Specifications

28 Catalog WSC/WDC-4
The right side drawing shows the unique McQuay movable discharge geometry. As the capacity
reduces, the movable unloader piston travels inward, reducing the discharge cross section area and
maintaining the refrigerant velocity. This mechanism allows capacity reduction to 10%.
Discharge Line Sound Packages
For extremely sensitive projects, an optional discharge line sound package is offered consisting of
sound insulation installed on the unit’s discharge line. An additional 2 to 4 dbA reduction normally
occurs.
ARI Standard 575 Sound Ratings
Sound data in accordance with ARI Standard 575 for individual units are available from your local
McQuay representative. Due to the large number of component combinations and variety of
applications, sound data is not included in this catalog.
Lubrication System
A separately driven electric oil pump assembly
supplies lubrication at controlled temperature and
pressure to all bearing surfaces and is the source
of hydraulic pressure for the capacity control
system.
The control system will not allow the compressor
to start until oil pressure, at the proper
temperature, is established. It also allows the oil
pump to operate after compressor shutdown to
provide lubrication during coast-down.
Lubricant from the pump is supplied to the
compressor through a water-cooled, brazed-plate
heat exchanger and single or dual five-micron oil
filters internal to the compressor. All bearing
surfaces are pressure lubricated. Drive gears
operate in a controlled lubricant mist atmosphere
that efficiently cools and lubricates them.
Lubricant is made available under pressure from
the compressor oil filter to the unit capacity
control system and is used to position the inlet
guide vanes in response to changes in leaving
chiller water temperature.
If a power failure occurs, an emergency oil reservoir provides adequate lubrication flow under
pressure, and prevents damage that could occur during the coast-down period with the oil pump
stopped.
Since the McQuay chillers are positive pressure, there is no need to change the lubricant or filter
on a regular basis. As with any equipment of this type, an annual oil check is recommended to
evaluate the lubricant condition.
Enhanced Surge Protection (Patent Pending)
ESP Minimizes Compressor Stall/Surge Damage
When centrifugal compressors operate at part load, the volume of refrigerant gas entering the
impeller is reduced. At the reduced flow, the impeller’s capacity to develop the peak load head is
also reduced. At conditions of low refrigerant flow and high compressor head (pressure
difference), stall and/or surge can occur (a stall is gas static in the impeller, a surge condition is
gas rapidly reversing direction through the impeller). A number of things can contribute to this
condition including inadequate maintenance of condenser tube cleanliness, a cooling tower or
control malfunction, unusual ambient temperatures, and others.