Refrigerant Machine Operator License Exam Prep Test

Charging with liquid can cause water to freeze in the tubes, which can lead to blockages and damage to the system.

If the spring in the TEV were to break, it would result in flooding the evaporator. This means that an excessive amount of refrigerant would enter the evaporator, causing it to become overwhelmed and unable to effectively cool the air. This can lead to a decrease in system efficiency and potentially cause damage to the components of the evaporator.

When running three compressors, the refrigerant leaving the third compressor would be in a highly superheated vapor state. This means that the refrigerant has been heated above its saturation temperature, resulting in a gas-like state with no liquid present. Superheating occurs when the refrigerant absorbs additional heat after it has completely evaporated, leading to an increase in temperature. In this case, the refrigerant leaving the third compressor has undergone significant superheating, indicating that it is mostly in a vapor form with very little or no liquid content.

The power head of a TXV (Thermostatic Expansion Valve) is color-coded to match the refrigerant charge in the system. Since R-22 refrigerant is commonly associated with the color green, the power head would be green if it was charged with R-22.

Using a constant pressure expansion valve instead of a thermostatic expansion valve under various loads will result in both starving and flooding the evaporator. A constant pressure expansion valve does not regulate the flow of refrigerant based on the temperature of the evaporator, leading to inconsistent refrigerant flow. This can cause the evaporator to be starved of refrigerant, leading to poor cooling performance. On the other hand, it can also result in excessive refrigerant flow, causing the evaporator to flood and potentially lead to liquid refrigerant entering the compressor, which can cause damage. Therefore, both options A and B are correct.

Ammonia is the refrigerant with the highest latent heat and refrigeration effect among the refrigerants used in commercial industries today. This means that ammonia has a high capacity to absorb and release heat during the refrigeration process, making it an efficient refrigerant. Ammonia's high latent heat allows it to absorb a significant amount of heat energy when it evaporates, while its high refrigeration effect enables it to provide effective cooling. Therefore, ammonia is preferred in industrial refrigeration systems where large cooling capacities are required.

Both A and B are correct because shell and tube condensers have the advantage of being able to remove the heads for cleaning the water sides of the tubes, as well as not having to disrupt the refrigerant connections. This allows for easier maintenance and cleaning of the condenser, ensuring optimal performance and efficiency.

The volume of a cylinder can be calculated using the formula V = πr^2h, where V is the volume, r is the radius, and h is the height. In this case, the radius is half of the bore, so it is 6 inches. The height is the stroke, so it is 16 inches. Plugging these values into the formula, we get V = π(6^2)(16) = 1808 cubic inches. Therefore, the volume of refrigerant in cubic inches would be closer to 1808.

If the flow of oil is restricted, it means that there is not enough pressure or force to lift the oil mixed with refrigerant. This results in insufficient head, which refers to the pressure difference needed to lift the oil. As a result, the oil will not be able to be lifted from the bottom of the evaporator.

In a multistage centrifugal compressor, the tip speed refers to the speed at which the outer edge of the impeller rotates. The given answer states that the tip speed is more with each stage. This means that as the refrigerant passes through each stage of the compressor, the impeller rotates at a higher speed. This increase in tip speed helps to increase the pressure and velocity of the refrigerant, resulting in a higher compression ratio and improved efficiency.

Unloaders are used to reduce capacity in a refrigeration system. They are designed to control the flow of refrigerant and adjust the system's capacity based on the cooling load requirements. By reducing the capacity, unloaders help maintain the system's efficiency and prevent overcooling. They achieve this by bypassing a portion of the refrigerant flow when the cooling demand is low, allowing the compressor to run at a lower capacity. This helps save energy and ensures optimal performance of the refrigeration system.

Excessive superheat at the evaporator outlet can be caused by any of the mentioned options. A starved evaporator occurs when there is insufficient refrigerant flow, resulting in high superheat. A leak in the system can cause a decrease in refrigerant charge, leading to inadequate cooling and high superheat. Similarly, a low refrigerant charge can cause insufficient cooling and high superheat. Therefore, any of these factors can contribute to excessive superheat at the evaporator outlet.

The correct answer is "ACCORDING TO DESIGN PRESSURE". When installing a pressure relief valve on a reciprocating compressor using R-12, it is typically set according to the design pressure. This means that the valve is adjusted to open and release pressure when the system reaches the predetermined maximum pressure that the compressor is designed to handle. Setting the relief valve according to the design pressure helps to ensure the safe operation of the compressor and prevent overpressure situations that could damage the equipment or pose a safety risk.

The rupture disk is always piped into the low side of the system. This is because the low side of the system operates at a lower pressure compared to the high side. The rupture disk is designed to burst and release pressure when it exceeds a certain limit. By piping it into the low side, it ensures that the excess pressure is safely vented without causing damage to the system or posing any safety risks.

The given question is asking for the pressure at 38°F based on the given pressures at 35°F and 45°F. We can observe that as the temperature increases, the pressure also increases. Therefore, we can infer that the pressure at 38°F would be between 62 PSI and 70 PSI. The closest option to this range is 64.4 PSI, which is the correct answer.

If the eliminator plates located below the fan in an induced draft-cooling tower have become clogged, it would most likely result in an increase in cooling tower water temperature being returned. The eliminator plates are responsible for removing water droplets from the air leaving the cooling tower. If they become clogged, the water droplets will not be effectively removed, leading to a higher water temperature being returned to the cooling tower. This can negatively impact the cooling efficiency of the tower and potentially cause other issues in the cooling system.

If the compressor was receiving liquid, the RMO (Refrigeration Machine Operator) would notice that frost may develop in the suction line. This is because when liquid enters the compressor, it can cause a drop in temperature and lead to the formation of frost in the suction line. This is a sign of potential damage to the compressor and can decrease the efficiency of the refrigeration system.

When the condensing pressure is low, it means that the pressure in the condenser is not sufficient to properly condense the refrigerant vapor into liquid form. This leads to a decrease in the liquid level in the condenser, causing the expansion valves to not be able to feed the refrigerant properly. As a result, the expansion valves will not be able to regulate the flow of refrigerant into the evaporator effectively, leading to inefficient cooling.

The correct answer is 213 psi because the head pressure of a refrigeration machine condenser is directly related to the temperature of the cooling water. As the cooling water temperature increases, the head pressure also increases. In this case, the cooling water is being supplied at 85°F and leaving at 95°F, indicating a temperature rise of 10°F. Based on industry standards and guidelines, a temperature rise of 10°F corresponds to a head pressure of approximately 213 psi.

Upon being assigned to a facility during inspection, if there has been a failure to maintain water treatment, the first evidence that would most likely be observed when inspecting the condenser water is an increase in compressor head pressure. This is because the failure to maintain water treatment can lead to the accumulation of contaminants in the condenser water, which can reduce the efficiency of heat transfer. As a result, the compressor needs to work harder to maintain the desired pressure, leading to an increase in head pressure.

The most likely cause of the frost formation on the suction line and compressor is that the expansion valve is open too wide. When the expansion valve is open too wide, it allows too much refrigerant to flow through the evaporator coil, causing the evaporator coil to become too cold. This can lead to frost formation on the suction line and compressor.

If the wet bulb temperature drops by 5°F while the dry bulb temperature remains constant, it indicates a decrease in the amount of moisture in the air. This decrease in moisture will result in a lower cooling water temperature return. As the air becomes drier, it will have less of a cooling effect on the water, causing a lower temperature return. Therefore, the operator should expect to see a lower cooling water temperature return in this scenario.

The pressure gauge reading of 120 PSI indicates the pressure at the bottom of the vertical water pipe. Since pressure in a fluid is directly proportional to the height of the fluid column, we can use the equation P = ρgh, where P is the pressure, ρ is the density of the fluid, g is the acceleration due to gravity, and h is the height of the fluid column. By rearranging the equation to solve for h, we get h = P/(ρg). Since the density of water is approximately constant, the height of the water column is directly proportional to the pressure. Therefore, the height of the pipe is 277 feet.

When 1000 BTU's are removed from 100 pounds of water at a temperature of 55°F, the final water temperature will be 45°F. This is because the removal of heat energy causes the water to cool down, resulting in a decrease in temperature.

The bimetal disk or klixon is used to protect the wiring and components against excessive current draw. When the current draw exceeds a certain limit, the bimetal disk or klixon will trip and open the circuit, preventing further damage to the wiring and components. This helps to prevent overheating and potential electrical fires.

A low head pressure in a refrigeration system can cause the expansion valve to not feed properly. The expansion valve is responsible for regulating the flow of refrigerant into the evaporator. If the head pressure is too low, there may not be enough force to push the refrigerant through the expansion valve, resulting in inadequate cooling and potentially causing the evaporator to not receive the proper amount of refrigerant. This can lead to inefficient cooling and reduced performance of the refrigeration system.

A fusible plug is designed to melt at a specific temperature in order to prevent excessive pressure build-up in a system. In this case, the correct answer is 450°F, which means that the fusible plug will melt and release pressure when the temperature reaches 450°F. This temperature is lower than the other options provided, indicating that the system requires a lower temperature threshold for pressure relief.

To convert Celsius to Fahrenheit, we use the formula F = (C x 9/5) + 32. In this case, the temperature dropped by 10°C. Plugging in the value into the formula, we get F = (10 x 9/5) + 32 = 18. Therefore, the temperature in °F is 18.

Low latent heat is the most undesirable property in a refrigerant because latent heat is the amount of heat energy absorbed or released during a phase change, such as during the evaporation or condensation process in a refrigeration cycle. A low latent heat means that the refrigerant will absorb or release less heat energy during these phase changes, which will result in poor cooling efficiency. This will require the compressor to work harder and consume more energy to achieve the desired cooling effect, making it less efficient and cost-effective.

The heat transfer rate in the condenser will increase with the velocity of the water in the tubes because higher water velocity promotes better heat transfer. When the water flows faster through the tubes, it increases the turbulence and improves the heat transfer coefficient. This results in a higher heat transfer rate between the hot vapor and the cooling water, leading to increased efficiency in the condenser.

When charging a system with liquid refrigerant using a set of manifold gauges, the valves on the manifold should be in the position of HIGH SIDE BACKSEATED and LOW SIDE FRONTSEATED. This means that the valve on the high side of the manifold should be closed or turned counterclockwise until fully closed, while the valve on the low side of the manifold should be open or turned clockwise until fully open. This configuration allows for the proper flow of refrigerant into the system without any backflow or leakage.

The correct order of the placement of accessories on the liquid line is drier, solenoid valve, and sight-glass. The drier is typically placed first in the line to remove any moisture or contaminants from the refrigerant. The solenoid valve is then installed after the drier to control the flow of refrigerant. Finally, the sight-glass is placed after the solenoid valve to allow for visual inspection of the refrigerant flow.

If the bulb to a TXV (Thermal Expansion Valve) has fallen off and the room is at 85°F, the evaporator would flood. The TXV is responsible for regulating the flow of refrigerant into the evaporator coil based on the temperature sensed by the bulb. Without the bulb, the TXV cannot accurately control the refrigerant flow, causing an excessive amount of refrigerant to enter the evaporator coil. This leads to flooding, where the evaporator is overwhelmed with refrigerant, resulting in poor heat transfer and reduced cooling capacity.

Based on the information given, the cycling times of the reciprocating refrigerating unit are normal, but the compressor compression and temperature readings are outside the normal rate. This suggests that there may be an issue with the compressor valves. Faulty compressor valves can cause abnormal compression and temperature readings, indicating a problem with the valves' ability to properly control the flow of refrigerant. Therefore, inspecting for faulty compressor valves would be the appropriate service requirement in this situation.

The solenoid unloaders on reciprocating compressors are designed to unload the clearance spaces in the cylinders. When the compressor is unloaded, the solenoid unloaders open the clearance spaces to allow the compressed air to escape, reducing the pressure in the cylinders. This prevents the compressor from continuously compressing air and allows it to operate more efficiently. By unloading the clearance spaces, the compressor can control its capacity by adjusting the amount of air being compressed and prevent excessive pressure buildup.

Liquid level gauges, except for bull's eye type, should have shut off valves that can be operated both manually and automatically. This means that the shut off valves can be closed either by manually turning a handle or by an automatic mechanism. Having both manual and automatic shut off valves ensures that the liquid level can be controlled and stopped in case of emergencies or maintenance requirements. This allows for greater flexibility and safety in operating and maintaining the liquid level gauges.

A flare fitting that is 3/4" or larger cannot be used because it cannot be tightened enough to create a good seal. Flare fittings rely on compression to form a tight seal, and larger fittings require more force to achieve this compression. Therefore, it is easier and more effective to use other methods, such as sweating or soldering, for larger fittings.

The compressor in this commercial refrigeration system is activated by the low side pressure stat. The low side pressure stat is responsible for monitoring and controlling the pressure on the suction or low-pressure side of the system. When the pressure drops below a certain set point, the low side pressure stat signals the compressor to turn on and start compressing refrigerant gas. This helps maintain the desired pressure and temperature levels in the system.

Flooded evaporators have high heat transfer per square foot, which means they are efficient at transferring heat. However, a disadvantage of flooded evaporators is that they require a higher refrigerant charge. This means that more refrigerant is needed to operate the system, which can be costly and may have environmental implications.

A rupture disc in a centrifugal refrigerating machine is normally located on the evaporator. The evaporator is responsible for absorbing heat from the surroundings and turning the refrigerant into a low-pressure gas. If there is a sudden increase in pressure or a malfunction in the system, the rupture disc on the evaporator will burst, allowing the excess pressure to be released and preventing any damage to the machine. This ensures the safety and proper functioning of the refrigerating machine.

The most likely cause for the significant increase in superheat temperature for the refrigerating fluid entering a reciprocating compressor is scale particles lodged in the TEV valve. Scale particles can obstruct the flow of refrigerant and disrupt the normal operation of the thermal expansion valve (TEV), leading to improper regulation of the refrigerant flow and an increase in superheat temperature. This can result in inefficient cooling and potential damage to the compressor.

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Using two compressors in a cascade system allows for the accomplishment of lower temperatures. The cascade system consists of two separate refrigeration cycles, with each compressor operating at different temperature levels. The lower temperature cycle is used to cool the higher temperature cycle, resulting in lower overall temperatures. This is beneficial in applications where extremely low temperatures are required, such as in scientific research or industrial processes. By dividing the cooling load between two compressors, the cascade system can achieve lower temperatures more efficiently and effectively.

According to the NYC Fire Handbook, the maximum quantity of refrigerant in gallons that can be legally filled in each container under any circumstances is 30.

The purpose of the equalizer line is to make up for the pressure drop in the evaporator. As refrigerant flows through the evaporator, there is a decrease in pressure due to the cooling process. The equalizer line allows for the equalization of pressure between the evaporator and the rest of the system, ensuring that the proper amount of refrigerant is metered and preventing any significant pressure drop.

The correct answer is 101.3. This is because 29.92" Hg is the standard atmospheric pressure at sea level in inches of mercury, and 1 inch of mercury is equivalent to 3.38639 kilopascals. Therefore, 29.92" Hg can be converted to 101.3 kilopascals.

The mechanism sitting above the condenser in a refrigeration system is known as the economizer. The economizer is responsible for improving the overall efficiency of the refrigeration cycle by utilizing the waste heat from the compressor to preheat the refrigerant before it enters the condenser. This helps in reducing the energy consumption of the system.

A stuffing box is a type of shaft seal that prevents vapor from leaking out of a compressor. It is a traditional sealing method that uses packing material, such as braided rope or graphite, to create a seal around the shaft. This prevents vapor from escaping and helps maintain the efficiency and performance of the compressor.

To produce colder water supply, the RMO should lower the compressor suction operating pressure. By reducing the suction pressure, the compressor will draw in less heat from the surrounding air, resulting in a colder water supply. Re-adjusting the TEV superheat setting, deactivating the freeze stat, or raising the compressor discharge operating pressure would not directly affect the temperature of the water supply.

When using a portable compressor recovery unit to remove vapor, the vapor density will decrease. This is because the compressor recovery unit is designed to remove vapor from a system, thereby reducing the concentration or density of vapor in the system.

A possible explanation for the correct answer, "LEAK IN THE SUCTION VALVE," is that a leak in the suction valve can cause a decrease in the efficiency of the compressor. When there is a leak, the compressor may not be able to draw in the required amount of gas, leading to a decrease in the compression ratio and overall efficiency. This can result in reduced performance and increased energy consumption.

Increasing the amount of sub-cooling in the condenser of a refrigeration system can improve the performance of a centrifugal compressor. Sub-cooling refers to the process of cooling the refrigerant below its saturation temperature, which helps to remove additional heat from the refrigerant before it enters the compressor. By increasing the amount of sub-cooling, the temperature of the refrigerant entering the compressor is lower, which improves the compressor's efficiency and reduces the risk of damage due to overheating. This ultimately leads to better overall performance of the refrigeration system.

The correct answer is "HIGH PRESSURE GAS AND LEAVES AS HIGH PRESSURE LIQUID." This is because the condenser is the component in a refrigeration system where the refrigerant, in its gaseous state and under high pressure, releases heat and condenses into a high-pressure liquid. This high-pressure liquid is then sent to the expansion valve to continue the refrigeration cycle.

Water, being denser than the refrigerant, would settle at the bottom. The refrigerant would occupy the middle layer, and the lubricating oil, being less dense than both, would float on top. Therefore, the correct order is water, refrigerant, and then oil.

The correct answer suggests that when a refrigeration unit with a low side float valve is experiencing short cycling of the motor compressor, the operator should consider adding additional refrigerant. This is because short cycling can be caused by a low refrigerant charge, which leads to inadequate cooling and causes the compressor to turn on and off frequently. By adding more refrigerant, the system can achieve the proper charge and prevent short cycling.

The saturation pressure of a refrigerant can be used to estimate the temperature of the chilled water being pumped to the building spaces that are being cooled. The saturation pressure of the refrigerant is directly related to its temperature, so by observing the gauge reading, the RMO can determine the temperature of the chilled water.

Frost appearing on the suction line and part of the compressor is caused by a flooded evaporator. When the evaporator is flooded, excess liquid refrigerant enters the compressor, causing the temperature of the compressor to drop below freezing. This leads to the formation of frost on the suction line and compressor.

Gate valves cause more leakage because they have a design that allows for a larger flow area when fully open, but when partially closed, the flow area is reduced, creating turbulence and increasing the chance of leakage. Globe valves, on the other hand, have a more restrictive flow path, which reduces the chance of leakage. Therefore, the statement "Gate valves cause more leakage" is the most correct.

The operator should avoid using the globe valve because it typically has a higher pressure drop compared to the other options. Globe valves have a more complex design with a curved flow path, which causes more resistance to flow and results in a higher pressure drop. In contrast, ball, plug, and gate valves have a more streamlined flow path, allowing for lower pressure drop. Therefore, to minimize pressure drop, the operator should avoid using the globe valve.

Shell and coil condensers have the advantage of having less chance of developing leaks. This means that compared to other types of condensers, shell and coil condensers are less likely to experience leaks in the long run. This is beneficial because leaks can lead to a loss of refrigerant and a decrease in system efficiency. By having less chance of developing leaks, shell and coil condensers offer improved reliability and performance.

If the operator throttles back on the discharge valve of the other pump, it would result in a reduction in the total flow rate to the condenser. This is because by throttling back on the valve, the operator is restricting the flow of water from the pump, thereby reducing the overall flow rate.

The correct answer is "Suction valve and discharge bypass both open". This is the proper procedure for starting the machine without unloaders. By opening the suction valve, the machine can draw in the necessary fluid. By opening the discharge bypass, the fluid can bypass the machine until it reaches the desired pressure or flow rate. This allows the machine to start up safely and prevents any damage or overload to the reciprocating machine.

An inline refrigerant cleaning system is advisable because refrigerant reacts with the lubrication oil. This means that if the refrigerant is not properly cleaned, it can contaminate the lubrication oil, leading to decreased efficiency and potential damage to the system. By using an inline cleaning system, any contaminants or impurities in the refrigerant can be effectively removed before it comes into contact with the lubrication oil, ensuring the smooth operation and longevity of the refrigeration system.

According to the NYC Fire Law Handbook, the maximum quantity of refrigerant that can be legally stored in the machinery room is 200 pounds.

The correct answer is 70 because PSIG is a unit of pressure relative to atmospheric pressure, while Hg absolute is a unit of pressure relative to a vacuum. To convert PSIG to Hg absolute, you need to add the atmospheric pressure to the PSIG value. Since atmospheric pressure is typically around 14.7 PSI, adding this to 20 PSIG gives a total of 34.7 PSI. Converting 34.7 PSI to Hg absolute gives a value of approximately 70 Hg absolute.

The BTUs absorbed by the condensing water will be the greatest when the condenser temperature is high and the condenser water temperature is low. This is because a high condenser temperature means that the refrigerant has a higher temperature difference with the water, allowing for more heat transfer. Additionally, a low condenser water temperature means that the water can absorb more heat from the refrigerant. Therefore, the combination of a high condenser temperature and a low condenser water temperature maximizes the heat transfer and results in the greatest amount of BTUs absorbed by the condensing water.

Lowering the condenser pressure results in a more efficient operation of a centrifugal compressor. When the condenser pressure is lowered, the temperature at which the refrigerant condenses decreases. This allows for a larger temperature difference between the condensing temperature and the evaporating temperature, which improves the overall efficiency of the refrigeration cycle.

The recovery process will slow down because the refrigerant pressure will decrease. When the pressure of the refrigerant decreases, it will take longer for the compressor to recover the vapor refrigerant from the machine. This is because the compressor needs a certain level of pressure to effectively and efficiently recover the refrigerant. With a decrease in pressure, the compressor will have to work harder and take more time to recover the refrigerant.

The heat in BTU per minute absorbed by the condenser water in a refrigerating plant is greater under the condition of low evaporative temperature and high condenser temperature1. This is because the heat transfer in a refrigeration cycle is driven by the temperature difference between the refrigerant and the surrounding medium (in this case, the condenser water). A low evaporative temperature means the refrigerant absorbs less heat, and a high condenser temperature means it can reject more heat to the condenser water. Therefore, these conditions would result in the greatest heat absorption by the condenser water.

As the suction pressure increases, the HP per ton of refrigerating effect would most likely decrease. This is because as the suction pressure increases, the compressor has to work harder to compress the refrigerant and achieve the desired cooling effect. This increased workload leads to a decrease in efficiency, resulting in a lower HP per ton of refrigerating effect.