Greenheck - Centering a wheel on a spun aluminum rooftop exhaust fan

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Today, we will be looking at centering a wheel on a spun aluminum rooftop exhaust fan.
For demonstration purposes we're going to use a cut-away fan so you can see better what we are doing.
Before beginning work on any exhaust equipment, it is important to adhere to all safety standards.
Be sure to wear appropriate Personal Protection Equipment, and adhere to all local codes.
As we will have our hands exposed to rotating elements, locking out the power source is always a must.
Now that the power is removed, we can safely open up the exhaust fan.
By removing the hood we expose internal supports and the motor.
A quick manual spin of the wheel can confirm that the component is out of alignment.
Identifying the interference will tell us which direction the wheel needs to be moved.
To move the wheel, we need to loosen the support pan bolts, being careful to not remove them.
A quarter inch or so should loosen the assembly enough to move it into different positions.
The number and location of support pan bolts will change depending on the size and model of the fan.
A best practice here would be to mark the bolt/washer location so that you can see how far and which direction you moved.
By grabbing the motor or support pan, we can maneuver the wheel to a proper position.
When you think you are in the right spot, simply give the wheel a slight spin to check for any interference.
Adjust as needed.
Now that we are happy with our wheel location, tighten one bolt at a time, moving in a start pattern.
Spin the wheel in between each one to confirm alignment has not changed.
In some circumstances the wheel’s vertical alignment may need to be checked and adjusted as well.
The products IOM, or Installation, Operation and Maintenance Manual, will show the proper overlap or gap needed.
Although this dimension is set at the factory, the vertical alignment could have changed during shipping.
The easiest way to check this dimension is to employ a piece of paper or wire with a bend in it.
Run the gauge between the wheel and venturi, hooking on the bottom of the wheel.
Make a mark where the gauge passes the venturi. Now remove the gauge and measure from marking to hook.
If adjustment is needed, mark the shaft at the wheel for current location.
This is to give you a reference as to how far the wheel has been adjusted.
The wheel will be held to the shaft with either two set screws through a bushing, or through the use of a tapered bushing.
In this video we will work on a fan that utilizes the tapered bushing.
If you have a set screw hub, please take a look at our video, Replacing a Centrifugal Wheel.
If you have a tapered hub, remove the two screws holding the bushing together.
Take the two socket head cap screws that were removed and install them into the visibly threaded holes on the wheel hub.
Alternate turning each bolt 1/8th of a turn at a time, until the hub comes loose from the bushing.
Reposition the wheel, and then reinstall the socket head cap screws into the aligned holes by hand until the heads of the socket head cap screws are seated against the mating surface.
Adjust the height of the wheel to the desired location referencing our earlier mark on the shaft.
When proper location is found, tighten the two socket head cap screws, 1/8 of a turn at a time in a alternating fashion.
Socket head cap screws should be torqued to 10 ft-lbs.
Now that we have proper alignment of the wheel, we can close the fan up, re-apply power, and listen for any misalignment.
This method can be applied to all Greenheck spun aluminum upblast and downblast models, with only slight differences.
On the downblast models we can loosen the support bolts and adjust the shroud, which has the motor attached so you can get your horizontal adjustment.
Thank you for your time, please check out our other videos on fan maintenance. Also, stop by Greenheck.com to look at any of the IOMs for products we've covered today.