User Guide

Page 10 / BULLETIN 10-9
loads for long periods of time, and if slightly higher than nor-
mal superheats can be tolerated at full load conditions.
Distributor Sizing — The proper sizing of the distributor
is extremely important for systems using methods of capac-
ity reduction. The function of the refrigerant distributor is to
evenly distribute refrigerant to a multi-circuited evaporator.
If the distributor cannot perform its function at all load condi-
tions erratic TEV operation can be expected. For the pressure
drop type distributor, the distributor nozzle and tubes must be
checked for proper sizing at both minimum and maximum load
conditions. See Bulletin 20-10 for further information.
Superheat Adjustment — The superheat setting of the
TEV should be set at the highest possible superheat that can
be tolerated at full load conditions. A high superheat setting
will reduce problems associated with mild TEV hunting at
low load conditions. High superheats are more acceptable on
air conditioning systems where the wide temperature differ-
ence between the refrigerant and the air allows the TEV to
operate at higher superheats without a significant loss in
coil capacity.
Evaporator Coil Design — When the evaporator is cir-
cuited to provide counterflow of the refrigerant relative to
the direction of the air flow, superheat will normally have
the least effect on evaporator capacity and suction pressure
fluctuations will be minimized.
Refrigerant velocity inside the evaporator should be high
enough to prevent excessive trapping of liquid refrigerant and
oil, which may cause TEV hunting. Multi-circuited coils should
be designed in such a manner that each circuit is exposed to
the same heat load. Air flow across the coil must be evenly
distributed.
Large capacity air conditioning evaporator coils are often split
into multiple sections so that one or more of these sections
can be shut off for capacity control during part-load operation.
Therefore, a TEV is required to feed each of these sections. The
methods used to split these coils are referred to as: row split,
face split, and interlaced. Generally, TEVs will operate best
on interlaced coils.
Suction Line Piping — Approved methods of suction line
piping including recommended bulb locations and use of traps
are covered in Bulletin 10-11. Where system designers and
manufacturers have tested and approved other methods of
piping, these methods should be used when installing or ser-
vicing their systems.
Sensing Bulb Location — The TEV’s sensing bulb should be
located on a horizontal section of suction line near the evapo-
rator outlet and, in the case of an externally equalized valve,
upstream of the equalizer connection on the suction line. Refer
to Bulletin 10-11 for additional information on bulb location
and installation.
Vapor Free Liquid Refrigerant — Another important
aspect in assuring proper TEV operation is providing
vapor free liquid refrigerant to the inlet of the TEV. Vapor
in the liquid line may severely reduce the capacity of the
TEV hindering proper refrigerant flow to the evaporator.
An adequately sized liquid-to-suction heat exchanger will
help assure vapor free liquid by providing some amount of
subcooling to the liquid. In addition, the heat exchanger pro-
vides an added advantage to the system by vaporizing small
quantities of liquid refrigerant in the suction line before the
liquid reaches the compressor. A Sporlan See•All
®
Moisture-
Liquid Indicator installed near the TEV inlet offers a visual
check for vapor free refrigerant.
Balanced Port TEVs
One of the factors limiting a TEV’s ability to operate at
part-load conditions is a variation in pressure drop across
the TEV during normal system operation due to changes in
head pressure. As previously discussed on Page 3, How The
Thermostatic Expansion Valve Works, pressure drop across
the TEV influences valve operation, particularly with the
larger capacity valves which possess larger port areas. To
counteract the effects of this force Sporlan has incorporated
balanced port design features into selected valve types.
Sporlan introduced this feature in 1946 using a double port
construction on two large capacity valves: the Types T and
W. The Type T valve later became our Type V valve when
the valve design was modified. This double port construction
features a piston which seats against two ports, and signifi-
cantly reduces the effects of pressure drop across the valve.
The refrigerant flow entering these valve types is divided
between the two ports, the force of the refrigerant flow being
transmitted to the midsection of the piston. The force of the
flow heading to the lower port is largely canceled out by the
force of the flow heading to the upper port due to the design
of the piston. A semi-balanced valve is achieved, allowing
the valve to operate at a lower percentage of its rated capac-
ity than a conventionally designed valve.
Sporlan introduced a discharge bypass valve with a fully
balanced design in 1965, the Type ADRHE-6. This design
was later used with the Type O TEV, which was introduced
in 1971.
The Type O valve is designed to eliminate the effects of
pressure drop across the valve. The Type O valve features a
piston which seats against the valve’s single port. See Figure
8. A passageway drilled through the piston allows liquid line
pressure to be transmitted to the bottom side of the piston.
A synthetic cup seal encircling the piston traps this pres-
sure underneath the piston, which causes the force due to
the liquid line pressure on top of the piston to be canceled.
Satisfactory operation down to 25% or lower of rated capac-
ity can be expected with the Type O valve provided that the
aforementioned design recommendations are followed.
Recent efforts by system manufacturers to reduce operating
costs of refrigeration systems by allowing condenser pres-
sures to fall or float with lower ambient temperatures has
created a need for a small capacity TEV with a balanced port
design and superior modulating characteristics. This effort
is particularly apparent with supermarket applications.
Sporlan introduced the Types (E)BF and EBS valves in 1984
to meet this need.
Pin Guide
Seal Cartridge
Pushrod
Pushrod Seal
Piston Assembly
Types (E)BF,
SBF, and EBF
Type O
Figure 8