Pulley Size calculation

Thanks in advance for any help I needed to come up with a pulley drive system for a piece of equipment I am putting to together. I have an out put shaft spinning at 3000 RPM I need to reduce it down to 750 RPM what sizes pulleys would I need, I've tried some of the calculator's on line but I get different results any help is appreciated,

Hello Jose,

The actual pulley sizes you need will be those closest to giving you a ratio reduction of 1:4. The smallest diameter goes on the motor and the largest diameter goes on the piece of equipment.

Welcome to the forum

Regards Brian

The pulley diameters (or one of them anyway) might limit the maximum or minimum size of the pulleys you can use (or obtain) but the ratio of the two pulley diameters will stay the same.

3000 down to 750 rpm requires a reduction ration of 4:1 which is quite reasonable in one stage of belt drive. If the motor pulley was 2" it would need to drive an 8" on the output device.

Ian P

Brian was a lot more concise than my effort

Ian P

1:4 ratio of effective diameter. Problem with fancy on-line calculators is that they use the particular effective pulley diameter - and that may be different for different belt cross sections.

Is your input speed actually 3000rpm under operating conditions? Do younneed exactly 750rpm output? Somehow I doubt one, or both are true.

Thanks to all of you for your response , to be more exact it a 4cyl, diesel engine driving a high pressure water pump. the diesel max RPM is 3000 and the max pump operating RPM is 750 . also any recommendations where I might be able to get these pulley on line I may have to have them custom cut to the shaft sizes ill need. thank again to all

With no idea of power requirements, can’t say.

Solutions using taper-lock systems will cover most sensible shaft sizes.

Almost certainly the engine will have some form of speed regulation.  More likely to need to pick an engine speed that matches the power of the pumping head.

Edited By not done it yet on 06/03/2018 16:49:50

If this is a reciprocating plunger type pump you may need to do a bit of research into the type of belt and/or

pulley size (not ratio ) required.

The torque requirement may be a bit high/low through the revolutions.

Get in touch with a drive line supplier who will help with both the sizing and supply of the parts.

Someone like Brammer might be a starting point....

**LINK**

Presumably the pump needs to be driven at 750 rpm, maximum for full capacity pumping?

Is the 3000 rpm of the engine the Rated Speed for full power, or the Flight Speed (Max No Load Speed)?

If 3000 rpm is Flight Speed then you may require a ratio of probably 2,700:750, or 2800:750 to obtain 750 rpm on the pump with the engine fully loaded.

The section of belt, and how many, will depend on what power the pump requires to be driven at 750 rpm fully loaded.

Howard