KWS Manufacturing

Bucket Elevator Horsepower Calculation

There are many variables to consider when designing a Bucket Elevator. These include bucket size, bucket spacing, speed, and various components. This information can act as a guide for determining the Horse Power (HP) requirements of a Bucket Elevator.

When designing a Bucket Elevator there are more variables to be consider that can be listed here. It should be noted that a small mistake in calculating the required HP of a small, low capacity Bucket Elevator may not result in a unit failure, but a small mistake on a large, high capacity bucket elevator may result in a catastrophic failure.

This is why it is important to always work with an experienced Bucket Elevator Manufacturer who can help in the design and implementation of a successful project.

Determining Horse Power

Bucket Elevator Guide

To be able to accurately determine the power requirements of a Bucket Elevator, it must first be understood the internal forces acting on the unit. Although there are many components in the Bucket Elevator, only the upward movement of the conveyed product needs to be considered.

This is because the weight of the Belt/Chain and Cups are identically balanced on both sides of the head shaft. Only the internal friction caused by the movement of these components needs to be considered when calculating the HP requirements.

There are many variations of Horse Power (HP) calculations found in historical and individual manufacturer’s literature. The formulas below are used to determine the power requirements of a Bucket Elevator throughout the industry.

Equation 1 – Power Formula

A basic power calculation is the measure of force over a distance per time period.

Equation Symbols

P Power
F Force
D Distance
T Time

Power Formula Equation


Equation 2 – Bucket Elevator Power Formula

In a Bucket Elevator the power requirement can be directly calculated using this formula.

Equation Symbols

P Power to convey the product
W Weight of material being lifted
H Lift Height
T Time
C HP required to overcome the friction in the system.

Bucket Elevator Power Formula Equation


Equation 3 – Bucket Elevator Power Formula

Using the above formula and substituting the gravimetric rate of a bucket elevator, the following equation can be derived.

Equation Symbols

P Power (HP)
G Gravimetric Rate (Pounds Per Hour)
DH Discharge Height (FT)
C HP required to overcome the friction in the system.

Bucket Elevator Power Formula Equation


System Friction

Friction includes the following variables:

  • Cup Digging
  • Belt slip on the head pulley
  • Chain slip on sprockets
  • Bearing friction
  • Drive Inefficiencies

Factor “C” is an estimate of the friction in the system and is required to accurately determine the power requirements of a Bucket Elevator.

Note: Motor inefficiency is not used because these formulas are used to determine the Motor size. Motor HP ratings include their inherent inefficiencies.

There are two methods used to determine the power required to overcome the friction in the system.

The first is the Length Equivalency Method. This method uses a factor of the tail pulley diameter to determine the additional power required to account for the system friction.

The second method is the Friction Factor Method. This method uses a multiplication factor of account for the friction in the system.


Length Equivalency Method

Equation 4 – Bucket Elevator System Friction – LEQ Method

System friction can be accounted for with a length equivalency factor. This factor is dependent on the pulley diameter and is shown below. The Length Equivalency Factor ranges from 5 to 15, depending on the application. Consult your Bucket Elevator Supplier for additional information.

Equation Symbols

C System Friction (HP)
G Gravimetric Rate (Pounds Per Hour)
d Tail Pulley Diameter (FT)
Leq Length Equivalency Factor

Bucket Elevator System Friction – LEQ Equation


Equation 5 – Bucket Elevator Power Formula – LEQ Method

Combining Equations 3 and 4 yields the following equation.

Equation Symbols

P Power (HP)
G Gravimetric Rate (Pounds Per Hour)
DH Discharge Height (FT)
d Tail Pulley Diameter (FT)
Leq Length Equivalency Factor

Bucket Elevator Power Formula – LEQ Equation

Example

A Customer would like to convey 100,000 lbs per hour of sand to a height of 105 feet. Determine the required HP.


Solution

Given
Rate (G) = 100,000 (Pounds per Hour)
Discharge Height (DH) = 105 (FT)

Assumed
Tail Pulley Diameter (d) = 2 (FT)
Leq = 7

Bucket Elevator Power Formula – LEQ Equation Example


Friction Factor Method

Equation 6 – Bucket Elevator Power Formula – Friction Factor Method

Another way to account for the system friction is to add a multiplication factor to the calculated HP in Equation 3. This multiplication factor typically ranges from 10% to 30%, depending on the application. Consult your Bucket Elevator Supplier for additional information.

Equation Symbols

P Power (HP)
G Gravimetric Rate (PPH)
DH Discharge Height (FT)
F Friction Multiplication Factor

Bucket Elevator Power Formula – Friction Factor Equation

Example

A Customer would like to convey 100,000 lbs per hour of sand to a height of 105 feet. Determine the required HP.


Solution

Given
Rate (G) = 100,000 (Pounds per Hour)
Discharge Height (DH) = 105 (FT)

Assumed
Friction (F) = 1.15

Bucket Elevator Power Formula – Friction Factor Equation Example