Expansion Valves (TXV's)

41. What are the opening and closing forces acting on a thermostatic expansion valve? a. the opening force is evaporator pressure and the closing forces are bulb pressure and superheat spring compression b. the opening force is bulb pressure and the closing forces are evaporator pressure and superheat spring compression c. the opening forces are evaporator pressure and superheat spring compression and the closing force is bulb pressure d. the opening forces are bulb pressure and superheat spring compression and the closing force is evaporator pressure

b

24. Which of the methods listed is most frequently used to control evaporator refrigerant flow rate in a shipboard refrigeration system? a. Direct expansion through a TXV with constant superheat b. Indirect expansion with constant superheat c. Low side float control d. High side float control

a

33. Concerning the proper installation of the sensing bulb of a thermal expansion valve that is attached to the evaporator tail coil on a horizontal run, what statement is true? a. the bulb should be attached so that the pinched off tubing should be oriented down and the capillary tube running to the valve diaghragm should be oriented up b. the bulb should be attached so that the pinched off tubing should be oriented up and the capillary tube running to the valve diaphragm should be oriented down c. the bulb should be attached so that the pinched off tubing should be oriented to one side and the capillary tube running to the valve diaphragm should be oriented to the opposite side d. the bulb should be attached with no regard to the orientation of the pinched off tubing or the capillary tube running to the valve diaphragm

a

34. In a refrigeration system, the thermal expansion valve sensing bulb is properly secured and insulated at what location? a. near the evaporator coil outlet b. near the evaporator coil inlet c. on the liquid line strainer d. at the solenoid valve outlet

a

44. In refrigeration systems with multiple evaporators, the metering of refrigerant to each refrigerated space evaporator is accomplished by what device? a. the king valve b. the individual thermal expansion valves c. the individual box solenoid valves d. the individual back pressure regulating valves

b

50. A thermostatic expansion valve is properly controlling evaporator superheat. Adjusting this valve to lower the evaporator superheat setting will result in which of the following? a. the evaporator pressure will decrease b. the evaporator feed will increase c. the expansion valve will further close d. the expansion valve diaphragm will rupture

b

39. Refrigerant flow through a thermostatic expansion valve is greatest under what conditions? a. when the evaporator has just begun feeding at relatively high box temperature b. just before the evaporator stops feeding at relatively low box temperature c. when the low side and high side pressures are equal d. when the low side pressure and the bulb pressure are equal

a

43. Which of the listed conditions would cause the thermal expansion valve to further open in a refrigeration system? a. a rise in the temperature at the evaporator outlet b. a drop in the condenser cooling water temperature c. a drop in the box temperature d. a drop in the temperature at the evaporator outlet

a

45. In a refrigeration system, what component is installed directly downstream of the thermal expansion valve? a. evaporator coil b. receiver c. compressor d. box solenoid valve

a

63. If the superheat setting of a thermostatic expansion valve is set too low, what would be the result, assuming that the system has a single evaporator? a. the suction line will be abnormally cold and liquid may flood back to the compressor b. the suction line will be abnormally warm due to a reduced amount of refrigerant returning back to the compressor c. the box temperature will be pulled way down below the normal temperature range d. the receiver level will be abnormally high due to a reduced amount of refrigerant returning back to the compressor

a

66. A small obstruction at the thermostatic expansion valve inlet will result in which of the following conditions? a. Lower than normal suction pressure. b. Higher than normal discharge pressure. c. Expansion valves are designed to pass small foreign particles so no adverse condition will occur. d. Ice is the sole cause of this and will soon melt due to superheat; no adverse condition will occur.

a

52. When replacing a thermostatic expansion valve power element, what is true concerning the thermal bulb? a. apply a light film of oil to increase heat transfer b. with steel wool or an abrasive cloth remove oxidation on the bulb and suction line c. apply a heavy coating of grease to function as a heat sink d. carefully coat the device with silicone sealant to reduce the effects of convective cooling

b

69. When a thermostatic expansion valve is installed in a refrigerated container unit, the sensing bulb almost always requires insulation. Why is this so? a. the insulation prevents air stream temperatures from influencing the bulb temperature b. the insulation prevents the bulb from vibrating loose c. the insulation prevents oil entrained in the suction gas from influencing the bulb temperature d. the insulation protects the clamp and screws from corrosion

a

1. In general, the thermal bulb for a thermal expansion valve used in a reciprocating air conditioning system is usually charged with what substance? a. distilled water b. the same refrigerant as the system c. bees wax d. mercuric sulfate

b

2. Flash gas formed in the liquid line of a direct reciprocating air conditioning system may cause what condition? a. pressure at expansion valve inlet to increase b. expansion valve pins and seats to erode c. expansion valve capacity to increase d. pressure difference across the expansion valve to increase

b

25. What is one function of the thermal expansion valve used in a refrigeration system? a. act as a pilot controlling the box solenoid valve b. regulate the amount of refrigerant flow to the evaporator coil c. regulate the water flow to the water-cooled condenser d. turn the compressor off and on

b

29. In a refrigeration system, the pressure within the power element of a thermostatic expansion valve depends directly upon what factor? a. temperature in the box b. temperature of the evaporator coil outlet c. compressor suction pressure d. heat transferred from the saturated liquid in the evaporator

b

31. In a refrigeration system, the bulb for the thermal expansion valve is always located where? a. in the middle of the evaporator coils b. at the evaporator coil outlet c. at the evaporator coil inlet d. at the beginning of the bottom row of the evaporator coils

b

40. A large evaporator coil has been determined to have a pressure drop exceeding 5 psig. How can this be compensated for in maintaining 10° of evaporator superheat as the system requires and avoid starvation of the evaporator? a. adjusting the TXV spring compression and raising the super heat value b. installing an externally equalized TXV a. I only b. II only c. Both I and II d. Neither I nor II

b

49. When a change in superheat setting adjustment to a thermostatic expansion valve is performed, which of the following is true? a. refrigerant must be bled off the sensing line before adjustments are made b. all refrigerant must be pumped into the receiver before adjustments are made c. time must be allowed for conditions to stabilize in the evaporator before further adjustments are made d. all refrigerant must be routed through the dehydrator while changing the superheat setting

c

51. Thermostatic expansion valves can be adjusted for which of the following? a. suction pressure only b. head pressure only c. evaporator superheat only d. suction pressure and box temperature

c

58. A constant hissing sound at the thermal expansion valve will always indicates what condition? a. proper refrigerant control b. a faulty refrigerant control valve c. a lack of refrigerant d. the flow of 100% liquid refrigerant passing to the evaporator

c

6. Rather than design an infinite variety of thermostatic expansion valve sizes to accommodate different capacities for heat removal, some manufacturers use a few standard valve body sizes in conjunction with what other feature? a. an externally adjustable superheat to accommodate different heat removal capacities b. a flexible diaphragm to accommodate different heat removal capacities c. internal needle valve orifices of various sizes to accommodate different heat removal capacities d. internal equalizers to accommodate different heat removal capacities

c

65. If the superheat value of the thermostatic expansion valve is adjusted too high, what would be the result? a. the heat removal capacity of the evaporator will increase b. the evaporator will be overfed with liquid refrigerant c. the suction line of the compressor will be abnormally warm d. the suction line of the compressor will be abnormally cold

c

7. What parameter is the thermostatic expansion valve designed to maintain constant? a. refrigerant flow b. box temperature c. evaporator superheat d. evaporator pressure

c

73. It is necessary to replace the defective thermal expansion valve in a refrigeration system. If the valve is improperly sized, what could be the result? c. starvation of the evaporator coil if the valve is undersized d. constant hunting of the TXV and pressure surging if the valve is oversized a. I only b. II only c. Either I or II d. Neither I nor II

c

74. In a direct expansion type refrigeration system, an externally equalized thermal expansion valve in installed in which of the following situations? a. when the refrigerant pressure drop through the evaporator coil is less than 4 psig b. when the air pressure drop across the evaporator is less than 4" of water column c. when the refrigerant pressure drop through the evaporator coil exceeds 4 psig d. when the air pressure drop across the evaporator exceeds 4" of water column

c

10. Constant superheat is maintained at the evaporator coil outlet of a refrigeration system or unit by the action of what device? a. solenoid valve b. low pressure cutout switch c. king valve d. thermal expansion valve

d

11. In a refrigeration system, the amount of superheat absorbed by the refrigerant flowing through the evaporator coil is adjusted at what device? a. the box solenoid b. the box thermostat c. the low pressure cut-out d. the thermal expansion valve

d

13. What does the thermal expansion valve used in a refrigeration system regulate? a. superheat of the gas leaving the compressor b. back pressure in the evaporator c. temperature in the refrigerated space d. degree of superheat of the gas leaving the evaporator

d

16. Besides the evaporator pressure, the thermal expansion valve reacts directly to changes in what parameter? a. temperature of the space being cooled b. liquid refrigerant pressure at the solenoid valve c. pressure drop across the evaporator coils d. temperature of the evaporator coil outlet

d

26. When a refrigeration compressor is in the 'off' cycle, how will the thermal expansion valve respond? a. it will remain open if the compressor is controlled by a low pressure cutout and evaporator pump down is featured b. it will attempt to control superheat as if the system was still in operation c. it will close if the compressor is controlled by a thermostat and evaporator pump down is not featured d. all the above

d

27. When a refrigeration compressor is in the 'off' cycle, the thermal expansion valve will react in what way? a. it will always open wide regardless of whether or not the system employs a pump down cycle b. it will always completely close regardless of whether or not the system employs a pump down cycle c. it will always remain in the same position just prior to the cycling off of the compressor d. it will continue to function as a result of the net balance of forces acting on the diaphragm

d

28. In the normal operation of a refrigeration system, when the refrigeration compressor cycles "off", the thermal expansion valve will react in what manner? a. immediately open wide b. immediately completely close c. close to a preset minimum opening d. respond according to operating forces acting on the valve

d

32. A thermostatic expansion valve is designed to respond directly to changes in which of the following parameters? a. refrigerated space temperature b. compressor suction pressure c. liquid line temperature d. evaporator superheat

d

36. When the sensing bulb of a thermostatic expansion valve is charged with a fluid different from the charge used in the system, what name of the charge is associated with the power element? a. blended charged b. straight charged c. mixed charged d. cross charged

d

37. Which of the listed statements is a characteristic of the liquid charged power element used with thermostatic expansion valves? a. At the designed operating temperature, the liquid refrigerant charge has changed to a vapor. b. The liquid refrigerant tends to collect at the bellows or diaphragm and reduces the valve sensitivity. c. The sensing bulb is empty of liquid refrigerant charge at the designed operating temperature. d. The sensing bulb is never emptied of liquid refrigerant under normal operating conditions.

d

56. Which of the installation steps listed is necessary for the proper operation of the thermostatic expansion valve? a. Attach the thermal bulb to the suction line using plastic ties. b. Clean off oxidation from the surface of the suction line and sensing bulb with fine abrasive cloth or steel wool. c. Remove excess lengths of the sensing bulb capillary tube from the device to increase sensitivity. d. Heat shrink insulating material around the device once the bulb has been properly secured.

b

59. Which of the problems listed represents the major difficulty encountered with thermal expansion valve operation? a. Lube oil passing through the system. b. Moisture in the system or foreign matter collecting at the valve inlet valve screen.. c. Variable spring tension caused by the changing temperature. d. Frost on the liquid line.

b

62. If a thermostatic expansion valve is adjusted for too low a superheat setting, what will be the result? a. the efficiency of the unit will be increased b. liquid may flood back to the compressor c. the box temperature will decrease causing an expansion of the volume of air d. the refrigeration effect will increase contributing to uncontrolled box temperatures

b

64. If a thermostatic expansion valve is adjusted for too high a superheat value in a TXV controlled single evaporator refrigeration system what will be the result? a. all of the system liquid will flow to and flood the evaporator coil b. an insufficient amount of liquid will be fed to the evaporator c. an excessive amount of liquid will be fed to the evaporator d. only the required amount of refrigerant will enter the evaporator regardless of the required superheat value

b

67. An obstructed expansion valve may be indicated by an incompletely cooled evaporator and what other symptom? a. a higher than normal discharge pressure b. frosting at the evaporator inlet c. a decrease in the amount of frosting across the drier d. frosting at the suction side of the compressor

b

76. Vapor bubbles present in the liquid upon arrival to the thermal expansion valve in a refrigeration system may cause erosion of the expansion valve's needle and seat. This, in turn, could cause what condition? a. TXV overheating b. TXV hunting c. TXV freezing shut d. TXV freezing open

b

12. What is he primary purpose of the thermostatic expansion valves in a typical multi-box shipboard refrigeration system? a. they control the individual refrigerated space temperatures b. they regulate the compressor suction pressure c. they regulate the amount of refrigerant superheat leaving the individual evaporators d. they control the refrigerant temperature entering the individual evaporators

c

14. What is the primary purpose of the thermostatic expansion valve as used in most refrigeration plants? a. regulate the box temperature b. ensure that liquid refrigerant returning to the compressor has the proper superheat c. maintain a constant degree of superheat at the evaporator coil outlet d. maintain constant evaporator coil pressure independent of suction pressure variations

c

15. What will remain constant during operation when a properly adjusted thermostatic expansion valve exhibits stable operation without any appreciable hunting of the valve? a. condenser sub cooling b. liquid line sub cooling c. evaporator outlet superheat d. compressor discharge gas superheat

c

30. In multi-box refrigeration systems, the sensing bulb of the thermostatic expansion valves used on the refrigerated boxes with elevated temperatures should be located where? a. in the diffuser fan inlet air stream b. in the diffuser fan outlet air stream c. before the back pressure regulating valve d. after the back pressure regulating valve

c

42. The thermostatic expansion valve in a refrigeration system further opens when the diaphragm flexes downward. With all other conditions being the same, what single condition causes this? a. an increase in the evaporator pressure b. a decrease in sensing bulb temperature c. an increase in sensing bulb temperature d. increasing the superheat setting of the valve

c

46. A thermal expansion valve installed in a refrigeration system is controlled by the action of what device? a. the box solenoid valve operating coil b. the compressor unloader mechanism c. the TEV sensing bulb mounted on the evaporator tail coil d. the receiver level controller

c

38. A typical shipboard domestic multi-box refrigeration system operates with one compressor and condenser. What is the purpose of the sensing line connected to the thermal bulb at the evaporator coil outlet? a. To open or close the solenoid valve when the box temperature increases or decreases. b. To open the back-pressure regulating valve when evaporator coil pressure increases. c. To direct evaporator outlet pressure to the lower part of the solenoid bellows. d. To transmit the bulb pressure (proportional to the coil temperature) to the thermal expansion valve diaphragm.

d

53. If the evaporator coil horizontal return line of a container refrigeration system is less than 0.875" (2.21 cm) in diameter (considered small), the thermostatic expansion valve sensing bulb should be attached where on the return line? a. on the bottom of the line to enable the bulb to absorb the maximum amount of heat b. as close as possible to the expansion valve c. directly below the point of maximum heat transfer d. on the upper surface of the line

d

54. Expansion valve maintenance should include which of the following procedures? a. Cleaning of in-line strainers as necessary. b. Ensuring that the thermal bulb is in good contact with the suction line and insulated. c. Checking that the thermal bulb is in the proper location. d. All of the above.

d

55. Which statement about calibrating a newly installed thermostatic expansion valve is correct? a. The procedure requires a refrigeration wrench and a digital thermometer to measure box temperature. b. No special tools are required as long as the solid state circuit control panels are functioning properly. c. This procedure is done at the factory with tools not available to a mariner. d. An accurate thermometer and suction pressure gage are essential to this process.

d

57. If the thermal bulb of an expansion valve is incorrectly placed at the center of the evaporator coil instead of the end (tail coil), it will have which of the following effects? a. increase the heat removal capacity of the evaporator coil b. increase the superheat present at the bulb location c. deliver more refrigerant to the evaporator coil d. decrease the heat removal capacity of the evaporator coil

d

61. Which of the following statements describes the accepted method for testing a thermostatic expansion valve? a. Heat the bulb by using a halide torch or similar device and observe the valve stem movement. b. Remove the power head from the unit, heat the bulb with a torch while using a scale to measure the distance the diaphragm has moved. c. Chill the bulb in ice water while observing the compressor for an increase in suction pressure. d. Place the sensing bulb in ice water and then warm by hand. Observe flood-through and temperature change at the suction line.

d

68. What maintenance may be carried out on a thermostatic expansion valve? a. The thermal bulb may be recharged. b. The rate action may be increased. c. The proportional action may be varied. d. The inlet screen may be cleaned.

d

75. Which of the problems listed could cause erosion of the expansion valve needle and seat? a. Overcharging the system with refrigerant b. Faulty compressor suction valve operation c. Failure of the high pressure cutout d. Flash gas formation in the liquid line

d