metering or expansion devices chapter 24

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  1. The 3 purposes of a capillary tube is to
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    • Regulate the refrigerant flow into the evaporator
    • lower the pressure of the liquid refrigerant
    • lower the boiling point of the refrigerant.
  2. If the power head of the txv valve loses its charge, the ________.
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    refrigerant flow to the coil will stop
  3. If a txv thermal bulb came loose from the suction line at the outlet of the evaporator, what would result.
    • liquid refrigerant would flow back to the compressor
    • the bulb pressure would increase and the txv would open
    • the superheat in the evaporator would decrease
  4. If the thermal bulb assembly develops a leak, what will occur
    The bulb pressure will reduce and the valve will close
  5. Balanced port txv valves are used__________.
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    to feed refrigerant at a normal rate with low condenser entering air temperature.
  6. A txv valve controls refrigerant flow to the evaporator based on___________.
    evaporator suction line superheat.
  7. A refrigerant system is operating with a vapor charge txv. the thermal bulb is sensing a suction line temp that is higher that the temp that allows liquid to be present in the bulb. any additional increases in the evaporator load will __________.
    have no effect on the position of the needle in the seat.
  8. a typical superheat for an evaporator under normal conditions would be_________.
    8 to 12*F
  9. When the load on the evaporator increases, the txv valve_________.
    increases the flow of the refrigerant.
  10. the pressure limiting txv valve does what_____.
    limits the refrigerant flow rate to the compressor capacity.
  11. the primary function of an expansion device is to
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    • regulate the flow of refrigerant into the evaporator
    • produce a reduction in the pressure on the liquid refrigerant
    • lower the boiling point of the refrigerant far enough below the temperature of the load to get the needed heat transfer rate
  12. the txv sensing bulb is mounted to what line, between what
    • suction line.    between the evaporator and the compressor
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  13. the cross liquid bulb at the txv contains fluid that
    has different characteristics from the system fluid
  14. the purpose of an externally equalized txv valve is to
    compensate for excessive evaporator pressure drop
  15. The step motor valve uses a small motor to control the valve's port, which in turn controls evaporator superheat.

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  16. An AXV valve works best when the evaporator load is not constant.

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  17. an automatic expansion valve does use a thermal bulb to help control the amount of refrigerant being fed into the evaporator.

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  18. As the load on an evaporator increases, the automatic expansion valve will close to allow less refrigerant to enter the evaporator.

  19. A capillary tube controls the refrigerant flow into the evaporator by it's size in diameter and the length of the cap tube.

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  20. A refrigerant system that continuously runs under high load conditions(hot pull downs) would most likely use thermostatic expansion valve with charged thermal bulb assembly.

  21. The TXV is one of the dividing points between what?
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    The high side and low side
  22. The TXV maintains a constant_________ in _______.
    • Superheat.
    • Evaporator
  23. What is the only pressure/force that acts to open the txv valve
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    the sensing bulb
  24. Balanced port TXV are used where.

                 5 part answer
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    • where low ambient temp exist
    • head pressure varies widely
    • evaporator loads vary widely
    • large pressure drops across the TXV
    • low liquid line temp exists
  25. Maximum operating pressure (MOP)TXV limit what.
    they limit the pressure to prevent the compressor from overloading
  26. The solid state controlled expansion valve uses a thermistor to do what.
    to monitor the evaporator outlet temp to control refrigerant flow to the evaporator
  27. Electronic expansion valves (EEV) use what for valve movement.
    They use heat motors or step motors for valve movement.
  28. The automatic expansion valve responds how when the load increases
    It will throttle the valve restricting or decreasing refrigerant. (opposite a regular TXV)
  29. What is another term for a fixed bore metering device
    capillary tube expansion device
  30. Capillary tube expansion devices are used in
    small systems
  31. 3 pressures acting on the diaphragm of a TXV.
    • Evaporator pressure
    • Spring pressure
    • Bulb pressure
  32. The four types of charges that the TXV uses to control refrigerant flow  are
    • Liquid charge
    • Cross liquid charge
    • Vapor charge
    • Cross vapor charge
  33. the bulb of the TXV is located at
    Evaporator outlet
Card Set:
metering or expansion devices chapter 24
2015-03-02 03:49:32
txv axv chapter24

the three most popular txv, operating characteristics,chapter 24
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