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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.

C1

Pump Down Schematic