What pulley do I need for my new air compressor motor

M

mreinsmith

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I was going to buy a new 3hp air compressor pump from Harbor freight

It lists the max RPM as 1050

But the 3 HP motors I'm finding (not at HF because they get bad reviews) are all 3450 RPM

I'm assuming (and you know what happens when you assume) that I need to get a pulley for the motor that will turn the pump at 1000 RPM or so?

If I'm correct can anyone point to something that will help me figure that out

Thanks a million
 
I'm thinking, divide 1050 by 3450, the product should be the ratio you need to size the motor pulley given the diameter of the compressor pulley, that should be close, but techiically, the pitch diameter of the pulleys rather than the ODs is what is needed for a more exact sizing.
 
Pitch diameter is about half the seating depth of the belt.
 
mreinsmith said:
Pitch Diameter? I have to look that up

Thanks
Click to expand...

That's a nightmare. First of all, it's a nightmare just because it always has been a nightmare. Second, it's a nightmare because the new cool way to measure this stuff is by "datum" diameter. Which means most of the time you have no idea what you're reading about. Third, it's a nightmare because discount, universal manufacturering takes liberties with a lot of things that are related.

If you look at the angled side of a belt, you're looking at about a third of the way down from the top corner (if it's flat on top), or just a whisker below the reinforcing band if it's visible. This is for practical purposes that do not involve sumbarines or space ships. Or benmychree's method will get you there too. The liberties taken on discounted stuff is great enough that the wierdness of both the belt sizing and the pulley sizing will probably swallow the tolerance between benmychree's method and mine.

Take either of those methods, shoot for 950 RPMs as that'll bury any excess tolerance/errors, and if you get the compressor pump and the motor both spinning in the right direction at the same time- Pat yourself on the back and call it a day.
 
Yes, good idea to run it a bit slower with less load on the motor, especially if it may be an Asian built motor that would likely be overrated in terms of actual horsepower.
 
A couple of years ago, I was talking to a compresser repairman aboit rebuilding a pump... he told me to never spin one faster than 900 rpms. According to him they will last much longer running at less than 900...

-Bear
 
Not enough information!

What is the HP of the motor?

Rpm of the compressor matters only on startup.

Operating pressure matters, the motor can only do so much work, higher pressure reduces motor ability to turn it.

There should be a chart in the compressor manual with the motor hp requirements as well as pulley sizes, look there.

If not in the manual, ask why not, it is critical to matching it.

We built many compressors over the years and overall never was really happy.

Last was using a 4 cylinder employee pump and 5 hp motor, but it did okay, but...

We got a bonus and bought one after 30 years...

7.5 hp champion, 2 stage, after-cooler, auto tank drain, commercial duty, and mag starter

Was $1950.00 way back. Others were less expensive, and we regret not doing it sooner.

Consider what you are going to spend on motor and compressor pump.

What about your tank?

Control system?

It all adds up.

Next, add your time in building it.

Add that all up and start shopping.

Consider the quality of what you are buying.

Do NOT buy at harbor freight.

TSC has good stuff, as does many INDEPENDENT stores.

Got ours from a mom and pop like place we saw in passing on the freeway.

They made a truckload buy of champion compressors and had a bunch of them in the front of the place to get our attention, saved $$$.

Sent from my SM-G781V using Tapatalk
 
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