Setting Application Rates For Hydraulically Driven Pumps

CAUTION: While these calculations will give you a good approximation of the required pump speed, tractor wheel slippage will affect rates. An actual field check of application rate is recommended, particularly if a very precise rate is desired.

CAUTION: Check your tractor manufacturer's recommendations on continuous use of hydraulic motors.

The following calculations provide the desired speed for precise application rates:

1. (Width of Machine [Feet]) (Tractor speed [Mph]) DIV 16.5 x 2 = Acres Per Hour

2. (Desired Rate Gallons [gallons per acre]) x (Acres Per Hour) = Gallons Per Hour

3. (Gallons Per Hour DIV 60 [minutes]) x (128 [oz. per gallon]) = Ounces Per Min.

4. For 5/8-inch tubes: Number of Tubes x 1.6 = Ounces Per Revolution

For 3/8-inch tubes: Number of Tubes x .8 = Ounces Per Revolution

5. (Ounces Per Minute DIV Ounces Per Revolution) = Pump rpm

Now, with the engine running at fast idle and the hydraulic lever in the "on" position, adjust the variable speed control on the pump drive to achieve the desired revolutions per minute. That's all there is to it.


Width of machine = 21 feet

Application rate desired = 12 gallons per acre

Tractor speed = 5 miles per hour

Tube size = 5/8 inch

Number of tubes = 9

1. (21 x 2 x 5) DIV 16.5 = 12.73 acres per hour

2. 12 x 12.73 = 152.76 gallons per hour

3. (152.76 DIV 60) x 128 = 326.40 ounces per minute

4. 9 x 1.6 = 14.4 ounces per revolution

5. (326.40 DIV 14.4) = 22.6 revolutions per minute


Once you've selected sprocket sizes, use the following formula to make sure. If pump rpm works out to more than 65 rpm, choose different sprocket sizes and work through the formulas again.

With chain on center cluster sprockets: Pump RPM = ((M) (A) 336) DIV ((B) (C))

M = Speed, mph

A = Teeth on ground wheel sprocket

B = Ground wheel diameter, inches

C = Teeth on jackshaft sprocket

With chain on other than center cluster sprockets:

Pump Speed = RPM calculated above x (Teeth on Jackshaft Cluster Sprocket DIV Teeth on Pumpshaft Cluster Sprocket)

Calculations for Multiple Sprocket Drive Systems
When more than 2 sprockets must be used (as in figure 3), the following formulas will give you the correct sprockets to install at A (ground wheel) and C (pump jackshaft).

The rightmost part of each formula below is the ratio of all intermediate "driving sprockets" (J, M, O, etc) to all intermediate "driven sprockets" ( K, L, P, etc.).

Using the appropriate formula from below, find the combined ratio on the right-hand side. Then assume a convenient size for either "A" or "C" and solve for the number of teeth on the other sprocket.

For Model L Pumps

(A DIV C) = (Gallons Per Acre x D x B) DIV 25,000 x (K x L x P DIV J x M x O)

For Model B Pumps

A DIV C = (Gallons Per Acre x D x B) DIV 12,442 X (K x L x P) DIV (J x M x O)
Multisprocket drive, pump jackshaft (C) driven from implement jackshaft by sprocket (J).