Refrigerant Machine Operator Test #2

When a compressor is said to have a safety head, it means that the compressor has a pressure relief valve. This valve is designed to release excess pressure in the compressor system to prevent any damage or failure. The pressure relief valve ensures that the pressure inside the compressor does not exceed safe limits, protecting both the compressor and the surrounding equipment or system.

The most likely cause for the condenser water pump cavitation in a refrigeration system employing R-22 refrigerant is a faulty cooling tower water level controller. This is because if the water level in the cooling tower is not properly controlled, it can lead to inadequate water supply to the condenser, resulting in cavitation. Cavitation occurs when the pressure in the pump drops too low, causing the refrigerant to vaporize and form bubbles, which can damage the pump and decrease its efficiency. Therefore, a faulty cooling tower water level controller is the most likely cause of this condition.

Chiller water temperature can be as low as 33°F. Chiller systems are used to cool buildings, industrial processes, and equipment. Lowering the chiller water temperature helps to remove heat more efficiently and achieve the desired cooling effect. However, going below this temperature may cause issues such as freezing of the water or damage to the chiller components. Therefore, 33°F is the recommended minimum temperature for chiller water.

The given question is asking for the pressure at 38°F based on the given pressures at 35°F and 45°F. To find the pressure at 38°F, we can use the concept of linear interpolation. Since the temperature is increasing, we can assume that the pressure is also increasing linearly. By calculating the slope using the given data, we can determine the pressure at 38°F. The slope is (70 PSI - 62 PSI) / (45°F - 35°F) = 0.8 PSI/°F. Now, we can calculate the pressure at 38°F by using the formula: pressure at 38°F = 62 PSI + (0.8 PSI/°F) * (38°F - 35°F) = 64.4 PSI. Therefore, the correct answer is 64.4.

The correct answer is 15-30 PSI HIGHER. In a compressor, the suction pressure refers to the pressure of the refrigerant entering the compressor. The oil pressure gauge measures the pressure of the lubricating oil in the compressor. The reading in the oil pressure gauge should be higher than the suction pressure because the oil pressure needs to be sufficient to ensure proper lubrication and cooling of the compressor components. A higher oil pressure helps to maintain the integrity and efficiency of the compressor.

The correct answer is CENTRIFUGAL CHILLED WATER PUMP. This type of pump is specifically designed to circulate chilled water in a centrifugal motion. It is commonly used in HVAC systems to transfer the chilled water from the chiller to the air handling units or other cooling equipment. The centrifugal force generated by the rotating impeller of the pump helps in creating the pressure needed to move the chilled water through the system.

In a reciprocating system using an evaporative condenser, the muffler is installed between the compressor and the evaporative condenser. The muffler is a device that helps to reduce noise and vibration in the system. By installing it between the compressor and the evaporative condenser, it helps to dampen any noise or vibration generated by the compressor before it reaches the condenser. This ensures that the condenser operates smoothly and efficiently without any disturbances caused by the compressor.

Using two compressors in a cascade system allows for accomplishing lower temperatures. By having two compressors working in tandem, the system can achieve a greater cooling capacity and reach lower temperatures than a single compressor alone. This is especially beneficial in applications where extremely low temperatures are required, such as in industrial refrigeration or cryogenic systems. Additionally, using multiple compressors can provide redundancy and improve system reliability, as one compressor can continue operating if the other fails.

Resistors are classified as electric devices that can be used to provide built-in defrosting of refrigerating machine evaporator units. Resistors are passive electrical components that restrict the flow of electric current, generating heat in the process. This heat can be utilized to defrost the evaporator units by melting any ice or frost that may have accumulated. Unlike relays, induction coils, and capacitors, resistors are specifically designed to generate heat and are therefore suitable for defrosting purposes.

The correct answer is 66 PSIG. In refrigeration systems, the evaporator temperature is directly related to the suction pressure. R-22 is a common refrigerant, and for a temperature of 38°F in the evaporator, the corresponding suction pressure should be 66 PSIG. The "PSIG" unit indicates that the pressure is measured in pounds per square inch gauge, which means it is measured relative to atmospheric pressure.

The state of the refrigerant as it leaves the compressor is superheated vapor because the refrigerant has absorbed heat from the surroundings and its temperature has increased above its saturation temperature. As the refrigerant leaves the condenser, it is in a warm sub-cooled liquid state because it has been cooled down below its saturation temperature but is still in a liquid form.

Recovery refers to the process of retrieving or extracting useful materials or energy from waste or discarded items. In the context of recycling, recovery involves collecting and processing waste materials to reuse or convert them into new products. It helps to minimize waste generation and conserve resources by giving a second life to materials that would otherwise end up in landfills. Recovery can also involve the extraction of valuable substances or energy from industrial processes or wastewater. Overall, recovery plays a crucial role in sustainable waste management and resource conservation.

The mechanism sitting above the evaporator is known as the purge unit. The purge unit is responsible for removing any non-condensable gases, such as air or moisture, from the refrigeration system. This is important because these gases can reduce the efficiency of the system and cause damage to the components. The purge unit typically uses a combination of pressure differentials and heat to separate and remove these gases from the system, ensuring that only the desired refrigerant remains in the system.

When a system does not have unloaders, other capacity control methods are needed. Unloaders are devices that control the capacity of a system by unloading or bypassing excess refrigerant. Without unloaders, other capacity control methods such as variable inlet guide vanes, an economizer, or a solenoid on the liquid line need to be implemented to regulate the capacity of the system. These alternative methods help to ensure that the system operates efficiently and effectively without the use of unloaders.

If the flame of a halide torch used to check for refrigerant leaks turns yellow, it indicates a restriction in the tube. This means that there is a blockage or obstruction in the refrigerant flow, preventing it from moving freely. This restriction can be caused by various factors such as debris, dirt, or ice buildup in the tube. It is important to address this issue as it can affect the performance and efficiency of the refrigeration system.

The clearance volume refers to the volume of space in the compressor that is not swept by the piston during the compression stroke. This volume affects the compressor capacity because it reduces the amount of refrigerant that can be compressed and delivered. A larger clearance volume results in a decrease in compressor capacity, while a smaller clearance volume increases the capacity. Therefore, the statement "AFFECTS COMPRESSOR CAPACITY" is the correct explanation for the given answer.

The primary reason for the insulation of a crankcase breather line is to prevent oil slugging in the compressor. Insulating the breather line helps to maintain the temperature of the oil and prevents it from condensing and accumulating in the compressor. This is important because oil slugging can cause damage to the compressor and reduce its efficiency. By insulating the breather line, the oil is kept at a consistent temperature and is less likely to cause any issues within the compressor.

In a centrifugal three-stage compressor, the pressure increases with each stage. This is because as the gas passes through each stage, it is compressed further, leading to an increase in pressure. Additionally, the impellers in each stage are of the same size. This ensures that the gas is compressed uniformly and efficiently throughout the compressor. Therefore, both statements A and B are correct.

The correct answer is EVAPORATIVE. An evaporative condenser uses both air and water for cooling. It works by allowing water to evaporate into the air, which removes heat from the system being cooled. This type of condenser is commonly used in air conditioning systems and refrigeration units. It is an efficient and cost-effective method of cooling, particularly in dry climates.

When an evaporator is not equipped with an equalizer line, you would most likely find a distributor. A distributor is used to evenly distribute the refrigerant flow to multiple evaporator coils. Without an equalizer line, the pressure between the inlet and outlet of the evaporator may vary, causing uneven refrigerant distribution. The distributor helps to ensure that each coil receives an equal amount of refrigerant, optimizing the cooling efficiency of the system.

The given question is asking for the conversion of 29.92" HG to kPa. The correct answer is 101.3 kPa. This is the standard atmospheric pressure at sea level.

According to the U.S. Environmental Protection Agency (EPA) regulations, the maximum percentage that a refrigerant can be stored in an EPA-approved cylinder is 80%. This guideline is in place to ensure safety during storage and transportation, as overfilling can lead to increased pressure inside the cylinder, potentially causing damage or posing a risk to those handling the refrigerant. Additionally, allowing some empty space in the cylinder accommodates the expansion of the refrigerant when exposed to heat and facilitates easier handling.

The heat that boils off in a condenser is latent heat. Latent heat refers to the heat energy required to change the state of a substance without changing its temperature. In the condenser, the vapor is condensed back into a liquid state, releasing latent heat. Sensible heat refers to the heat energy that causes a change in temperature, while superheat refers to the additional heat energy added to a substance above its boiling point. However, in the context of a condenser, the heat being boiled off is specifically latent heat.

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Gate valves have a linear motion and a full bore design, which means that when fully open, the flow path is unrestricted. However, when partially open, the flow is restricted, leading to a higher pressure drop and potential for leakage. Globe valves, on the other hand, have a more complex design with a plug and seat arrangement, which allows for better throttling control and lower leakage rates compared to gate valves. Therefore, the statement "Gate valves cause more leakage" is the most correct.

A stuffing box is a type of shaft seal that prevents vapor from leaking out of a compressor. It is a traditional and commonly used sealing method in various industries. The stuffing box consists of packing material, such as braided or molded graphite, which is compressed around the shaft to create a seal. This prevents the escape of vapor and helps maintain the desired pressure within the compressor.

The correct answer is PRESSURE GAUGE AND GLOBE VALVE. This is because the arrow is pointing towards a device that measures pressure (pressure gauge) and a type of valve (globe valve) that is commonly used to control the flow of fluid in a pipeline. The other options mentioned different combinations of accessories that are not indicated by the arrow.

A sudden drop in crankcase pressure can cause oil foaming in the crankcase of an R-12 reciprocating system. When the pressure drops suddenly, it creates a vacuum in the crankcase, causing the oil to vaporize and form foam. This can lead to reduced lubrication and potential damage to the system.

A centrifugal compressor generates high volume, low pressure inside. This means that it takes in a large volume of air or gas and compresses it to a lower pressure. This is achieved by using centrifugal force to accelerate the air or gas and then converting the kinetic energy into pressure. The high volume, low pressure output is suitable for applications such as cooling, ventilation, and pneumatic conveying.

The correct answer is "ALL THE ABOVE". Compressor motors that operate inside the refrigerant atmosphere must use materials compatible with the system refrigerants, as the refrigerants can have corrosive effects on certain materials. These motors must also be assembled in a clean atmosphere and kept dry to prevent any contamination or damage. Additionally, they are not worked on in the field, meaning any maintenance or repairs must be done in a controlled environment to ensure the motor's integrity. Therefore, all of the given statements are true for compressor motors operating inside the refrigerant atmosphere.

Refrigerant recycling is the correct answer because it refers to the process of cleaning and purifying used refrigerant so that it can be reused in the same system or in another system. This is an inline refrigerant cleaning system, which means it is designed to clean the refrigerant while it is still in the system, rather than removing it for cleaning. Recycling the refrigerant helps to reduce waste and environmental impact by reusing the refrigerant instead of disposing of it or releasing it into the atmosphere.

If the crankcase and compressor discharge temperature have dropped significantly and the suction line pressure is high, it indicates that the compressor valves are faulty. Faulty compressor valves can lead to a decrease in compression efficiency, causing lower temperatures in the crankcase and compressor discharge, and higher pressure in the suction line. This is the most likely cause of the given set of conditions.

In an induced draft cooling tower, the dry bulb temperature refers to the actual air temperature, while the wet bulb temperature is the lowest temperature that can be achieved through evaporative cooling. Since the wet bulb temperature is determined by the moisture content in the air, it is always lower than the dry bulb temperature. Therefore, the correct answer is "DRY BULB HIGHER THAN WET BULB."

When running three compressors, the refrigerant leaving the third evaporator coil would be in a state of superheated vapor. This means that the refrigerant has absorbed enough heat to completely vaporize, and then it has been further heated beyond its saturation temperature. In this state, the refrigerant is fully vaporized and any remaining liquid has been evaporated.

Shell and coil condensers have the advantage of having less chance of developing leaks. This means that they are less likely to experience any leakage issues compared to other types of condensers. This can be beneficial as it reduces the risk of refrigerant leakage, which can lead to decreased efficiency and potential safety hazards. Additionally, it implies that the condenser will have a longer lifespan and require less maintenance and repair work.

The compression ratio of a centrifugal chiller is calculated by dividing the discharge pressure by the suction pressure. In this case, the discharge pressure is given as 6 PSIG and the suction pressure is given as 18" HG vacuum. To convert the suction pressure from inches of mercury to PSIG, we need to use a conversion factor. 1 inch of mercury is equal to 0.491 PSIG. Therefore, the suction pressure in PSIG is 18" HG vacuum * 0.491 PSIG/inch of mercury = 8.838 PSIG. Now we can calculate the compression ratio: 6 PSIG / 8.838 PSIG = 0.679. Therefore, the correct answer is not provided in the options.

When charging a centrifugal system, the position of the valve is "back seated." This means that the valve is fully closed, preventing any flow of fluid through the system. This position is typically used when the system is not in use or when it needs to be temporarily shut off for maintenance or repairs. By back seating the valve, it ensures that no fluid can enter or exit the system, allowing for safe and controlled charging of the system.

Bubbles in the sight glass are most likely caused by a partially plugged filter/drier. The sight glass is used to indicate the presence of liquid refrigerant in the system. If there are bubbles in the sight glass, it suggests that there is a lack of liquid refrigerant reaching the sight glass, which can be caused by a partially plugged filter/drier. This obstruction can prevent the proper flow of refrigerant, leading to the formation of bubbles in the sight glass.

If a low-pressure refrigeration system has a pinhole in the evaporator, the most likely result would be high head pressure. This is because the pinhole would cause a leak in the system, leading to a decrease in refrigerant flow. As a result, the compressor would have to work harder to maintain the desired pressure, leading to increased head pressure.

Superheating of the vapor flowing into a reciprocating compressor can decrease the capacity of the compressor and the refrigeration machine. When the vapor is superheated, it means that it has a higher temperature than its saturation temperature at a given pressure. This reduces the density of the vapor, leading to a decrease in the mass flow rate and ultimately reducing the capacity of the compressor and the refrigeration machine.

The volume of a cylinder can be calculated using the formula V = πr^2h, where r is the radius and h is the height. In this case, the diameter is given as 6', so the radius would be half of that, which is 3'. The length of the condenser is given as 20', so the height would be 20'. Plugging these values into the formula, we get V = π(3^2)(20) = 180π cubic feet. Since 7.48 gallons is equal to 1 cubic foot, we can convert cubic feet to gallons by multiplying by 7.48. Therefore, the volume in gallons would be 180π * 7.48 ≈ 4227.

If the insulation on the suction pipe between the evaporator coil and the compressor is unraveled, it would result in a flooded evaporator. This is because the thermal bulb, which is responsible for sensing the temperature of the suction line, would be exposed to the warm ambient temperature of the machine room. As a result, the thermal bulb would not accurately sense the temperature of the refrigerant in the suction line, leading to a malfunction in the control of the expansion valve. This could cause an excessive flow of refrigerant into the evaporator, leading to a flooded condition.

When a compressor is running fine at full flow and suddenly stops running normally (short cycle) after throttling down the flow, it is likely due to a low pressure cut out. A low pressure cut out is a safety feature in compressors that shuts off the compressor when the pressure in the system drops below a certain threshold. Throttling down the flow reduces the pressure in the system, causing the low pressure cut out to activate and stop the compressor from running.

When a hermetic compressor operates with a low refrigerant charge, it means there is not enough refrigerant circulating through the system. This can lead to inadequate cooling and cause the compressor to operate at a higher temperature. Without enough refrigerant to absorb and carry away heat, the compressor will have to work harder and generate more heat, resulting in a higher operating temperature.

The condition of water entering the condenser at 88°F suggests that the water valve is stuck open. If the valve is stuck open, it means that the valve is not regulating the flow of water properly, allowing too much water to enter the condenser. This can result in high head pressure, as there is an excessive amount of water in the condenser causing the temperature to rise.

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 there is a larger temperature difference between the condensing refrigerant and the condensing water, allowing for more heat transfer. Additionally, a low condenser water temperature helps to maintain a larger temperature gradient, further enhancing the heat transfer process.

The correct answer is HIGH SIDE PRESSURE. A water regulating valve in a water-cooled condenser is responsible for controlling the flow of water to maintain the desired operating conditions. The high side pressure, which refers to the pressure on the high-pressure side of the refrigeration system, directly affects the operation of the condenser. By adjusting the valve based on the high side pressure, the flow of water can be regulated to ensure efficient cooling and proper functioning of the condenser.

If the external equalizer line disconnects when there is a 5 lb pressure drop across the evaporator, the evaporator would starve. This means that the flow of refrigerant to the evaporator would be restricted or reduced, leading to insufficient cooling capacity. As a result, the evaporator may not be able to remove enough heat from the system, causing a decrease in cooling performance.

When the insulation on the suction line is removed and the engine temperature is at 85°F, excessive superheat will occur. Superheat refers to the temperature of the refrigerant gas above its boiling point. When the insulation is removed, the suction line is exposed to higher ambient temperatures, causing the refrigerant gas to become excessively heated before entering the compressor. This leads to excessive superheat, which can negatively affect the performance and efficiency of the refrigeration system.

Condenser operation, dirty tubes or cooling water control may be causing this set of conditions. When the condenser operation is not functioning properly, it can lead to high crankcase temperature, low compressor discharge temperature, and high suction line temperature. Dirty tubes or inadequate cooling water control can also contribute to these abnormal temperature conditions.