There are complicated formulas for determining pulley ratios but in generic, layman terms, simply divide the driven component (pump) by RPM, the driver component (motor or engine) rated by RPM to get the required ratio. In the example below, the pump RPM is 1070, for full output, while the motor is 1750 RPM.
How do I choose a pulley?
Generally, it is advisable to gear down, or use a smaller pulley on your motor than your weapon. For your smaller pulley, it may not be a bad idea to choose the smallest available. However if you elect for a larger one, choose one smaller than the can of the weapons motor.
Does a bigger drive pulley increase speed?
By changing the diameter of the pulley wheels, speed can be changed. A smaller pulley turning a larger pulley results in the larger one moving more slowly but with more shaft power.
Where should a belt sit on a pulley?
Place belts on the drive. Never force the belts into the pulley using a lever. Doing so can cause irreversible cord damage and/or fabric tearing. Always move the driver unit forward so the belts can be slipped into the pulley grooves without damage to the belts.
Which pulley will turn faster?
A larger pulley turning a smaller pulley results in the smaller one turning faster but with less shaft power. For example, a truck in high gear would have a slower turning engine but faster turning wheels, resulting in a faster truck.
What is pulley ratio?
The ratio of any two drive accessories can be determined by dividing the diameter of the smaller pulley into the larger one. For example, if a 6-inch water-pump pulley is used in conjunction with a 7-inch crank pulley, the pulley ratio is 1.16:1.