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Quiz: Construction Classes, Materials and Spark Resistance

Test your understanding of construction class, construction materials, spark-resistant construction, high temperature and high moisture construction, and insulated fans with these review questions.

1. Which of these materials does NOT qualify as non-ferrous for spark-resistant construction?

  1. Monel
  2. Brass
  3. Type 316 stainless steel
  4. Aluminum/nickel/bronze
Show Answer

The correct answer is C. A non-ferrous material is a metal or alloy that is not based on iron. Stainless steel is an iron-based alloy, so it is ferrous even though it resists corrosion. FanPedia's list of typical non-ferrous materials for spark-resistant construction is aluminum, aluminum/nickel/bronze, Monel, copper, brass and bronze, which includes options A, B and D. Reading "stainless" as non-ferrous is a common trap.

Concept Tested: Non-Ferrous Material

See: Non-Ferrous Material

2. What is steel/double wall construction?

  1. A removable 2-inch insulating blanket wrapped around the housing in labeled pieces
  2. A second structural outer housing of at least 14 gauge steel, built by Twin City Fan around the inner housing with insulation between them
  3. A stucco-embossed aluminum skin installed by an outside vendor over insulation
  4. A housing made of two layers of stainless steel welded together for corrosion resistance
Show Answer

The correct answer is B. Double wall construction is built by Twin City Fan as an outer shell of at least 14 gauge mild steel (or stainless steel if requested) around the inner housing, with fiberglass or mineral wool insulation between them unless otherwise specified. Option A describes an insulated jacket, and option C describes aluminum clad construction, the other two insulated constructions. Option D is not an insulated construction at all.

Concept Tested: Double Wall Construction

See: Insulated Fans

3. How does construction class differ from fan class?

  1. Construction class sets the maximum safe speed of a fan size, while fan class sets its materials
  2. They are two names for the same designation, defined by AMCA Standard 99-2408
  3. Construction class applies only to centrifugal fans, while fan class applies only to axial fans
  4. Construction class describes what the fan is built from and how, for its airstream, while fan class is a pressure and speed rating
Show Answer

The correct answer is D. Construction class is the set of construction choices, such as material, spark resistance, temperature package and insulation, that make the housing and impeller fit for the airstream. Fan class (Class I to IV, defined by AMCA Standard 99-2408) is a pressure and speed rating that decides how fast a fan size may safely run. The two are independent and both go on the order. Option A reverses them, and options B and C are not supported by the chapter.

Concept Tested: Construction Class

See: Construction Class

4. Which statement best describes spark-resistant Type C construction on a centrifugal fan?

  1. The impeller and housing stay steel, and non-ferrous parts such as an aluminum inlet funnel and rub plate are placed where contact is most likely
  2. Every airstream component is non-ferrous, and the bearings are restrained
  3. The impeller is non-ferrous, and it contacts a steel inlet cone if the fan fails mechanically
  4. The fan becomes explosion-proof, so no motor rating needs to be checked
Show Answer

The correct answer is A. Type C is the minimal spark-resistant construction: the impeller and housing stay steel, and non-ferrous parts go at the likely first contact points. On a centrifugal fan these are an aluminum inlet funnel and an aluminum rub plate where the shaft passes through the housing. Option B describes Type A, and option C describes Type B. No spark-resistant type makes a fan explosion-proof, and the motor is a separate decision (D).

Concept Tested: Spark Resistant Type C

See: Spark Resistant Type C, Rub Plates and Rub Rings

5. A 550°F dryer exhaust fan stands beside an operator platform, and maintenance staff open its access door and drain every month. Which insulated construction is the best recommendation?

  1. Aluminum clad construction, because a vendor-built skin is the most permanent
  2. No insulation, because a high temperature package already protects personnel
  3. An insulated jacket, because it protects personnel and can be opened or removed to reach access doors and drains
  4. Steel/double wall construction, because its outer shell can be removed in labeled pieces
Show Answer

The correct answer is C. The job needs both personnel protection and easy monthly access. FanPedia notes that insulated jackets can serve as a safety device to protect personnel, and the jacket can be opened or removed to reach access doors and drains; at 550°F it wraps around a cooler box. Double wall construction (D) is a structural outer shell, not something removed in labeled pieces, and the chapter does not describe the vendor-built aluminum clad skin (A) as made for opening. A temperature package (B) protects the fan, not people touching the hot housing.

Concept Tested: Insulated Jacket

See: Insulated Fans

6. An Arrangement 4 plug fan in high temperature construction will recirculate oven air at 270°F, and the customer asks for an aluminum impeller. What is the correct response?

  1. Accept it, because the standard aluminum impeller limit is 275°F
  2. Decline it, because aluminum rotating parts in Arrangement 4 high temperature fans are limited to 250°F
  3. Accept it, because the 181°F to 300°F package allows aluminum at any temperature in its band
  4. Decline it, because aluminum is never used in spark-resistant or high temperature fans
Show Answer

The correct answer is B. FanPedia limits aluminum rotating parts in high temperature Arrangement 4 centrifugal and plug fans to 250°F. Since 270 > 250, the impeller must be mild steel and Corten or stainless steel. The 275°F limit (A) belongs to the standard aluminum impeller on high temperature axial fans, a different part on a different fan type. The package band (C) does not override the part limit, and aluminum is widely used in spark-resistant construction (D). Twin City Fan engineering adds that current practice does not use Arrangement 4 for high-temperature applications (standard ranges run up to about 180°F). The 250°F limit is FanPedia's rule for the construction it describes.

Concept Tested: Aluminum Construction

See: Aluminum Construction

7. An Arrangement 1 centrifugal fan will recirculate furnace air at 720°F. Which construction line follows FanPedia's rules?

  1. 601°F to 800°F package with mild steel and Corten or stainless steel, high temperature grease, fixed and floating bearings, and a shaft cooler
  2. 501°F to 600°F package with aluminum rotating parts and standard grease
  3. 801°F to 1,000°F package, because the band must sit above the design temperature by at least 100°F
  4. Engineering review only, because every fan over 600°F requires it
Show Answer

The correct answer is A. 720°F lies between 601°F and 800°F, so the fan takes that package, with mild steel and Corten or stainless steel, high temperature grease, and fixed and floating bearings for shaft growth. Because the temperature is over 300°F, FanPedia recommends a shaft cooler. Option B uses the wrong band and materials. Option C invents a margin rule, and engineering review (D) is required only in the 1,001°F and over band.

Concept Tested: High Temperature Construction

See: High Temperature Construction

8. A centrifugal fan is quoted with the 301°F to 500°F package, a coating whose sheet lists 350°F (illustrative), and nominally leak-tight construction. The design temperature is 420°F. Does the selection pass?

  1. Yes, because 420°F is inside the package band
  2. Yes, because leak-tight construction is recommended up to 600°F
  3. No, because the package must be raised to 501°F to 600°F
  4. No, because the fan's limit is the lowest part limit, 350°F, and the coating is the weak link
Show Answer

The correct answer is D. A fan's maximum operating temperature is the lowest limit of any element on its construction line: min(500, 350, 600) = 350°F. Because 420 > 350, the selection fails, and the coating, not the package, is the weak link. Options A and B each check only one element. Raising the package (C) does nothing for the coating; the fix is a coating rated at least 420°F or a material that needs no coating.

Concept Tested: Maximum Operating Temperature

See: Maximum Operating Temperature

9. A specification calls for spark-resistant Type C on a radial bladed fan whose standard impeller is already non-ferrous. What should the order say, and why?

  1. Type C with a Monel rub ring, because the specification must be followed exactly
  2. Type B, because a fan with a non-ferrous impeller as standard already meets the stricter requirement
  3. Type A, because a non-ferrous impeller means every airstream part must be non-ferrous
  4. No spark resistance, because a non-ferrous impeller cannot strike a spark
Show Answer

The correct answer is B. FanPedia's Type C pages for radial bladed fans and pressure blowers note that if the fan has a non-ferrous impeller as standard, the order should be Type B, because a non-ferrous impeller is what defines Type B. Option A ignores that note. Type A (C) requires every airstream part to be non-ferrous, which the standard fan does not provide. Spark resistance is still needed (D), because other parts can rub and no type makes a fan explosion-proof.

Concept Tested: Spark Resistant Construction

See: Spark Resistant Type C, Rub Plates and Rub Rings

10. An Arrangement 9 axial fan exhausts steam, and the exhaust reaches 220°F. Why can't it simply be quoted with both high moisture and high temperature construction?

  1. High moisture construction is offered only on centrifugal fans
  2. Steam at 220°F is not hot enough for any high temperature package, so only high moisture construction applies
  3. A drain at the lowest point already handles both the steam and the heat
  4. FanPedia states that high moisture construction cannot be combined with high temperature construction, and 220°F falls in an axial high temperature package, so the inquiry goes to engineering review
Show Answer

The correct answer is D. High moisture construction is offered on Arrangement 9 axial fans only and is meant for steam or condensation in the housing. But 220°F falls in the axial 201°F to 250°F high temperature package, and FanPedia states that high moisture and high temperature construction cannot be used together. The stack of answers contradicts itself, so the inquiry goes to engineering review. Option A reverses the fan type, B misreads the temperature bands, and a drain (C) removes water but does not address the temperature.

Concept Tested: High Moisture Construction

See: High Moisture Construction