Metering Devices

Question 1

Metering devices can be orifices of fixed size or ____, which can vary flow depending on loads.

Answer 1

valves

Question 2

Metering devices are always in stalled between the liquid line and the ____.

Answer 2

evaporator

Question 3

The main purpose of a metering device’s orifice is to produce ____.

Answer 3

a pressure drop

Question 4

What are the most common types of metering devices.

Answer 4

Capillary Tube (cap tube)
Metering Orifice
Thermostatic Expansion Valve (TXV)
Automatic Expansion Valve (AXV)
Electronic Expansion Valve (EEV)
Low-Side Float (LSF)
High-Side Float (HSF)

Question 5

Capillary tubes are used extensively in ____ systems.

Answer 5

refrigerators and window ac unit

Question 6

(T/F) The limited amount of refrigerant allowed to pass through a metering device into the evaporator is at high pressure.

Answer 6

False

Low pressure due to the pressure drop

Question 7

(T/F) The rate of flow through fixed metering devices is relatively constant when the compressor is running.

Answer 7

True

Question 8

(T/F) Because modulating metering devices can change refrigerant flow based on load, they operate more efficiently than fixed metering devices.

Answer 8

True

Question 9

For increased system efficiency, a capillary tube is usually positioned so that a portion of it is in contact with the ____.

Answer 9

suction line

Question 10

An advantage of capillary tubes over modulating metering devices is that capillary tubes have no ____.

Answer 10

moving parts

Question 11

Capillary tube failure will most likely occur when it is ____.

Answer 11

bent or crimped

Question 12

When a capillary tube is replaced, it is good practice to also replace the ____.

Answer 12

liquid line filter-dryer

Question 13

Piston-type metering orifices are most often used on ____ systems.

Answer 13

heat pump

Question 14

The main value that influences the operation of a TXV is ____.

Answer 14

superheat

Question 15

If the pressure in a sensing bulb is ____ the combined pressure from the evaporator and the spring, a TXV’s valve is forced open.

Answer 15

greater than

Question 16

When a thin layer of fluid adheres to a solid, but the two substances are not mixed together, ____ occurs.

Answer 16

adsorption

Question 17

Describe the difference between adsorption and absorption.

Answer 17

Adsorption occurs when an thin layer of fluid (gas or liquid) adheres to a solid, but are not mixed together.
Absorption when two substances are mixed and become one substance.

Question 18

(T/F) By using an external equalizer, a TXV is able to provide the correct refrigerant flow, even when there are large pressure drops through the evaporator.

Answer 18

True

Question 19

A sensing bulb charged with the same refrigerant as the system, some of which is always in a liquid state.

Answer 19

Liquid-charged

Question 20

A sensing bulb charged with a different refrigerant than what is in the system, and some of it is always in a liquid state.

Answer 20

Liquid cross-charged

Question 21

A sensing bulb charged with the same refrigerant as the system and which is completely vaporized at a predetermined temperature.

Answer 21

Gas-charged

Question 22

A sensing bulb charged with a refrigerant that is different form that in the system and which is completely vaporized at the desired temperature.

Answer 22

Gas cross-charged

Question 23

A sensing bulb that contains two substances: one is a non-condensing gas and the other is a solid.

Answer 23

Adsorption gas cross-charged

Question 24

On systems with small-diameter horizontal suction lines, the sensing bulb should be mounted on the ____ of the suction line.

Answer 24

top

Question 25

A sensing bulb must not be affected by the air or liquid being cooled. it should be wrapped in insulation so that only ____ affects the bulb.

Answer 25

suction line temperature

Question 26

Before a sensing bulb is installed, use steel wool to clean ____.

Answer 26

the suction line and sensing bulb

Question 27

(T/F) Once all of the refrigerant is a gas cross-charged sensing bulb is vaporized, the valve is at its maximum operating pressure.

Answer 27

True

Question 28

If the orifice of a TXV is over sized, too much refrigerant will pass into the evaporator and cause the suction line to ____ before the sensing bulb can close the valve.

Answer 28

sweat or frost

**Will also hunt

Question 29

If the superheat setting is increased to correct for an over sized TXV orifice, the evaporator will be ____ much of the time.

Answer 29

starved

Question 30

(T/F) Automatic expansion valve (AXV) operation is based on its sensing bulb.

Answer 30

False

Work off of low side pressure

Question 31

To maintain a constant pressure in the evaporator when the system is running, an AXV ____ when evaporator pressure begins to increase.

Answer 31

decreases refrigerant flow