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Thread: Pulling a draft

  1. #1
    Forum Member fftrainer's Avatar
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    Default Pulling a draft

    A question for all of you water supply experts out there.

    We ran a drill not too long ago on Water Supply/Pump Operations. By the time you put everyone together who has either learned simply from experience, or from instructor Bob at the academy or instructor Tim from some independent training outfit you get a hundred different opinions on how to do things.

    We had two members have a semi-heated debate (only because one of them is NEVER wrong, but that's a whole nother subject!) over RPM necessary to pull a draft.

    Situation at the time was:
    - Front Mounted Intake
    - 2 Lengths of hard suction
    - Float Strainer
    - 'normal' incline - nothing severe
    - slow moving river, no rapids to make air in the line

    My question is given the above situation what would YOU run your RPM's up to if you were the operator, before attempting to pull that draft.

    We had arguments ranging from 14/15 to 25/26. This is a common draft site for us and I have always been able to pull a draft there at anywhere from 15 - 17.

    Your thoughts?!?


  2. #2
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    It's not that big of a deal what RPM you are at as long it don't hurt the pump and it will hold the water once it gets there. The primer pump sucks the air out, atmospheric pressure pushes the water up the suction line into the pump.All the water pump has to do then is hold it until a discharge is slowly opened. once it stablises with flow you throttle up or down.
    How do I spell check on these posts?

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    I have to agree with everything GPM said. The pump is in gear and spinning and no matter how fast you turn the pump with high RPM's, the prime pump isn't going to work any faster. My department uses a standard of 1100 RPM to draft but I have pulled a draft at idle 500-600 RPM without a problem.

    If you want to use a basis for your drafting procedures, go by the pump manufacturers test pressures and RPM's that give you your pump rating (1000, 1250, 1500, 1750 etc.). On the pump panel should be a metal tag or label that states what your pump rating (GPM) is and at what RPM's the truck was running to get that pressure. Most of the time it's between 1480 and 1780 RPM's for full capacity. According to the Waterous Pump Manufacturer tag on the side of my 1500 GPM pumper, it says the pump should flow 1510 GPM at 1580 RPM's and 150 PSI (in single stage or volume setting). That's as per NFPA pump test requirements drafting from a static water source (lake, pond, stream, reservoir etc.)

    Hope this helps.

    Engine/Rescue Lt. Kevin C. (aka Pokey)

  4. #4
    Forum Member MetalMedic's Avatar
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    Ok, maybe I have been doing it wrong for the past 21 years... but I have always pulled a prime the way I was first trained.

    With the pump in gear, FIRST, you pull the primer pump handle until you observe a vacuum on the pressure gauge. THEN, you increase the RPMs gradually while releasing the primer until you acheive your desired pump pressure. I can't recall ever having any problems with this method.

    To be quite honest, I never really paid that much attention to the tachometer. On many of the older trucks I have seen, the tachometer on the pump panels are not even working. Especially on a front mount, you can tell by the sound of the engine if it is over revving.
    Richard Nester
    Orrville (OH) Fire Dept.

    "People don't care what you know... until they know that you care." - Scott Bolleter

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    Metal, you haven't been doing anything wrong. I prime the same way you do. Like I said, our SOP's are to run the pump at 1100 RPM before activating the prime pump. After attending Waterous pump school I have also found that priming at idle and then increasing the RPM's, as you said does the same thing.

    GPM says basically the same thing.

    I just gave a possible solution to FFTrainer's arguments about what RPM's to set the truck at for drafting. They can run at idle or they can throttle the pump up to red line. The manufacturer however states on that tag I talked about that the optimum GPM is attained at a certain pressure so anything over that RPM is useless (because GPM output goes down as RPM increases) hence FFTrainers argument against the higher RPM's on draft.

    Engine/Rescue Lt. Kevin C. (aka Pokey)

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    I'm no exspurt (drip & and a has been) but I vote for let it idle untill you get water in the pump. The pump is'nt whats pulling the water up, the vacum from the primer is.
    What cools the pump? Water.
    I can see a scenario where an extended time to aquire a prime could cause some damage.I'm sure alot of us have been on a fireground and heard a primer scream for what seems forever before the "operator" decided to check and see what the problem is.Add an engine thats been spinning the pump at red line this whole time and it can't be good for wear rings.

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    A good point F02, A pump going at hi RPM with no water.. Not good. But Our trucks will loose it if not throttled up a bit. I guess it depends on the pump condition and a few other variables.

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    MembersZone Subscriber jsdobson's Avatar
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    One of the main reasons for a specific RPM while drafting is the electrical power needed for primer pump. Around 1000-1200 rpm is needed for the alternator to produce enough of that power for the primer pump.

    For the cases of idle rpm and obtaining a draft, congradulations on working with an exceptional apparatus and tight pump.
    BE SAFE
    Before Everything, Stop And First Evaluate

  9. #9
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    Four group 31 batteries should supply plenty of power.
    A centrifigal pump won't pump air. No matter what the condition or the rpm
    If it would we would'nt need a primer.
    If your having trouble priming there's a leak somewhere.Suction hose gaskets,packing,drain valves,is the pump cooler valve closed? etc.

    Get some water in it, then grab the throttle.

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    I agree that an RPM increase will help maintain the truck's voltage for priming. Sure it will work at idle RPM, but the primer will run cooler with a higher voltage and do a better job of priming. This is an issue with older engines with smaller alternator capacities, probably not so much with the newer stuff. (Our newer engines have 250A alternators versus 140A on the old stuff) I know our older Macks really drag down with all the warning lights operating and the primer doing its thing. I think 1000-1200 RPM would be fine, no reason to have the engine screaming.

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    I've really never known why, but I was taught to run the RPM to 1,000, then prime. I know (because I've run this little experiment) that this gets me a prime on the first try just about every time, but leaving the very same engine (with the very same setup for drafting in the very same place) at idle and priming yields more like a 50-50 chance of getting it on the first try.

    I've kind of left this in the category of "I know what works, so I just do it." It's interesting to see some ideas on why it works.

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    Interesting replies... but one thing not mentioned is the fact that some early model trucks (we have two of them) use manifold vacumm for priming the front mount pump. With this being the case, the highest amount of vacumm is achieved at or just above idle on a carburated engine. This is usually why the old timers taught us how to prime at idle. However with a seperate oil sealed priming pump the main consideration should be wear on a dry pump, which if the priming pump is working right usually lasts only a few seconds. Then there's the point if your system can handle the sudden load on the pump with the engine at idle ( will the engine die), with a properly tuned engine and a pump that is in decent shape you shouldn't have any trouble.

    Just another wrench to throw in,
    Be Safe, Frank

    [ 08-24-2001: Message edited by: FSRIZZIO ]

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    I guess the bottom line to this and most of the other threads we get caught up in is this. Without 100% knowledge of what xyz Dept/person has for their equipment and the maintenance of same all we are doing is giving it our best Scientific Wild A** Guess (SWAG) To the author of this thread please help us all by being a little more specific about the type of pump and primer we are trying to help you with

  14. #14
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    From the front suction you can pull a draft at idle, but with all the piping from the front to the pump the friction loss is amazing. Its a last resort in my F.D.

    However from the side with a butterfly valve, if all connections are tight you can start the tank waterto flood the pump then get the rpms going up at the same time you are opening the butterfly valve. You will pull a draft without even touching the primer handle. It takes alot of practice and good mechanically sound pumps, but it can be done.
    LEATHER FOREVER

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    Running the pump dry at any speed for more than 10 seconds begins to heat up seals and packing inside the pump. Extended runs will ruin the them.

    We have a 750 gpm front mount that I prime without the pump in gear. It's true that the impeller spinning will not help the prime. This truck has always been slow to prime. It uses the truck engine's vacuum instead of a gear pump.

    After connecting the hard suction, I pull the primer handle. I watch the hard suction hose for sagging as the water fills it. After a few seconds more I reach over and nudge the pump into gear. If I have a prime the pressure gauge comes up. If not I disengage the pump and wait a few seconds more.

    Works fine on front mounts, I'm not sure how you could do it with a midship.

    Just another way to skin a cat.


  16. #16
    MembersZone Subscriber jsdobson's Avatar
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    How about priming your pump without using the primer pump and while still flowing water from your booster tank ?

    This may take a few minutes to read so bare with me if you will.

    I realize some departments will not flow water from their booster tank until a water supply to the attack engine so this evolution is a mute point.

    1. While flowing from your booster tank to a pre-connect handline, set-up your hard suction hose to your steamer port. Hopefully you have a keystone valve or the equivalent on that port.
    2. Open your tank fill valve to less that 25% of its capacity.
    3. Open your keystone valve just a notch or two and wait for any pressure fluctuations to stabilize.
    4. Repeat step three until the keystone valve is fully open.
    5. Slowly close the the tank to pump valve.
    6. Open the tank fill valve until the booster tank is full.
    7. On a 500 gallon booster tank flowing 160-180 gpm, you should have about 150 gallons remaining in the tank before begining to refill the tank.
    8. KEY POINT: The reason the tank fill valve is open slightly is to give air in the draft hose a place to escape to and not cause your pump to cavitate. I'm sure you are aware your fire pump cannot pump air. It is the action of the impeller creating a vacuum that is evacuating the air in the draft hose and that air will cause the fire pump to cavitate if you do not open the tank fill valve.

    I instruct this "finesse" method to engineer candidates before teaching them how to use the primer pump. My theory is to give several ways to prime a pump and not be dependant on the primer pump.

    Try it, you make like it !
    BE SAFE
    Before Everything, Stop And First Evaluate

  17. #17
    blackb16
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    Or, you could skip all the finess training, that has a way of killing guys on the inside when you screw up, and simply put a clapper or your stariner and never be wrong.

  18. #18
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    well i agree with most every one. you should be able to get a prim at idle. for those of you who say you have to have x amount of rpm's for your altenator, you might want to get new batteries before they leave you sitting on the side of the road.

    by the way who says you have to use a primmer? why cant you just back fill your hard suction with tank water then run up your rpm's untill you have reached the psi you want?

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    Originally posted by blackb16:
    <STRONG>Or, you could skip all the finess training, that has a way of killing guys on the inside when you screw up, and simply put a clapper or your stariner and never be wrong.</STRONG>
    OK, how does a clapper pull a draft?

  20. #20
    blackb16
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    A clapper at the strainer, will allow you to back fill the hose with about 35 gallons of water and not use the primer to get a prime. Plus you can pull attack lines off the draft rig without endangering the attack crew.

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