Commercial Refrigeration Ch.5
Questions and Answers (Graded
A)
What is the primary function of a metering device? - ANSWER - To provide
refrigerant to the evaporator in a condition essential for efficient heat absorption.
What are two ways the metering device accomplishes its primary function? -
ANSWER - Changes incoming liquid to a spray, and lowers its temperature.
What are two ways the metering device lowers the temperature of refrigerant as it
enters the evaporator? - ANSWER - Drop in pressure and adiabatic expansion, or
flashing off of some liquid
Why is superheat important in a TEV system? - ANSWER - It acts as a margin of
safety to prevent compressor damage due to flooding.
The suction pressure at the outlet of the evaporator is 65 PSIG on an R404 system,
and the temperature of the suction line at the bulb is 35°. What is the superheat? -
ANSWER - 8°
According to TROT, what is the approximate evaporator superheat setting for a
medium temperature walk-in box? - ANSWER - 10°
According to T.R.O.T., what is the approximate evaporator superheat setting for a
walk-in freezer? - ANSWER - 5°
Can you use a pocket thermometer to calculate superheat? Why or why not? -
ANSWER - No, they are not accurate enough for measuring line temperature
If the compressor is 60' from the evaporator, can you use the suction pressure at
the compressor suction valve to calculate evaporator superheat? Why or why not? -
ANSWER - Probably, if you allow for a 2 PSIG pressure drop in the suction line.
, When is the best time to take superheat readings? - ANSWER - When the space
temperature is within 5° of design temperature.
What are the three primary forces on a TEV? - ANSWER - Bulb pressure, evaporator
pressure, and spring pressure
What are the three criteria needed for a TEV to work correctly? - ANSWER - Valve
sized correctly, bulb installed correctly, and complete liquid to the valve.
How do you know if a TEV is flooding? - ANSWER - No superheat
What are the first three things to check if TEV is flooding? - ANSWER - Ice in valve,
bulb sensing properly, and superheat
How do you know if a TEV is starving? - ANSWER - High superheat
What is the only opening force on a TEV? - ANSWER - The sensing bulb pressure.
What is the prime consideration when installing a sweat type TEV? - ANSWER - Not
to overheat the valve.
What type of evaporator will need an externally equalized valve? - ANSWER - Multi-
circuit evaporator with equalizer tube.
Why are externally equalized valves needed on some evaporators? - ANSWER -
Because of the high pressure drop in the distributors.
When adjusting a Sporlan TEV for 2° more superheat, how many turns of the
adjustment stem are needed and in what direction? - ANSWER - Clockwise (in) one
half turn
Questions and Answers (Graded
A)
What is the primary function of a metering device? - ANSWER - To provide
refrigerant to the evaporator in a condition essential for efficient heat absorption.
What are two ways the metering device accomplishes its primary function? -
ANSWER - Changes incoming liquid to a spray, and lowers its temperature.
What are two ways the metering device lowers the temperature of refrigerant as it
enters the evaporator? - ANSWER - Drop in pressure and adiabatic expansion, or
flashing off of some liquid
Why is superheat important in a TEV system? - ANSWER - It acts as a margin of
safety to prevent compressor damage due to flooding.
The suction pressure at the outlet of the evaporator is 65 PSIG on an R404 system,
and the temperature of the suction line at the bulb is 35°. What is the superheat? -
ANSWER - 8°
According to TROT, what is the approximate evaporator superheat setting for a
medium temperature walk-in box? - ANSWER - 10°
According to T.R.O.T., what is the approximate evaporator superheat setting for a
walk-in freezer? - ANSWER - 5°
Can you use a pocket thermometer to calculate superheat? Why or why not? -
ANSWER - No, they are not accurate enough for measuring line temperature
If the compressor is 60' from the evaporator, can you use the suction pressure at
the compressor suction valve to calculate evaporator superheat? Why or why not? -
ANSWER - Probably, if you allow for a 2 PSIG pressure drop in the suction line.
, When is the best time to take superheat readings? - ANSWER - When the space
temperature is within 5° of design temperature.
What are the three primary forces on a TEV? - ANSWER - Bulb pressure, evaporator
pressure, and spring pressure
What are the three criteria needed for a TEV to work correctly? - ANSWER - Valve
sized correctly, bulb installed correctly, and complete liquid to the valve.
How do you know if a TEV is flooding? - ANSWER - No superheat
What are the first three things to check if TEV is flooding? - ANSWER - Ice in valve,
bulb sensing properly, and superheat
How do you know if a TEV is starving? - ANSWER - High superheat
What is the only opening force on a TEV? - ANSWER - The sensing bulb pressure.
What is the prime consideration when installing a sweat type TEV? - ANSWER - Not
to overheat the valve.
What type of evaporator will need an externally equalized valve? - ANSWER - Multi-
circuit evaporator with equalizer tube.
Why are externally equalized valves needed on some evaporators? - ANSWER -
Because of the high pressure drop in the distributors.
When adjusting a Sporlan TEV for 2° more superheat, how many turns of the
adjustment stem are needed and in what direction? - ANSWER - Clockwise (in) one
half turn
