CHAPTER 23 | Fan Shafts

Replace Fans, Wheels- Small BAC Counterflow


-2' Wrecking bar and heavy hammer (for crate removal)
-6" Angle grinder with grinding wheel (optional)
-4.5" Angle grinder with cut off blade- plus spare blades
-Combination wrench set 5/16" to 3/4" plus 1-1/8" size
-3/8" socket set with ratchet
-Allen Wrenches (U.S. and metric)
-1/2" impact gun with impact socket set including 1-1/8" socket (and/or ratchet)
-Pocket knife
-Crocus cloth
-Vinyl gloves
-WD40, LPS3
-Grease, oil
-Tape measure
-All thread rod (typically 3/8") & nuts to make shaft positioning guages

These towers typically have one to four 15" fan wheels on a 7/16"D solid steel shaft.

The most practical approach is to replace the entire rotating assembly with factory supplied parts.

It may be ok to keep the driven sheave but check to make sure it can be removed without damage before keeping it. The driver sheave and bushing will be prime candidates for replacement along with new belts.

New bearings will be needed.
Order bearing oil if there are any sleeve bearings and a tube of grease for the ball bearings. Proper lubrication is essential; DO NOT USE ANYTHING BUT FACTORY RECOMMENDED LUBRICANTS.

Check the fan housings for soundness particularly on the underside.

Take the time to shut the unit down and inspect the fan snouts from inside the tower. Avoid finding out they need replacing after the fan shaft is removed. Otherwise, plan on considerable down time and expedited freight costs.

Check the condition of the inlet rings.

Make sure the threaded belt tension adjustment rod
is in good shape. Get a new one if necessary.

Order the parts.

Check all parts upon arrival. If there are any sleeve type bearings, take the big oil cups from the old bearing(s), install them on the new bearing(s) and fill them so that the oil can be soaking into the graphite material while the work is proceeding. Wipe the protective coating from the new shaft with rags and solvent. (Removing a good deal of the coating with a pocket knife first will reduce the number of rags needed.)

Note the spot milled flats that are intended to accept the fan wheel set screws. Picture sliding the fan in place and it's apparent that the fan wheel hub will cover the area. To facilitate fan attachment later, it's a good idea to measure the length of shaft that will be inside the hub and use this dimension to make some tic marks that straddle the milled flats on the shaft so that they will be visible when the fan is in place. This will make it easy to rotate the fan to the correct position and slide it along the shaft to just the right position for the set screws to line up with the hidden flats. An engraving tool works good. Alternately, a punch or file can be used.

Important: Inspect the shaft and polish off any nicks or imperfections with crocus cloth. Wipe the shaft down. Then, take one of the new ball bearings and slide it along the entire length of the shaft. Polish off any imperfections that keep the bearing from sliding smoothly down the shaft. Be careful not to nick the shaft again before installation. In a similar fashion, slide each fan wheel on to the shaft to make sure the set screws are backed off sufficiently and that there's nothing in the bore of the wheel.

Shut the tower down and lock it out.

Remove the air inlet screens. Remove the end access panels. (This is where the impact gun- if you have one- will save time.)

Mark the bearing supports so that a new bearing can be located in the same place.

Before removing the belts, remove the driver sheave if it is being replaced and the driven sheave if it is being saved. (See the bushing section for removal instructions if necessary.)

Cut the belts off with the 4.5" angle grinder fitted with a cut off blade.

Remove the inlet rings from the fan housing sides. (A little fore thought will allow some of the inlet rings to stay in place.)

Do not try to save the rotating assembly- just chop it out. Determine places where the shaft will be cut. Hold the 6" grinding wheel against the shaft with the grinder shaft parallel to the fan shaft. A helper will slowly rotate the fan shaft while the operator cuts a deep trench around the perimeter of the shaft at each cut location. Leave enough material so the shaft doesn't collapse. Then, go back in with the small grinder with its thin cut off wheel for the final cut at each location. Remove the bearing bolts. (Again the impact gun saves time.) Discard the old parts. If the proper orientation of a forwardly curved fan wheel is unfamiliar, notice the orientation of the old fan wheel blades before removal. (Mark the shim pack for each location. Shims can be cleaned and reused or new ones of equivalent thickness substituted.)

Clean the bearing supports.

Check inside the fan housings. Patch as required. This is a good time to recoat the inside if there is time. (See the section on housing/snout replacement if necessary.) Set the new fan wheels in the fan housing(s). Note the fan blades are forwardly curved.

Attach the new bearings and shims. Slide the bearings up to the previously made mark and tighten enough to hold the weight of the shaft and wheels. Place the inlet rings in their approximate location.

Begin shaft insertion remembering to impale everything in the correct order including inlet rings, bearings, locking collars, etc.. Do not attempt without extra help except for all but the smallest single fan units. Even with the best preparation, insertion can get difficult. Sometimes it is necessary to temporarily install the driven sheave on the shaft- like a steering wheel- so the installer can rotate the shaft while pushing it in. Remove the sheave once the shaft is in place. An equal amount of shaft should stick out on each end.

Attach each fan wheel(s) to the shaft. The previously made marks help insure each set screw engages the center of the 'flat' machined into the shaft. Tighten the screws being careful not to drop the wrench through the fan.

Position the shaft so it looks level. Lightly snug the bearing bolts. Check that the fan shaft is centered in the housing by eyeballing the rim of the fan vs the circular opening in the side of the fan housing. Add shims and slide the bearings on their mounts as necessary. Cut a piece of all thread rod that fits loosely between the fan shaft and the pan next to the bearing mount. Place two nuts on each end of the rod. (Using the long coupling nuts on the ends works good.) Adjust the nuts so the assembly fits snugly between the shaft and the pan and lock the nuts together so as to hold the spacing- like a giant feeler guage. Check the spacing at each bearing. Make another guage to check vertical alignment. Tighten the bearing mounting bolts and recheck alignment.

Rotate the assembly. Operation should be smooth. Move the entire assembly horizontally so as to place the fan(s) in the center of the housing(s). Then, lock the eccentric locking collars on the ball bearings. (See bearing section for the proper procedure.)

Attach the inlet rings. Rotate the fans to check for rubbing.

Install and align the sheaves. Tension the belt(s). (See the sections on bushings, alignment and belt tensioning.

The all thread belt adjustment rod should not protrude. If it does, screw it into the motor base until the nut contacts the support base channel. Then, tighten jamb nut inside the channel to lock the rod in place. Protect the threads from rust with LPS3 or anti seize grease.

Grease the ball bearings being careful to pump the gun slowly until the grease just peeks out.

Fill any sleeve type bearing cups with oil recommended by the manufacturer.

Spray or brush a suitable coating (Like LPS3) on the fan shaft and bushings.

Install the inlet screens and end panels.

Place the tower back on line.

Replace Shaft, Wheels- Large BAC Counterflow Type

These towers are distinguished by large diameter, hollow fan shafts and fan housings that come apart allowing fan shaft replacement from the face of the tower. While the fans can be replaced from the front, it is much easier to slide the new shaft in place from the end. Fan housings should only be taken apart if there is not enough room to install the shaft from the end.

As with all repairs, make sure all necessary parts are ordered before taking anything apart. Check the housings, snouts, inlet rings, sheaves, bushings and motor adjustment rod. Order new belts and bearings.

Remove the end access panels.

Do any required work on sheaves that are to be reused first. [Easier to do before the belts are removed.]

Cut the old belts off with a cut-off disc installed on a 4.5" grinder.

Remove the vanes and inlet rings, mark the bearing supports so that the new bearings can be located in the same place, unbolt the old bearings and cut the fan shaft with the cut-off disc in as many places as required to remove the old parts making note of the orientation of the forwardly curved fan wheel blades. Release the clamps and remove the shaft segments from the fans

Set the shim packs aside to be cleaned and reused. Or, replaced by shims of the same thickness.

If replacing housings, snouts, motor adjustment rod, etc. see the appropriate sections.

Installation from the end:

Assuming the fan shaft will be inserted from the end, check the integrity of the clamping tabs and bend them back slightly. Set the fan wheels (oriented properly) into each housing.

Clean each end of the fan shaft with solvent and polish out any dings with crocus cloth. Test fit the bearings.

Place two large C-clamps on each bearing support at the bearing locations to help support the shaft as it is installed.

With 3-4 people holding the shaft, thread it through the first inlet ring, the first fan wheel, the second and third inlet rings, etc. until each journal is near its eventual location. Don't forget that one bearing will need its eccentric locking collar installed before the bearing.

Slide the bearings on with the grease fittings oriented properly and loosely install the bearing bolts. Place the large C-clamps on the bearing supports resting against the end of each bearing to keep them from sliding down the supports. Using a pry bar, lift each bearing and slip the shim packs underneath. Then, slide the bearings to the mark made earlier and tighten the bolts. The fan wheels should be located in the center of the housing opening. If they are not, center them by adding/removing shims and sliding the bearings on their supports.

Note that with only two self aligning bearings, it is impossible to impose stress on the shaft from an improper number of shims. The shim count is less important than if, say, there were three or more bearings.

After the bearings are tight, slide the shaft until there is an equal amount of journal sticking out on each end. Lock the collars. (See Ball Type Bearings) Center each wheel in its housing and mark the shaft with a Sharpie. Spread factory supplied adhesive on the shaft, spin the wheel to work it in. If reusing the wheels, automotive trim contact cement in aerosol cans works well.

Install the clamps per the factory supplied sketch. Torque them evenly per factory instructions. Be careful not to drop wrenches through the fan as they can be difficult to retrieve.

Install the sheaves. (See Bushings and Sheaves). Align (see Alignment). And tension (See tensioning).

The bearings are shipped with the proper type and amount of grease. If adding grease, make sure it meets factory specs.

Installation from the front:

When removing a split housing to change the fan shaft and wheels, the upper portion stays in place and the lower section is removed. (See the section on 'Fan Housing Replacement').

It will be necessary to build a wood support on which to roll the shaft with the wheels in place- but unattached- into the housing.

The vertical fan housing side affords substantial vertical support to the casing which is lost with part of the housing removed. Use timbers to restore this support. If water must remain in the basin, note that its weight will distort the basin side making alignment with the housing difficult.

Prop Fan Replacement- Large, Belt Drive, Vertical Shaft, Crossflow BAC Tower

This is one of the most difficult cooling tower repair jobs and requires considerable pre planning. It is typically a two day job requiring two people.

Typical tools include:

-Saw to cut planks
-Machinist's level
-Torque wrench (Capable of max. torque requirement)
-Combination wrench set (Required sizes can be large)
-Socket set (Required sizes can be large)
-Tri pod
-Come along
-Fixture for attachment to fan
-Miscl. Tape measure, allen wrenches, screw drivers, punches, pliers, alignment string, hammers, pry bar, key stock, chain, rope, rubber boots... lots of stuff Inspect the tower closely and order all necessary parts. If there is a right angle sheet metal part that the fan shaft passes through between the bearings, order it. [Otherwise, the shaft will have to be cut in half to retrieve it for reuse.]
Plan the procedure well in advance and figure out how to make the described tri pod, the platform, a jig that attaches to the fan for hoisting, means of securing the fan, required tools, etc.
Always get new bearings, shaft, fan collar and bushings. Check both sheaves closely. If the driven sheave shows any sign of deterioration, get a new one as it will make installation a lot easier. The driver sheave and belt are almost always shot. Check the motor adjustment rod, motor base and fan.
If the tower has an internal walk way- great. Service platform- even better.

Lock out the fan.

Bring planks inside the tower and build a platform under the fan big and strong enough to hold two people plus parts.

Remove the fan discharge screen and slide it out of the way. Presumably, the fan will be reused. [See how to build a tripod in the 'Tips and Tools' section.] Detach the fan from the shaft. (This can be difficult. Check the attachment method beforehand and have the necessary tools available.) Lift the fan using the tri pod and a come along. Small fans can be slid to the side and secured in place. Large fans can be lifted slightly and supported by wood blocks under the fan tips and secured to the discharge cowl. When the fan stays in place, make sure the hook on the end of the come along is detachable so the cable can be threaded through center of the fan when lowering/lifting the shaft assembly.

Connect a chain to the section of fan shaft between the bearings and connect the chain to the come along. Remove the bearing mounting bolts and lower the shaft/bearing/sheave assembly to the platform.

Closely measure the distances between the end of the old shaft and sheave, sheave to bearing, distance between bearings, etc. and build up a new assembly to match the old. Don't forget to insert the new sheet metal right angle piece- oriented correctly- between the bearings. Lock the upper bearing's eccentric locking collar to the shaft. (As an extra precaution against slippage, lock the collar that fits under the fan on top of the upper bearing.) Install the driven sheave and torque the bolts to spec. Pull the new parts in place with the come along. The locking collar for the lower bearing can be loosely tightened to keep the bearing from sliding down the shaft, but once the bearing is mounted, unlock the collar.

Install the bearing mounting bolts. Check to make sure the fan shaft is centered in the cowl by measurement. Use a machinist's level to check that the shaft is vertical. Tighten the mounting bolts.

Make sure the new collar that goes under the fan is in place. Reinstall the fan and torque to spec.. Slide the collar up and tighten. Knock down the tri pod. Reinstall the screen.

Check sheave alignment. Adjust the height of the driver sheave if necessary- it's easier than moving the driven sheave.

Install and tension the belt. Rotate the fan to check for interference and to insure the belt stretches uniformly during tensioning.

Lock the collar on the bottom bearing.

Remove tools, planks.

Observe operation.