FDNY Z-51 Exam: 250+ Real Exam Questions and Answers for Refrigerant Engineers (2024-2025), Exams of Nursing

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FDNY Z-51 EXAM WITH 250+ REAL EXAM QUESTIONS AND

CORRECT ANSWERS GRADED A+ LATEST 2024- 2025

A refrigerant engineer verifies that a chilled water pump is cavitating. Of the following, the most likely cause for this condition is? - ANSWER✔✔Water leaks through the mechanical seals There is an decrease in the efficiency of a reciprocating compressor. This mostly likely caused by? - ANSWER✔✔Leaking suction valve The suction and discharge valve of the reciprocating compressor are mounted as follows: - ANSWER✔✔Discharge valve on top of the valve plate and suction valve below You are the engineer running a 2000 ton (steam driven turbine) centrifugal refrigeration system, a refrigeration system supplies chilled water to a college campus with multiple buildings. While making your rounds, you noticed that the discharge pressure of your

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condenser water pump is significantly lower than the normal. Which following action would you avoid taking: - ANSWER✔✔Put on an additional surface condenser pump and lower the chilled water set point A water pump is discharge against head 92 feet of water, this is approximately to a pressure of:

ANSWER✔✔ 40 Which of the following will connect to the middle port on a gauge manifold? - ANSWER✔✔Vacuum pump The most important reason for installing a muffler in reciprocating refrigerant machine is? - ANSWER✔✔To contain the compressor pulsation noise Of the following, the statement that most accurately characterizes a hermetic compressor is that it: - ANSWER✔✔Will have both the compressor and motor enclosed is gas tight housing

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In the picture, the valve is in what position - ANSWER✔✔The valve is cracked open What is the order of components on the liquid line of reciprocating system from the condenser? - ANSWER✔✔King valve, filter drier, solenoid valve, sight glass A high side float valve is used to maintain: - ANSWER✔✔Constant level of refrigerant in the evaporator Picture of a pump - ANSWER✔✔Ninety degrees reducing elbow, pump suction, pump casing, pump discharge, check valve Picture of a compressor - ANSWER✔✔Oil charging port allows for the addition and removal of oil from the compressor

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A facility has failed to maintain water treatment to a refrigerant system - ANSWER✔✔Increase in the condenser pressure Which of these compressors is not a positive displacement type compressor? - ANSWER✔✔Centrifugal Efficiency of the refrigerant cycle is affected by the operations of the condenser. Of the following, a more efficient centrifugal compressor operation results from: - ANSWER✔✔Lowering the condensing pressure The heat removed from the refrigerant in a condenser is: - ANSWER✔✔Sensible and latent heat The refrigerant unit that you have been assigned to is being taken out of service for a major repair. You have been assigned to withdraw refrigerant for storage in suitable containers. According to the NYC Fire Code, you must ensure that the containers: - ANSWER✔✔Are approved by the US Dept. of Transportation

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Which of the following best describes how the cylinder unloader works? - ANSWER✔✔Keep in the suction valve opened while the compressor is in the return stroke In most semi-hermetic compressors, the suction vapor is used to: - ANSWER✔✔Cool the motor The amount of refrigerant that flows through the orifices of an economizer is determined by the: - ANSWER✔✔Differences between the high side and low side pressure The installation of an inline refrigerant cleaning system is advisable: - ANSWER✔✔To remove impurities from the system The type of refrigerant system that is least likely to leak refrigerant into the building space that are being cooled: - ANSWER✔✔Indirect system

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The suction pressure of a reciprocating compressor is 65 PSIG. The discharge pressure of this compressor is 120 PSIG. The atmospheric is 14.7 PSI. The compression ratio for the given condition is closest to: - ANSWER✔✔1. A superheated vapor is: - ANSWER✔✔Dry vapor above the saturation temperature A refrigerant engineer verifies that a condenser water pump is cavitating. Of the following, the most likely cause for this condition is: - ANSWER✔✔A faulty cooling tower water level controller A centrifugal water pump is known as a lift pump when the: - ANSWER✔✔The water supply to the pump suction inlet is below the pump level A TXV is used to maintain constant: - ANSWER✔✔Evaporator superheat The chilled water supply to the building is 55 deg F. If the chiller is being used for human comfort, should you be concerned about this, and why? - ANSWER✔✔Yes, this temp is too high for human comfort purposes

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The packing gland of a centrifugal pump serves to: - ANSWER✔✔The drip part of the packing gland gives evidence that there is water in the pump Capacity control of reciprocating hermetic compressor is typically achieved through: - ANSWER✔✔Operation of the hot gas bypass valve The most important reason to sub-cool the refrigerant in the condenser is to ensure that: - ANSWER✔✔A pure liquid refrigerant will enter the metering device A refrigeration engineer is logging readings from a reciprocating system. Compressor discharge temperature have dropped significantly and the suction line pressure is high. Which of the following that may be causing this set of condition? - ANSWER✔✔An expansion valve that is open too wide

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A low side float valve is used to maintain: - ANSWER✔✔The level of the refrigerant in the evaporator Regarding fire safety, which ASHRAE refrigerant safety classification indicates no flammability and lower toxicity? - ANSWER✔✔A When an expansion valve is operating properly, at the end of the evaporator will contain: - ANSWER✔✔Only superheated vapor What information is not contained in a Material Safety Data Sheet? - ANSWER✔✔Cost of the material In a steam turbine, what is the function of the Kingsbury thrust bearing? - ANSWER✔✔Maintain axial positioning of the rotor shaft

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A centrifugal water pump is considered to the fully primed when? - ANSWER✔✔The pump is full of liquid Copper tubing refrigerant lines must be installed for a new system. It is a well known service practice that tubing collapses at bends that must be made, the refrigerant engineer should use?

• ANSWER✔✔Level type tubing bender A reciprocating compressor is making a knocking sound during operation. If the refrigerant worn parts are not causing the knocking, what probably the cause? - ANSWER✔✔Slugging of the liquid refrigerant In order for a refrigerant to become superheated, it must be heated in a section of the low side refrigerant line: - ANSWER✔✔Where no liquid refrigerant is present All liquid has been recovered from a system to be overhauled, the system: - ANSWER✔✔Should not be opened until all vapor has been recovered

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When a refrigerant engineer uses a portable compressor recovery unit to remove vapor refrigerant from a refrigeration system the removal rate of the refrigerant will gradually slow down because? - ANSWER✔✔The compressor efficiency is decreasing You are the engineer running a 2000 - ton (steam driven turbine) centrifugal refrigeration system, a refrigeration system supplies chilled water to a college campus with multiple buildings. During the course of making your rounds, you check the 9 cell cooling tower on the roof. You note the water level in all of the cooling tower cells is very low. Which one of the following immediate actions would take? - ANSWER✔✔Add additional make up water to the cooling tower A rooftop water cooling tower is connected to a water pump in the building basement with a 12 inch diameter pipe. With the pipe turned off, a pressure gauge at the pumps inlet show a pressure of 140 PSIG the height of the water column, in feet, would be closest to: - ANSWER✔✔ 323

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What device protects the steam turbine from excessive speed? - ANSWER✔✔Governor assembly A refrigeration compressor has failed to turn on. The refrigeration engineer on duty verifies that the electrical circuit to the motor, including all switches and circuit breakers, is complete according to recommended service practice, the next item to be checked would likely be the: - ANSWER✔✔Temperature and pressure controls Refrigerants are characterized by their physical properties included flashpoint, refrigeration effect, and others. Of the refrigerants in commercial and industrial, the one with the highest latent heat and refrigerant effect is: - ANSWER✔✔Ammonia Of what characteristics is ASHRAE refrigerant safety group classification system: - ANSWER✔✔Flammability and toxicity

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Of the following, an example of an in line refrigerant cleaning system that may be used with a centrifugal compressor containing R-123 refrigerant is: - ANSWER✔✔Recycling Information about the physical and chemical properties of a hazardous material can be found in: - ANSWER✔✔Material Safety Data Sheet What is the function of the turbine auxiliary oil pump? - ANSWER✔✔Establish oil pressure during turbine start up The rupture disc for a low pressure centrifugal refrigeration machine is normally located on the:

• ANSWER✔✔Compressor suction What is the primary reason ribbed metal piping is used for electrical wires connected to the refrigeration system shown below? - ANSWER✔✔It allows for flexibility and accounts for vibrations

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A multi cylinder reciprocating compressor uses cylinder unloaders to regulate capacity, what would not occur if some of the unloaders fail to operate when needed? - ANSWER✔✔The chill water temperature will increase As shown in the picture below, the suction gauge of a condenser water pump reads 55 PSI. The pipe supplying the pump is 75 feet long and 12 inches in diameter. Approximately, how many gallons of water do you expect to obtain if the pipe is drained completely? - ANSWER✔✔ 440

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A water chiller system uses refrigerant R-123. A leak in the evaporator shell may result in: - ANSWER✔✔A higher than normal high side pressure Capacitors are used on refrigeration motors. Of the following, the function of these devices is to: - ANSWER✔✔Store electrical chargers during starting and running the motor Of the following, centrifugal refrigerant machine is best characterized by: - ANSWER✔✔A high volume, low pressure machine Which of the following ASHRAE refrigerant safety classifications is the most flammable? - ANSWER✔✔A Which of the following correctly describes the object in the picture below? - ANSWER✔✔Standpipe hose outlet, to put out fires in case of emergency

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Modern compressors usually seal the rotating shaft as it exits the compressor housing a spring - ANSWER✔✔Metal or carbon The British Thermal Unit (BTU) is the measurement of heat of energy. If 10 BTU's are transferred to 10 pounds of water, the water temperature increase will be closest to: - ANSWER✔✔1 deg F A reciprocating compressor cylinder has a 10 inches bore and 14 inches stroke. The volume of the refrigerant , in cubic inches, will be closer to: - ANSWER✔✔ 1099 An electrically operated control requires 24 volts to operate. To change the available 110 volts to 24 volts - ANSWER✔✔Transformer In an indirect refrigeration system, of the following, the one that would not be used as a cooling medium for the building spaces being cooled is: - ANSWER✔✔R- 22

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On a steam turbine, what would cause the atmospheric valve to open? - ANSWER✔✔All answers (low vacuum in the surface condenser, leaking tubes in the surface condenser, dirty tubes in the surface condenser) You are the engineer running a 2000-ton (steam driven turbine) centrifugal rerigeration system, a refrigeration system supplies chilled water to a college campus with multiple buildings. Making your rounds, you notice that the condenser water pump #1 is making a lot of noise, the discharger guage reading of the condenser water pump is fluctuating drastically, and motor of the condenser pump #1 is running very hot. Which of the following would you take: - ANSWER✔✔Turn on pump #2, shut off pump #1, and troubleshoot pump # Electric devices may be used to provide built in defrosting of refrigeration machine evaporator units. These devices are classified as? - ANSWER✔✔Resistors The flash point of a compressor lubricating oil: - ANSWER✔✔Should be higher than the compression temperature

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The primary way of achieving capacity control of a centrifugal compressor is by: - ANSWER✔✔Adjustment of the impeller inlet pre-rotation vanes Cooling tower water requires the addition of chemical additives in order to: - ANSWER✔✔Reduce the formation of scale and algae In the picture below describes the equipment's function: - ANSWER✔✔Remove noncondensables from the condenser The viscosity of lubrication oil is described by a number. A low viscosity number describes oil that: - ANSWER✔✔Flows easily The most likely reason for refrigeration engineer to use a psychrometer is to measure: - ANSWER✔✔Relative humidity level of the atmosphere

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The most important reason to use at least two compressors in a cascade system is to: - ANSWER✔✔Avoid very high compression ratio for each compressor The suction service valve of a reciprocating compressor is front seated and the compressor runs until the low pressure cut out shuts the compressor off. When the machine is stopped, the refrigeration engineer notices that the suction pressure increases rapidly. The most probable cause of this pressure rise is: - ANSWER✔✔Malfunction of a compressor valve Regarding the functioning of a steam turbine, why is it advisable to keep moisture in the inlet low as possible? - ANSWER✔✔Keeps turbine blades wear to minimum According to the attached Material Safety Data Sheet, R-134 is a: - ANSWER✔✔Clear, odorless liquid and vapor Under normal conditions, the refrigerant enters the compressor as a: - ANSWER✔✔Low pressure, super-heated vapor and leaves as a high pressure vapor

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While operating an R-22 single acting compressor system, the refrigeration engineer noticed oil foaming in the crankcase. This condition most likely, would have been caused by a: - ANSWER✔✔Sudden drop in the crankcase pressure Assume that an engineer is able to observe refrigerant water and oil together. The fluids would settle in the container from top to bottom as follows: - ANSWER✔✔Oil, water, refrigerant What is the function of the vacuum breaker in the steam turbine? - ANSWER✔✔To achieve a faster cost down cycle An equalizer line on a TXV is used to: - ANSWER✔✔Compensate for the pressure drop across the evaporator coil If R-134 accidentally touches a refrigerant engineer's skin, what first aid should be applied from the MSDS? - ANSWER✔✔Promptly flush the skin with water until all chemical is removed

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In a multi-stage centrifugal compressor, each stage: - ANSWER✔✔Is identical in volume to the other stages A refrigeration engineer notices excessive cycling of the temperature control for a reciprocating compressor refrigeration unit. The crankcase temperature is high, the compressor discharge temperature is low, the suction line temperature is high. Of the following, the one that may cause this set of condition is? - ANSWER✔✔Faulty compressor valves On an operating centrifugal compressor refrigerant unit, the refrigeration engineer notices that the compressor is short cycling. The unit is using a low side float valve as a metering device. Of the following requirements, this would indicate that: - ANSWER✔✔The system is undercharged with refrigerant The vessel depicted below may used in connection with - ANSWER✔✔Refrigerant recovery

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A refrigeration system uses jet ejector to raise settled oil mixed with refrigerant to the oil pump. If a restriction in the refrigerant flow to the jet ejector develops: - ANSWER✔✔There may be insufficient head to lift the oil An indirect, low temperature refrigerant system frequently uses glycol, instead of salt brine as the intermediate cooling medium. An advantage of this choice is: - ANSWER✔✔The elimination of corrosion In relation to the suction pressure of a compressor, the reading on the oil pressure guage should read in the range, closer to: - ANSWER✔✔15 to 30 PSI higher Non-condensable gases like air, oil vapor, or nitrogen travel through a refrigerant system with the refrigerant they usually accumulate in the: - ANSWER✔✔Condenser The advantage of forced draft cooling tower over natural draft cooling towers is: - ANSWER✔✔Smaller tower size

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The sole refrigeration engineer on duty in a building is permitted to leave the building refrigeration system when it is in operation only when: - ANSWER✔✔Relieved by another licensed refrigeration engineer A system controlled by a TXV shows high discharge pressure and high normal subcooling. The cause is most probably a: - ANSWER✔✔Refrigerant overcharge Which of the following is a correct statement? - ANSWER✔✔2.5 gallons of water weighs 20.8 pounds Liquid level gauge glasses (except the bull's eye) are generally equipped with: - ANSWER✔✔Automatic shut off valves only

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Copper and aluminum are frequently used for condenser tubes in refrigeration system. These metals are used because of their: - ANSWER✔✔High heat transfer coefficient Assume that a refrigeration engineer has a choice of four valves to select from. Which of the following is the most effective type of valve to control pressure? - ANSWER✔✔Plug valve Where must the Material Safety Data Sheets be located? - ANSWER✔✔Where available to all employees The oil collected in an oil separator is generally: - ANSWER✔✔Returned to the compressor What is the function of gland steam? - ANSWER✔✔Seal the turbine rotor carbon rings Regarding the functioning of steam turbine, how is the water level controlled in the surface condenser hot well? - ANSWER✔✔Operation of the recirculation and overboard valves

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The cause of the starved evaporator might be: - ANSWER✔✔Low refrigerant charge A refrigeration engineer is running two centrifugal condenser water pumps in parallel. One of the pumps is at it's maximum pumping rate. If by mistake, the refrigeration engineer throttles back on the discharge valve of the other pump, the most likely effect will be: - ANSWER✔✔A reduction on the total flow rate to the condenser The total amount of heat to be removed from the refrigerant in a condenser equals the heat picked up in the: - ANSWER✔✔Evaporator plus the heat of compression The amount of electrical power used to operate a solenoid valve or a motor is measured in: - ANSWER✔✔Volts Of the following, the most common metering device used today in reciprocating commerical refrigeration system under three tons capacity is: - ANSWER✔✔TEV

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The purpose of wear rings in a centrifugal pump is to: - ANSWER✔✔Prevent wearing of the pump housing and impeller You are the engineer running a 2000-ton (steam driven turbine) centrifugal refrigeration system, a refrigeration system supplies chilled water to a college campus with multiple buildings. While making rounds, you notice that the condenser water coming back down from the 9-cell cooling tower on the roof is at a temperature of 90F. You want to make an adjustment to bring the temperature of the condenser water down to 85F. Which one of the following immediate actions would you take? - ANSWER✔✔Increase the speed of the cooling tower fans A water chiller is equipped with a reciprocating compressor, a thermostatic expansion valve, and an air cooled condenser. A restriction in the refrigerant liquid line would result in: - ANSWER✔✔High suction superheat