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How the Jaws of Life Work


Spreaders
This combination spreader/cutter has its arms fully extended. Notice the cutter blades between the arms.
This combination spreader/cutter has its arms fully extended. Notice the cutter blades between the arms.

­­Spreaders and cutters are probably the two pieces of equipment that most people think about when they hear about the Jaws of Life on a news report. The powerful jaws of these machines can tear apart most vehicles like cutting through a tin can. The spreader is used to pull pieces of the structure apart, or it can be inserted into the side of the vehicle to tear a section out. The cutter, as the name suggests, is used to cut through the vehicle like a pair of giant bolt cutters. The mechanics of how these two devices work are very similar, and some Jaws of Life equipment combine the cutter and spreader into one machine.

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A spreader consists of pincer-like, aluminum alloy arms with tips made of heat-treated steel to provide maximum strength for tearing into a vehicle or building. There are spreaders of different sizes, so the specifications differ as to how much spreading force the equipment possesses or how much space can be opened up on a vehicle. Let's look at the ML-32 Hurst Jaws of Life spreader as an example. This particular spreader provides:

  • 16,000 pounds (71 kiloNewtons) spreading force
  • 14,400 pounds (64 kN) pulling force
  • 32 inches (81.9 cm) opening distance

Other spreaders can provide more or less spreading and pulling force. The body of the ML-32 spreader is made out of aluminum alloy and the piston and piston rod are made from forged alloy steel. When the portable engine is started, oil flows through a set of hydraulic hoses into the hydraulic pump inside the machine's housing. A typical power unit might be a 5-horsepower gasoline engine that operates at 5,000 pounds per square inch (psi), although the pressure differs in different power units. This type of engine can run on about 0.5 gallons (2 liters) of gas for about 45 minutes to an hour.

To open the arms of the spreader, the operator slides a valve switch that causes the hydraulic fluid to flow from one hose into the cylinder, pushing the piston and rod up. This rod is attached to linkages that are conjointly attached to the spreader's arms. When the rod pushes up, it causes the linkages to rotate, which opens the arms. To close the arms, the operator moves the valve in the opposite direction, which causes the hydraulic fluid to flow through a second hose.

The valve at the base of the spreader/cutter controls the flow of the hydraulic fluid.
The valve at the base of the spreader/cutter controls the flow of the hydraulic fluid.

To use the spreader, a rescue worker inserts the closed spreader arms into an opening in the vehicle or structure, such as a door jamb. The spreader can also clamp down on a structure to crush any material between its arms.

As you will see in the next section, cutters are very similar to spreaders in how they operate.


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