity) with the remaining pressure drop
available to the valve.
When applying a TEV and distributor, the two compo-
nents perform together to provide stable system operation.
Application of these components is much more critical on
systems that operate at part-load conditions much of their
operating time, e.g., variable air volume (VAV) systems
and refrigeration systems with compressor unloading. See
Bulletin 20-10 for complete information on refrigerant
distributors.
Refrigeration Applications
Ordinary refrigeration applications may be divided into the
following three categories: commercial refrigeration, low
temperature refrigeration, and extremely low temperature
refrigeration. For each of these categories, Sporlan has
developed a Selective Charge to provide optimum valve per-
formance. These charges are described below.
Type C Charges — The charges listed under the commer-
cial refrigeration section in the Recommended Thermostatic
Charges table on Page 18 are collectively known as C
Charges. These charges are liquid-cross charges and have
an operating range from an evaporating temperature of
50°F to –10°F. Figure 6 illustrates a typical superheat
characteristic curve of the C Charge. For comparison
purposes, the superheat characteristic curve of a straight
liquid charge is also shown. The flatter curve of the C
Charge allows the valve to respond in a more stable man-
ner to changes in evaporator pressure. Depending on the
static superheat requirements, the Type C Charge has been
applied by some manufacturers to display cases operating
at both medium and low temperature.
Types Z and ZP Charges — The charges listed under
the low temperature refrigeration section are the Types Z
and ZP Charges. The Z Charges (FZ, VZ, SZ, RZ, and PZ)
are liquid-cross charges having an operating range from an
evaporating temperature of 0°F to –40°F. A typical super-
heat characteristic curve of the Z Charge is illustrated in
Figure 6. Since the curve slopes upward to the right, the
valve will control at lower superheat values as evaporator
temperature decreases, providing operational advantages for
low temperature refrigeration. This characteristic prevents
Page 8 / BULLETIN 10-9
R-22
196 psig
(100°F)
P
1
= 94 psig
(56°F)
P
2
= 69 psig
(40°F)
66 psig (Superheat to 50°F)
66 psig
(38°F)
tnaregirfeR egrahCcitatsomrehT
-POM igsp
yrotcaF
tseTriA
lanimoN
metsyS
21
06PCF 60 50
PCF 40 30
PZF 20 12
22
001PCV 100 90
AGV
* *
PCV 65 55
04PZV 40 30
a431
06PCJ 60 50
PCJ 40 30
A404
511PCS 115 105
PCS 75 65
PZS 45 35
205
511PCR 115 105
PCR 75 65
PZR 45 35
705 PZP 45 35
* s.noitidnocgnitarepolamronevobA
Figure 7
Table 3