Why Don’t the Mechanical Parts Fail?
We use belts in HVAC equipment because they’re cheap and don’t require the lubrication and maintenance of chains. This raises the question though: why don’t all the OTHER mechanical components wear out too? If we’d have to lubricate chain drives and gears, why don’t we have to lubricate motors too?
The Big Killer: Friction
Almost all hardware failure is because of friction. Two surfaces touch and gradually chew each other up, create heat that weakens them THEN chew themselves up, or otherwise just get worn down from sliding and grinding together. Eventually, something will have just been ground down to the point it has shorted out or no longer works. Without friction, most equipment would last nearly indefinitely.
Modern equipment uses a lot of techniques to reduce wear and tear. The contact areas are reduced as much as possible and those areas that do grind together have sacrificial components. These parts are usually made of tougher materials, contain special lubricants, and are meant to be replaced over the lifetime of a piece of equipment. This allows things like motors and pumps to last longer, be rebuilt, and seemingly never fail.
The Humble Bearing
Perhaps the most common friction-reducing part is the bearing. Your motors likely have a few bearings in them. The armature, the shaft that spins inside the motor, only touches two things: the bearings and the output device (your blower wheel, belt pulley, etc). As much as the shaft spins, it’ll never wear on the magnets or windings. It can only wear on the bearings.
Bearings themselves are simple pieces of equipment. They’re perhaps the cheapest component of any HVAC System. Generally, a bearing contains either balls or little cylinders packed tightly between two rings. We can seal these rings in, allowing us to pack lubricants into the assembly, helping reduce the actual friction when the bearing spins.
All the load of the spinning equipment is transferred to multiple balls or cylinders inside the bearing. The individual ball bearings spin, spreading out the wear around them, reducing the long term damage. This bearing set up allows most of the equipment to experience essentially no wear from mechanical load. There’s little to no harm from spinning or moving equipment.
When a bearing wears, it’s not remotely the end of most equipment. Your HVAC Contractor can disassemble the pump, motor, or whatever the bearing was in, pull the bearing off, and put a new one on. It’s a bit harder than it sounds, often involving special pressing equipment, but the concept is straight forward enough. Wear down the sacrificial part, replace the sacrificial part.
We can’t remove friction, but what’s key is that we reduce it as much as possible. By using bearings, we can center all the wear in one place. We also reduce the amount and the places that need lubrication. By concentrating all our wear in these places, we can make incredibly durable parts, for fairly low costs, and replace them as needed over a component’s lifetime.