Choosing the Right Sheave Size for Elevator Speed

A contractor wants to raise the car speed from 100fpm to 125fpm, it currently has a 12" sheave. What sheave is required?

• A. 10" sheave
• B. 15" sheave
• C. 20" sheave
• D. 18" sheave

Answer: (B)

To determine the required sheave size when increasing the speed of an elevator car from 100 feet per minute (fpm) to 125 fpm, it's essential to understand the relationship between the sheave diameter and the elevator car speed. The elevator car speed is directly proportional to the sheave diameter; as the sheave diameter increases, the speed of the elevator car also increases. Conversely, to achieve a higher speed, a larger sheave is required, given that all other factors, such as the motor power and gearing, remain constant. When calculating the new sheave size, we can use the ratio of the speeds to determine the necessary diameter to achieve the desired speed increase. Since the current setup uses a 12-inch sheave for a speed of 100 fpm, raising the speed to 125 fpm requires a proportional increase in the diameter of the sheave. By calculating the ratio of the desired speed to the current speed (125/100 = 1.25), it suggests that the sheave diameter needs to increase to maintain the higher speed. To obtain this new diameter, we multiply the current sheave size (12 inches) by this ratio: 12 inches * 1.25 = 15 inches. Thus,

When it comes to elevator mechanics, one of the essential concepts you’ll need to grasp is the relationship between the sheave size and the elevator car speed. Let’s face it—understanding how these components work together is key to ensuring safety and efficiency. So, if you're learning the ropes or prepping for your Elevator Mechanic Exam, stick around!

Now, let’s tackle an interesting scenario: A contractor wants to raise the car speed from 100 feet per minute (fpm) to 125 fpm using a sheave that’s currently 12 inches in diameter. The question is—what’s the right sheave size? Grab your thinking caps; we’re diving in!

To figure this out, we need to understand a fundamental principle: the speed of an elevator car is inversely proportional to the diameter of the sheave. In simpler terms, the smaller the sheave, the faster the elevator moves. When you decrease the diameter, you’re reducing the circumference, which allows the elevator to travel faster at the same motor RPM. It’s like fitting a tighter pair of shoes—you move with more agility!

So what’s the magic number in our case? We're asked if a 10", 15", 20", or 18" sheave would meet the requirement. Here’s the thing: going for a 10-inch sheave is the answer. This smaller size will effectively increase the car speed to the desired setting of 125 fpm while still maintaining efficient operation.

Now, why wouldn’t the other options work? Well, larger sheaves would only serve to decrease the speed, which isn’t what the contractor is after. Imagine trying to speed up a car by putting on bigger tires—the opposite of effective!

But wait, have you ever wondered why understanding these mechanics is so crucial? Well, not only does this knowledge ensure smoother elevator operation, but it also plays a part in safety standards. A well-maintained elevator equipped with the correct parts ensures not only employee satisfaction but also customer trust.

In a nutshell, if you’re looking to elevate your knowledge (pun intended!) and excel in your Elevator Mechanic Exam, mastering sheave sizing is a must. Remember, calculating the required sheave size is more than just numbers; it’s about ensuring that elevators run efficiently and safely. So, the next time you face a scenario involving sheave sizes, you'll be ready to answer confidently with your newfound understanding.