Mixed Deck — All CARO Topics Flashcards

Why is it important to pitch refrigerant suction lines toward the compressor?

Answer: To ensure oil and liquid refrigerant drain back to the compressor rather than trap in low spots

Suction lines are pitched toward the compressor so that oil and any liquid refrigerant flow back naturally, preventing oil logging in the evaporator and liquid slugging in the compressor.

A low-pressure controller on an ammonia system is set to cut out at a specific suction pressure. What does a cut-in pressure setting represent?

Answer: The pressure at which the compressor restarts after a low-pressure shutdown

The cut-in pressure is the suction pressure at which the low-pressure controller closes and allows the compressor to restart after conditions have returned to acceptable levels.

Why is preventive maintenance critical in refrigeration systems?

Answer: To extend equipment lifespan

Preventive maintenance is critical in refrigeration systems because it helps identify and address minor issues before they escalate into major failures. Regular inspections, cleaning, and adjustments reduce wear and tear, optimize system performance, and significantly extend the operational lifespan of expensive refrigeration equipment. This proactive approach ultimately saves on costly repairs and replacements.

A refrigeration system has high suction pressure and high discharge pressure. What is the most likely cause?

Answer: Dirty or fouled condenser reducing heat rejection

A dirty condenser restricts heat rejection, causing both condensing pressure (discharge) and suction pressure to rise as the system struggles to remove heat from the refrigerant.

What PPE is most essential when handling refrigerants?

Answer: Gloves and safety goggles

When handling refrigerants, gloves and safety goggles are essential PPE because refrigerants can cause severe frostbite if they come into contact with skin or eyes due to their extremely low temperatures. Some refrigerants can also cause chemical burns or irritation. This PPE provides critical protection against direct exposure and potential splashes.

A pilot-operated pressure regulating valve (PRV) in refrigeration is used to:

Answer: Automatically maintain a set downstream pressure regardless of upstream pressure changes

A pilot-operated pressure regulating valve uses a small pilot valve to sense downstream pressure and modulate the main valve to maintain a constant set pressure, enabling precise automatic pressure control.

In the event of a major, uncontrolled outdoor ammonia release, which of the following is the most important factor for determining a safe personnel evacuation route?

Answer: The current wind direction.

Ammonia vapor is carried by the wind. To evacuate safely, personnel must move upwind and crosswind to avoid the traveling plume of hazardous gas. Windsocks are often required at facilities for this reason. The other factors are secondary to avoiding the ammonia cloud itself.

What is the purpose of a wet suction riser in an ammonia refrigeration system?

Answer: To carry a mixture of vapor and liquid upward without trapping liquid at the compressor

A wet suction riser is designed to carry two-phase refrigerant (liquid and vapor) upward in the piping while preventing liquid slugs from reaching the compressor.

Why are leak inspections required for refrigeration systems above certain charge sizes?

Answer: To minimize environmental impact

Leak inspections are required for refrigeration systems above certain charge sizes primarily to minimize their environmental impact. Refrigerants, particularly HFCs, are potent greenhouse gases, and leaks contribute significantly to climate change. Regular inspections help detect and repair leaks promptly, reducing harmful emissions and ensuring compliance with environmental regulations.

Which refrigerant type is most harmful to the ozone layer?

Answer: CFCs

Chlorofluorocarbons (CFCs) are the refrigerant type most harmful to the ozone layer. They contain chlorine atoms that, when released into the atmosphere, rise to the stratosphere and catalytically destroy ozone molecules, leading to the depletion of the protective ozone layer. Due to their severe environmental impact, CFCs have been largely phased out globally.

An ammonia system's suction pressure gauge reads 0 psig. What approximate evaporating temperature does this correspond to for ammonia (R-717)?

Answer: -28°F

For ammonia (R-717), 0 psig (atmospheric pressure) corresponds to a saturation temperature of approximately -28°F, which is its normal boiling point at atmospheric pressure.

An operator notices a strong ammonia odor in the engine room, but the permanently installed ammonia detectors have not gone into alarm. Which of the following statements is the most accurate explanation for this situation?

Answer: The odor threshold for ammonia is very low, and it can be easily detected by smell well below the concentration required to trigger a low-level alarm.

Ammonia has a very low odor threshold, typically detectable by humans at concentrations around 5 parts per million (ppm). Safety alarm systems are set at much higher concentrations, often with a low-level alarm at 25-50 ppm (the TWA-TLV) and high-level alarms at 150 ppm or more. Therefore, it is common to smell ammonia before a detector alarms, serving as an early warning of a small leak.

How can vibration in a refrigeration system be reduced during preventive maintenance?

Answer: Tighten mounting and connections

Vibration in a refrigeration system can indicate loose components, which can lead to increased noise, wear, and potential equipment failure. During preventive maintenance, tightening mounting bolts, brackets, and connections helps secure components. This action reduces excessive vibration and ensures the system operates smoothly and reliably, preventing premature damage.

A refrigeration system shows normal discharge pressure but abnormally low suction pressure with high suction superheat. The TXV bulb is properly clamped. What is likely wrong?

Answer: Plugged liquid line filter-drier or partially closed liquid line valve starving the TXV

A plugged filter-drier or closed liquid line valve restricts liquid refrigerant flow to the TXV, starving the evaporator and causing low suction pressure with high superheat even though the TXV is functioning correctly.

When isolating a section of refrigeration piping for repairs, the correct procedure is to:

Answer: Close isolation valves, relieve trapped pressure safely, verify pressure is zero, then open the line

After closing isolation valves, any trapped refrigerant must be safely relieved and pressure verified at zero before opening piping, to prevent sudden release of pressurized refrigerant or ammonia exposure.

What is the primary function of a slide valve in a large screw compressor?

Answer: To provide a means of capacity control.

The slide valve is a movable component within the screw compressor housing that changes the point where compression begins. By adjusting its position, it effectively alters the volume of refrigerant being compressed, allowing for smooth, continuous capacity control to match the cooling load.

What does 'pipe schedule' refer to in refrigeration piping specifications?

Answer: The wall thickness of the pipe relative to its nominal diameter

Pipe schedule designates the wall thickness of a pipe; higher schedule numbers indicate thicker walls and higher pressure ratings, which is critical for high-pressure refrigeration applications.

The purpose of using unloaders on a multi-cylinder reciprocating compressor is to:

Answer: Reduce the starting torque and provide capacity control.

Unloaders work by holding the suction valves open on one or more cylinders. This prevents those cylinders from compressing gas, which significantly reduces the load on the motor during startup. It also serves as a method of capacity control by effectively reducing the compressor's pumping volume to match lower cooling demands.

Which of the following is a mandatory verification step in a Lockout/Tagout (LOTO) procedure that must be performed after applying the lock and tag but before beginning maintenance?

Answer: Attempting to operate the normal machine controls to ensure the equipment does not start.

A critical step in the LOTO process is verification. After the energy-isolating device is locked and tagged, the authorized employee must verify that the isolation is effective. This is typically done by attempting to operate the equipment through its normal controls (e.g., pushing the start button) to ensure it is de-energized. This step confirms that the correct energy source was locked out and the procedure was successful.

Which federal agency regulates refrigerant emissions in the United States?

Answer: EPA

The Environmental Protection Agency (EPA) is the federal agency responsible for regulating refrigerant emissions in the United States. Under the Clean Air Act, the EPA establishes rules for the handling, recovery, recycling, and disposal of refrigerants. These regulations aim to protect the ozone layer and mitigate climate change by controlling harmful emissions.