From the hand cranked A-frames of the early tow trucks of 1916s to today’s flat beds and the truck cranes of today one of the most contributory technologies to efficiency of the wrecker is the inclusion of hydraulic systems.
Hydraulics is the transmission of force from one object to the other using a non-compressible liquid, usually hydraulic oil. Pascal’s Law states “…all pressure exerted on a confined, incompressible fluid is distributed throughout the fluid.”
Pascal’s Principle & Force Multiplication in Fluids
Force multiplication in fluids like most other force multipliers trade distance for more force. Fluid delivered from the pump at 100 psi to a 2-inch cylinder will multiply that force to 317 lbs. force, but a cost of higher volume (distance). A 4-inch cylinder jumps to 1260 lbs. but a much larger volume. The 2-inch will consume 31.7 cubic inches or little over ½ a quart to push a ram 10 inches, while 4-inch ram will need 126 cubic inches for 10 inches of travel or about 2.2 quarts. Force multiplication is simply calculated by taking the fluids pressure and multiplying by the area of the piston’s diameter. The here numbers here are rounded and approximated but illustrates the idea of hydraulic force multiplication. They also operate at much higher pressures, 1000 psi or higher.
Tow Truck Hydraulics
Tow trucks use hydraulics depending the type of design of the tow. A wheel lift truck uses hydraulics to lift the frame and boom to lift and tow the vehicle. The winch can be either electric or incorporate a hydraulic motor in place of the electric one. Flat bed trucks use two ram systems. One tilts the bed and another set controls the bed extension by sliding the bed along rails forward to haul and backwards to load. Again a hydraulic or electric powered winch will cable the vehicle onto the tilted and extended sliding bed.
Tow Truck Booms
In some trucks the booms are hydraulic controlled as well. Lift flatbed tow trucks are popular in Europe. A flat bed truck has a hydraulic operated crane that can lift a car from a parallel parking spot and onto the truck bed for towing. Many European police agencies use these trucks. The boom tow trucks are little more than truck mounted cranes. Boom lift and extension are hydraulic. The winch is used for the cable and is probably hydraulic, and the stabilizing extensions are hydraulically operated and controlled.
Hydraulic Power Steering
Power steering systems are hydraulic assisted. Your automatic transmission depends on all sorts of hydraulic systems to operate clutches and bands for shifting and your brakes for stopping are hydraulic as well, hence brake fluid.
Hydraulics for Wreckers
The details have changed but the basic design of the tow truck is the same as it was a 100 years ago. Just the details and power sources have changed. Jerry Holms, the grandson of Ernest Holms, Sr. and inventor of the tow truck, started the Century Wrecker Co. after selling Ernest Holmes and Company. This was in 1974. It was Century and Jerry Holmes that introduced hydraulics to wreckers. Dover Corp., who bought Ernest Holms & Company thought there was no way that hydraulic and wreckers went together and where dismissive of Century’s efforts. By 1987 Century employed over 300 people.
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Hydraulics and wreckers are now one. The hydraulic is far more efficient than the straight mechanical tow truck.
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