Based on the following input:

      Engine: CAT 3512 - 3158 cu.in. displacement

      Min Cranking RPM: 120

      Number of Teeth on Flywheel: 183

      Number of Teeth on Starter Pinion: 11

      Ambient Temp: 100°F (560°Rankin)

      Accumulator Precharge: 1650psi w/N2

      Accumulator Gross Volume: 60 gal ((4) 15 gal units)

      Starter Motor Displacement: 5.1 in³/rev

      Accumulator Pressure - Hydraulic (fully charged): 2800psi

      Cranking Time Required: 30 seconds ((3) 10 second cranks)

      Customer prefers (3) accumulators, (4) max

 

Cranking Oil Volume Required:

      Cranking speed times the ratio of teeth in the drive gears

      120 rev/min x 183/11 = 1996 rpm

 

Flow Rate of Oil Required:

      Displacement of the cranking motor divided by 231 to convert to gallons times motor rpm

      5.1 in³/rev x 1996 rpm / 231 in³ per gallon = 44 gpm

 

Gallons of Oil Required:

      Flow rate times cranking time required

      44 gal/min x 30 seconds / 60 seconds per min = 22 gallons

 

Accumulator Volume Available:

      Using the equation: (P1V1) / T1 = (P2V2) / T2

 

      Where P = Pressure is in psi

            V = Volume is in gallons

            T = Temperature is in degrees Rankin (F+460 = Degrees

Rankin)

            to derive the nitrogen volume.

 

      Nitrogen volume from fully charged to fully discharged is:

      2800V1 / 560 = 1650 x 60 / 528

      V1 = 37.5

 

      Oil volume from fully charged to fully discharged is:

      60 total volume - nitrogen volume = 60 - 37.5 gallons = 22.5 gallons

 

CONCLUSION:

With 22.5 gallons available and 22 gallons required, the use of (4) 15 gallon accumulators is adequate for the required cranking speed and time.