Fire Pumps, Fire Apparatus, Fire and Defense Equipment

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How does Darley determine if a driveline layout is acceptable for a pump installation?
Asked by: Tom High. Siddons Martin

Answer.

Darley closely reviews four key categories before approving a driveline application. We begin by determining if the driveline diameter can handle the maximum torque to be transmitted. PTO pumps rated to 1,500 gpm utilize a Spicer 1410 series driveline. Larger PTO driven pumps up to 3,000 gpm use a Spicer 1550 series driveline. Midship pumps typically use the same series driveline as provided by the chassis manufacturer.

Second, we review the maximum driveline length allowed for the maximum speed at which the driveline is capable of spinning. Most Spicer 1410 drivelines utilize a 3.5” or 4” tube outside diameter, both with .095” thick tubing walls. The 3.5” tube is generally acceptable for a 68” universal joint center to universal joint center length for speeds up to 2,500 RPM. The 4” tube is generally acceptable for a 72.75” length for speeds up to 2,500 RPM. Increasing maximum driveline speeds to 3,500 RPM would imply the 3.5” tube driveline could be used up to a 57.25” length, while the 4” tube could be used up to a 61.5” length.

Third, Darley examines driveline balancing. Darley requires that drivelines be balanced to ISO 1940 Grade 16 Standard. Most reputable driveline manufacturers have equipment that allows them to spin a completed driveline and then precisely attach balancing weights. You should be fine if you utilize such equipment.

Fourth, we review maximum torsional vibrations the driveline may experience due to the geometry of the installation. Torsional vibration is the speeding up and slowing down of the driveline as it rotates around at what you think is a constant RPM. Unless your driveline is a straight arrow shot from the drive source to the pump, your driveline will experience some amount of torsional vibration. If torsional vibration is less than the recommended limits, your driveline layout should experience a long life free of any noticeable shaking.

This fourth component, however, is not as simple to ascertain as the first three. To assist in finding the maximum torsional vibration, Allison Transmission has created a computer program that calculates vibration based on your particular driveline layout. Darley can share this program and usage instructions with you. As long as your driveline layout has less than 500 radians per second squared torsional vibration, 1,000 radians per second squared inertial drive vibration and 1,000 radians per second squared inertial coast vibration, the driveline layout should pass muster. As with any firefighting need, please feel free to contact Darley with your questions, and we will happily provide a solution to meet your needs. Demand Darley.