1. #1
    Forum Member

    Join Date
    Oct 2003

    Default Auto Master Stream Tips, Electronic Engine Governors

    Hypothetical Apparatus Setup:

    1,250 or 2,000 gpm deck gun with an automatic tip corresponding to the gun’s flow range (let’s say a TFT 150-1,250gpm or 300-2,000gpm tip), low-friction loss plumbing to the gun, and a typical electronic engine governor (FRC, Class 1, Detroit, etc).


    To operate the master stream in the above-mentioned setup, what pressure do you set the engine governor at to properly supply the tip at any given flow? How do you ensure it stays at that flow?

    We know that the governor will have to be set at at least 100 psi to meet the pressure requirement of the automatic tip. Beyond that you have the friction loss in the valve, plumbing, and gun itself. If this were all designed to be low friction loss, then the only other pressure requirement will be the slight pressure variation as the auto tip moves throughout its flow range (assuming a properly maintained and functioning nozzle), i.e. the manufacturer says that the nozzle will regulate at 100psi throughout it rated flow range, but the pressure will probably end up being a little lower at the low end of the flow range, and a little bit higher at the high end of the flow range.

    The Point:

    With the above-mentioned setup, you will have to set your engine governor for just over 100 psi for the entire flow range of the nozzle. Most of that accounts for the pressure required by the nozzle. However, the EXACT pressure that the nozzle is operating at for a certain flow on any given day could easily vary, and could even vary during a single use of the nozzle (nozzle’s pressure regulator is a little bit stuck that day and starts out regulating at ~110psi, has water flowing through it for a couple of minutes and loosens up a little bit and begins regulating at 100psi). Can you imagine setting up your master stream and a few minutes later hear your engine starting to race and see your supply lines collapsing?

    Is there some simple solution here that I am missing? Please don’t come back with “yes, use a smoothbore” or “yes, don’t spec engine governors on your trucks”.

  2. #2
    MembersZone Subscriber

    Join Date
    May 2000
    Wheaton IL


    Calculate the FL in the pipe by using a SB and a pitot gauge.
    Once the flow is figured out. Add 100 psi to that for the correct flow with your automatic.
    You will never know for sure without a calibrated flow meter what your automatic is flowing, but you will be close.
    If your worried about the gov causing the rig to outrun the supply simply switch to RPM mode when the correct flow is met. Also stay at the panel, you shouldn't leave the rig unattended.

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