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Vol. 1.2 © 2020 Hanbell Precise Machinery Co., Ltd.
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3. Suction Structure
3.1 Inlet Guide Vanes
The cooling capacity of RTM Series centrifugal compressors is modulated with change in angles of
inlet guide vanes. As illustrated in Figure 3.1, Refrigerant gas from the evaporator outlet flows through
the suction nozzle to the compressor suction inlet. After the inlet nozzle, gas flow velocity increases
due to the narrow passage. By changing angles of IGV, velocity and volume are changed as well as
cooling capacity.
Figure 3.1 Compressor inlet
3.1.1 Control of inlet guide vanes
Angles of inlet guide vanes are automatically controlled through a vane actuator with a lever arm, and
IGV opening ranges from 20% (minimum load) to totally open.
Opening of the vane actuator in percentage (%) has a linear relation to the control signal voltage.
However, cooling capacity does not relate the angle changes of guide vanes. Therefore, vane actuator’s
opening in percentage (%) is not the same as the cooling capacity in percentage (%)
Note 1
：
When inlet guide vanes are completely closed, a small hole will be formed in the middle to
keep a basic amount of gas flow into the compressor.
When inlet guide vanes are fully closed,
only Min. mass flow passes so the smallest cooling capacity will be established.
Note 2
：
The lower pressure ratio stands for the lower minimum unloading capacity.
Actuator
Inlet guide vane
Impeller
Suction
