An old vehicle that is not all at sea is brought up-to-date

Most discussions on military finances revolves around examples of excessive spending. This could be said to be an example exactly opposite, with a refurbishment programme to extend the useful life of some very costly American Army 1950s equipment well into the next century.

The equipment is a fleet of LARC LX 60 amphibious vehicles used to transport heavy equipment from cargo ships to army units on land. In essence, a LARC LX 60 is a 100ton ocean-going ship equipped with huge wheels for land travel. It has a ramp and cargo-bay, capable of 100ton loads, and is able to handle the largest tanks and self propelled guns. Each vehicle is 70ft long, 30ft wide and 16ft high.

A detailed examination of the fleet showed that the basic structural components and many of the accessory systems were still sound, but the engines and propulsion systems had reached the point at which additional repairs simply were not cost justified.

Given a choice between replacing the vehicles or upgrading the engines and hydraulic systems that power them, the army chose the latter course. The hydraulic systems are provided by Modern Technologies, using pumps, motors and controls supplied by Denison Hydraulics.

Each LARC LX 60 is equipped with four 310hp diesel engines. Each engine drives a Denison P24P axial piston hydrostatic pump supplying power for water propulsion, and a tandem driven P8W axial piston variable volume pump powers the onboard systems for ventilation, cargo-handling, steering, bilge pumps and so on.

Water propulsion is supplied by a pair of propellers, each powered by a Denison M24G fixed displacement motor connected to two engine driven P24P transmission pumps in parallel. The motors are directly connected to the propellers through a fixed ratio 3.2:1 speed reducer.

The P24P pumps and M24G motors are engineered to work together as a closed loop transmission system. Because LARC LX 60s are military vehicles, fail safe and redundant features are built into the propulsion systems at many places to accommodate battle damage or mechanical failure. For example, the integral vane type servo pumps in each P24P can be connected together so that one of them can control both cams in the pumps, thus driving one motor to prevent backdriving the diesels in case of damage or system failure.

All hydraulic power for the LARC’s auxiliary functions is provided by four Denison P8W axial piston pumps driven off the back of the P24Ps used for propulsion. Output from these pumps are fed into a central hydraulic header system which is automatically maintained at 1500psi by a load sensing control system.

Over the years various contractors have built LARC LX 60s such that minor differences in the vehicles produced serious clearance problems for the motor and pump installation. However, the compact, efficient modern design of the pumps and motors made it possible to fit the upgraded propulsion system in the very compact space available.

Denison Hydraulics Tel: 01924 826021