1 HVACR317 – Core for Refrigeration Solenoid Valves Pump Down Systems
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HVACR317 – Core for Refrigeration
Solenoid ValvesPump Down Systems
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Solenoid Valves
• Solenoid Valves are a mechanical/electrical valve. – The mechanical part is in the refrigeration
or water line.– The electrical portion is a coil that is
attached to the top of the valve.
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Solenoid Valves
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Solenoid Valve
• The valve in the closed position is not powered and the flow of liquid is being blocked by the plunger in the DOWN position.
• In the closed position the coil does not produce any magnetic field as it is not powered.
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Solenoid Valve - Closed
Valve is blockingflow of liquid.
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Solenoid Valve - Open
• The valve opens when the coil is powered.
• The coil generates a magnetic field and pulls the plunger into the up position.
• This allows fluid flow through the central passage of the valve.
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Solenoid Valve - Opening
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Solenoid Valve - Open
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Solenoid Valves
• In refrigeration solenoid valves mainly have two uses– Hot Gas By-Pass Defrost– Pump Down Systems
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Pump Down System
• The solenoid in the pump down system is used in the liquid line prior to the metering device and after the receiver.
• The solenoid is in the normally closed position.
• When the thermostat calls for cooling the solenoid opens.
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Pump Down System
• This releases refrigerant into the liquid line and raises the pressure of the system.
• A pressure switch senses this pressure increase and turns on the compressor.
• When the call for cooling is complete the thermostat de-energizes the solenoid
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Pump Down System
• The solenoid closes and blocks the flow of refrigerant into the liquid line.
• The refrigerant gets pumped into the receiver which is mounted after the condenser coil.
• Once the refrigerant is pumped down into the receiver the pressure on the system drops.
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Pump Down System
• Once the pressure has dropped to a pre-determined point the pressure switch opens and shuts off the compressor.
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Pump down system
• The thermostat controls the solenoid - not the compressor.
• The pressure switch controls the compressor.
• The purpose of a pump down system is to prevent liquid refrigerant from migrating to the evaporator on off cycles.
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Pump down system
• If liquid refrigerant is in the evaporator it will be sucked as a liquid into the compressor on start up.
• Liquid refrigerant in the compressor can break valves, crank shafts and cause premature compressor failure.
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Pump Down Systems
• Pump down systems are most often found on commercial freezers and low temp refrigerators. – Low temp systems–Medium temp systems
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Pump Down OFF Cycle
C
MD
CONDENSER
EVAPORATOR
OFF
20100
OFF
`
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Pump Down Starting Cycle
C
MD
CONDENSER
EVAPORATOR
ON
35100
OFF
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Pump Down On Cycle
C
MD
CONDENSER
EVAPORATOR
ON
40150
ON
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Pump Down Satisfied Cycle
C
MD
CONDENSER
EVAPORATOR
OFF
30150
ON
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Pump Down OFF Cycle
C
MD
CONDENSER
EVAPORATOR
OFF
20100
OFF
`
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NSSL1
C
S
R
Setpoint: 35 degrees F. Temp is 55 Degree F.
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Pump Down Schematic