Refrigeration Metering Devices and Capacity Controls

Question 1

The most widely used refrigerant control that has a thermal power element consisting of a bellows or a diaphragm chamber connected to a temperature sensing bulb by means of a small capillary tube is a/an:

A) Thermostatic expansion valve
B) Automatic expansion valve
C) Low-pressure float-valve
D) High-pressure float-valve
E) Hand operated expansion valve

Answer 1

A) Thermostatic expansion valve

Question 2

Manual or hand operated expansion valves are seldom used in modern refrigeration systems except for occasionally:

A) In the bypass line around the automatic control valve
B) To control the temperature of the cooling medium
C) To control the temperature of the condenser
D) To control the temperature of the evaporator
E) In the compressor oil cooling system

Answer 2

A) In the bypass line around the automatic control valve

Question 3

What will be the effect if an insufficient amount of liquid refrigerant is admitted to the evaporator by a thermostatic expansion valve?

A) Insufficient force will be generated against the diaphragm and spring to open the expansion valve
B) The heat in the vapour leaving the evaporator causes the pressure in the thermal element to increase opening the expansion valve
C) The thermal element reaches an equilibrium leaving the expansion valve in the same position
D) The room temperature will decrease closing the expansion valve
E) The expansion valve will freeze in position

Answer 3

B) The heat in the vapour leaving the evaporator causes the pressure in the thermal element to increase opening the expansion valve

Question 4

Which control is used to maintain a constant level of liquid refrigerant in the liquid accumulator of a flooded evaporator?

A) A high pressure float-valve
B) A low pressure float-valve
C) A thermostatic expansion valve
D) An automatic expansion valve
E) A hand operated expansion valve

Answer 4

B) A low pressure float-valve

Question 5

The control which restricts the flow of liquid from the condenser to the evaporator and maintains a pressure difference between the two units by using a pressure drop resulting from resistance between the device’s length and small bore is called a/an:

A) Low-pressure float valve
B) High-pressure float valve
C) External float chamber
D) Bypass line
E) Capillary tube

Answer 5

E) Capillary tube

Question 6

Which of the following are refrigeration metering or flow control devices?

1. Orifice meter
2. Automatic expansion valve
3. Bourdon tube
4. Thermostat
5. Low-pressure float
6. Capillary tube

A) 4, 5, 6
B) 2, 4, 6
C) 3, 4, 5
D) 2, 5, 6
E) 1, 2, 3

Answer 6

D) 2, 5, 6

Question 7

In a system controlled by a high pressure float valve, insufficient liquid will cause which of the following?

A) Starving the evaporator and reducing the capacity of the system
B) Liquid being carried over to the compressor with the vapour
C) Automatic system shutdown
D) All of the above
E) Boosting the compressor’s pressure

Answer 7

A) Starving the evaporator and reducing the capacity of the system

Question 8

The type of operation that stops the compressor when the desired low temperature of the substance to be cooled is reached and starts the compressor up again when the temperature rises to a set level is called:

A) Intermittent operation
B) Continuous operation with reduced output
C) Unloading operation
D) Variable guide operation
E) Cylinder bypass operation

Answer 8

A) Intermittent operation

Question 9

Which of the statements about automatic expansion valves is false?

Incorrect Response
A)

The valve maintains constant pressure in the evaporator during compressor operation regardless of the load

B) When the compressor stops, the valve automatically shuts off
C) The spring force is countered by evaporator pressure acting upward against the diaphragm which closes the valve
D) A spring exerting a downward force on the diaphragm tends to open the valve
E) The control valve may be used with multiple cooling coils connected to the same compressor

Answer 9

E) The control valve may be used with multiple cooling coils connected to the same compressor

Question 10

The thermostatic expansion valve operates on the principle of balancing:

A) Condenser pressure against a return spring
B) Evaporator pressure against a return spring
C) The volumetric expansion of a fluid against a return spring and evaporator pressure
D) Evaporator temperature against a return spring
E) Condenser temperature against a return spring

Answer 10

C) The volumetric expansion of a fluid against a return spring and evaporator pressure

Question 11

Use of evaporator capacity control results in refrigeration system load changes and thus requires simultaneous:

A) Reduction in air conditioning requirements
B) Compressor capacity control
C) All these answers are correct
D) Cooling tower flow rate changes
E) Heating system capacity control

Answer 11

B) Compressor capacity control