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  1. #1
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    Default Pressure Control Governors

    I am looking for some help in understanding/troubleshooting a (possible) issue with a pressure control governor. I am a new driver and am still trying to learn what is "normal" operating proceedures when pumping apparatus equiped with pressure control governors. The problem I am having is specific to one apparatus and I have not been able to duplicate it on any other apparatus equiped with pressure governors. When attempting to throttle up while in the Pressure mode the system allows for initial increase in RPMs but within a few seconds of reaching the desired pressure the governor returns to idle and will not hold pressure. If I throttle up in RPM mode and then switch to pressure mode the pressure will hold however at I now have no ability to manually control the throttle. Any throttle adjustments require me to switch back to RPM mode, make throttle adjustments and then return to Pressure mode. As I am not regulary assigned to this truck, and as I stated previously, all other engines in our fleet that are equiped with pressure governors will allow me to increase/decrease throttle in either pressure or RPM mode, I am unsure if there is a problem with this specific governor or if its possible that it could be designed to only allow throttle adjustments while in RPM mode?? The drivers regulary assigned to the truck are saying that it is "normal" for that truck, but I am unsure if "normal" for that truck is the same as "normal for the system??? any help would be appreciated as I am unsure of safety issues that may arise if I am required to remove the system from pressure mode every time a throttle adjustment is needed.


  2. #2
    Forum Member Tim1118's Avatar
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    Default

    It sounds like either a problem with the governor, or a pressure sensor issue. I would definitely get in touch with the manufacturer of the governor. "Normal for this truck" doesn't sound normal at all...

    EDIT: This is provided all else is as it should be. Not losing prime, valves are in proper positions, etc.
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  3. #3
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    Thanks. Everything (to the best of my limited knowledge) appears to be as it should. I actually (first) encountered the problem while performing the basic morning pump check out. pump in gear, tank to pump and tank fill open, throttle up in pressure and RPM modes to check coordinting discarge pressure and RPMs. It was during this check out that I first noticed I couldnt use the throttle while in pressure mode. I then connected LDH to a hydrant, connected a 2-1/2 and a 1/34 line and attempted to pump the lines to simulate fire ground ops. I encountered the same issues while flowing water.... I had to switch out of pressure mode to control the throttle. Even though I cant wrap my head around why we would have a system in service that doesnt allow for throttle control in pressure mode, its a touchy situation when senior drivers assigned to the vehicle are mind set that this is how this truck works.... so was hoping to see if anyone else had ever had a pressure governor system (working correctly) that would not allow manual throttle control when in pressure mode. Dont want to step on toes unless I have done my homework....also would you know.. if you cant throttle up in Pressure mode would you still be able to successfully pull a draft?? It was my understanding that when pulling a draft you start in RPM mode until you obtained the draft and had a steady stream of water flowing , but then switched to Pressure mode to throttle up to desired dischard pressure? If I had to leave the pump in RMP are there risks be to loosing the draft while increasing the pressure??

  4. #4
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    Default

    What brand of pressure governor is this?

  5. #5
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    Default

    It doesn't explain everything, but I have seen systems where the tank fill is large enough that the pump can't maintain pressure while recirculating and will automatically go to idle. That may or may not explain the ability to throttle in pressure mode and doesn't explain why is stays set if you switch to pressure mode once at pressure.

    It may not be your issue, but just a thought.

  6. #6
    Forum Member FIREMECH1's Avatar
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    Default

    Need a few answers before I try to help out.

    1. Does this rig have a V-Mux or ES-Key electrical system??? (Wheldon or Class 1)

    2. What year is it???

    3. Brand and type of governor???

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  7. #7
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    I was told it's a Pierce Command Zone, 2001, Detroit Deisel engine... I was not able to find the book on it at the station, but am on shift again today and will see if I can the info from the mechanic. I do appreciate the help!
    Last edited by DEBSO; 12-01-2010 at 02:11 PM.

  8. #8
    Forum Member Fire304's Avatar
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    Default

    I believe the Pierce system is a Class 1 Captain Governor (all manuals on their web site) with a Pierce designed control panel. Unfortunately, the Pierce panel does not allow access to Class 1's troubleshooting codes. It does sound like you have a problem with the system however. Easiest thing to try is put a new pressure transducer on it, do you have another truck with the same governor on it? Transducers are a few hundred bucks, but easy to swap out. The Class 1 manuals will tell you what the voltages should be for the transducer as well.
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  9. #9
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    Default

    If you are somewhat proficient with a multi-meter then you can check the transducer out fairly easily. It will typically have 3 wires.

    red- usually supplying 5 volts reference to the sensor
    black- ground
    white- a lower voltage that gets translated based on pressure @ the sensor. (say .5 volts ambient, will rise to 4.5 at maximum pressure)

    To check it, just make sure you are getting good ground at the sensor, your full reference voltage, then operate the governor in RPM mode while back probing the white wire at the sensor. You should see the voltage rise proportionally as the pressure increases. If that checks out I would suspect a problem with programming or a bad display head.

    However, this has just been my experience, your truck may be different.. Hope it helps you out however!
    If you can't fix it with a hammer, you have an electrical problem.

  10. #10
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    Thumbs up

    Quote Originally Posted by DEBSO View Post
    Thanks. Everything (to the best of my limited knowledge) appears to be as it should. I actually (first) encountered the problem while performing the basic morning pump check out. pump in gear, tank to pump and tank fill open, throttle up in pressure and RPM modes to check coordinting discarge pressure and RPMs. It was during this check out that I first noticed I couldnt use the throttle while in pressure mode. I then connected LDH to a hydrant, connected a 2-1/2 and a 1/34 line and attempted to pump the lines to simulate fire ground ops. I encountered the same issues while flowing water.... I had to switch out of pressure mode to control the throttle. Even though I cant wrap my head around why we would have a system in service that doesnt allow for throttle control in pressure mode, its a touchy situation when senior drivers assigned to the vehicle are mind set that this is how this truck works.... so was hoping to see if anyone else had ever had a pressure governor system (working correctly) that would not allow manual throttle control when in pressure mode. Dont want to step on toes unless I have done my homework....also would you know.. if you cant throttle up in Pressure mode would you still be able to successfully pull a draft?? It was my understanding that when pulling a draft you start in RPM mode until you obtained the draft and had a steady stream of water flowing , but then switched to Pressure mode to throttle up to desired dischard pressure? If I had to leave the pump in RMP are there risks be to loosing the draft while increasing the pressure??
    We experienced this same problem with our 2003 pierce. We contacted our dealer, who in turn sent us a new pressure transducer. The problem disappeared after changing it out. Had a neighboring department that told us about the fix after their engine did the same thing.

  11. #11
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    Our pierce command zone (1998) throttles up in pressure mode. My limited knowledge about them would say it is not suppose to do that. But then again i do not know alot about the inter-working of them.

    On the draft question. I learned that you pulled a draft in RPM mode. This is due to the need to increase the RPMS before pulling your primer. Pulling the draft reduces the pressure in the pump to allow for the water to be pulled into the pump. When the pressure governor (in pressure mode) senses that it cannot maintain the pressure it is at the truck returns to idle. To prevent this you pull the draft in RPM mode which will allow for the truck to remain at an above idle RPM. Once you get your draft you can switch to pressure mode and pump like you normally would.

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