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  • firemedicgm
    replied
    It's true that if the water is being forced from a pumper rather than a hydrant we (the FD) can control the water flow. However, the problem we have is exactly what EFD840 said - if the relay man is monkeying with the throttle, relief valves or discharges - then we aren't controlling the water flow very well. It's easier to run the pump when the intake remains constant, which it generally does from a hydrant (at least in our town).

    But the real question isn't "How will relay pumping affect this?" but rather "Is relay pumping necessary ?". If it isn't necessary, why screw around with it? We're only tying up an apparatus that could possibly be used elsewhere.

    The ammount of water available for use was dramatically increased
    I disagree with this statement. If your hydrant is flowing 1000 gpm, adding a relay pumper will increase the pressure, but cannot increase the volume - at least not without risking collapsing your main. Once you start drafting out of your hydrants, you're going to have some serious problems - and a very angry city council.

    The only way that a relay pumper could increase the volume of water available would be to open the tank to pump valve on your relay and allow the tank water to supplement the hydrant water. This WILL increase your volume - until the tank runs dry.

    So reviewing our situation with the new knowledge you guys have given me......

    Our department does not have trouble getting the minimum 20 psi pressure from our hydrants. We use good 5" intake hose, so there is minimal friction loss. A relay pumper cannot add volume to the water flow, only pressure (with the exception of the tank idea expressed above). At a single-family dwelling house fire, why would we ever need to relay pump?

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  • cozmosis
    replied
    Originally posted by firemedicgm
    And, talking to our best pump operator, he has told me that it's a lot harder to run the attack pumper when the relay pumper is pushing the water at him.
    The higher the pressure the water is when it comes into the attack pumper, the less the attack pumper has to work. This is regardless of whether that water is coming from a strong hydrant or from a relay pumper.

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  • Dalmatian90
    replied
    It all depends on how much water you're trying to flow and over what distance

    Yeppers.

    Standard fireground intake pressure (minimum) is 20psi.

    That gives you a margin if something happens "upstream" to momentarily disrupt your water supply, and it the water & health department people don't like super-low residuals on hydrants.

    Say you have a hydrant that can develop 1500gpm with a 25psi residual.

    A) If you hook up a good 5" line, like Hi-Vol, you could put the pumper a whopping 50' away and still get full flow. That would give you 20psi intake, and 5psi to overcome friction.

    B) From the other perspective, how many GPM could go through the whole 500' with 5psi? 550gpm @ 500' -- in reality, probably more since as your flow went down, the residual on the hydrant would go up giving you more "umph". Probably 700-800gpm would be my average real-world guesstimate for 500' lay.

    C) Now, same hydrant still. 25psi residual @ 1500gpm. Hookup a 1500gpm pumper to the hydrant, you can now pump 150psi + 25psi incoming pressure and put out 1500gpm @ 175psi. That'll easily get you 1500gpm @ 500', indeed it'll go nearly 2,000'.

    D) One last scenario, let's have a really good hydrant. Say 1500gpm @ 60psi residual. Got 40psi to work with, and that's enough to send the whole 1500gpm through 500' of hose and leave 20psi pump intake pressure at the fireground.

    So, if your hydrants are like "B" and you're only working a house fire, 700gpm should be plenty and no need for a source or relay pumper.

    If your hydrants are like "C" and your working a commercial fire, especially going to master streams, best have a pumper on the hydrant.

    If you have great hydrants on a good grid, like "D", even for a commercial fire you don't need a source pumper.

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  • dmleblanc
    replied
    It all depends on how much water you're trying to flow and over what distance. ALL hose has some amount of friction loss. I don't have my handy-dandy friction loss calculator with me right now, but I would think that 500' of 5" hose would have a very minimal amount of friction loss, and you probably wouldn't need a relay. However, the same distance of 2.5" or 3" hose would have a significant amount of friction loss, and you might need to boost the pressure to get the volume you need. Still, this is dependent on the amount of water you're actually flowing. That same 3" supply line might keep up with one or two 1.5" handlines, but add a couple more and maybe a deck gun, and you might not keep up. It's not whether the HYDRANT has the available water, it's how much pressure you're losing due to friction loss getting it from the hydrant to the nozzle. The more water you try to push through a given size line, the more the friction loss increases. Anybody out there have the figures handy?

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  • EFD840
    replied
    And, talking to our best pump operator, he has told me that it's a lot harder to run the attack pumper when the relay pumper is pushing the water at him.
    This doesn't sound right. The relay pumper is simply boosting the pressure from the hydrant. Unless the relay operator is doing something that causes his discharge pressure to vary greatly like monkeying with the throttle, adjusting relief valves, or flowing discharges, the attack operator shouldn't have any problem. It should just seem like he's attached to a super-strong hydrant.

    If the intake pressure is greater than what the attack operator needs, he may have to gate down discharges or intakes but that can happen any time you hit a strong hydrant.
    Last edited by EFD840; 10-23-2003, 01:31 PM.

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  • Adze39
    replied
    Originally posted by firemedicgm
    And, talking to our best pump operator, he has told me that it's a lot harder to run the attack pumper when the relay pumper is pushing the water at him..
    Ask him how is it harder to take water that is being forced in from a pumper than to take water that is forced in from a hydrant?

    At least with a pumper feeding you, you (the FD) can control the pressure of the intake water.

    You can regulate a hydrant with gates to decrease the pressure if needed, but you cannot increase the pressure unless you have a pump pushing it to you.
    Last edited by Adze39; 10-23-2003, 01:22 PM.

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  • Smoke20286
    replied
    Thats what I thought till this past summer when we did a little training evolution during which we put one pumper at the hydrant then relayed to a second pumper (the attack pumper) The ammount of water available for use was dramatically increased

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  • firemedicgm
    replied
    Well, you're pretty much confirming what I thought. In a situation where your lay is say 500' maximum, through 5" hose, from a hydrant providing adequate volume, there wouldn't be a need to relay, right? I mean, if we're getting adequate gpm from the hydrant, and it's getting to our attack pumper with ANY pressure at all, our pumper should be able to boost the pressure as high as we need it, right? We don't need that water pushed to the attack pumper at 150 psi, do we?

    Also, by adding an unnecessary relay pumper, aren't we just adding one more link to the chain that can fail?

    And, talking to our best pump operator, he has told me that it's a lot harder to run the attack pumper when the relay pumper is pushing the water at him.

    Am I understanding you right? Am I making sense? There seems to be some disagreement regarding this topic in our department.

    Leave a comment:


  • dmleblanc
    replied
    We roll two engines on all structure fires, and our procedure is for the first-in engine to forward lay a supply line and for the second engine to set up at the hydrant and pump the relay. The main reason we do this is that we have only 3" supply line and the friction loss is too great to supply the first engine without some help. We'd like to get some 5" supply line but right now we are unable to make the financial commitment. Also, both of these engines have 1000 gallon tanks, so the relay pumper can provide its water to the attack engine while the water supply is being established.

    Leave a comment:


  • Dalmatian90
    replied
    If we go over 4000' *and* want flows over 1000gpm. Life is good with 5".

    It's pretty rare for us to relay pump, and I think I've seen it more during drills than fire situations, although I've also seen an 8000' lay with significant elevation increase that used three relay pumpers.

    Leave a comment:


  • ScottMA64
    replied
    I live in a town that does not have hydrants. So, we have 2 choices, relay, or shuttle. If we are VERY lucky, a water hole is within 2000ft away. But, we are still trained to dress a hydrant for mutual aid reasons.

    Scott

    Leave a comment:


  • MalahatTwo7
    replied
    We practice it occasionally for the reasons that Adze stated: Long lays. We have a lot of long twisty and pretty steep driveways in our area, where we may not be able to get the Engine or Tanker up close enough, so we would send the F350 up and do a reverse lay down to the Engine, and port-a-tanks, and go from there.

    Sometimes thats the only way to get the water where it needs to be.

    Leave a comment:


  • Adze39
    replied
    We relay pump when we have a long lay. Actually, our SOP is for a engine to pump at the hydrant if another lays in. That's even relay pumping.

    The rationale for relay pumping is that due to friction loss in long lays, you technically do not get the water supply that you need. Relay pumping boosts the pressure in the supply lines to overcome the friction loss.

    Leave a comment:


  • firemedicgm
    started a topic Relay pumping

    Relay pumping

    Okay, this topic has probably been beat to death here, but I have missed those threads, so here's my question.

    Do any of your departments relay pump? If so, under what circumstances? What is the rationale for relay pumping?

    Any input (for, against, or otherwise) would be appreciated.

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