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    Default Pressure or Volume?

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    A Waterous 625 pump made around 1987. Has a switch from pressure to volume. I have not seen it yet but will be using it next week in training. I'm thinking that it is a two stage pump. I have never operated one of these. I read that for fire attack you would use the pressure setting and the volume would normally be used only in water relay. Would this be correct?, and feel free to add comments.

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    pressure for pumping at less then 50% capacity of the pump

    Volume for pumping more then 50% capacity of the pump

    system are pumped in volume. relays are done in volume.

    thats the cut and dry answer. I am sure some of the pump experts will go more in detail.
    Last edited by RFD21C; 05-25-2010 at 01:53 PM. Reason: spelling

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    Quote Originally Posted by RFD21C View Post
    pressure for pumping at less then 50% capacity of the pump

    Volume for pumping more then 50% capacity of the pump
    _____________

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    Default Two Stage

    If there is a pressure/volume option, a “Transfer Valve” it is at least a two stage pump. The Waterous 625 throws me a little, I think it is most likely a 1250 GPM pump.

    Our pumpers were all two stage units from well before my arrival in the late 70s until 1991 when we started to make the change to single stage pumps. We always ran the pumps in “Pressure” for a couple of reasons. First off the booster line was very commonly used and the second most common line was the 1 ½” both have high friction loss and fairly low GPM flow rates. Since the pump could supply more water than these lines could flow, even with two 1 ½” lines flowing the pump (in reality the motor) would not have to work as hard to overcome the friction loss.

    Our protocol was to “change over” to volume when we needed to pump more than ½ the rated capacity of the pump.

    Two stage pumps were almost a necessity with the old gasoline motors in fire apparatus. With the power in power horse power and torque from a diesel a single stage pump is very efficient. There is less maintenance on a single stage pump. For those of us old enough to have maintained two stage units many of the pump problems were related to or in the Transfer Valve.

    Then there is the training, much easier to teach pump operations when it is not getting complicated with the pressure/volume scenario.

    Important to remember in pressure you will only be able to deliver ½ the rated water flow of the pump. If you have or are putting a two stage pump into service you need to have very clear operational protocols in place and train your pump operators well. There are operational difficulties you will see with a two stage pump you would never see with single stage pump and the operators need to know this and what appropriate actions can/should be taken.

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    Quote Originally Posted by SpecCapt
    If there is a pressure/volume option, a “Transfer Valve” it is at least a two stage pump. The Waterous 625 throws me a little, I think it is most likely a 1250 GPM pump.

    Our pumpers were all two stage units from well before my arrival in the late 70s until 1991 when we started to make the change to single stage pumps. We always ran the pumps in “Pressure” for a couple of reasons. First off the booster line was very commonly used and the second most common line was the 1 ½” both have high friction loss and fairly low GPM flow rates. Since the pump could supply more water than these lines could flow, even with two 1 ½” lines flowing the pump (in reality the motor) would not have to work as hard to overcome the friction loss.

    Our protocol was to “change over” to volume when we needed to pump more than ½ the rated capacity of the pump.

    Two stage pumps were almost a necessity with the old gasoline motors in fire apparatus. With the power in power horse power and torque from a diesel a single stage pump is very efficient. There is less maintenance on a single stage pump. For those of us old enough to have maintained two stage units many of the pump problems were related to or in the Transfer Valve.

    Then there is the training, much easier to teach pump operations when it is not getting complicated with the pressure/volume scenario.

    Important to remember in pressure you will only be able to deliver ½ the rated water flow of the pump. If you have or are putting a two stage pump into service you need to have very clear operational protocols in place and train your pump operators well. There are operational difficulties you will see with a two stage pump you would never see with single stage pump and the operators need to know this and what appropriate actions can/should be taken.
    Now I know why I had a headache at 3:42 today.

    We've been a two stage pump department until 2008, then went to single stage pumps, because the power outputs have increased.

    I can't add a damn thing to what the SpecCapt posted. He is dead on, in every aspect. Well done Capt.

    FM1
    I'm the one Fire and Rescue calls, when they need to be Rescued.

    Quote Originally Posted by EastKyFF
    "Firemens gets antsies. Theys wants to goes to fires. Sometimeses they haves to waits."

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    Waterous Multi-stage midship pumps are generally designated with the letter M for multi-stage or S for a single stage. There is also a size designator that identifies the larger casting for pumps over 1250 gpm. Your 2 stage pump would most likely be identified as a CM pump while a 1500 and greater would be a CMU series. There are also letter designators for the transfer case types.

    Generally speaking, when you want to supply “small” volumes (3 – 1 ¾” PC’s and maybe an additional 2 ½” line) of flows less than 600 gpm, you would probably choose the “Series” or pressure mode. This arrangement allows the engine rpm to be a little lower while providing pressures above 160 psi. Think about the relationship of discharge pressure and RPM. As you increase engine and therefore pump RPM, the discharge pressure increases. By arranging the valving such that the discharge of the first stage directly feeds into the intake of the second stage we get a doubling of the discharge pressure while holding the RPM constant. You might have a pump that has a discharge of 80 PSI at 1050 rpm, but by stacking two of these, you would get an output of 160 psi with an engine speed of 1050 rpm. Staying in “Parallel” or volume, might require an engine speed of 1600 rpm to reach the same 160 psi. Remember you must reach the proper discharge pressure when supplying a nozzle.
    If your normal operation is as an attack engine operating out of the apparatus tank, then you might want to keep the pump in pressure mode until a master stream device is placed in operation.
    Larger discharge volumes generally require wider impellers and higher torque to move larger volumes at lower pressures. (relay operations) Thus by changing valves to the “Volume” position, you effectively double the impeller width but at a lower discharge pressure. If you make the change over properly, it should result in a slightly lower operating RPM for the layout.

    Any attempt to supply 250 psi while in “Volume” will usually result in excessively high RPM before reaching the desired output pressure. Try to avoid operating above 80% of the Governed No Load speed stamped on the builders plate. An example might be a GNL (Mack) of 2150 rpm. That should not operate above 1720 rpm for long periods.

    An exception to the small volume = pressure mode rule would be where a high incoming pressure results in an excessively high discharge pressure with the motor still at idle. Example might be a 100 psi hydrant pressure that results in discharge pressures to hand lines over 200 psi. Then you might try switching to the “Volume” mode as this will result in higher rpm thus keeping the batteries charged properly.

    The best advice is to play with the engine both at draft and while being fed by an adequate hydrant supply and change the amount of water being discharged each way.
    The second best advice is to exercise the valve on a regular basis. Charge the pump every chance you get and operate the transfer valve several times in each direction.

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    I'll take an guess and say the OP has a Canadian pumper and the capacity
    is in imperial gallons so that translates into a 750 gpm. ????

    Don

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    Quote Originally Posted by KuhShise
    The second best advice is to exercise the valve on a regular basis. Charge the pump every chance you get and operate the transfer valve several times in each direction.
    ^^^ Excellent advice for any 2 stage pump.

    FM1
    I'm the one Fire and Rescue calls, when they need to be Rescued.

    Quote Originally Posted by EastKyFF
    "Firemens gets antsies. Theys wants to goes to fires. Sometimeses they haves to waits."

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    Kuh's advice to operate the transfer valve frequently is well taken. Add to that list, the relief valve, if it has one, and the primer.

    Switching to volume when pumping over 50% capacity is a good general rule of thumb, but not an absolute, especially when working from hydrants or in relay. My personal rule is to make the switch at about that time, but pay attention to any change in engine rpm. Whatever produces the desired output at the lower engine rpm is where you want to be.

    Also, since we got CAFS, we find that there are some times (not always) when operating in volume is useful. This is to bring the engine rpm, and consequently the compressor rpm and air flow up. Most of the time we get sufficient air in pressure mode but there have been those few times when volume worked better.

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    yes Don 120. 625IMP gallons. Sorry I forgot to tell you that. Thanks for the graet advice all.

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