Housing Construction and Exploded Views¶
Summary¶
This chapter takes a closer look at how fan housings are built: scroll side plates and wrappers, the cutoff, straightening vanes, horizontal, three-way, and pie split housings, housing framing, access panels, cast housings, discharge cones, belt guards and belt tubes, and roof exhauster shrouds and curb caps. It shows how to read the exploded views FanPedia uses to name every part. After completing it, readers can read an exploded view and explain what each housing feature is for.
Concepts Covered¶
This chapter covers the following 20 concepts from the learning graph:
| Concept | Concept Impact Score |
|---|---|
| Housing Side Plate | 3 |
| Scroll Wrapper | 1 |
| Cutoff | 2 |
| Straightening Vanes | 2 |
| Horizontal Split Housing | 1 |
| Three-Way Split Housing | 1 |
| Pie Split Housing | 1 |
| Motor Cover | 1 |
| Roof Exhauster Shroud | 1 |
| Curb Cap | 1 |
| Exploded View | 3 |
| Belt Guard | 2 |
| Belt Tube | 1 |
| Housing Framing | 2 |
| Discharge Cone | 1 |
| Housing Access Panel | 1 |
| Nozzle and Windband | 1 |
| Cast Housing | 1 |
| Mounting Panel | 2 |
| Insulation Plug | 1 |
Prerequisites¶
This chapter builds on concepts from:
- Chapter 3: Basic Fan Anatomy
- Chapter 4: Centrifugal, Axial and Mixed Flow Fans
- Chapter 5: Roof, Wall and Specialty Exhaust Fans
- Chapter 6: Industrial Fans and Application Product Lines
Taking the Fan Apart on Paper
A customer calls about a "bent piece of sheet metal near the outlet" and wants a replacement. By the end of this chapter you will open the right FanPedia drawing, put a name and a purpose to that part, and know whether the housing can come apart to reach it. Let's follow the airflow.
In Chapter 3 you learned that a fan housing directs air from the inlet to the outlet and supports the other key components. FanPedia puts it the same way: the housing is the "main structure to support other key components such as inlet, outlet, framing and structural supports," and it is also known as the side, scroll or casing (FanPedia p. 59). Not every fan has one. Plenum fans, plug fans, panel fans and ring fans run without a housing of their own.
This chapter works through the pieces a housing is built from, the ways a housing can be split, and the guards, covers and panels that attach to it. First, though, you need the tool FanPedia uses to name all of those pieces.
Reading an Exploded View¶
An exploded view is a drawing of an assembly with its parts pulled apart along the lines they assemble on, so each part is visible and can carry its own label. Parts that bolt together sit on a shared line of travel, so the drawing shows both what each part is called and roughly where it goes. FanPedia's Fan Basics section opens with eleven pages of them (pp. 9–19), one or two fan families per page, each labeled in the shop's own vocabulary. The Housing Construction pages (pp. 59–66) add housing-only views that zoom in on the shell.
The table below lists where each family's exploded view sits, so you can open the right page while you read this chapter.
| Fan family | Exploded view pages | Housing detail pages |
|---|---|---|
| Housed centrifugal, direct drive and belt driven | 9–10 | 60 (SWSI), 61 (DWDI) |
| Plenum fans | 11–12 | none (unhoused) |
| Plug fans | 13–14 | 66 |
| Tubeaxial and vaneaxial fans | 15–16 | 63 |
| Inline centrifugal and mixed flow fans | 17 | 64 |
| Panel fans | 18 | none |
| Centrifugal roof exhausters | 19 | none |
| Pressure blowers (cast) | none | 62 |
| Square inline fans | none | 65 |
Three habits make an exploded view easier to read:
- Find the airflow first: inlet funnel or collar on one side, outlet flange or discharge on the other.
- Separate the housing parts (the shell and what is welded or bolted to it) from the rotating parts (impeller, shaft, bearings) and the drive parts (motor, belt, sheave).
- Note the caption under the drawing, such as "Arr. 9 Fan" or "Direct Drive Shown," because the same family can show different parts in different arrangements.
A Drawing Is a Parts List
Notice that every label in an exploded view is a word you can put on an order or a replacement-parts request. Read the drawing as a parts list with pictures, and the vocabulary of this whole book starts to hang together.
The Scroll Housing: Side Plates, Wrapper and Cutoff¶
A housed centrifugal fan's shell is built from three kinds of pieces. FanPedia's SWSI housing view (p. 60) labels them HOUSING SIDE, HOUSING SCROLL and CUTOFF.
A housing side plate is one of the two flat sides of a scroll housing. On a single width, single inlet (SWSI) fan, the inlet side plate carries the round inlet opening, which in turn holds the inlet collar, inlet funnel or inlet flange; the opposite side plate faces the drive. On a double width, double inlet (DWDI) fan (p. 61), both side plates carry inlets, and each side also supports a bearing on a structural support. Because the side plates hold the inlet hardware and often the bearing supports, they are the stiffest, most load-bearing panels of the shell.
The scroll wrapper (FanPedia's "housing scroll") is the curved band of sheet metal that wraps around the impeller between the two side plates and runs out to the discharge. In standard fan engineering terms, the scroll's spiral shape gives the space between impeller and housing a gradually growing cross-section. That shape collects the air the impeller throws off, slows it down, and turns part of its velocity into static pressure before it leaves through the outlet. When FanPedia describes housed centrifugal fans as having "single or double width scroll housings" (p. 4), the width it refers to is the width of this wrapper.
The cutoff is the point near the outlet where the scroll wrapper comes closest to the impeller, like a tongue that separates air leaving through the discharge from air that would otherwise keep circling the housing. FanPedia groups it with the wiper bar as a feature that "helps to direct air through the housing ... to prevent turbulence and to increase efficiency" (p. 59). On the p. 60 drawing the cutoff sits at the discharge end of the scroll, while the wiper bar is a curved fin mounted on the inner end of the inlet funnel, so it sits in the inlet funnel area; Chapter 18 covers the wiper bar.
Before you look at the interactive drawing below, recall the inlet and outlet hardware from Chapter 3: the inlet collar is a short cylinder at the inlet opening, the inlet funnel is the shaped piece that guides air into the impeller, and the inlet and outlet flanges are the bolting rims that connect to ductwork. Framing is covered in the next section, and the pedestal is the stand that carries the bearings (and, on some arrangements, the motor).
Diagram: SWSI Housing Callout Explorer¶
Run SWSI Housing Callout Explorer Fullscreen
SWSI Housing Callout Explorer
Type: infographic
sim-id: ch07-swsi-housing-callout-explorer
Library: html
Status: Specified
Bloom Level: Remember
Bloom Verb: identify
Learning Objective: The learner will identify ten labeled parts of a single width, single inlet centrifugal fan housing from a one-sentence description of each part's job.
Prerequisites: exploded view, housing side plate, scroll wrapper, cutoff, wiper bar, inlet collar, inlet funnel, inlet flange, outlet flange, housing framing, pedestal (all defined in the chapter sections above and in Chapter 3).
Evidence of Mastery: In quiz mode the learner is shown one description at a time and clicks the part it describes. An answer is correct when the clicked part matches the "Part" column below. Mastery is 8 of 10 correct on the first attempt. Clicking callouts in explore mode is exploration, not evidence.
Misconceptions: (1) The cutoff and the wiper bar are the same piece in the same place. (2) The side plate and the scroll are one continuous part. (3) The inlet collar and the inlet funnel are interchangeable names.
Instructional Rationale: Remember-level identification needs retrieval practice with immediate correction, so the learner first explores labeled callouts, then retrieves each name from its function with the labels hidden.
Content:
| # | Part (callout label) | Description shown on click and in quiz mode |
|---|---|---|
| 1 | Housing Side | One of the two flat sides of the scroll housing; on an SWSI fan the inlet side carries the round inlet opening. |
| 2 | Housing Scroll | The curved wrapper between the side plates that collects air from the impeller and carries it to the outlet. |
| 3 | Cutoff | The tongue near the outlet where the scroll comes closest to the impeller, separating discharged air from air that would keep circling. |
| 4 | Wiper Bar | A bar near the inlet funnel area that helps direct air through the housing to reduce turbulence. |
| 5 | Inlet Collar | A short cylinder at the inlet opening that the inlet hardware mounts to. |
| 6 | Inlet Funnel | The shaped piece that guides air smoothly into the impeller eye. |
| 7 | Inlet Flange | The bolting rim at the inlet that connects the fan to inlet ductwork. |
| 8 | Outlet (Discharge) Flange | The bolting rim at the outlet that connects the fan to discharge ductwork. |
| 9 | Framing | The angles or channels fastened to the housing that stiffen it and support it on its base. |
| 10 | Pedestal | The stand that carries the bearings and, on some arrangements, the motor. |
The drawing is a line drawing of an SWSI housed centrifugal fan with the ten callouts above; no other parts are labeled. A note on the drawing reads "Based on FanPedia p. 60. Rubbing bars, shown there on spark-resistant fans only, are covered in Chapter 20."
Provenance: Part names and positions: FanPedia p. 60 (Centrifugal Fans SWSI). Cutoff and wiper bar function: FanPedia p. 59. Housing, framing and structural support role: FanPedia pp. 59 and 185. Scroll description and cutoff tongue description: standard fan engineering, as stated in this chapter's section "The Scroll Housing."
Rules: Explore mode: clicking a callout shows its description; any number of clicks. Quiz mode: the 10 descriptions appear once each in shuffled order. A click on the matching part is correct. Clicking a non-callout area does nothing and uses no attempt.
Learner Activity:
- The learner clicks each callout in explore mode and reads its description.
- The learner switches to quiz mode. Callout labels are hidden; a description appears.
- The learner clicks the part the description fits. The part is marked correct or incorrect and its label is revealed.
- After 10 descriptions the score and a list of missed parts are shown, and the learner can retry the quiz with a new shuffle.
Feedback: 10 items, shuffled, one attempt each. Correct: "Correct:
Starting State: Explore mode with all ten callouts visible and the prompt "Click any part to see what it does."
Chapter Anchors: The chapter states the drawing is based on FanPedia p. 60, that the cutoff sits at the discharge end of the scroll, and that the wiper bar sits near the inlet funnel.
Housing Framing and Cast Housings¶
Housing framing is the structural steel (formed angles or channels) fastened to the outside of the housing to stiffen the sheet metal and give the fan feet to sit on. FanPedia labels FRAMING along the bottom of both the SWSI and DWDI housing views (pp. 60–61), and shows separate STRUCTURAL SUPPORTS on the DWDI fan, where each side plate carries a bearing. Unhoused fans need framing too: the plenum fan views (pp. 11–12) and the square inline view (p. 65) label a FRAME that holds the inlet panel, motor and pedestal together in place of a housing.
Most fan housings are fabricated: cut from sheet or plate and welded or bolted together, as Chapter 3 described. A cast housing is instead poured as a single metal casting. FanPedia's p. 62 shows pressure blowers built two ways, with a cast aluminum housing and with a cast iron housing, each with its inlet, outlet, pedestal and structural support. A casting gives a pressure blower's narrow housing its shape in one piece. Cast parts appear elsewhere on these blowers as well; FanPedia lists a slide gate damper with a cast aluminum frame for cast aluminum pressure blowers (p. 192).
Split Housings¶
Chapter 3 introduced the split housing: a housing built in sections that bolt together, so it can be taken apart. FanPedia names three kinds for centrifugal fans (pp. 156–157 and 194), and each one is named by where the cut runs.
A horizontal split housing is cut along the housing's horizontal centerline, so the upper half lifts off the lower half. FanPedia calls this the "standard split" and notes that size 807 and above may be split by the shop for shipping purposes.
A three-way split housing is cut into three sections, up to 180 degrees. FanPedia says this split is "normally required either for shipping or to enable the fan to enter a specific sized opening," such as a doorway or roof hatch on a retrofit job. Three-way splits need additional drafting and engineering time, so they should be identified early in a quote.
A pie split housing is cut at angles of 90 degrees or greater, removing a wedge of the housing so the impeller can come out "without disturbing inlet or outlet" ductwork. FanPedia shows two styles:
- Mohawk (newer style): splits between the scroll and the inlet housing side; the inlet side itself has no split. It is not used on double width fans or on fans with attached inlet boxes.
- Standard (older style): splits all the way down to the funnel or inlet plate. Weld nuts on the inside of the split take bolts from outside the housing, and studs are welded to the outside.
FanPedia's arrangement descriptions show where pie splits are built in: Arrangements 3SI and 7SI (single inlet fans with an attached or integrated inlet box) and 7DI include a pie split housing "for easy impeller removal" (pp. 164–168).
The table below summarizes the three splits you have just read about.
| Split | Where the cut runs | Main reason | Note |
|---|---|---|---|
| Horizontal | Along the horizontal centerline | Standard split; shipping large sizes | Shop may split size 807 and above for shipping |
| Three-way | Three sections, up to 180 degrees | Shipping, or passing through a specific opening | Extra drafting and engineering time |
| Pie | A wedge at 90 degrees or greater | Impeller removal without disturbing inlet or outlet | Mohawk or standard style |
Splits and Tight Housings Don't Mix Easily
Watch out for split housings on nominally leak-tight or RTO jobs: every split is another joint that can leak. FanPedia says split housings are "not recommended" for nominally leak-tight construction, and when a split is used there, it needs gasketing, close bolt spacing and centering plates to seal around the shaft seal and inlet (pp. 120–121), so flag it before the quote goes out. Chapter 21 covers those requirements.
The following MicroSim gives you a set of job situations and asks you to pick the split each one calls for, using the rules from this section.
Diagram: Split Housing Selector¶
Run Split Housing Selector Fullscreen
Split Housing Selector
Type: microsim
sim-id: ch07-split-housing-selector
Library: p5.js
Status: Specified
Bloom Level: Evaluate
Bloom Verb: recommend
Learning Objective: The learner will recommend a horizontal, three-way, Mohawk pie, standard pie or no split housing for eight described centrifugal fan situations, justifying each choice with a FanPedia rule.
Prerequisites: split housing, horizontal split housing, three-way split housing, pie split housing, Mohawk and standard pie styles, attached inlet box, double width fan, nominally leak-tight construction (defined in the section "Split Housings" above and in Chapter 3).
Evidence of Mastery: For each situation the learner commits one recommendation and then picks one justification from four offered. A situation is correct when both the recommendation and the justification match the table below. Mastery is 6 of 8 situations correct on the first attempt.
Misconceptions: (1) Any split will let the impeller out without touching the ductwork. (2) The Mohawk pie split works on any fan. (3) Adding a split is always harmless. (4) A horizontal split is only for maintenance, never shipping.
Instructional Rationale: Evaluate-level judgment needs the learner to weigh a situation against stated criteria and defend the choice, so each recommendation is paired with a chosen justification rather than a bare answer.
Content:
Choices for every situation: Horizontal split; Three-way split; Pie split, Mohawk style; Pie split, standard style; No split recommended.
| # | Situation | Correct recommendation | Correct justification (shown as feedback) |
|---|---|---|---|
| 1 | A size 807 SWSI housing is too large to ship assembled. The customer only needs it in two halves. | Horizontal split | The standard split runs along the horizontal centerline, and size 807 and above may be split by the shop for shipping. |
| 2 | A replacement fan must pass through an existing doorway that is smaller than the housing even when split in two. | Three-way split | A three-way split is normally required to ship a fan or to enter a specific sized opening. |
| 3 | Maintenance wants to pull the impeller of an SWSI fan with no inlet box without disturbing the ductwork, and wants the inlet side left unsplit. | Pie split, Mohawk style | The Mohawk splits between the scroll and the inlet housing side; the inlet side has no split. |
| 4 | The same impeller-removal need, but on a double width, double inlet fan. | Pie split, standard style | The Mohawk style is not used on double width fans. |
| 5 | An Arrangement 3SI fan with an attached inlet box needs easy impeller removal. | Pie split, standard style | Arrangement 3SI includes a pie split, and the Mohawk style is not used on fans with attached inlet boxes. |
| 6 | An Arrangement 1 fan in nominally leak-tight service. Nothing about shipping or access requires a split. | No split recommended | FanPedia states split housings are not recommended for nominally leak-tight construction. |
| 7 | A replacement SWSI housing must match the existing pie split on an older fan, which runs all the way down to the inlet plate. | Pie split, standard style | The standard (older style) pie split runs all the way down to the funnel or inlet plate. |
| 8 | A retrofit fan must be lowered through a roof hatch smaller than half the housing, and the quote has not yet allowed for drafting time. | Three-way split | Three sections fit the opening, and three-way splits need additional drafting and engineering time, so the quote must allow for it. |
Justification options offered for situation n are its own justification plus the justifications of the next three rows after n (counting past row 8 back to row 1) whose correct recommendation differs from row n's, so no distractor is a valid reason for the same split.
Provenance: FanPedia pp. 156–157 and 194 (split housing types, Mohawk and standard styles, size 807, three-way drafting time); pp. 164 and 168 (Arrangements 3SI, 7SI, 7DI include a pie split); p. 120 (split housings not recommended for nominally leak-tight construction). The situations are illustrative and must be labeled "illustrative situations."
Rules: One recommendation and one justification per situation. A situation counts correct only when both match the table. Situations 3, 4, 5 and 7 all involve a pie split; the style is decided only by the facts stated in each situation text (inlet side left whole, double width, attached inlet box, matching an older split), and the sim gives no other hint.
Learner Activity:
- The learner reads situation 1 and selects one of the five recommendations. The choice is locked.
- Four justifications appear in shuffled order. The learner selects one.
- The sim marks the recommendation and justification correct or incorrect and shows the feedback.
- The learner moves to the next situation until all eight are done, then sees a summary table of their answers beside the correct ones.
Feedback: 8 situations in fixed order, one attempt each. Both correct: "Correct:
Starting State: Situation 1 shown with the five recommendation choices and the question "Which split, if any, should this fan have?"
Chapter Anchors: The chapter states that the shop may split size 807 and above for shipping, that a three-way split has up to 180 degrees and three sections, that a pie split is at 90 degrees or greater, that the Mohawk style is not used on double width fans or fans with attached inlet boxes, and that split housings are not recommended for nominally leak-tight construction.
Getting Inside: Housing Access Panels¶
Chapter 3 introduced the access door, a small bolted or quick-opening door in the housing for inspecting and cleaning the impeller. FanPedia shows access doors on the housings of tubeaxial, vaneaxial, inline centrifugal and mixed flow fans (pp. 63–64) and lists bolted, raised and quick-open styles among its common accessories (p. 125).
A housing access panel is larger: a whole removable side of the housing rather than a door cut into it. The clearest example is the square inline fan. FanPedia describes square inline centrifugal fans as "built with square housings and removable side panels" (p. 6), and its p. 65 view labels the ACCESS PANEL as "REMOVABLE, 3 SIDES." Taking off a panel exposes the impeller, motor and drive at once, which is why square inline fans are easy to service in tight ceiling spaces.
Tubular Housings: Straightening Vanes, Discharge Cone and Belt Tube¶
Inline centrifugal, mixed flow and axial fans use a tubular housing, and their exploded views (pp. 15–17) show three parts a scroll housing does not have.
Straightening vanes are fixed vanes inside a tubular housing, downstream of the impeller, that take the swirl out of the air leaving the impeller and turn it back into straight-through flow. FanPedia labels STRAIGHTENING VANES on both the inline centrifugal and the mixed flow views (pp. 17 and 64). On a vaneaxial fan the same job is done by the guide vanes of Chapter 4, which FanPedia says "help straighten the airflow as it moves through the fan" (p. 7). Recovering that swirl as useful pressure is why a vaned tubular fan can develop more pressure than a plain tube.
A discharge cone is a tapered section at the outlet end of the tubular housing. FanPedia's belt driven inline centrifugal and mixed flow view (p. 17) labels it at the discharge, where it guides the air leaving the impeller and vanes toward the outlet connection.
A belt tube (FanPedia: "BELT TUBE, aka Belt Fairing") is an enclosed passage through the side of a belt driven tubular housing. In an axial or inline fan the motor sits outside the tube while the impeller shaft is inside it, so the belts have to cross the airstream. The belt tube shields the belts and sheaves from the moving air and from whatever the air carries. It appears on the belt driven tubeaxial, vaneaxial, inline centrifugal and mixed flow views (pp. 15–17, 63–64).
Diagram: Inline Centrifugal and Mixed Flow Fan Parts¶
Run Inline Centrifugal and Mixed Flow Fan Parts Fullscreen
Inline Centrifugal and Mixed Flow Fan Parts
sim-id: ch07-inline-centrifugal-mixed-flow-overlay
Library: html + FP.Overlay
Status: built
Bloom Level: Remember
Learning Objective: The learner will identify the twelve labeled parts of a direct drive inline centrifugal fan and a belt driven mixed flow fan on FanPedia's exploded views, given each part's function or appearance.
Content: 12 numbered markers: Tubular housing, Straightening vanes, Shaft, Impeller (inline centrifugal), Inlet funnel, Motor, Impeller (mixed flow), Bearing housing, Belt guard, Belt tube, Sheave, Discharge cone
Provenance: FanPedia page 17, "Exploded Views: Inline Centrifugal & Mixed Flow Fans, direct drive (left) and belt driven (right)", with the printed labels removed. Drawing: FanPedia, Twin City Fan, p. 17.
Guards and Covers¶
A belt guard encloses the belts and sheaves on the outside of a belt driven fan so that no one can reach the moving drive. FanPedia shows one beside the belt tube on the belt driven inline view (p. 17) and lists it as a common accessory (p. 125). FanPedia also notes that spark-resistant axial fans keep a mild steel belt guard (p. 109); Chapter 20 explains why that matters. A related accessory, the shaft/bearing guard and coupling guard, protects the exposed shaft and coupling on direct drive fans (p. 126).
A motor cover, also called a weather cover, is a hood placed over the motor to protect it from rain, snow and sun. FanPedia lists "Motor Cover / Weather Cover" as a common accessory (p. 126), and the centrifugal roof exhauster view (p. 19) labels a MOTOR COVER on top of the unit, above the MOTOR HOUSING that encloses the motor.
Guard or Tube? Ask Where the Belt Runs
Here's a quick check when a drawing shows a belt drive: if the belts cross the airstream inside a tube, you need a belt tube; if they run outside the housing where people can reach them, you need a belt guard. A belt driven inline fan, as on p. 17, has both.
Plug Fan Hardware: Mounting Panel and Insulation Plug¶
A plug fan has no housing; it is "plugged" into the wall of the customer's plenum, which acts as the fan housing (FanPedia pp. 5 and 172). Two parts take the place of the housing's structure.
The mounting panel is the flat plate that fastens the fan to the customer's wall. FanPedia explains that "the mounting panel is mounted to the outside wall and the impeller inside the plenum wall" (p. 5); the inlet funnel and impeller hang inside the plenum, while the shaft, bearings and motor stay outside the process airstream. On Arrangement 9 plug fans the wall carries the whole fan. On the grade-mounted versions (Arrangements 1P, 4P, 8P and 9P), the fan stands on the foundation instead, and FanPedia lists the mounting panel as optional (pp. 170–172). Not every plug fan model is built in every arrangement; Chapter 6 gives the arrangements the current catalogs list.
The insulation plug is an insulated section mounted with the panel that fills the opening in the plenum wall around the fan, so the wall keeps its insulating value where the fan passes through it. It appears on both plug fan exploded views (pp. 13–14) and on the Arr. 9P detail "Mounting Panel with Insulation Plug" (p. 66). Plug fans often serve hot equipment such as ovens, so the plug matters in high-temperature service. For Arrangement 9 high-temperature plug fans, FanPedia's two designs set the rule by the thickness of the plug or wall (p. 113, which refers to Fan Engineering Letter FE-3200). With a plug or wall less than 4" thick (Design #1, a gap for the shaft cooler), the insulated plug is optional up to 500°F. With a plug or wall 4" or more thick (Design #2, a recess cone for the shaft cooler), the insulated plug is required at 301°F and above. The two statements do not conflict because they apply to different wall thicknesses.
Diagram: Belt Driven Plug Fan Parts¶
Run Belt Driven Plug Fan Parts Fullscreen
Belt Driven Plug Fan Parts
sim-id: ch07-belt-driven-plug-fan-overlay
Library: html + FP.Overlay
Status: built
Bloom Level: Remember
Learning Objective: The learner will identify the ten labeled parts of an Arrangement 9P belt driven plug fan on an exploded view, given each part's function.
Content: 10 numbered markers: Impeller, Insulation plug, Mounting panel, Pedestal, Motor slide base, Motor, Belt, Sheave, Bearings, Shaft
Provenance: FanPedia page 14, "Exploded Views: Plug Fans, 'Belt Driven Plug Fans' (Arr. 9P fan)", with the printed labels removed. Drawing: FanPedia, Twin City Fan, p. 14.
Rooftop Hardware: Shroud, Curb Cap, Nozzle and Windband¶
Roof-mounted fans need parts that seal them to the building and send the exhaust where it should go.
A curb cap is the base plate or frame of a roof-mounted fan that sits on and covers the roof curb, the raised frame built around the roof opening. FanPedia's centrifugal roof exhauster view (p. 19) stacks CURB CAP directly on ROOF CURB, and its roof mounted axial fans are shown "with hood and curb cap" or "with stack cap and curb cap" (p. 7). On vertical inline and axial fans mounted on a roof, the motor is centered on the curb cap (p. 57).
A roof exhauster shroud is the sheet-metal shell around the impeller of a centrifugal roof exhauster that guides the air the impeller throws off. FanPedia labels the SHROUD between the impeller and the curb cap on its upblast and downblast views (p. 19), with a SKIRT and bird screen around the downblast unit, where air is turned down and outward. Chapter 5 described these upblast and downblast discharges.
A nozzle and windband sit at the top of a lab exhaust fan. The nozzle accelerates the contaminated exhaust into a high-velocity jet, and the windband around it draws in fresh outside air, which FanPedia calls entrained flow (pp. 4 and 6). The fresh air mixes with the contaminated air to dilute it and carry it up and away from the building. Chapter 5 introduced entrained flow; here you can see that the nozzle and windband are the housing parts that produce it.
The last MicroSim pulls the chapter together: you sort parts into the fan family whose FanPedia exploded view shows them.
Diagram: Which Exploded View Shows This Part¶
Run Which Exploded View Shows This Part Fullscreen
Which Exploded View Shows This Part
Type: microsim
sim-id: ch07-exploded-view-part-sorter
Library: p5.js
Status: Specified
Bloom Level: Analyze
Bloom Verb: attribute
Learning Objective: The learner will attribute twelve housing parts to the fan family whose FanPedia exploded view or housing detail shows them, using what each part does to decide.
Prerequisites: exploded view, housing side plate, scroll wrapper, cutoff, straightening vanes, guide vanes, discharge cone, belt tube, mounting panel, insulation plug, roof exhauster shroud, curb cap, motor cover (all defined in this chapter above).
Evidence of Mastery: The learner drops each of 12 part cards into one of four family bins and presses Check. A card is correct when its bin matches the "Correct family" column below. Mastery is 10 of 12 correct on the first check.
Misconceptions: (1) Straightening vanes belong to scroll housings. (2) A plug fan has a scroll. (3) A belt tube is the same as a belt guard and appears on every belt driven fan. (4) Curb caps are only for centrifugal roof exhausters.
Instructional Rationale: Analyze-level attribution asks the learner to connect each part's function to the airflow path of a family, so the learner commits all placements before any feedback, then reads the reason for each.
Content:
Bins: Housed Centrifugal (scroll housing); Tubular (axial, inline centrifugal, mixed flow); Plug Fan; Centrifugal Roof Exhauster.
| # | Part card | Correct family | Why (shown as feedback) |
|---|---|---|---|
| 1 | Housing Side | Housed Centrifugal | A flat side plate of the scroll housing (FanPedia pp. 60–61). |
| 2 | Housing Scroll | Housed Centrifugal | The curved wrapper exists only on scroll housings (p. 60). |
| 3 | Cutoff | Housed Centrifugal | The tongue where the scroll meets the outlet (p. 60). |
| 4 | Straightening Vanes | Tubular | Fixed vanes that remove swirl in inline centrifugal and mixed flow housings (pp. 17, 64). |
| 5 | Guide Vanes | Tubular | The vaneaxial version of straightening vanes (pp. 16, 63). |
| 6 | Discharge Cone | Tubular | Tapered outlet section on the belt driven inline and mixed flow view (p. 17). |
| 7 | Belt Tube | Tubular | Carries belts across the airstream to a shaft inside the tube (pp. 15–17). |
| 8 | Mounting Panel | Plug Fan | Fastens the fan to the customer's plenum wall (pp. 13–14, 66). |
| 9 | Insulation Plug | Plug Fan | Insulates the plenum wall opening around the fan (pp. 13–14, 66). |
| 10 | Shroud | Centrifugal Roof Exhauster | Shell around the roof exhauster impeller (p. 19). |
| 11 | Curb Cap | Centrifugal Roof Exhauster | Sits on the roof curb in the exploded view (p. 19); roof mounted axial fans also use one (p. 7). |
| 12 | Motor Cover | Centrifugal Roof Exhauster | Weather cover on top of the roof exhauster (p. 19). |
Provenance: FanPedia exploded views pp. 13–19 and housing detail pages pp. 60–61, 63–64 and 66, as cited in each row.
Rules: Each card goes in exactly one bin. The answer key is the family whose FanPedia exploded view (pp. 9–19) or housing detail (pp. 59–66) labels the part; for Curb Cap the exploded view on p. 19 decides, and the feedback notes the roof mounted axial use. Cards can be moved freely until Check is pressed.
Learner Activity:
- The learner sees 12 cards in shuffled order and four empty bins.
- The learner drags each card into a bin. Cards can be moved between bins before checking.
- The learner presses Check. Each card is marked correct or incorrect, and clicking a card shows its "Why" text.
- The learner can press Retry to send the incorrect cards back to the pool and place them again; retries are not counted toward mastery.
Feedback: 12 cards, shuffled, one first check counted for mastery, unlimited retries. Correct card: "Correct:
Starting State: All 12 cards in the pool, the four bins empty, and the question "Which fan family's exploded view shows each part?"
Chapter Anchors: The chapter states that FanPedia's exploded views run from p. 9 to p. 19, that straightening vanes appear on pp. 17 and 64, that the belt tube is also called a belt fairing, and that roof mounted axial fans are shown with a curb cap on p. 7.
Key Takeaways¶
- An exploded view separates an assembly along its assembly lines so each part carries a label; FanPedia's run from p. 9 to p. 19, and its housing details from p. 59 to p. 66.
- A scroll housing is built from two housing side plates and a curved scroll wrapper; the cutoff at the outlet keeps discharged air from recirculating.
- Housing framing stiffens the shell and supports it; a cast housing, as on cast aluminum or cast iron pressure blowers, is poured in one piece.
- A horizontal split housing is the standard split; a three-way split housing is for shipping or passing through a specific opening; a pie split housing lets the impeller out without disturbing the ducts, in Mohawk or standard style.
- Housing access panels remove a whole side (three sides on square inline fans), while access doors are cut into the housing.
- Tubular housings add straightening vanes, a discharge cone and, on belt drives, a belt tube; a belt guard and motor cover protect people and the motor outside the airstream.
- Plug fans use a mounting panel and an insulation plug at the plenum wall; roof fans use a curb cap, a roof exhauster shroud, and on lab exhaust a nozzle and windband.
You Can Read the Drawing Now
You can now open any FanPedia exploded view, find the cutoff, the side plates, the straightening vanes or the curb cap, and say what each one is for. That "bent piece near the outlet" from the start of the chapter is most likely the cutoff, and you know to confirm it on p. 60 before anyone orders a part.