Belt Drive Fans vs. Direct Drive Fans: Which is Right for Your Application?

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Are V-belt drives good for fans? Of course, it always depends, but we do have a point of view to share for your consideration.

In this detailed whiteboard video, AirPro Sales Manager / Senior Application Engineer Chet White details direct-drive versus belt-drive fans and how to determine your stance on the V-belt.

Full Transcript:

The two different types of drives that are the most common ways to drive your industrial fan are the V-belt or direct drive. And the question being asked is, “Is a V-belt drive good for your fan application?”

To answer that, I’ve just got to ask why would we do a V-belt drive to begin with. And the common assumption of why someone would maybe say V-belt drives are good is if they would say, “I want the option to change my speed.” Let’s say I plug this thing in and it’s belted for 2250 RPM and I find out that I’m 10% short on what I need for my volume and I’ve still got 30% available in the motor. I want to be able to go down to my local machine shop, grab a new V-belt drive, put new sheaves on, and run that thing 10% faster so I can get my flow. That was a common reason for why you’d want a V-belt drive.

Another reason is to protect the motor (typically the most expensive spare part on a fan) from potential problems that can happen in the fan, the wheel, or the bearings, and from having to replace the motor. So those are two common reasons. A third one could be that you’re planning to move materials and you want to protect the motor from that. You want to isolate the motor from the vibrations that are happening within the fan that are expected, so you put this on a separate base.

So those are the common reasons that I hear for wanting a V-belt. The question to ask is, which of those reasons do Variable Frequency Drives (VFD) not fix? If your reason for a V-belt drive is that you want to vary the speed of the fan, that’s exactly what a VFD does. So my personal view on “are V-belt drives good for fans?” I see a lot more negatives than positives.

First, any time you put a V-belt on a fan, you’re going to get a loss of horsepower coming out of your motor. If you want an efficient process, you want all the horsepower being generated by the motor, passed directly into the fanwheel. You don’t want to lose any of it. V-belts will make you lose some of it. A rule of thumb is 3-6 percent of your motor horsepower is lost in the transition from the motor shaft to the fan shaft due to the belt.

Number two, think about the parts. You’ve got a bushing on the motor shaft, a sheave on the motor shaft, the individual belts themselves - you might have up to 10, 12 belts, or a big banded belt - plus another sheave on the fan shaft, and a bushing on the fan shaft. So you have five components: two bushings, two sheaves, and then the belts, and that makes up the belt drive, and then you always have to have a shaft and two bearings when you do a V-belt drive. So if you’re going to go with a V-belt drive, your maintenance components will be bushing, sheave, belts, sheave, bushing, shaft, bearings. You will have those parts.

If it works within the fan’s technology, you can go to Arrangement 4 and have just a motor. You don’t have to grease fan bearings, or check the tightness of the belts (because the belts will get loose over time - you need to get back in, check the tension, and make sure it’s within the tension parameters set forth by your fan drawing) and you’re constantly going to have to be messing with these belts. So there’s far less maintenance to go to an Arrangement 4.

If you have less maintenance, I guess the only concerns would be:
Varying speed - but a VFD can do that.
The risk of damage to the motor if there’s a problem inside the fan - but you can take care of that issue by moving the motor away through an Arrangement 8 coupled drive, which does add a couple of extra parts to maintain, but you still have fewer parts than the V-belt, and you don’t have any loss associated with it from the motor throughput to the wheel.

So my answer to “Are V-belt drives good for fans?” is that it depends on your application, but by and large, I would say with current technology, I just don’t see a lot of benefit to it.

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