Mechanical Master License Exam

Mechanical Master License Exam Practice Test Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of a backflow preventer in a hydronic

heating system?

• To increase flow rate
• To maintain system pressure
• To prevent contamination of potable water
• To balance return flow

Backflow preventers ensure that non-potable water does not reverse flow into potable water systems, maintaining safety and health standards.

• Which of the following gases is commonly used in leak detection for HVAC

systems? 1 / 4

• Oxygen
• Nitrogen
• Carbon dioxide
• Helium

Nitrogen is inert and safe for pressure testing; oxygen is avoided due to combustion risk.

• What is the minimum slope required for horizontal drainage piping less

than 3 inches in diameter?

• 1/8 inch per foot
• 1/4 inch per foot
• 3/8 inch per foot
• 1/2 inch per foot

A slope of 1/4 inch per foot ensures proper drainage and prevents solids from settling in the pipe.

• What is the typical voltage for most residential HVAC blower motors?

A. 110V

B. 208V

C. 240V

D. 480V

Most residential HVAC systems use 240V for blower and compressor motors to ensure efficient operation. 2 / 4

• What type of valve is best suited for throttling flow in a hydronic system?
• Gate valve
• Globe valve
• Ball valve
• Check valve

Globe valves are designed for precise flow control due to their linear motion design.

• Which material is most resistant to corrosion in a high-temperature steam

system?

• Copper
• Stainless steel

C. PVC

• Cast iron

Stainless steel withstands high temperatures and corrosion, making it ideal for steam systems.

• In refrigeration, the component that separates the high-pressure side

from the low-pressure side is the:

• Evaporator
• Compressor 3 / 4

• Expansion device
• Condenser

The expansion device drops refrigerant pressure before entering the evaporator, dividing high and low sides.

• What is the purpose of a trap in a condensate line?
• To prevent freezing
• To remove debris
• To prevent air leakage
• To increase flow

A trap holds water to prevent air from bypassing the drain line and affecting system balance.

9. The function of a thermal expansion valve (TXV) is to:

• Control compressor speed
• Regulate refrigerant flow into the evaporator
• Increase condenser efficiency
• Maintain suction pressure

The TXV meters refrigerant based on superheat, optimizing system performance.

• / 4