Advanced Arrangements and Configuration Variants

Summary

This chapter returns to fan arrangements with the variants that build on motors, bases, and installation: Arrangements 8, 9, and 10; plug arrangements 1P, 4P, 8P, and 9P; plenum arrangements 3HS, 3HA, 3SM, 3VA, 3VS, and 4V; Arrangements 3F, 9F, 9H, and 9ST/9SS; vertical and horizontal inline variants; and swingout and clamshell fans and their door assemblies. It closes with motor positions L and R, the standard and swingout motor position rules, inline motor positions A to H, and ventilating sets. After completing it, readers can identify any arrangement code in a FanPedia or catalog drawing.

Concepts Covered

This chapter covers the following 28 concepts from the learning graph:

Concept	Concept Impact Score
Arrangement 8	23
Arrangement 9	34
Arrangement 1P Plug	23
Arrangement 4P Plug	22
Swingout Fan	6
Clamshell Fan	3
Arrangement 3F	1
Arrangement 4VI and 4HI	1
Plenum Arrangements 3HS and 3HA	1
Plenum Arrangement 3SM	1
Plenum Arrangements 3VA and 3VS	1
Plenum Arrangement 4V	1
Arrangement 10	2
Arrangement 4S Swingout	1
Arrangement 7SI and 7DI	1
Arrangement 9F	1
Arrangement 9H	1
Arrangement 9ST and 9SS	1
Arrangement 8P and 9P Plug	22
Arrangement 4CS and 9CS	1
Arrangement 4SO and 9SO	1
Motor Positions L and R	3
Swingout Door Assembly	1
Double Door Clamshell	1
Ventilating Set	1
Standard Motor Position Rule	2
Inline Motor Positions A to H	1
Swingout Motor Position Rule	1

Prerequisites

This chapter builds on concepts from:

• Chapter 3: Basic Fan Anatomy
• Chapter 11: Drives and Standard Fan Arrangements
• Chapter 12: Discharge Positions and Rotation
• Chapter 13: Rotation and Discharge Codes
• Chapter 14: Fan Motors and Enclosures
• Chapter 15: Motor Ratings, Speed Control and Positioners
• Chapter 17: Bearing Details, Lubrication and Pedestals
• Chapter 22: Fan Bases and Vibration Isolation
• Chapter 23: Spring Isolators, Restraints and Field Measurement

Every Letter on the Drawing Means Something

A customer's drawing says "Arr. 9SS, CCW, R" and the order desk wants to know if it can ship. By the end of this chapter you will read that code, picture the fan, and know whether the motor and conduit box can go where the customer wants them. Let's follow the airflow.

From Base Numbers to Variants

Chapter 11 introduced the base arrangement numbers: 1, 3, 4 and 7 for housed centrifugal fans, plus the plug, plenum, axial and lab exhaust families. Real orders rarely stop at the base number. A drawing title block is just as likely to read 9H, 3SM, 8P or 4CS, and each suffix changes what the factory builds: where the motor sits, what holds the fan up, and how a mechanic gets to the impeller.

This chapter takes the variants in groups: the overhung pedestal arrangements 8, 9 and 10; frame and inlet variants of 3, 4 and 7; plenum and plug variants; and swingout and clamshell construction. It closes with the motor position rules that go with them.

Most suffixes abbreviate a word in FanPedia's drawing captions, where the key letter is underlined (FanPedia pp. 20–28):

Suffix	Stands for	Seen on
F	Extended frame that carries the motor	3F, 9F
H	Motor mounted horizontally on the side of the pedestal	9H
SI, DI	Integral inlet box on a single or double width fan	3SI, 7SI, 3DI, 7DI
VI, HI	Fan hung from its own inlet, vertical or horizontal shaft	4VI, 4HI
P	Pedestal plug fan, mounted to grade	1P, 4P, 8P, 9P
S, ST, SS, SO	Swingout construction (ST top motor, SS side motor)	4S, 9ST, 9SS, 4SO, 9SO
CS	Clamshell construction	4CS, 9CS
HS, HA, SM, VA, VS, V	Plenum motor mounting variants	3HS, 3HA, 3SM, 3VA, 3VS, 4V

The Overhung Pedestal Family: Arrangements 8, 9 and 10

Arrangements 1, 8, 9 and 10 share one skeleton. The impeller is overhung, mounted on the end of the shaft, and both bearings sit on a bearing pedestal outside the housing (FanPedia p. 30). What separates the four is the drive and the motor's location.

Arrangement 8

Arrangement 8 is a direct drive, overhung fan in which the Arrangement 1 bearing pedestal is extended to carry the motor, and a flexible coupling joins the motor shaft to the fan shaft. FanPedia calls it "a modified version of Arrangement 1 used for direct drive" (FanPedia p. 165). The fan keeps its own shaft and two bearings, so the impeller does not hang on the motor bearings as it does in Arrangement 4.

That is the reason to specify it. Arrangement 4 fans "are typically limited up to size 365" (FanPedia p. 164) and put the motor against the housing; Arrangement 8 lets the fan bearings carry the impeller and keeps the motor away from the airstream. The layout also appears in BAIFE and BCIFE lab exhaust fans and in wall-mounted plug fans (FanPedia pp. 26, 29, 174).

The cost is length, with motor, coupling, bearings and housing in a line. FanPedia calls the Arrangement 8 plug fan "the least common plug fan arrangement due to the length of the assembly" (FanPedia p. 171). FanPedia notes that inertia bases "are typically used on longer, direct drive fans to mitigate assembly deflection, maintaining proper alignment between the motor, coupling, shaft and bearings" (FanPedia p. 175), a base covered in Chapter 22.

Worked example: direct drive above the Arrangement 4 range. A process engineer wants a direct drive SWSI exhaust fan with no belts to maintain, and the selection lands on a fan size larger than 365.

1. Try Arrangement 4 first. Size 365 is its typical upper limit, so this selection is outside it.
2. Keep the overhung impeller. The engineer wants both bearings out of the airstream, which rules out the center hung Arrangement 7.
3. Choose Arrangement 8. The Arrangement 1 pedestal is extended for the motor, and a flexible coupling transmits the power.
4. Plan the support. The assembly is long, so the engineer asks whether an inertia base is needed to hold coupling alignment, and adds an alignment check to start-up.

The order line then adds rotation and discharge as in Chapter 13, but no motor position letter: the motor sits on the shaft centerline.

Arrangement 9

Arrangement 9 is a belt driven, overhung fan with the motor mounted on the side of the fan's own bearing pedestal. FanPedia states that it "is available as belt driven only," that "a motor slide base is mounted on the side of the bearing pedestal," and that the arrangement "permits the unit to ship as a complete assembly with the motor and drive mounted" (FanPedia p. 165). Unlike Arrangement 1, whose motor stands on the floor or a fan base, Arrangement 9 is one package with one footprint.

FanPedia also uses Arrangement 9 for plug fans ("the most common plug fan arrangement", p. 172), for axial and inline fans that need "the motor to be out of the airstream" (p. 173), and for lab exhaust fans (p. 175). In every family the motor is outside the air path and a sheave change can retune the speed. The motor side follows rotation, left for CW and right for CCW (FanPedia p. 165), a rule covered at the end of this chapter.

Worked example: choosing within the 9 family. An industrial customer needs a belt driven SWSI fan for a hot process exhaust. The plant wants the fan shipped as one assembly, belt tension that a millwright can set without special tools, and spring isolators under the fan. The candidate variants are 9, 9F, 9H and 10:

1. Arrangement 9 fits: the motor is on a slide base on the side of the pedestal, the unit ships complete, and the bearings are outside the hot airstream.
2. The motor size check. The selection calls for a large motor. If it is too large for the pedestal, FanPedia's answer is Arrangement 9F (p. 166), but 9F "is not suitable for mounting vibration isolators directly under the fan" and FanPedia's advice when isolators are required is to "use an Arrangement 1 fan with a separate isolation base" (p. 166).
3. The adjustment check. If the millwright prefers to move the motor horizontally to tension the belts, Arrangement 9H puts the motor on the side of an extended pedestal for horizontal adjustment (p. 166).
4. The decision. The motor fits on the pedestal, so the engineer offers Arrangement 9, CW, with spring isolators. Had the motor been too large, the quote would have switched to Arrangement 1 with an isolation base, not 9F.

Arrangement 9F

Arrangement 9F is an Arrangement 9 whose fan frame is extended to carry a motor that is too large for the bearing pedestal. The motor sits horizontally on the extended structural frame, "similar to an Arrangement 1 fan" (FanPedia p. 166), and the F in the code stands for that frame (FanPedia p. 22). The frame ties the fan and motor together, but it also means the fan cannot float on isolators: FanPedia states that 9F "is not suitable for mounting vibration isolators directly under the fan," and directs the reader to Arrangement 1 with a separate isolation base when isolation is required (FanPedia p. 166). Its motor position follows the same CW (L) / CCW (R) standard as Arrangement 9 (FanPedia p. 52).

Arrangement 9H

Arrangement 9H is an Arrangement 9 in which the pedestal is extended on one side so the motor mounts horizontally on the side of the pedestal. FanPedia offers it "when horizontal motor adjustment is preferred" (FanPedia p. 166). The drawing shows two ways to hold the motor: a slide base or rails, and a pivot base (FanPedia p. 22). Heavy-duty slide rails mounted on a pedestal are shown for Arrangement 9H only, and the automotive pivot base is used on 9H pedestals (FanPedia pp. 76–77). As with Arrangement 9, the motor is typically on the left side for CW fans and on the right side for CCW fans (FanPedia p. 166).

Arrangement 10

Arrangement 10 is a belt driven, overhung fan with the motor mounted inside the bearing pedestal. FanPedia states that it is "available as belt driven only," that the motor bases are "mounted inside the bearing pedestal," and that it "offers a more compact design than the Arrangement 9 and is suitable for roof or outdoor installations when supplied with the optional weather cover" (FanPedia p. 167). The arrangement drawing shows two motor mounts: sizes 122–365 with the motor on an adjustable plate at the bottom of the pedestal, and sizes 402 and larger with the motor on a slide base on the side of the pedestal (FanPedia p. 22). FanPedia lists the Arrangement 10 motor position as "unique to pedestal design (no options)" (FanPedia p. 52).

Ventilating Set

A ventilating set is the trade name for a compact Arrangement 10 centrifugal fan in the smaller sizes. FanPedia states that "for Class I and II fans, sizes 122 through 365, Arrangement 10 units are commonly referred to as Ventilating Sets," and refers the reader to TCF Catalog 600 for details (FanPedia p. 167). So a specification that asks for a "vent set" is asking for a compact Arrangement 10 package, Class I or II, with no motor position to choose.

One Skeleton, Four Motor Homes

Notice that Arrangements 1, 8, 9 and 10 share one skeleton: an overhung impeller and a two-bearing pedestal. Only the motor's home changes: on the floor (1), coupled at the end of the pedestal (8), hung on the side (9), or tucked inside (10). Picture the skeleton first, and each code becomes a question of where the motor lives.

Frame and Inlet Variants of Arrangements 3, 4 and 7

These variants solve mounting problems: carrying the motor on the fan, hanging the fan from its inlet, or moving bearings out of a hot airstream.

Arrangement 3F

Arrangement 3F is an Arrangement 3 fan with an extended frame that carries the motor. For single width fans, FanPedia describes it as "an Arrangement 3 with extended angle frame to mount the motor and horizontal slide base as an assembly," and notes that the fan is welded to the frame and "typically not suitable for mounting vibration isolators directly under the fan" (FanPedia pp. 20, 163). The double width version is built differently: FanPedia describes an "integral extended base" with "brackets to accept vibration isolators," available to size 660, with motor positions W and Z as standard and X and Y by factory consultation (FanPedia p. 167). The same code therefore carries different isolation answers for SWSI and DWDI fans, so check which width the drawing shows before promising springs.

Arrangement 4VI and 4HI

Arrangements 4VI and 4HI are modified Arrangement 4 fans that mount directly on their own inlet. The whole fan, motor included, "is supported by the inlet flange only" (FanPedia p. 21). In 4VI the air enters vertically and the motor shaft is vertical; in 4HI the air enters horizontally and the shaft is horizontal (FanPedia pp. 164–165). Both have reinforced inlets and a removable motor side, so "the rotating assemblies [can] be removed without removing the housing from the mounting structure" (FanPedia p. 164). Either can use a C-face mounted, foot mounted, or combination foot and C-face motor (FanPedia p. 21).

Arrangement 7SI and 7DI

Arrangements 7SI and 7DI are direct drive, center hung fans with integral inlet boxes that keep the bearings out of the airstream. 7SI is single width; 7DI is double width. In both, the impeller is mounted between the bearings and the pedestal carries "the motor, flexible coupling and one bearing" (FanPedia pp. 165, 168). A pie split housing allows the impeller to be removed, the assembly is mounted on a unitary base as standard, and an inertia base is optional (FanPedia pp. 165, 168). FanPedia describes the 7DI's bearing location as "allowing for elevated operating temperatures and relatively clean air" (FanPedia p. 168). They are the coupled counterparts of 3SI and 3DI, covered in Chapter 11, whose motors the customer locates off the fan assembly (FanPedia pp. 164, 167).

Plenum Fan Variants

A plenum fan, as Chapter 11 described, is an unhoused fan that sits inside the plenum it pressurizes, with its motor and drive in the same space. Because the fan sits inside an air handler, the plenum variants are mostly about where the motor fits: on top of the fan, beside it, or below it in a vertical unit. Two kinds of motor mount appear throughout. A slide base is a NEMA-type base whose motor slides along adjusting screws to tension the belts. An adjustable motor base carries the motor on a post mount or a pivot/bolted design and sets belt tension by moving the motor plate (FanPedia pp. 76–78; Chapter 15).

Plenum Arrangements 3HS and 3HA

Plenum Arrangements 3HS and 3HA are horizontal Arrangement 3 plenum fans with the motor mounted on top of the fan. FanPedia says both provide "a means for mounting the motor on top of the unit," a design "often desirable when floor space is limited" (FanPedia p. 169). They differ only in the motor base. 3HS uses a slide base, and "due to limited belt center range, NEMA 'slide base' option is available on sizes 182 and larger only." 3HA uses a heavy-duty adjustable motor base that "is available for all fan sizes" (FanPedia p. 169). So a top-mounted motor on a fan smaller than size 182 is a 3HA.

Plenum Arrangement 3SM

Plenum Arrangement 3SM is a horizontal Arrangement 3 plenum fan with the motor mounted on the side of the fan frame on a slide base. FanPedia calls it "an economical and space-saving means to supply plenum fans with motors mounted to the side of the fan frame," with the slide base allowing "quick and easy belt adjustments" (FanPedia p. 169). Its standard motor position is (R); position (L) is normally ordered with an F1 conduit box, with F2 selected if there are clearance issues (FanPedia p. 55).

Plenum Arrangements 3VA and 3VS

Plenum Arrangements 3VA and 3VS are vertical Arrangement 3 plenum fans with a side mounted motor, used where the air handler turns the airflow vertically. 3VA uses the heavy-duty adjustable motor base, available for all fan sizes; 3VS uses a slide base, available on sizes 182 and larger only because of the limited belt center range (FanPedia pp. 169–170). The A and S letters therefore mean the same thing in the vertical pair as in 3HA and 3HS. On the motor position page, 3VA shows a single Top Center (TC) position, and 3VS shows Standard (S) and Optional (O) positions (FanPedia p. 55).

Plenum Arrangement 4V

Plenum Arrangement 4V is the vertical form of the direct drive Arrangement 4 plenum fan, with the impeller mounted on the motor shaft. FanPedia states that it "is available for mounting with either vertical up airflow (inlet under the motor) or vertical down airflow (inlet above the motor)" (FanPedia p. 170). It keeps the Arrangement 4 benefits, a compact unit with no belts and "less maintenance than other arrangements" (FanPedia p. 170), in an air handler whose air path runs vertically. Since there are no belts, there is no motor base and no motor position to choose.

The table below gathers the five belt driven plenum variants just described, so they can be compared on one line each.

Arrangement	Orientation	Motor location	Motor base	Size note (FanPedia p. 169–170)
3HS	Horizontal	Top of fan	NEMA slide base	Sizes 182 and larger
3HA	Horizontal	Top of fan	Heavy-duty adjustable base	All sizes
3SM	Horizontal	Side of fan frame	Slide base	None stated
3VA	Vertical	Side of fan	Heavy-duty adjustable base	All sizes
3VS	Vertical	Side of fan	NEMA slide base	Sizes 182 and larger

Spell the Code Out Loud

Here's a shortcut for plenum codes: read the letters after the 3 as "Horizontal or Vertical, then Slide or Adjustable." 3VS is "vertical, slide base," so before quoting it, check that the fan is size 182 or larger; if it is smaller, offer 3VA.

Pedestal Plug Arrangements

A plug fan, from Chapter 11, is an unhoused fan whose impeller sits inside the customer's enclosure while the shaft, bearings and motor stay outside, normally carried by the customer's wall through a mounting panel. The wall-hung plug arrangements are 4, 8 and 9. Each has a pedestal plug counterpart, marked with a P, in which the fan stands on its own pedestal at grade and the wall only seals around it. FanPedia gives the same reason for every P variant: it is "typically used where the customer's wall may not be sufficient by itself," and "mounting to the foundation also makes it better for meeting lower vibration requirements," with the mounting panel optional (FanPedia pp. 170–172). The belt driven Arrangement 1P has no wall-hung counterpart in FanPedia's set.

Arrangement 1P Plug

Arrangement 1P is a belt driven pedestal plug fan in which the fan is mounted to grade and the motor is mounted separately on the floor or a fan base. FanPedia describes it as "a belt driven arrangement where the fan is mounted to grade and the motor is mounted separate from the fan," and notes that it is "typically used on larger fans and/or larger HP motors where the customer's wall may not be sufficient by itself" (FanPedia p. 170). Its motor mount is the NEMA type slide base listed for pedestal plug fans 1P and 9P (FanPedia p. 76). The difference from 9P is the same as the difference between Arrangements 1 and 9 on a housed fan: in 1P the motor stands apart from the fan pedestal.

Worked example: a large belt driven plug fan. An air handler builder needs a large belt driven plug fan with a high horsepower motor. The casing wall is a double-wall insulated panel.

1. Start from the default. The most common plug arrangement is the wall-hung Arrangement 9 (FanPedia p. 172), but the builder's wall is not designed to carry a large fan and motor.
2. Move the fan to grade. A P variant puts the fan on a pedestal on the unit floor or foundation. The choice is between 9P, with the motor on the fan pedestal, and 1P, with the motor separate.
3. Size the motor. With a large motor, the builder prefers the motor on its own base beside the fan, where it can be reached for belt changes from the service side of the unit. That is Arrangement 1P.
4. Write the result. "Arrangement 1P plug fan, belt driven, motor on separate base," adding a mounting panel if the builder wants one. The foundation also helps with lower vibration.

Arrangement 4P Plug

Arrangement 4P is a direct drive pedestal plug fan: the impeller is mounted on the motor shaft and the fan is mounted to grade. FanPedia defines it as "same as the Arrangement 4 fan except the fan is mounted to grade" (FanPedia p. 171), where the plain Arrangement 4 plug fan is wall mounted (FanPedia p. 26).

The Arrangement 4 plug fan's own strengths and limits carry over. FanPedia notes that Arrangement 4 "is more compact and requires less maintenance due to not having fan shaft, bearings or belts," but that "high airstream temperatures may limit the use of this arrangement" (FanPedia p. 171), since the motor bearings carry the impeller and the motor sits close to the air path. Twin City Fan engineering (2026-10-09) is more direct: Arrangement 4 is not used for high-temperature applications, and its standard ranges are typically up to about 180°F. 4P adds the floor support without changing those facts.

Worked example: choosing between 4 and 4P. A pharmaceutical air handler needs a direct drive plug fan at room-temperature air, driven by a VFD. The engineer first checks the temperature limit: the air is not hot, so Arrangement 4 is acceptable. Next comes the wall. The unit casing is a lightweight panel, and the owner's specification sets a strict vibration limit for the supply fans. Both points match FanPedia's reasons for a P variant: a wall that may not be sufficient by itself, and lower vibration requirements. The engineer offers Arrangement 4P. Had the air been hot, the temperature limit would have pointed to a belt or coupled arrangement with the bearings outside the airstream instead, either 8P or 9P.

Arrangement 8P and 9P Plug

Arrangements 8P and 9P are the grade-mounted versions of the Arrangement 8 and 9 plug fans. FanPedia defines each as "same as the Arrangement 8 [or 9] fan except the fan is mounted to grade," for larger fans or motors where the wall may not be sufficient and for lower vibration, with the mounting panel optional (FanPedia pp. 171–172). In 8P the motor is coupled to the fan shaft on the pedestal (direct drive); in 9P the motor sits on a slide base on the pedestal and drives the fan through belts (FanPedia pp. 13, 26–27, 76).

Both keep a fan shaft on two bearings outside the enclosure, so they suit hot air better than 4P: the motor bearings do not carry the impeller. Between them, the choice is Chapter 11's direct drive against belt drive trade: 8P has no belts but a fixed speed unless a VFD is used, and a long assembly; 9P is shorter and its speed is set by sheaves.

Worked example: a hot recirculation fan. A dryer manufacturer needs a plug fan to recirculate hot air in a large dryer. The dryer wall is insulated panel, and the fan and motor are large.

1. Rule out 4 and 4P. High airstream temperatures may limit Arrangement 4 (FanPedia p. 171), and this air is hot.
2. Rule out wall mounting. The wall may not be sufficient for a large fan and motor, so the fan goes to grade with a P variant.
3. Compare 8P and 9P. The duty may need retuning after start-up, and the crew is used to belt drives, so 9P fits. Had the owner banned belts, 8P with a VFD would meet the duty with a longer assembly.
4. Order: "Arrangement 9P plug fan, belt driven, motor on pedestal slide base, fan mounted to grade."

Plug arrangement	Drive	Fan support	Motor location
4	Direct, impeller on motor shaft	Customer's wall	Motor shaft carries impeller
4P	Direct, impeller on motor shaft	Pedestal at grade	Motor shaft carries impeller
8	Direct, coupled	Customer's wall	End of pedestal, coupled
8P	Direct, coupled	Pedestal at grade	End of pedestal, coupled
9	Belt	Customer's wall	On fan pedestal
9P	Belt	Pedestal at grade	On fan pedestal, slide base
1P	Belt	Pedestal at grade	Separate, on floor or fan base

The P Does Not Fix a Temperature Problem

A common trap is assuming that putting a fan on a pedestal also protects it from heat. The P only changes what holds the fan up; a 4P still hangs its impeller on the motor shaft. For hot air, choose the drive first (8P, 9P or 1P) and the support second.

Swingout and Clamshell Construction

Some fans must be opened often, such as washdown exhausts and process fans that collect residue. Swingout and clamshell constructions build the opening into the fan, so no ductwork has to be unbolted.

Swingout Fan

A swingout fan is a fan whose rotating assembly is mounted on a hinged door, so the impeller swings out of the housing for cleaning and inspection. FanPedia states that swingout fans "are designed for frequent cleaning and provide full access to the impeller and inner casing of the fan," and that "the entire impeller/shaft/bearing assembly is mounted on a large swingout door" (FanPedia p. 123). Swingout construction is available for centrifugal, inline centrifugal and axial fans (FanPedia p. 123). The housed centrifugal versions are Arrangements 4S, 9ST and 9SS; the axial and inline centrifugal versions are Arrangements 4SO and 9SO (FanPedia p. 123).

The duct connections and housing stay in place while the rotor swings clear. FanPedia also notes an isolation advantage: vibration isolators directly under a fan are "usually limited to fans with 36.5" diameter impellers or less," with "an exception … made for swingout housed centrifugal fans, any size impeller, with flat pads only" (FanPedia p. 134).

Worked example: a washdown exhaust fan. A food processor needs a belt driven SWSI exhaust fan that is cleaned every week.

1. Housed centrifugal, belt driven. That points to the 9-family swingout arrangements, 9ST or 9SS, rather than 4S (direct drive) or 4SO/9SO (axial and inline).
2. Swing side. FanPedia notes that the door "can swing left or right depending on the application" (FanPedia p. 22). The cleaning aisle is on the left of the fan, so the engineer asks for a left swing.
3. Motor mount. 9ST puts the motor on a NEMA slide base above the pedestal; 9SS puts it on the side of the pedestal on an automotive pivot base (FanPedia p. 166). The plant prefers the side mount for reach, so the choice is 9SS.
4. Check the rotation. A left swing 9SS is limited to CCW rotation with motor position (R) and requires an F2 conduit box (FanPedia p. 53). The duct layout gives CCW, so the order reads "Arrangement 9SS, left swing, CCW, motor position (R), F2 conduit box." Had the layout required CW, the engineer would switch to a right swing 9SS or to a 9ST.
5. Isolation. If isolators are wanted directly under the fan, FanPedia allows swingout housed centrifugal fans of any impeller size on flat pads only (FanPedia p. 134).

Step 4 shows why swingout fans have their own motor position page: swing side, rotation and motor position are tied together.

Swingout Door Assembly

The swingout door assembly is the hinged door and reinforced framework that carry a swingout fan's rotating parts. On the housed centrifugal Arrangements 4S, 9ST and 9SS, FanPedia describes the motor and impeller assembly as "mounted to reinforced framework to support the opened housing" (FanPedia pp. 164, 166), and the general description puts the "entire impeller, shaft and bearing assembly" on "a large swingout door" (FanPedia p. 195). On the axial and inline 4SO and 9SO, "the rotor assembly is built onto a swingout door that allows maintenance personnel to easily inspect, clean or repair out of the airstream" (FanPedia p. 173). The door assembly is the structural heart of the design: it must hold bearing alignment when closed and carry the rotor's weight when open.

Arrangement 4S Swingout

Arrangement 4S is "a modified Arrangement 4 fan intended for easy access to the impeller and housing interior" (FanPedia p. 164). The impeller stays on the motor shaft, as in every Arrangement 4, but the motor and impeller are mounted on reinforced framework so the assembly swings out with the door (FanPedia pp. 20, 164). It is the direct drive housed centrifugal swingout choice. Because there is no fan shaft or belt, there is no motor position to choose; the motor rides on the door.

Arrangement 9ST and 9SS

Arrangements 9ST and 9SS are the belt driven housed centrifugal swingout fans, both modified Arrangement 9 fans "intended for easy access to the impeller and housing interior" (FanPedia p. 166). They differ in the motor mount, and the second letter says where. In 9ST the T is for top: the motor is mounted above the bearing pedestal, on a NEMA type slide base only. In 9SS the second S is for side: the motor is on the side of the bearing pedestal, on an automotive pivot base only, and "motor location is restricted based on the fan's rotation" (FanPedia pp. 22, 166). Both come in right swing and left swing versions, and both put the drive on the swinging door.

Arrangement 4SO and 9SO

Arrangements 4SO and 9SO are the swingout versions of the direct drive Arrangement 4 and belt driven Arrangement 9 axial and inline centrifugal fans. In both, "the rotor assembly is built onto a swingout door" so maintenance staff can "inspect, clean or repair out of the airstream" (FanPedia p. 173). 4SO keeps the compact Arrangement 4 envelope with the impeller on the motor shaft; 9SO keeps the motor out of the airstream with a fixed or adjustable V-belt drive. FanPedia's drawings show axial fans, and notes that inline centrifugal fans "are available with the same arrangements but use different impellers" (FanPedia p. 28).

Clamshell Fan

A clamshell fan is an axial or inline centrifugal fan whose casing opens on a hinged door to give access to the inside without removing the duct. FanPedia states that clamshell fans "are designed to provide complete access to the interior of the fan for maintenance or cleaning without removal of ductwork," that the construction "is available for inline centrifugal and axial fans," and that it "is typically used in vertical mount applications" (FanPedia p. 123). The difference from a swingout fan is what moves. In a swingout fan the rotor rides out on the door; in a clamshell fan the casing opens around a rotor that stays in place. Clamshell fans come in single door and double door versions (FanPedia p. 123).

Double Door Clamshell

A double door clamshell is a clamshell fan with two access doors instead of one. FanPedia notes that "for the double door configuration, one of the two access doors is wide enough for impeller removal" (FanPedia pp. 123, 180). The second door matters when the impeller must come out of the fan entirely, for a rebalance or a blade change, rather than simply be cleaned in place. Both single door and double door clamshell fans are offered in Arrangements 4CS and 9CS (FanPedia p. 123).

Arrangement 4CS and 9CS

Arrangements 4CS and 9CS are the clamshell versions of the axial and inline centrifugal Arrangements 4 and 9. In 4CS the impeller is "mounted directly on the fan motor shaft … for a compact envelope"; in 9CS a fixed or adjustable V-belt drive keeps the motor "out of the airstream." In both, "a spacious clamshell door gives maintenance personnel access to the rotor assembly for ease of inspection, cleaning or repair" (FanPedia pp. 172–173). Choose between them the way you choose between Arrangements 4 and 9 for an inline fan, then add the clamshell for access.

Diagram: Swingout and Clamshell Fans

Run Swingout and Clamshell Fans Fullscreen

Swingout and Clamshell Fans

sim-id: ch24-swingout-clamshell-overlay
Library: html + FP.Overlay
Status: built
Bloom Level: Remember
Learning Objective: The learner will identify the housed centrifugal, axial and inline centrifugal swingout fans and the double door and single door clamshell fans on FanPedia's drawings, given a description of each.

Content: 5 numbered zones: Centrifugal swingout fan (Arrangements 4S, 9ST, 9SS), Axial swingout fan (Arrangements 4SO, 9SO), Inline centrifugal swingout fan (Arrangements 4SO, 9SO), Double door clamshell fans (Arrangements 4CS, 9CS), Single door clamshell fans (Arrangements 4CS, 9CS)

Provenance: FanPedia page 123, "Special Construction: Swingout & Clamshell (three swingout fans, top; double door and single door clamshell fans, bottom)", with the printed labels removed. Drawing: FanPedia, Twin City Fan, p. 123.

What Moves When the Door Opens?

Think of the two constructions by asking what moves when the door opens. In a swingout fan the rotor swings out with the door; in a clamshell fan the casing opens and the rotor stays put. That one question tells you which codes (S, ST, SS, SO or CS) can answer a customer's cleaning problem.

Before the motor position rules, the interactive decoder below brings the arrangement variants in this chapter together. Every code in it, and every feature in its descriptions, was defined in the sections above.

Diagram: Arrangement Variant Decoder

Run Arrangement Variant Decoder Fullscreen

Arrangement Variant Decoder

Type: microsim sim-id: ch24-arrangement-variant-decoder
Library: p5.js
Status: Specified
Bloom Level: Analyze
Bloom Verb: differentiate
Learning Objective: The learner will differentiate twelve arrangement variants by naming the arrangement code that matches a written description of a fan's drive, motor location, support and access features.

Prerequisites: overhung and center hung impellers, direct drive and belt drive, bearing pedestal, slide base, adjustable motor base, plug fan, pedestal plug, plenum fan, swingout and clamshell construction (all defined in this chapter and Chapter 11).

Evidence of Mastery: For each of the 12 descriptions the learner commits one code from the answer list. An answer is correct when it matches the Correct code column. Mastery: 10 of 12 correct on the first attempt. Revealing feature hints is exploration, not evidence.

Misconceptions: (1) Any direct drive fan is Arrangement 4. (2) The P suffix changes the drive. (3) Swingout and clamshell are the same construction. (4) 9F is the right fix whenever a large motor needs isolators.

Instructional Rationale: Differentiating near-identical codes forces the learner to attend to the one feature that separates them (motor location, support, or door type), which is the analysis an application engineer does on a drawing.

Content:

Answer list (shown for every item): 8, 9F, 9H, 10, 3F, 4, 4VI, 7DI, 3HS, 3HA, 3SM, 3VS, 4V, 1P, 4P, 8P, 9P, 9ST, 9SS, 4SO, 9SO, 9CS. (Arrangement 4 and the axial and inline swingout 9SO are included so that the added messages for items 1 and 12 can appear; FanPedia pp. 164 and 173.)

Each item also has a feature hint the learner may reveal before answering: drive type, impeller position, fan support, and motor location, as listed in the description.

#	Description shown	Correct code	Why (feedback)
1	Housed SWSI fan, overhung impeller, two bearings on a long pedestal, motor coupled to the fan shaft at the end of the pedestal	8	An Arrangement 1 pedestal extended for a coupled motor is Arrangement 8.
2	Housed SWSI fan, belt driven, motor too large for the pedestal, carried on an extended structural frame	9F	The F is the extended frame that carries a motor too large for the pedestal.
3	Housed SWSI fan, belt driven, motor inside the bearing pedestal, sold as a ventilating set	10	Arrangement 10 puts the motor inside the pedestal; small Class I and II sizes are vent sets.
4	Direct drive SWSI fan hung entirely from its inlet flange, vertical motor shaft	4VI	VI is vertical inlet-mounted; the inlet flange carries the whole fan.
5	Direct drive DWDI fan, impeller between bearings, integral inlet boxes, motor coupled on a pedestal	7DI	A coupled double width fan with integral inlet boxes is 7DI.
6	Horizontal belt driven plenum fan, motor on top on an adjustable motor base, size smaller than 182	3HA	Top-mounted motor with an adjustable base is 3HA; the 3HS slide base starts at size 182.
7	Horizontal belt driven plenum fan, motor on the side of the fan frame on a slide base	3SM	SM is side-mounted motor on a slide base.
8	Vertical direct drive plenum fan, impeller on the motor shaft, inlet under the motor	4V	4V is the vertical direct drive plenum fan, offered for up or down airflow.
9	Belt driven plug fan on a pedestal at grade, motor on its own base beside the fan	1P	The motor is separate from the fan pedestal, so this is 1P, not 9P.
10	Direct drive plug fan, impeller on the motor shaft, fan floor mounted	4P	Arrangement 4 mounted to grade is 4P; the P does not change the drive.
11	Belt driven housed SWSI fan, rotor on a hinged door, motor on the side of the pedestal on a pivot base	9SS	ST is top-mounted motor; SS is side-mounted motor on a pivot base.
12	Belt driven inline fan, casing opens on a door while the rotor stays in place	9CS	The casing opens and the rotor stays put: that is clamshell, not swingout.

Provenance: Descriptions and codes from FanPedia pp. 20–28 (arrangement drawings) and pp. 163–173 (technical descriptions), local copy fanpedia.pdf; summarized in this chapter's sections on each arrangement.

Rules: One code per item. Exact match with the Correct code column. Item order is shuffled once per session. The answer list never changes between items.

Learner Activity:

1. The learner reads a description and may reveal its feature hint.
2. The learner selects a code and presses Check. The item is scored and the Why text appears.
3. The learner advances to the next item. After item 12 a summary lists every missed item with its correct code.
4. A Retry Missed option re-presents only the missed items; retries are not counted toward mastery.

Feedback: 12 items, shuffled, one scored attempt each. Correct: "Correct: Arrangement ." Incorrect: "This is Arrangement . ." Added messages: choosing 4P or 4 for item 1: "There is a coupling and a separate fan shaft, so the impeller is not on the motor shaft." Choosing 9P for item 9: "In 9P the motor sits on the fan pedestal; here it stands apart." Choosing 9F for item 3: "The motor is inside the pedestal, not on a frame." Choosing 9SO for item 12: "In a swingout fan the rotor moves; here only the casing opens." A running "Correct: n of 12" score is shown.

Starting State: Item 1 of the shuffled set, hint hidden, no code selected, score "Correct: 0 of 12." Prompt: "Which arrangement code matches this fan?"

Chapter Anchors: Arrangement 4 is typically limited to size 365; 3HS and 3VS slide bases start at size 182; 3HA and 3VA bases are available for all sizes; vent sets are Class I and II, sizes 122 through 365.

Motor Positions for Arrangement Variants

Chapter 12 introduced motor position as the location of a belt-drive motor relative to the fan, read from the drive side, and the four AMCA positions W, X, Y and Z used on Arrangements 1 and 3. The variants in this chapter use other systems, because their motors are tied to the fan's own pedestal, frame or casing. Four rules cover them.

Motor Positions L and R

Motor positions L and R name the two sides of the bearing pedestal or fan frame on which a belt-drive motor can hang, left or right as seen from the drive side. They are used where the motor is carried by the fan itself rather than standing on the floor: Arrangements 9, 9F, 9H and the swingout 9ST and 9SS, and the plenum 3SM (FanPedia pp. 52–55). On the plenum Arrangements 3HS and 3VS, FanPedia names the positions Standard (S) and Optional (O), and labels them "also known as" R and L respectively (FanPedia p. 55). Floor-standing motors on Arrangements 1 and 3 use the four AMCA letters W, X, Y and Z instead.

Standard Motor Position Rule

The standard motor position rule is FanPedia's default pairing of motor side with rotation on pedestal-mounted motors: clockwise fans take position (L), counterclockwise fans take position (R). FanPedia prints it as "Standard Motor Position: CW (L) / CCW (R)" for Arrangements 9 and 9F (FanPedia p. 52), and the technical descriptions say the same for Arrangements 9 and 9H: "the motor is mounted on the left side of the pedestal for CW rotation fans and on the right side for CCW rotation fans" (FanPedia pp. 165–166). FanPedia adds on the same page that position (L) "is normally ordered with F1 conduit box. Select F2 if clearance issues" (FanPedia p. 52).

Treat any other pairing as a special request to confirm with the factory before quoting.

Swingout Motor Position Rule

The swingout motor position rule ties motor position to the swing side of a 9ST and to the rotation and swing side of a 9SS (FanPedia p. 53):

• 9SS right swing: CW rotation and (L) motor position only.
• 9SS left swing: CCW rotation and (R) motor position only, and the fan "must have F2 conduit box for this orientation."
• 9ST right swing: standard motor position (R).
• 9ST left swing: standard motor position (L).

The 9SS limits are firm ("only"); FanPedia gives the same rotation-motor pairing for the automotive pivot base on 9H and 9SS fans (FanPedia p. 77). The 9ST positions are standards. On a 9SS, choosing the swing side fixes rotation and motor position.

Swing Side Is Not a Late Detail

Watch out for orders that settle rotation from the duct layout and leave the swing side "to be decided." On a 9SS the swing side fixes the rotation, so a late swing change can force a different discharge. Settle swing side, rotation and motor position together, on the same drive-side sketch.

Inline Motor Positions A to H

Inline motor positions A to H are the eight motor locations around the casing of a belt driven Arrangement 9 inline, mixed flow or axial fan in a horizontal configuration, lettered as seen in the discharge view with A at the top and the letters running around the casing (FanPedia p. 56). A duct or ceiling mounted fan can take any of the eight. A floor mounted fan shows only G, H, A, B and C, the five positions not blocked by its floor supports (FanPedia p. 56). Vertical inline fans have no specified motor position: the motor is centered on the curb cap or between the support brackets (FanPedia p. 57).

The table below collects the motor position systems for the arrangements in this chapter.

Arrangement	Positions	Standard or limit	Source
9, 9F	L, R	CW (L) / CCW (R)	FanPedia p. 52
9H	L, R	Typically left for CW, right for CCW	FanPedia p. 166
9SS right / left swing	L / R	CW (L) only / CCW (R) only, F2 required	FanPedia p. 53
9ST right / left swing	R / L	Standard (R) / Standard (L)	FanPedia p. 53
10	None	Unique to pedestal, no options	FanPedia p. 52
3SM plenum	L, R	Standard (R); (L) with F1, F2 if tight	FanPedia p. 55
3HS, 3VS plenum	S ("R"), O ("L")	Standard (S)	FanPedia p. 55
3HA, 3VA plenum	TC	Top Center only	FanPedia p. 55
9 inline, horizontal	A to H	Floor mount: G, H, A, B, C	FanPedia p. 56
9 inline, vertical	None	Centered on curb cap or between brackets	FanPedia p. 57

Ten Rows Is a Lot to Hold

If this table feels like a lot to memorize, that is normal; nobody keeps it in their head. You already know the logic from Chapter 12, read from the drive side and find the arrangement first. Work through the checker below one order at a time, and keep FanPedia pp. 52–57 open as your reference.

The checker below practices these rules on orders like the ones an inside sales desk sees. Each term it uses (L and R, the standard rule, swing side, conduit box F1 and F2, and the inline letters) is defined in the sections above and in Chapter 13.

Diagram: Motor Position Rule Checker

Run Motor Position Rule Checker Fullscreen

Motor Position Rule Checker

Type: microsim sim-id: ch24-motor-position-rule-checker
Library: p5.js
Status: Specified
Bloom Level: Apply
Bloom Verb: apply
Learning Objective: The learner will apply FanPedia's motor position rules to ten order lines, judging each as standard, allowed with a condition, or not allowed, and stating the correct position or conduit box when the line is wrong.

Prerequisites: drive side, CW and CCW rotation, motor positions L and R, standard motor position rule, swing side, swingout motor position rule, conduit box F1 and F2, plenum positions S, O and TC, inline motor positions A to H (defined in this chapter and Chapters 12–13).

Evidence of Mastery: For each order line the learner commits a verdict (Standard, Allowed with condition, Not allowed) and, for Not allowed, picks the correction from a list. Correct when both match the Content table. Mastery: 8 of 10 correct on the first attempt.

Misconceptions: (1) L and R are free choices on every pedestal-mounted motor. (2) A 9SS can take either motor position on either swing. (3) Arrangement 10 has a motor position to choose. (4) A floor mounted inline fan can take any of A to H.

Instructional Rationale: Applying a rule to an order line, then correcting it, is the exact task an order desk performs; judging and correcting forces use of the rule, not recognition of it.

Content:

Verdict options: Standard; Allowed with condition; Not allowed. Correction options: change motor to (L); change motor to (R); change to F2 conduit box; change to Top Center (TC); remove motor position (none applies); choose a position from G, H, A, B or C.

#	Order line shown	Verdict	Correction	Why (feedback)
1	Arr. 9, CW, motor (L), F1	Standard	none	CW (L) is the standard; (L) is normally ordered with F1.
2	Arr. 9F, CCW, motor (R)	Standard	none	9F follows CW (L) / CCW (R).
3	Arr. 9, CW, motor (L), F2, wall close to conduit side	Allowed with condition	none	FanPedia: select F2 for (L) if there are clearance issues.
4	Arr. 9SS right swing, CW, motor (R)	Not allowed	change motor to (L)	A right swing 9SS is CW and (L) only.
5	Arr. 9SS left swing, CCW, motor (R), F1	Not allowed	change to F2 conduit box	Left swing 9SS must have the F2 conduit box.
6	Arr. 9ST left swing, motor (L)	Standard	none	9ST left swing standard is (L).
7	Arr. 10, CW, motor (L)	Not allowed	remove motor position (none applies)	Arrangement 10 motor position is unique to the pedestal, no options.
8	Plenum 3SM, motor (R)	Standard	none	3SM standard motor position is (R).
9	Arr. 9 inline, horizontal, floor mount, motor position E	Not allowed	choose a position from G, H, A, B or C	Floor supports block the lower positions; floor mount shows G, H, A, B, C.
10	Plenum 3HA, motor (L)	Not allowed	change to Top Center (TC)	A top-mounted motor on an adjustable base has one position, Top Center.

Provenance: FanPedia pp. 52, 53, 55 and 56, local copy fanpedia.pdf; rules restated in this chapter's section "Motor Positions for Arrangement Variants". The clearance situation in item 3 is illustrative.

Rules: Standard = the pairing FanPedia lists as standard. Allowed with condition = a FanPedia-listed option tied to a stated condition. Not allowed = a pairing FanPedia excludes ("only", "must", "no options", or a position not shown for that mount). The correction is scored only when the verdict is Not allowed.

Learner Activity:

1. The learner reads an order line and selects a verdict.
2. If the verdict is Not allowed, the correction list opens and the learner selects one correction.
3. The learner presses Check; the sim shows a sketch of the fan in its reference view (drive side, or discharge view for the inline item) with the motor in the correct position, and the Why text.
4. The learner advances; after item 10 a summary shows misses with their rules.

Feedback: 10 items, fixed order (pedestal arrangements, then swingout, then plenum and inline), one scored attempt each, then the answer is revealed. Correct: "Correct. ." Incorrect verdict: "Check the rule for Arr. : ." Correct verdict but wrong correction: "Right verdict; the fix is ." Score "Correct: n of 10" counts items with verdict and correction both right.

Starting State: Item 1 shown with no verdict selected and an unlabeled drive-side sketch of an Arrangement 9 fan. Prompt: "Would this order line ship as written?"

Chapter Anchors: CW (L) / CCW (R) standard for 9 and 9F; (L) normally with F1, F2 if clearance issues; 9SS right swing CW (L) only, left swing CCW (R) only with F2; 9ST right swing standard (R), left swing standard (L); Arrangement 10 no options; 3SM standard (R); 3HA and 3VA Top Center only; floor mounted inline shows G, H, A, B and C.

Key Takeaways

• Suffixes change what is built: F adds a motor frame, H side-mounts the motor for horizontal adjustment, P puts a plug fan on a pedestal at grade, and S, ST, SS, SO and CS add swingout or clamshell access.
• Arrangements 1, 8, 9 and 10 share an overhung impeller and a two-bearing pedestal and differ in where the motor lives. Arrangement 10 in Class I and II sizes 122–365 is a ventilating set.
• 9F and SWSI 3F cannot take isolators directly under the fan; DWDI 3F has isolator brackets.
• 4VI and 4HI hang from the inlet flange; 7SI and 7DI couple the motor to a center hung fan with integral inlet boxes.
• Plenum codes read orientation, then motor base: slide bases (3HS, 3VS) from size 182 up, adjustable bases (3HA, 3VA) at all sizes.
• Pedestal plug fans answer a weak wall or a strict vibration limit; they do not change the drive, so hot air still points to 8P, 9P or 1P.
• Swingout fans carry the rotor out on a door; clamshell casings open around a fixed rotor.
• Motor positions follow the arrangement: CW (L) / CCW (R) on the 9 family, swing-dependent rules on 9ST and 9SS (F2 required on a left swing 9SS), no options on Arrangement 10, and A to H on horizontal inline fans.

You Can Read the Whole Title Block

You can now take any arrangement code from a FanPedia or catalog drawing, from 8P to 9SS to 3VA, and say how the fan is driven, what holds it up, how it opens, and which motor positions it accepts. That is the last piece of the arrangement picture, and it is the one the order desk checks first.

See Annotated References