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Overhung or Center Hung Sorter

Run the Overhung or Center Hung Sorter MicroSim Fullscreen

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About This MicroSim

Every centrifugal arrangement number is built on one of two impeller positions (FanPedia p. 79): an overhung impeller sits on the end of the shaft, beyond both bearings, and a center hung impeller sits between the two bearings. Where the impeller sits decides where the bearings must stand, and that decides whether a bearing is in the airstream.

Each card gives a one-line description of an arrangement. You make two choices:

  • Impeller: Overhung or Center hung
  • Bearings: All out of airstream, At least one in airstream, or No fan bearings

A card is correct only when both choices match; there is no partial credit, but the feedback says which choice was wrong and why. After Check, a side-view schematic of that arrangement appears with the impeller and the bearings highlighted and the airstream shaded between dashed edges, so you can see which bearings the air reaches.

Card Impeller Bearings
Arrangement 1 SWSI Overhung All out of airstream
Arrangement 3 SWSI Center hung At least one in airstream
Arrangement 3 DWDI Center hung At least one in airstream
Arrangement 3SI Center hung All out of airstream
Arrangement 3DI Center hung All out of airstream
Arrangement 4 SWSI Overhung No fan bearings
Arrangement 7 DWDI Center hung At least one in airstream
Arrangement 7SI Center hung All out of airstream
Arrangement 7DI Center hung All out of airstream
Arrangement 8 SWSI Overhung All out of airstream
Arrangement 9 SWSI Overhung All out of airstream
Arrangement 10 SWSI Overhung All out of airstream

The twelve cards come in a shuffled order, one attempt each. Mastery is 10 of 12 correct on the first attempt. The schematics are simplified side views; the Twin City Fan arrangement drawings are in FanPedia pp. 20–23, and the impeller groups come from FanPedia p. 30.

How to Use

  1. Read the card. Choose Overhung or Center hung, then one of the three bearing options. Check turns on once both are chosen.
  2. Press Check (or Enter). A correct card reads "✓ Correct: Overhung, All out of airstream." in a solid green box. A wrong one reads "✗ Not quite." in a dashed red box, names the wrong choice and gives the reason. The schematic appears either way.
  3. Press Next card (or Enter). "Correct: n of 12" keeps the running score.
  4. After card 12 the summary shows the first-attempt score, the mastery line and every missed card with its answer. Retry missed runs the missed cards again as practice (not scored); Start over deals a new shuffled round.

Keyboard: 1 Overhung, 2 Center hung, 3 All out of airstream, 4 At least one in airstream, 5 No fan bearings; Enter checks the card, and Enter again goes to the next one. Tab reaches every button; Space on a focused option picks it.

Data label: "Source: FanPedia pp. 30, 79, 162–168 · Schematics simplified", at the bottom left of the drawing.

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Lesson Plan

Learning Objective

The learner will classify twelve fan arrangements as overhung or center hung and state whether each arrangement's bearings sit in or out of the airstream, from a one-line description of each arrangement (Bloom: Understand, verb: classify).

Audience

Adult professional development: new application engineers, sales staff, representatives and facilities staff who have read "Where the Impeller Sits on the Shaft" in Chapter 11.

Duration

10-15 minutes

Prerequisites

  • Overhung impeller and center hung impeller
  • Bearing pedestal and airstream
  • SWSI and DWDI fans, inlet box
  • Direct drive, belt drive and shaft coupling

Activities

  1. Sort (6-8 min): Work through the twelve cards. Before choosing, say where the impeller sits relative to the two bearings.
  2. Review (3 min): Read the missed cards on the summary, then press Retry missed and sort them again (not scored).
  3. Discuss (2-4 min): Compare the Arrangement 3 SWSI and Arrangement 3SI schematics. What does the inlet box change, and what does it leave the same?

Common Misconceptions Addressed

  • Direct drive means center hung: Arrangements 4 and 8 are direct drive and overhung; marking the Arrangement 4 or Arrangement 8 card center hung adds "Direct drive does not decide impeller position."
  • Arrangement 4 has fan bearings in the airstream: its only bearings are inside the motor, so its bearing answer is "No fan bearings."
  • Every Arrangement 3 has its bearings out of the airstream: Arrangement 3 SWSI and 3 DWDI both put a bearing in the inlet.
  • Center hung fans always have a bearing in the airstream: 3SI, 3DI, 7SI and 7DI use inlet boxes to move the bearings out, and their schematics show the bearings outside the shaded airstream.

Assessment

  • "Correct: n of 12" is the running score. At the end the sim shows "First-attempt score: n of 12" and the mastery line; mastery is 10 of 12 cards with both choices right on the first attempt.
  • Follow-up: why does FanPedia limit standard DWDI fans to clean air at 130°F, and which arrangement removes that limit?

References

  1. Centrifugal fan - Wikipedia overview of centrifugal fan construction, impellers, housings and drives.
  2. Plain bearing and rolling-element bearings - the shaft bearings whose location the sorter asks about.
  3. FanPedia: The Fan & Blower Encyclopedia - Twin City Fan's reference; p. 30 lists the overhung and center hung arrangements and pp. 162–168 describe each arrangement.