04 - Sheaves / Pulleys Flashcards
What are sheaves / pulleys?
A grooved wheel with two flanges that is used to change rotational direction, increase or decrease rotational speed, or provide mechanical advantage.
What should be checked when performing preventative maintenance on pulleys?
What does pulley wear look like?
How do you check pulley alignment? What is pulley alignment?
When belts are used to connect a motor to a compressor, fan, or blower, the pulley on the belt-driven unit and the motor pulley must be in-line with each other. This is what is meant by alignment. The centerline of both shafts must be parallel with each other. Also, the pulley grooves must be in-line with each other as well. This will ensure the longevity of the pulleys, belts, and bearings.
Pulleys should be aligned using the straight edge/string method. By achieving four points of contact across both pulleys, alignment can be verified. A laser tool can also be used for fast and accurate alignment.
How to check run out on the face of a pulley
How do you check pulley balance?
How do you know when proper tightness has been achieved on a pulley setscrew, what is the setscrew? What is a keyway/key?
The setscrew is a fastener with a threaded rod that has no length or tip. It is used to secure the pulley to the shaft. The pulley manufacturer can be referenced to find the desired torque.
The keyway is square channel machined into the shaft which allows the pulley to be locked into place with a square piece of metal called the key. The key is slid into the square space created between the pulley and the shaft to create an exact fit.
What is the procedure for replacing a pulley?
How do you clean a pulley?
How do you select a pulley for replacement?
What are some of the classifications of a pulley?
A-with and B-width are some of the most common. A-width pulleys fit belts up to 1/2” wide. B-width groove pulleys fit belts that are 1/2” to 21/32” wide.
What are some different kinds of pulleys?
Step pulley: A pulley which is made of multiple grooves of different diameters, for driving a fan or blower. By changing the belt from one groove to another, a technician can change the speed of the fan or blower.
Variable-pitch pulley: These are made with half of the pulley threaded on the hub of the other half. A setscrew locks the variable half in place after it has been properly adjusted. By turning the variable half of the pulley, a technician can narrow or widen the pulley’s V-shaped groove. Widening the groove allows the belt to ride closer to the hub, reducing the speed of a belt-driven blower or fan. Narrowing the groove moves the belt farther from the hub, increasing the blower or fan speed. The speed of a belt-driven unit can be varied by as much as 30% using a variable-pitch pulley. (Increasing the speed of the fan can also raise the current of the motor, always check the amperage of the motor after adjusting to ensure it does not exceed the FLA rating.)
