How does the fire department use hydraulic multiplication?

Answer 1

The term hydraulic multiplication is usually applied in fire fighting to indicate that water pressure is increased by the use of multiple "stages" to jack up pressure and delivery rates. Let's look at an example. An engine company arrives at a structure fire and the engine commander knows that fighting this with water in the tank will not be a good tactic. He orders a reverse lay (2 x 2 1/2" lines, or perhaps a 4" supply line, depending), and the engine is then set up at the hydrant to act as a manifold. The engineer connects the pump suction to the hydrant. There is pressure in the mains that feed the hydrant, but the pump in the engine will take that pressure and step it up to pump water through the two lines to the "scene" of the fire. The second-in engine sets up at the end of those two lines, and connects one to the suction of itspump. Let's review what is happening as regards the hydraulic multiplication. Pressure in the mains (at the hydrant) is multiplied by the first-in engine and delivered to the second-in engine. The second-in engine multiplies that to deliver water to large (almost certainly 2 1/2") handlines on the fire ground. Any appliance on that second engine is also employed to direct a stream. If a truck arrives (which it should, eventually), it can hook up to the second-in engine, and that engine will then pump to the suction of the truck's pump. That's hydrant outlet to an engine, to another engine, and on to the truck. The truck will deploy its high reach nozzle(s) to get more wet stuff on the red stuff. It's easy to see that the hydrant can only be tapped for so much flow, but the hydraulic multiplication of the three pieces of apparatus here is a no brainer. If water needs to be moved up a long, steep hill, like perhaps in San Francisco, it might not be unusual for several engines to pump that water up the hill. And there might even be a fire boat at the bottom as the first link in the chain. The San Francisco Bay is a virtually unlimited water source!