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  • Onan Hydraulic Generator

    Anyone have one of these newer versions that are not shaft driven? If you have them on an engine, where is the unit located on the truck? Any problems with this unit or setup?

  • #2
    To my knowlege these are brand new and I doubt anyone would have them installed yet.

    It is my understanding that the Hydraulic pump mounts directly to the PTO and then you would run your hydraulic lines to whereever it is that you locate your reservoir & generator. Most of the time being in a dunnage area or the hosebed.

    We are currently looking into adding one on our truck.

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    • #3
      We have 8 engines (2005 models) with the Onan hydraulic generators. The generators have been fine. No more or less problems than any other manufacturers that we've dealt with. (we also have Harrison and AMPS gensets)

      Todd is right. The hydraulic PTO pump mounts inside the frame rail behind the transmission. The main generator can be mounted in various areas but usually is mounted in the dunnage area above the pump.
      I can't believe they actually pay me to do this!!!

      One friend noted yesterday that a fire officer only carries a flashlight, sometimes prompting grumbling from firefighters who have to lug tools and hoses.
      "The old saying is you never know how heavy that flashlight can become," the friend said.
      -from a tragic story posted on firefighterclosecalls.com

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      • #4
        OK, I don't know a lot about generators, and I'm curious. What's the main advantage of a hydraulic generator as compared to a more traditional set-up?
        What if the hokey pokey IS what it's all about?

        Apparatus Operator
        Salem Fire Department
        IAFF Local 314

        Comment


        • #5
          Originally posted by grains
          OK, I don't know a lot about generators, and I'm curious. What's the main advantage of a hydraulic generator as compared to a more traditional set-up?
          Are you speaking of the advantage of a Hydraulic Generator over a direct-drive PTO style?

          The main advantage is that a hydraulic pump can provide consistent RPM's for the generator by regulating the flow of the hydraulic fluid throughout a wide range of engine RPM's.

          A direct-drive PTO generator may rely on the engine remaining at idle RPM's or a specific high-idle setting to get proper RPM's for the generator to operate. Therefore they are impractical on pumpers since the engine is required to be able to run through a wide range of RPM's to drive the fire pump.

          This is why you see larger direct-drive PTO generators on heavy rescues and ladder trucks (without pumps) and you see hydraulic generators on pumpers and quints.

          Both hydraulic and direct drive PTO generators have the advantage of saving precious compartment space when compared to mounted diesel and gasoline powered generators.
          I can't believe they actually pay me to do this!!!

          One friend noted yesterday that a fire officer only carries a flashlight, sometimes prompting grumbling from firefighters who have to lug tools and hoses.
          "The old saying is you never know how heavy that flashlight can become," the friend said.
          -from a tragic story posted on firefighterclosecalls.com

          Comment


          • #6
            Thanks IronMan,

            That explains it nicely.

            Now, if I can ask a couple more quetions then:

            1. Which of the two are less expensive? Direct drive vs Hydraulic (everything else being equal of course).

            2. A direct drive generator in most cases would be the generator of choice for a piece of apparatus that does not have a fire pump. Is this correct?

            Thanks for the information.

            Greg
            What if the hokey pokey IS what it's all about?

            Apparatus Operator
            Salem Fire Department
            IAFF Local 314

            Comment


            • #7
              Greg, I'm glad I can help.

              1. Direct-drive units are usually less expensive watt for watt

              2. From a reliability standpoint, it is my opinion that direct drive units are better than hydraulic units for the purpose you stated. Just remember that the rig must be parked and the PTO set before you can turn on the genset with direct-drive units. Therefore it would be a good idea to have some 12v lighting on each side of the rig if you want to be able to utilize extra lighting while searching for addresses and such.

              -Irons
              I can't believe they actually pay me to do this!!!

              One friend noted yesterday that a fire officer only carries a flashlight, sometimes prompting grumbling from firefighters who have to lug tools and hoses.
              "The old saying is you never know how heavy that flashlight can become," the friend said.
              -from a tragic story posted on firefighterclosecalls.com

              Comment


              • #8
                Direct drive

                IronsMan has explaine the differences very clearly. We do have a direct drive gen set on a non-pumping vehicle. If you want a gen set on an engine or even, to my way of thinking, a ladder, hydraulic or free standing gen sets are pretty much a necessity. Proper installation of hydraulic units along with ventilation and routing of hydraulic hoses is critical! Even the selection of hose fittings is important.

                If you can live with the vehicle engine operating at a constant speed (necessary to maintain frequency control), direct drive units are considerably less money. They also weigh less and take up less space because there is no hydraulic drive unit to contend with. Proper ventilation is much simpler, also. You only have to consider the generator itself.

                Caveats: The PTO shaft angles have to be correct. I've seen some really bad installations because someone didn't pay attention to that. Even with the best installation, you do have to pay attention to the shaft U-joints. I've replaced 2 sets in 12 years on ours. Engine noise is also a consideration. Ours 20 kw unit is set up so that the Cummins C8.3 runs at 1400 rpm. It is pretty noisy. Where the exhaust goes is another concern. We have about 20 feet of 4" repair shop hose that we carry on board. If necessary, we connect it to the tailpipe and try to direct the exhaust to a less annoying place.

                On the balance though, it's a good arrangement. It comes to work every day and does what we ask it to do. But it's not right for every application.

                Stay safe out there, everyone goes home!
                Last edited by chiefengineer11; 11-28-2006, 09:02 AM.

                Comment


                • #9
                  engine speed

                  A neighboring department has a hydralic drive generator on their air and light truck. The truck was built by their city shop. When they have their light tower up, the truck engine sounds like it at max and between the truck engie noise and when from the generator, its pretty noisy.

                  We have a 6 kw diesel generator on our rescue - pretty quiet unit at load.

                  Comment


                  • #10
                    Irons and ChiefEngineer,

                    Thanks for the info. That is all very useful and I'll remember it when we go to build our Air rig soon.

                    Clear skies.

                    Greg
                    What if the hokey pokey IS what it's all about?

                    Apparatus Operator
                    Salem Fire Department
                    IAFF Local 314

                    Comment

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