7
APP-001f
SEPT 2016
TEMPERATURE SENSORS
There are three temperature sensors on the purger. All
three temperature sensors are type J thermocouples.
a)The evaporator shell temperature sensor is mounted
to the outside of the evaporator shell, and controls
the 3333 EVAP TEMP> 40F (4C) indication. It may be
replaced without pumping-out the purger.
b)The plate heater temperature sensor is mounted in
the bottom plate of the evaporator shell, between the
two electric heaters. It is used to control the heaters
to maintain adequate temperature of the plate when
CONCENTRATING WATER. It may be replaced without
pumping-out the purger, but may be very hot if the
heaters are energized.
c)The liquid temperature sensor measures the temperature
of the liquid inside the evaporator. It is used to indicate
liquid temperature when CONCENTRATING WATER. It
also is used to end the CONCENTRATING WATER cycle
and indicate READY TO DRAIN when the water has
reached the desired temperature. The purger must be
pumped-out to replace it because it is in direct contact
with the ammonia/water solution.
PRESSURE TRANSDUCERS
There are two pressure transducers on the purger. Each
provides a 4-20 mA output proportional to pressure from
30 in-Hg to 285 psig (-1.0 bar to +19.7 bar).
a)The low side pressure transducer measures the pressure
in the evaporator shell. It is used to adjust the set point
temperature to which the ammonia/water solution is
heated if the suction is operating in a vacuum, which
prevents boiling off the water. It also controls the
low-side pressure-assist solenoid valve (F) to maintain
positive pressure for draining water if the suction is in
a vacuum.
b)The high side pressure transducer measures the pressure
in the air separator chamber. It controls the 2222 FOUL
GAS<80 PSI (5 BAR) indication, which prevents the purge
gas solenoid valve (C) from energizing if the purger has
insufficient pressure.
SINGLE POINT LEVEL SENSORS
There are two single point level sensors on the purger,
which operate on the principle of capacitance to determine
whether liquid or gas is present. The level sensor has
a relay contact which is open when the sensor is in gas,
and which closes when the sensor is in liquid ammonia.
Further information may be found in bulletin P105.
a)The liquid make-up level sensor controls the low-
pressure pumped-liquid solenoid valve (B) to maintain
the ammonia level in the evaporator shell.
b)The low liquid level sensor prevents the electric heaters
from energizing if no liquid is present, which protects
the heaters from damage. It also controls the water
purge line solenoid valve (G) while draining water. While
water is draining, the water purge line solenoid valve
(G) will remain energized for 10 seconds after the low
liquid level sensor goes dry, and then will shut.
WATER CONCENTRATION SENSOR
The water concentration sensor measures temperature
and pressure in a single sensor, compares the two, and
outputs a 4-20 mA signal of the water concentration. A
current of 12 mA or less indicates no water. Each mA
above 12 mA is equivalent to 7.5% water concentration.
For example, 13 mA indicates 7.5% water, 14 mA indicates
15% water, and 15 mA indicates 22.5% water.
The maximum range for the water concentration sensor is
20 mA which indicates 60% water. Any water concentration
above 60% is out of range. The APPT display will only
indicate a maximum of 60% water, even if the concentration
is greater than 60%.
The water concentration sensor will only provide an
accurate reading when immersed in liquid. For example,
when the APPT is pumped-out, the water concentration
sensor will indicate 60%, because it senses low pressure
(1 atmosphere) and warm temperature (room temperature),
which would mean a high concentration of water if it were
sensing a liquid ammonia/water solution.
ELECTRIC HEATERS
The APPT has two electric heaters, which are used during
the CONCENTRATING WATER mode. When the purger is
CONCENTRATING WATER, the ammonia/water solution
is heated to evaporate as much ammonia as possible, so
that when the water is released it has as little ammonia
as possible. Each heater is 750 W.
PURGE POINT SOLENOID VALVES
For the customer-supplied purge point solenoid valves,
Hansen recommends our HS8A with close-coupled strainer.
This is a 1/2” port, heavy-duty, pilot-operated solenoid
valve with stainless steel piston. The purge point solenoid
valve must be a minimum of 1/2” port size to avoid excess
pressure drop across the valve.
The standard molded coil is for 115V, (208/230V or 24V
are available). Flange connections available are 1/2”,
3/4”, and 3/8” FPT, socket weld, and weld neck. To order,
specify catalog number HS8A with close coupled strainer,
required connection style and size, and volts. Specify DIN
plug solenoid connection if needed.
Both 115V and 220V models APPT08, APPT16, and APPT24
supply 115V to the purge points.
SECTION 3 COMPONENT DESCRIPTIONS
