Unit 9: Refrigeration Flashcards
Capillary Tubes
Is the simplest of all metering devices. Its basically a very thin tube that creates resistance to flow which creates a pressure drop along its length. This pressure drop allows refrigerant to flow from the condenser to the evaporator and maintain the right amount of cooling in the system. Used on small refrigeration units only that do no require modulating cooling.
Sectional Evaporators
Can increase or decrease cooling by adding or removing an evaporator section into service to meet load demands
Evaporator Dampers
Can vary the amount of air passing over an evaporator
Cylinder Unloading (Reciprocating Compressors)
Simply removes one of the compressors of a system out of duty to reduce cooling out put
Cylinder Bypass ((Reciprocating Compressors))
Allows one or move compressor cylinders to be bypassed reducing the cooling capacity in half if 2 compressors are used.
Centrifugal Compressor Capacity Control
Unlike Reciprocating Compressors on refrigeration systems, Dynamic or Centrifugal Compressors can vary cooling more directly through motor control or suction control.
Variable Position Slide Valves
Used on screw compressors to control capacity. Generally, these solenoid valves can vary the amount of refrigerant that is sucked into the compressor. They do this by feeding back or discharging some of this suction back into the suction line.
Does CSA B52 Require permanently installed pressure gauges on any refrigeration system?
No, none are required by the standard
Refrigeration Oil Separators
Oil is used in the crankcase of the compressor to keep the pistons lubricated. Since the oil used is miscible with the refrigerant generally being used it must be separated. This is done in a surge tank or accumulator while the refrigerant is in a vapor state. The accumulator must be kept warm enough to prevent condensation of the refrigerant. This often requires the accumulator to be placed next to the compressor and be protected from air drafts. The oil drops to the bottom of the accumulator and the refrigerant vapor rises to the compressor inlet. This oil is then drained and re-enters the crankcase of the compressor. This oil must have a high flash temperature and not produce carbon deposits.
Filter-Drier
Is used to remove moisture from liquid refrigerant. If this moisture is not removed from the system it will cause ice build-up at the metering device and corrosion.
Sight Glass
Used to detect moisture levels present in liquid refrigerant lines. Special chemicals that change colors in the presence of moisture will display a chemical dot that changes from green to yellow under the sight glass.
Ammonia Piping Materials
Only Approved Steel listed in ASME b31.5 can be used. No copper or copper alloys
Liquid Receiver and Vapor Space Gauge Glasses
Both the liquid and vapor spaces on refrigeration systems will have a gauge glass to see the level of refrigerant in the system. If the gauge glass breaks there is a steel ball that will prevent refrigerant from escaping. Also the gauge glass is made from reflex glass that are clear in color but use prismatic action to indicate the presence of clear liquids as black.
Pressure Relief Valves used in refrigeration systems are required when?
The vessel contains liquid refrigerant, has a gross volume exceeding .085m^3 or the vessel can be isolated by valves
These pressure relief valves must be replaced or recertified every 5 years
They do not allow the pressure in the vessel from rising more than 10% above the setting of the pressure relief device.
Emergency Discharge Systems
Is used to discharge refrigerants rapidly into the atmosphere in the case of a fire or emergency. Must be installed on horizontal pipe, in a glass fronted box painted red, and put on the outside of the building. Must be also placed 2.3 meters above the ground to prevent tampering.
