Chapter 7: Metering Devices

Which of the following best describes the operation of a High side float? (A) Feed the evaporator when sufficient quantity of refrigerant has been condensed (B) Feed the evaporator as refrigerant pressure decreases (C) Feed the condenser as refrigerant is needed (D) Maintain the level of condenser water in the cooling tower

(A) Feed the evaporator when sufficient quantity of refrigerant has been condensed

How would reducing the length of a capillary tube affect a unit's operation? (A) High evaporator pressure (B) High condensing pressure (C) High evaporator temperature (D) Reduce evaporator capacity

(A) High evaporator pressure

Modern centrifugal chillers are likely to use which if the following type of metering device? (A) Orifice plates (B) Low side floats (C) High side floats (D) TEV's

(A) Orifice plates Orifice plates are one of the most popular devices for the measurement and control of fluid flow. In modern centrifugal chillers, orifice plates are used as restriction devices to regulate the refrigerant flow or reduce the flowing pressure downstream of the orifice plate.

What will happen if an expansion valve meters too much refrigerant into a DX coil? (A) Possibility of liquid in the compressor (B) Evaporator temperature will be too cold (C) Reduced system capacity (D) Possible motor burnout

(A) Possibility of liquid in the compressor

In addition to evaporator pressure, what other forces influence the operation of an automatic expansion valve? (A) Spring pressure (B) Condensing pressure (C) Cut-in pressure (D) Design pressure

(A) Spring pressure

If the ball float of a "Low side float metering device" was punctured and sunk to the bottom of the float chamber, how would the system be affected? (A) The suction pressure would rise (B) The head pressure would rise (C) The suction pressure would fluctuate (D) The compressor would stop immediately

(A) The suction pressure would rise In a Low side float setting the float chamber sits on side of evaporator.As the refrigerant vaporizes in the evaporator the valve opens allowing liquid refrigerant to fill the flooded evaporator and chamber. If the float was puncture, it would sunk to the bottom, allowing vast quantities of unwanted liquid refrigerant to fill the evaporator which would cause the suction pressure to rise.

Which of the following determines the amount of refrigerant passing through an orifice plate? (A) Number of orifice plates in the system (B) Difference between high side and low side pressure (C) Number of stages in the compressor (D) Operation of the economizer

(B) Difference between high side and low side pressure

In a flooded evaporator equipped with a Low side float, the operation of the float mechanism is determined by the rate at which: (A) Refrigerant is condensed (B) Refrigerant evaporates (C) Chilled water discharged (D) Superheat is produced

(B) Refrigerant evaporates

How would a partially blocked orifice affect the operation of a thermostatic expansion valve? (A) Flood the evaporator (B) Starve the evaporator (C) Low superheat (D) Increase refrigerant velocity

(B) Starve the evaporator

High pressure drop is produced as refrigerant travels through the metering devices orifice. Which of the following best describes where this component is located? (A) At the valve's inlet (B) At the valve's diaphragm (C) At the valve's seat (D) At the top of the valve's system

(C) At the valve's seat

Which of the following metering devices requires that the refrigeration system be maintained at a critical charge? (A) TEV (B) Low side float (C) High side float (D) Orifice plate

(C) High side float

Which of the following best describes the state of the refrigerant at the leaving side of the metering device? (A) HPL(High-Pressure Liquid) (B) HPV(High-Pressure Vapor) (C) LPL(Low-Pressure Liquid) (D) LPV(Low-Pressure Vapor)

(C) LPL(Low-Pressure Liquid) The High pressure and high temperature liquid refrigerant in the liquid line, enters the metering device and exits as a Low pressure and Low temperature liquid.

Which feature distinguishes a manual metering device from a globe valve? (A) Valve seat (B) Valve stem (C) Needle point (D) Outlet diameter

(C) Needle point

In addition to controlling the flow of refrigerant to the evaporator, what other task is performed by a metering device? (A) Increase compressor capacity (B) Filter refrigerant (C) Separate the High side of the refrigeration system from the Low side (D) Shed load as load increases

(C) Separate the high side of the refrigeration system from the low side

If an automatic expansion valve is mistakenly installed in a system that operates at variable loads, what is likely to take place when the valve experiences a high load condition? (A) The system will operate satisfactorily (B) The compressor will be damaged (C) The evaporator will be starved (D) The evaporator will be over-fed

(C) The evaporator will be starved Unlike a Thermostatic Expansion Valve, an AEV or Automatic Expansion Valve, feeds the same amount of refrigerant into the evaporator coil Regardless of demand as it attempts to keep a constant pressure. If a AEV was installed on a variable load system, during a high load, high demand condition. The AXV would starve the coil as it would not feed enough refrigerant into the evaporator.

Which of the following metering devices are designed to maintain constant superheat? (A) Automatic expansion valve (B) High side float (C) Thermal expansion valve (D) Capillary tube

(C) Thermal expansion valve A TEV or Thermostatic Expansion Valve is a refrigerant metering device design to maintain a constant level of superheat. It regulates the superheat over a wide range of loads and outdoor temperatures. Most manufacturers of HVAC equipment designed for the TEV to maintain about 10-15 of superheat. This allows for the system to operate at its maximum efficiency by utilizing the system evaporator coil in its full capacity.

An electric expansion valve is being used in a refrigeration system contains a halocarbon refrigerant. Which of the following power sources would be used to operate this valve? (A) 6 volts AC or DC (B) 12 volts AC (C) 18 volts DC (D) 24 volts AC or DC

(D) 24 volts AC or DC Control systems for a refrigeration plant are automatic controls which enables the system to be autonomous with little manual inputs from the operator. This controls can be actuated by different energy means one of which is electrical current. The electrical current for refrigeration controls is a low voltage power which comes from stepping down regular voltage of 120 volts to 24 volts with the use of a step-down transformer.

Which of the following metering devices have no means of adjustment? (A) Thermostatic expansion valve and automatic expansion valve (B) Automatic expansion valve and capillary tube (C) Automatic expansion valve and orifice plate (D) Capillary tube and orifice plate

(D) Capillary tube and orifice plate

A horizontal shell and tube cooler is equipped with a float mechanism to control the refrigerant's liquid level in the shell of the cooler. If the equalizer line at the top of the float chamber should become obstructed, which of the following is likely to take place? (A) Compressor will tend to over speed (B) Liquid level in the cooler will keep alternately rising and falling (C) Cooler will continue to operate normally for a considerable length of time (D) Liquid level in the cooler will not correspond to that in the float chamber

(D) Liquid level in the cooler will not correspond to that in the float chamber

If the ball float of a high side float metering device is punctured and sinks to the bottom of the float chamber, how will the operation of the system be effected? (A) Flood the evaporator (B) High suction pressure (C) Low head pressure (D) Starve the evaporator

(D) Starve the evaporator