SRL Service Manual
Revision 00
July 2007
Page 17 of 56
Piston Compressor:
SRL
250
Scroll Compressor:
SRL
325 to 6000
3.2.1 The Thermal Mass Concept
The combined air side heat exchanger assembly serves an additional purpose as a “Thermal Mass” –
that is a mass of material with high thermal retention – or the capacity to absorb a significant quantity
of heat without a rapid rise in temperature.
As the heat exchanger assembly absorbs heat from the air, it disperses this heat throughout its mass.
The controls of the SRL dryer monitor the temperature of the heat exchanger, and at reduced heat
loads (i.e. inlet air temperatures or flow rates below the rated maximum), it cycles the refrigerant
compressor on and off to keep the heat exchanger between upper and lower temperature limits.*
The less the heat load in the incoming air, the less heat is transferred to the heat exchanger, the
slower the temperature rises, the less the refrigerant compressor needs to come on, and the lower the
overall power consumption.
* This is a simplified explanation. For full details on cycling operation please refer to Section 8.
3.2.2 Compressor
All models (with the exception of the SRL-250*) are
equipped with compliant scroll refrigerant compressor
with a three phase motor. These compressors are
maintenance-free and installed on vibration damping
mountings.
The compressor reduces the pressure in the evaporator
ensuring the refrigerant evaporates at the correct
pressure (and therefore temperature). It compresses
the evaporated refrigerant and sends it to the
condenser.
The scroll compressor has two spirals (scrolls). One
stays stationary, while the other orbits within it. As this
motion occurs, the pockets between the two spirals are pushed to the centre while simultaneously
being reduced in volume. When the pocket reaches the center of the scroll form, the gas, now at a
high pressure, is discharged.
The SRL-325 to 1400 (60Hz) and SRL-120 to 520 (50Hz) are equipped with thermal overload
protection via a thermo amperometric internal switch. The SRL-1600 to 6000 (60Hz) and SRL-630 to
1800 (50Hz) are equipped with external electronic thermal protection.
Compliant scroll compressors are not damaged by liquid returns, and as such, they do not require pre-
heating upon start-up. They also offer significant advantages in terms of energy savings, reliability,
high efficiency and quiet operation.
* The SRL-250 uses a hermetically sealed piston compressor.
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