LDH Drills for Pump Operators
3260: Pump Operators never get enough time moving water. In the course of any fire there are usually several things that jump up to bite you, and you are forced to recognize the cause from the effect. The rapid recognition of the cause and a subsequent action to correct the condition are usually the result of years of operating and exposure to actual fireground conditions.
Operating in a long relay for most rural pump operators is an unusual occurance. One area that is seldom practiced is laying out LDH while other operators observe the hose leaving the bed at different speeds. I know it is a pain for the probies and grunts, but trying different loading techniques and different speeds is a good learning exercise for everyone. We typically use first gear on the Mack and run at 1500 to 1800 rpm during the lay. By limiting the speed, we dont get the adrenalin doing strange things like causing a high speed lay problem. This exercise is OK for the probies and drivers, but becomes a pain for the grunts. Once you all know what methods to use in loading and the speeds are determined for laying out, then an SOP on loading hose and laying LDH should serve you well for many years.
Actually establishing and operating a relay is another matter. I like to divide this into two different aspects. Pumping long lays forces the operator into using the radio, as hand signals are rarely usable considering distances, turns and apparatus placement. The biggest effects of an actual long lay-out are fill rates and reaction times for pressure changes. When a change is made on the fireground like shutting down a line, it takes some time for the change to work its way back to the supply engine.
One way to practice operating multiple engine relays is to replace the LDH with 3 hose. Since the K factor for 3 with 2 ½ couplings is 1, and the K for 5 is 1/15th then a 100 ft section of 3 has the same losses as 1500 ft. of 5 LDH. We use 25 ft. sections (2) in hooking to Mae West hydrants, so we can set up 1500, 1100, 750 & 400 ft equivalent relay distances. (Extend short pieces with 5 LDH if necessary) Start this exercise by placing an engine at the source with the pump operators panel facing away from the water source. Park each succeeding engine with the operators panel facing inward and run all the 3 around the outside. (Circle the Wagons) This allows each pump operator to observe the effect his actions have caused for every other operator in the relay. It is important to remember that, with modern pressure governors, only the attack engine should be operated in the pressure control mode with the governor. This should be a minimal problem when using the short sections of 3, but long lays of 5 have a significant volume change as pressures change in the system. Sometimes (not always) it is possible to set up a delayed reaction between engines caused by running multiple engines in the pressure control mode.
Let us say that after the relay has been established, a large line shuts down on the fireground. The resulting increase in discharge pressure causes the attack engine to throttle back. At the same time the reduced flow in the relay causes the intake on the attack engine to rise, further causing the pressure governor to again throttle down to keep discharge pressures at the original set point. Because of the delay, the relay engine does not see the spike in pressure immediately. About the same time as the attack engine is cutting back, the relay engine also starts to throttle back, but the expansion in the LDH keeps the change from being transmitted rapidly as the hose is now shrinking slowly causing another delay in the reaction. Eventually what happens is a surging action is established causing pulses in the system. To avoid this, place all engines except the attack engine in the rpm mode, and chain the pump operators to the panels.
Careful selection of the discharge on the draft and relay engines is necessary to avoid large internal pump losses. Since LDH supply hose is rated and tested at 200 psi, we need to set a max operating pressure on the relay of 185 psi. Assuming 20 psi intake pressure minimum, then the friction loss needs to be limited to 165 psi including internal pump discharge losses. Using the friction loss equation, we can find that 100 of 3 (1500 ft. of 5) will supply 1280 gpm, 75 of 3 (1100 ft. of 5) will supply 1480 gpm, 50 of 3 (750 of 5) will supply 1816 gpm, and 25 of 3 (400 of 5) will handle about 2500 gpm at 185 psi discharge on each relay engine. By running parallel and series hose lines, almost any layout can be simulated using short lays of 3 between engines. This makes it easy to set-up relay practices without the time constraints of repacking large quantities of LDH. It also keeps the equipment readily available should an alarm require the response af any engine assigned to the drill.
Have fun playing!