Control System; Temperature Elements, Pressure Transmitters And Indicators; Critical Application Guidelines - Emerson VILTER VSS Installation, Operation And Service Manual

Section 2 • Theory of Operation

Control System

The compressor unit is controlled by the micro-proces-
sor, i.e. Vission 20/20 panel or PLC panel. This panel's
main function is to control the refrigeration system from
the data that it receives from the sensors around the
unit. For additional information, re fer to micro-proces-
sor manual.
Temperature Elements, Pressure
Transmitters and Indicators
Temperature elements (TE), pressure transmitters (PT)
and pressure indicators (PI) are instruments used to
measure temperatures and pressures at specific loca-
tions on the compressor unit. Temperature elements are
typically mounted on the compressor, suction pipe, dis-
charge pipe, oil separator, oil filter inlet and outlet pipe.
Pressure transmitters are typically mounted on the block
and bleed assembly. The pressure transmitters measure
suction pressure, inlet and outlet oil pressure, and dis-
charge pressure in the oil separator. Typically, pressure
indicators are not mounted from the factory, except for
a pressure indicator to show the nitrogen holding charge
for shipping and storage purposes. If required, end us-
ers have the ability to mount pressure indicators at the
block and bleed assembly.
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VSS/VSR/VSM/VSH/VSSH Compressor • Installation, Operation and Service Manual • Emerson • 35391S

Critical Application Guidelines

To ensure the successful operation of the Single Screw
Compressor, the guidelines described below should be
followed.
1. Proper lubrication is critical to the operation of the
single screw compressor. The compressor relies on
the injected oil to absorb and remove the heat of
compression, to seal the compression chambers
formed in the flutes of the screw, and to lubricate all
moving parts. For this reason, it is imperative that the
oil chosen be of correct viscosity, and that sufficient
oil flow be provided at all times, using an auxiliary
oil pump when necessary. The oil chosen must be
compatible with the process gas as well, to prevent
absorption of the gas into the oil, which would dilute
the oil and reduce the viscosity. Also, oil filtration to
25 micron nominal particle size is required to ensure
that only clean oil is injected into the compressor.
For assistance in choosing the correct oil for the ap-
plication and in sizing an auxiliary oil pump, consult a
Vilter representative.
TM
2. Injection oil temperature must be closely controlled
for optimum performance. Oil temperature must be
maintained a minimum of 15 - 20°F above the gas
mixture dew point at anytime to prevent conden-
sation or liquid knockout from occurring within the
compressor.
Note for CO2 and Heat Pump Applications
Because the oil system on the Single Screw
Compressors utilizes discharge gas pressure as the
means to move the injection oil through the system,
it must be remembered that all components of the
oil system are exposed to full discharge pressure
and must be pressure rated accordingly.