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  1. #1
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    Default RPM Mode Vs. Pressure Mode on a Tanker

    What is the difference between RPM mode and Pressure mode on a tanker?


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    Quote Originally Posted by erocktxmade View Post
    What is the difference between RPM mode and Pressure mode on a tanker?

    This mat be the same as volume pumping compared to pressure. When pumping you are going to supply a target (hose line, another rig) with a certain amount of water without worrying so much about the pressure at which it is supplied. In pressure mode you are more concerned with just that, the pressure, you want the target to receive.

    For tanker ops I would work in volume mode when supplying another rig.

    I am sorry I don't have a way to make this more clear. I don't have my driver operator guide nest to me to give a better answer.

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    Forum Member Chauffeur6's Avatar
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    It doesn't have anything to do with volume vs pressure, that's a completely different concept dealing with the operation of a dual-stage pump and how the intake of water is routed through the impellers to the discharge side of the pump (either series or parallel).



    What he is asking about is the automatic pressure governor that most new apparatus have, not just "tankers". It also serves as the pressure relief valve on most applications.

    Basically, it works like this:

    RPM Mode (Throttle Control): The increase/decrease switch only adjusts engine speed up or down, just like a mechanical throttle would do. There are no automatic adjustments made by the apparatus, and unless you have a separate pressure relief valve on the rig, you are operating without one in RPM mode.

    PSI Mode (Pressure Control): The increase/decrease switch is adjusting the engine speed based on the outgoing pressure. In this mode, once you get the pump to the desired PSI, the apparatus will monitor it and make automatic adjustments as needed. This may mean that if you open another discharge, the truck will increase engine speed to compensate for the additional required water, or if you shut down a discharge the apparatus will decrease engine speed. In this mode, the pressure relief valve is automatically set at the same pressure.


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    MembersZone Subscriber swarmy's Avatar
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    Pump in "pressure" mode. That is the main point. With most set-ups, is the only way that your pump governor is going to work properly.

    Remember our goal is to pump to a specific GPM. We use pressue calculations in an attempt to get those GPMs. When you pump in RPM mode fluctuations with intake and out-take pressure will increase or decrease your PDP. If you are in Pressure mode, the pump governor will automatically account for pressure changes and react accordingly (keeping your PDP where it needs to be).

    If you still don't understand... you really shouldn't be operating your tender.
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    Quote Originally Posted by swarmy View Post
    If you still don't understand... you really shouldn't be operating your tender.
    Just make sure when you get back from training to explain why you're asking if you trained on similar but different equipment.
    The pumper I learned on at a state run fire school was of the type that once you put the truck tranny in gear and engaged the PTO,you then took the truck trnsmission lever and put it in "Neutral".
    I asked about that on my return because we also ran a 1982 Ford chassis Pierce pumper.The engineer looked at me like I was nuts and explained that on ours "One does not take the truck out of gear when the pump is needed unless you want to stop the water flow,do you get me young Padawan Learner?".
    The next year,he took the same course for requalification and ran into e during the lunch break and said he'd seen what I was talking about.
    The thing is ,different rigs have different manual of arms so to speak,that must be understood if you're pressed into service on a fireground.

  6. #6
    MembersZone Subscriber swarmy's Avatar
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    If you still have issues, I would post this question (with a few pictures of your pump panel) on "The Engineer" forum (located in the Apparatus section).
    "...there isn't a firefighter in the free world who is forced to join this profession." -John Norman

  7. #7
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    Cool

    Originally posted by Chauffer6
    It doesn't have anything to do with volume vs pressure, that's a completely different concept dealing with the operation of a dual-stage pump and how the intake of water is routed through the impellers to the discharge side of the pump (either series or parallel).



    What he is asking about is the automatic pressure governor that most new apparatus have, not just "tankers". It also serves as the pressure relief valve on most applications.

    Basically, it works like this:

    RPM Mode (Throttle Control): The increase/decrease switch only adjusts engine speed up or down, just like a mechanical throttle would do. There are no automatic adjustments made by the apparatus, and unless you have a separate pressure relief valve on the rig, you are operating without one in RPM mode.

    PSI Mode (Pressure Control): The increase/decrease switch is adjusting the engine speed based on the outgoing pressure. In this mode, once you get the pump to the desired PSI, the apparatus will monitor it and make automatic adjustments as needed. This may mean that if you open another discharge, the truck will increase engine speed to compensate for the additional required water, or if you shut down a discharge the apparatus will decrease engine speed. In this mode, the pressure relief valve is automatically set at the same pressure.
    Listen to this fella, he knows what he is talking about. It doesn't have anything to do with Pressure vs. Volume mode. It's all about pressure regulation..... which is done either by automatically adjusting the pressure (compensating) or the R.P.M. of the motor/pump (slow they R.P.M.s as they begin to rise).

    For any additional questions, you should reference your manual for the pump and the manual for the pressure relief device.
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    Guess I'm just not up to date on those fancy gizmos. Sorry my info was wrong for the question.

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    Forum Member ThNozzleman's Avatar
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    In this mode, the pressure relief valve is automatically set at the same pressure.
    I've never seen a governor system with a pressure relief valve, let alone an automatic one. What's the point of having both?

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    Forum Member Chauffeur6's Avatar
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    That didn't come out right. What I meant to express was that by switching to PSI/Pressure Mode, it takes the PLACE of a discharge pressure relief valve. If you pump in RPM/Throttle Mode, it's no different than taking an older style pumper and pumping without turning on or setting the relief valve.

    That being said, I actually HAVE seen a few trucks with both. It's not very common, but one dept I know of that spec'd their pumper with both an electronic governor AND manual discharge relief valve did it for a few reasons:

    1. As a backup to the automatic governor, should the truck for some reason not compensate for an overpressure situation and lower the idle

    2. The manual relief valve can still be operated when the automatic governor is in RPM/Throttle Mode

    3. If you are pumping at near-idle in PSI/Pressure Mode at 80 PSI with 80 PSI incoming, and you have your intake relief valve set at 200 PSI, and all of a sudden the incoming water supply surges to 180 PSI, there is very little the automatic governor can do (since the truck is already at or near idle speed). With a manual relief valve set at 100 PSI, however, it will ensure none of that excess pressure makes its way into the hoses

  11. #11
    Forum Member ThNozzleman's Avatar
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    With a manual relief valve set at 100 PSI, however, it will ensure none of that excess pressure makes its way into the hoses
    Well, I could see this using a modern relief valve that monitors pressure on both the intake and discharge side of the pump. Hell, we'd be lucky if our hydrants would surge that high.

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    Forum Member Chauffeur6's Avatar
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    True, most hydrants probably wouldn't surge that high, but I was thinking more along the lines of being fed from another truck.

  13. #13
    Forum Member ThNozzleman's Avatar
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    True, most hydrants probably wouldn't surge that high, but I was thinking more along the lines of being fed from another truck.
    Makes sense to me.

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    Cool No Joke......

    This is no joke, I worked at an Airport that when the pumps would kick-on our hydrant pressure was around 210 p.s.i.

    Needless to say, all of our vehicles with pumps that connected to the system all have Intake Pressure Relief Valves. All of our Steamer Port Intakes have the adjustable Intake P.R. Valves. Most manufactures build them into the valves I believe.
    "Be LOUD, Be PROUD..... It just might save your can someday when goin' through an intersection!!!!!"

    Life on the Truck (Quint) is good.....

    Eat til you're sleepy..... Sleep til you're hungry..... And repeat.....

  15. #15
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    Talking Wow...........

    I am FINALLY used to working with Dacron Hose instead of Leather, and now this discussion starts up............
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    Forum Member ThNozzleman's Avatar
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    I am FINALLY used to working with Dacron Hose instead of Leather, and now this discussion starts up............
    Well...governing engine speed means more than just pulling back on the reins these days.

  17. #17
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    Default I was just asking this question.....

    We have a pumper/tanker with the RPM and Pressure pump settings, and I not being the engineer, asked what the difference was between this and the Pressure/Volume setting on other apparatus. I was told it was the same as the Pressure/Volume settings for the 2 stages of the pump.

    "But Captain, it's a single stage pump......" ( Blank stare as he reads the pump plate that says "Single" in the stage slot.

    We have no literature on this pump, even though it is only a couple of years old, and the manufacure has been slow in getting it after my request. ( I run the maintenance program, I want details on what I'm putting a wrench to )

    Thanks for the clarification folks. It makes sense now that it has been explained.

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    Forum Member Chauffeur6's Avatar
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    You're welcome, glad to help clear things up. It's a common misconception that it has something to do with the pressure/volume settings of a 2 stage pump, but as you can see it's something completely different!

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    I have heard from a few people say with the class 1 governor's that if you are drafting water you should use the RPM mode, is this true? or has anyone else heard this?

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    Dacron hose, not leather? What is next, getting rid of rotary and piston pumps?

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