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Quiz: High Temperature, Leak-Tight and RTO Construction

Test your understanding of high temperature construction, spark-resistant Types A and B, nominally leak-tight fans and RTO service with these review questions.

1. According to FanPedia, what is a nominally leak-tight fan?

  1. A fan whose housing is guaranteed to have zero leakage at any pressure
  2. A fan built to reduce leakage to a level agreed with the customer, verified by shop testing
  3. A fan whose housing is welded shut so that no access doors or flanges are used
  4. A fan rated for leak-tight service only when its airstream stays below 300°F
Show Answer

The correct answer is B. FanPedia states that a fan generally cannot be built totally leak-tight, so a nominally leak-tight fan is one built to reduce leakage to a level agreed with the customer, verified by shop testing and recorded on the inspection form. "Nominally" is a promise about the method and the agreed level, not zero leakage (A). Leak-tight fans still have flanges and access doors, sealed with double gaskets (C), and the stated temperature limit is 600°F, not 300°F (D).

Concept Tested: Nominally Leak-Tight Fan

See: What "Nominally Leak-Tight" Means

2. What is a cooler box on a high temperature fan?

  1. An insulated enclosure that keeps the shaft cooler warm during start-up
  2. A sealed housing that holds the high temperature grease for the bearings
  3. A guard that surrounds the motor and shields it from the hot housing
  4. An uninsulated open area around the shaft cooler so it can dissipate heat
Show Answer

The correct answer is D. FanPedia makes the cooler box standard on fans with aluminum clad insulation and on housings with insulation pins. Without it, the insulation would bury the shaft cooler, leaving it no cool air to throw heat into. Option A reverses its purpose: the box is deliberately left uninsulated. Option C describes a motor heat shield, and option B confuses it with lubrication parts.

Concept Tested: Cooler Box

See: Shedding and Blocking Heat at the Shaft

3. Why do FanPedia's high temperature packages call for one fixed and one floating bearing?

  1. The floating bearing lets the shaft grow axially as it heats, so growth is not forced into the bearings as thrust
  2. The floating bearing carries the impeller's weight while the fixed bearing only seals the shaft
  3. Two different bearing types let the factory use cheaper grease in one of them
  4. The fixed bearing cools the shaft, and the floating bearing insulates it from the housing
Show Answer

The correct answer is A. Hot steel grows: a 60 in. shaft warming 300°F grows about one-eighth of an inch. If both bearings clamped the shaft axially, that growth would have to be absorbed as thrust. The fixed bearing locates the shaft, and the floating bearing lets it grow. In the chapter's "block, shed or allow" scheme, both bearings do the "allow" job. Neither bearing cools or insulates (D), and the pairing has nothing to do with grease cost (C).

Concept Tested: Thermal Expansion

See: Thermal Expansion

4. A carbon steel shaft has 40 in. between bearing centers and warms by 400°F in service. Using \( \Delta L = \alpha L \Delta T \) with \( \alpha = 6.5 \times 10^{-6} \) in./in./°F, about how much does it grow?

  1. 0.010 in.
  2. 0.026 in.
  3. 0.104 in.
  4. 1.04 in.
Show Answer

The correct answer is C. \( \Delta L = 6.5 \times 10^{-6} \times 40 \times 400 = 0.104 \) in., roughly one-tenth of an inch. That is the same order of growth as the chapter's 60 in. example (about 0.12 in.) and it explains why a floating bearing is needed. Option D misplaces the decimal by a factor of ten. Options A and B come from dropping one of the three factors in the formula.

Concept Tested: Thermal Expansion

See: Thermal Expansion

5. A customer requests an Arrangement 4 centrifugal fan for a 400°F oven. Which FanPedia high temperature package band applies?

  1. 301-500°F, a standard package with no review needed
  2. 181-300°F, the Arrangement 4 low temperature band
  3. 301°F and over, which requires engineering review
  4. No package is needed, because Arrangement 4 is rated to 600°F
Show Answer

The correct answer is C. Package bands depend on the fan family. The 301-500°F band (A) belongs to Arrangements 1, 8, 9, 9F and 10, not Arrangement 4. Arrangement 4 centrifugal fans have only two bands: 181-300°F and 301°F and over. The upper band always requires engineering review, and aluminum rotating parts on Arrangement 4 are limited to 250°F. At 400°F the job falls outside the 181-300°F band (B), and Arrangement 4 is not rated to 600°F (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). FanPedia's band list is still how this question is scored.

Concept Tested: High Temperature Package

See: High Temperature Packages

6. Which statement correctly distinguishes Spark Resistant Type A from Type B?

  1. Type A makes every airstream component non-ferrous; Type B makes only the impeller non-ferrous and adds a rub plate
  2. Type A uses an aluminum inlet cone only; Type B makes the whole housing aluminum
  3. Type A allows bearings in the airstream; Type B keeps them outside it
  4. Type A applies only to axial fans; Type B applies only to centrifugal fans
Show Answer

The correct answer is A. Type A, the highest degree of spark resistance, requires all fan components in the airstream to be non-ferrous and restrains the bearings. Type B requires a non-ferrous impeller and an aluminum rub plate at the shaft opening. The housing, inlet funnel and shaft stay steel. Option B swaps the types and describes Type C's inlet cone. No type allows bearings in the airstream (C). FanPedia illustrates both types for centrifugal and axial fans (D).

Concept Tested: Spark Resistant Type A

See: Spark-Resistant Construction, Types A and B

7. A grain-handling customer asks for a "spark-resistant" pressure blower without naming a type. The blower already has a cast aluminum impeller as standard. What should the order specify?

  1. Type C, because an aluminum impeller already exceeds Type C requirements
  2. Type A, because any spark-resistant request defaults to the highest type
  3. No spark-resistant type, because the aluminum impeller is sufficient on its own
  4. Type B, adding the rub plate, with the type confirmed in writing on the order
Show Answer

The correct answer is D. For radial bladed fans and pressure blowers, FanPedia's rule is that if the fan already has a non-ferrous impeller as standard, Type B is used. The standard impeller nearly satisfies Type B, so the order adds the rub plate at the shaft opening and keeps the bearings outside the airstream. The type must be stated in writing because "spark-resistant" alone does not tell the factory what to build. That rules out option C, and option A ignores FanPedia's rule.

Concept Tested: Spark Resistant Type B

See: Type B

8. A chemical plant asks for a nominally leak-tight fan at 350°F for a toxic vent and suggests an Arrangement 4 fan with a split housing. What revision best fits FanPedia's leak-tight requirements?

  1. Keep Arrangement 4 and the split housing, but add single gaskets to every joint
  2. Propose an Arrangement 1 or 8 fan with a solid drive side, and avoid the split housing if possible
  3. Reject the job, because leak-tight construction is not offered above 300°F
  4. Keep Arrangement 4, but replace continuous welds with intermittent stitch welds
Show Answer

The correct answer is B. FanPedia limits nominally leak-tight fans to Arrangements 1, 8 and 9, with a solid drive side. It does not recommend split housings. If one is truly needed, it gets centering plates and double gaskets. 350°F is under the 600°F limit, so the job is possible (C is wrong). Leak-tight construction calls for double gaskets, not single (A), and for continuous welds, because stitch welds leave gaps (D).

Concept Tested: Nominally Leak-Tight Fan

See: Nominally Leak-Tight Fans

9. An RTO fan for an automotive paint shop runs at 300°F normally, with a weekly bake-out that raises the inlet to 650°F. Which reading of the inquiry is correct?

  1. It needs engineering review because the bake-out exceeds the 600°F recommended limit, and gasketing must be a non-silicone alternative
  2. It can be quoted as standard because the normal 300°F temperature is well under 600°F
  3. Silicone sponge gasket is required because it is the RTO standard on every job
  4. The bake-out can be ignored because it lasts only a few hours each week
Show Answer

The correct answer is A. RTO construction is not recommended above 600°F, and the bake-out is a service condition that sales must specify. The high temperature package is chosen for the bake-out temperature, not the normal one, so options B and D miss the governing condition. Silicone sponge and caulk are the RTO default, but automotive jobs require an alternative to silicone (C), because silicone contamination causes paint finish defects.

Concept Tested: RTO Service Conditions

See: RTO Service Conditions

10. Why does FanPedia pair gasketing on leak-tight fans with close bolt spacing of 3 in. to 4 in. centers?

  1. Close bolt spacing lets the factory skip the soap bubble test
  2. Closely spaced bolts make the flange strong enough to replace the gasket
  3. Widely spaced bolts let the flange bow open between them, so the gasket is not clamped
  4. Close bolt spacing is needed only so the flange matches ANSI pipe dimensions
Show Answer

The correct answer is C. A gasket only seals as well as the clamping force on it. With widely spaced bolts, the flange bows open between them and the joint leaks whatever gasket is used. That is why close-centered bolt patterns come with gasketing on inlet and outlet flanges, access doors, funnels and split housings. The bolts work with the gasket, not instead of it (B). The soap bubble test is still performed (A). An ANSI pattern is acceptable only when it is standard for the fan (D).

Concept Tested: Gasketing

See: Gasketing

11. An oven builder raises an Arrangement 10 recirculation fan's setpoint from 550°F to 700°F. What is the appropriate response?

  1. Keep Arrangement 10 and add a second motor heat shield to reach 700°F
  2. Propose an Arrangement 1, 8 or 9F fan with a separated pedestal, or send the request for engineering review
  3. Keep Arrangement 10 with an insulated panel pedestal, which is rated to 1,000°F
  4. Switch to an Arrangement 4 fan, whose motor sits away from the hot housing
Show Answer

The correct answer is B. Both Arrangement 10 pedestal forms, the motor heat shield and the insulated panel, stop at 600°F. FanPedia draws the separated pedestal design, with a gap of up to 3 in. between housing and pedestal, for Arrangements 1, 8 and 9F at 601°F and above. Adding shields (A) or overstating the insulated panel's limit (C) ignores the pedestal limit. Arrangement 4 puts the impeller on the motor shaft, FanPedia sends it to engineering review above 300°F, and Twin City Fan engineering does not use it for high-temperature applications at all (D).

Concept Tested: High Temperature Pedestal

See: High Temperature Pedestals and Heat Shields