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    Default Does the size of hard suction really matter?

    We are currently spec'ing a new engine. One of our members believes we should use 8" suction tubes instead of our 6" we normally use. He believes this will help us gain more volume or GPM's at the pump. My initial thoughts are this.
    1. We would still need to use 6" couplings because of the pump and the strainers / float dock use 6" couplings.
    2. We will have a front intake which will be 5" which would seem to negate any gain from the 20' of suction hose.
    3. Even though we will be using an air primer it will still take longer to make up the volume difference in the 8" compared to the 6".
    Any thoughts or comments would be greatly appreciated.

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    Get the suction hose that is rated for your pumps volume.
    "This thread is being closed as it is off-topic and not related to the fire industry." - Isn't that what the Off Duty forum was for?

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    Just one element of this... Consider the difference in priming 8" suction from draft compared to 6".

    Think of the air volume involved:

    6" hard suction, 10' long: 3,392 cubic inches of air to remove
    8" hard suction, 10' long: 6,031 cubic inches of air to remove

    So your primer would have to do nearly twice as much work to pull prime through 8" vs. 6".
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    Presumably you're getting a Trident Air Primer. They normally take their air from the truck's air system. The amount of air in those systems it limited, that is, you can use it all up unless you spec extra air tank capacity. If you are trying to evacuate too great a volume of atmospheric pressure (air) from the sleeves you can run out of truck air. Contact them at 215 293 0700. Talk to Jim or Rich. They are very up front about what its limits are.

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    How big is the pump and how much water do you expect to flow when drafting? It is one thing to buy a 2000 gpm or greater pump and another thing entirely to consistently flow that amount of water from a foldatank operation. YES, it can be done, but it is rarely done due to tender shuttle operations more than restrictions in drafting ops.

    Further have you ever used 8 inch hard suction? Even with the lightweight stuff I would think it would be clumsy, awkward and heavy to hook up.

    We have gone from front suctions to rear suctions. Far less friction loss due to elbows and ours is 6 inch to the rear. The elbows and reduction in pipe size for your front intake pretty much negate any gain the 8 inch would have. Frankly I would go with twin 6 inch side suctions versus 8 inch suction hose and just carry 2 extra lengths of 6 inch if you feel the need for more water coming in.
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    are you really ever going to flow any where near capacity from draft any tome except during pump test.? If one six wont handle it, use both steamers during pump test.
    ?

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    Thanks for the information guys. I am by no means a proponent of this and am only trying to quell the argument towards the larger hose. I am happy in the fact that so much air is needed to make up the difference. We knew it was going to be bigger and harder to manuver around. Again thanks for the info.

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    Quote Originally Posted by slackjawedyokel View Post
    are you really ever going to flow any where near capacity from draft any tome except during pump test.? If one six wont handle it, use both steamers during pump test.
    If you're never going to flow near the capacity of the pump, why was it spec'd that high in the first place?? Why have that capacity if you aren't prepared to take advantage of it?? Sure, there aren't that many fires that you have to pump at capacity, or even near it. But when that time comes, you should be ready to do it. If that means a single 8" line, or multiple 6" lines, you should already know you have the capability.

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    From Rural Fireground Water Movement data by Larry Davis:

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    Quote Originally Posted by johnsb View Post
    If you're never going to flow near the capacity of the pump, why was it spec'd that high in the first place?? Why have that capacity if you aren't prepared to take advantage of it?? Sure, there aren't that many fires that you have to pump at capacity, or even near it. But when that time comes, you should be ready to do it. If that means a single 8" line, or multiple 6" lines, you should already know you have the capability.
    Well, maybe you don't need a 2000 gpm pump all that often but if you do a lot of relay operations you may need that extra capacity to be able to flow 1500 gpm at 200 psi, or 1000 at 250 psi.

    Or you may infact have looked at your territory like we did and installed twin 6 inch dry hydrants to allow us to draft to capacity to supply lines near 2 of our highest risk locations and if necessary relay pump to supply a good portion of our community through a ldh relay.

    Honestly the reality is in most circumstances a 500 gpm pump would suffice for the everyday SFD fire. But we don't buy 500 gpm pumpers do we?
    Last edited by FyredUp; 02-20-2014 at 01:20 PM.
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    Quote Originally Posted by kuh shise View Post
    From Rural Fireground Water Movement data by Larry Davis:
    I am afraid I don't see the point...(Sorry I couldn't help being a smart alec since obviously you meant to attach something and it didn't attach.)
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    I believe Waterous developed an intake manifold that allowed 2 6" suctions to be used on the same side of the pump. I think it was done in a "wye" style configuration. I believe this was developed for FDNY to be used on some of their high volume pumps. If they needed to go to draft they could get the capacity of the pump from one side without having to run hard suction under or around the truck from the far side and still use the standard 6" suction hose.

    I will try and get Greg G to confirm this

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    Marathon Ashland Petroleum Company near here has an E-One Liquidator pumper that is rated at 6000gpm. It has three suctions on the engineer's side; from the photo they look like they might be 8".

    Scroll down to Engine 2:
    http://www.kentuckyfiretrucks.com/Ph...8613&k=FXTS3PW
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    Quote Originally Posted by EastKyFF View Post
    Marathon Ashland Petroleum Company near here has an E-One Liquidator pumper that is rated at 6000gpm. It has three suctions on the engineer's side; from the photo they look like they might be 8".

    Scroll down to Engine 2:
    http://www.kentuckyfiretrucks.com/Ph...8613&k=FXTS3PW
    Looks like 5 inch storz on the panel and 6 inch hard suction to me. But I have been wrong before.
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    I saw one of those Liquidators at one my visits to E-One. They had 8" with adapters to 6" storz. Of course, the delivered truck shown can/may vary. Also, the one I saw was 10,000gpm.
    "This thread is being closed as it is off-topic and not related to the fire industry." - Isn't that what the Off Duty forum was for?

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    Quote Originally Posted by Bones42 View Post
    I saw one of those Liquidators at one my visits to E-One. They had 8" with adapters to 6" storz. Of course, the delivered truck shown can/may vary. Also, the one I saw was 10,000gpm.
    Like I said "I have been wrong before."
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    Sorry, Fired. This forum sucks for posting attachments... Or it might just be me that can't figure out how to do it properly. By the way, I agree completely with your points about pump capacity at elevated pressures. Most new pump operators dont study the 70% and 50% capacity idea as it relates to apparatus limitations. Sometimes you see the light bulbs come on when they finally realize that a 2,000 gpm pump is only good for 1,000 gpm at 250 psi. For manmilj: Yes, the size of the suction tube CAN matter a great deal, but is not the only consideration. There are four physical limitations that determine the flow capacity of a pump. First is the ambient air pressure, which at seal level and not stormy conditions is about 14.7 psi. This 14.7 pounds is all that is available to "PUSH" the water into the strainer, up the sleeve and into the pump. A fifth limitation could be the temperature, but since we are not pumping hot or warm water, we won't talk about it. This 14.7 psi. gets used up in the following ways; Inertia - it takes energy to accelerate standing water to water moving through strainer holes and up the suction tube. Strainer hole area should be at least 5 times the area of the suction sleeve in well designed strainers. ( think about 2 to 3 psi for strainer and inertia) LIFT - This is 0.435 psi. per foot of elevation between the surface of the draft water and the eye of the impeller. So a 10 ft. lift uses 4.35 psi. when drafting 10 ft of lift. (some large pumps are rated at only a 6 ft. lift) Friction loss in the strainer, suction tube, and pump casting (24 ft ?) Think on the order of 5 psi at 2000 gpm. But this is not the whole story... every 90 degree turn represents another round of inertia, so from the intake manifold casting on a mid-ship pump to the entry into the impeller vanes we have 2 more 90 deg. bends. (about 2 psi each) so we now need about 17 psi air pressure to achieve 2,000 gpm. This is why from 1750 gpm and up the spec requires two (2) six-inch suction sleeves to reach capacity. This reduces the friction loss in the system from 5 psi to 1.25 psi, allowing the pump to reach specified capacities. Friction loss is affected by the roughness of the waterway and the diameter of the suction. The losses are reduced by the 5th power of the diameter, or 7776 (6 to the 5th) divided by 32,768 (8 to the 5th) and using our example would bring the friction loss in the tube down from 5 psi to 1.18 psi. Very nearly what two parallel 6" sleeves could do as specified by the pump manufacturer. Transitions (changing 6" to 5" storz) or (8" sleeve to 6" inlet) requires an inertia change since the velocity is changing. While you reduce the friction loss, you increase the inertial loss at the transition. This change also increases the turbulence of the water after the transition causing some additional friction losses. Hope this sheds some light on your question.
    Last edited by kuh shise; 02-21-2014 at 01:39 PM.

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    Quote Originally Posted by FyredUp View Post
    Well, maybe you don't need a 2000 gpm pump all that often but if you do a lot of relay operations you may need that extra capacity to be able to flow 1500 gpm at 200 psi, or 1000 at 250 psi.

    Or you may infact have looked at your territory like we did and installed twin 6 inch dry hydrants to allow us to draft to capacity to supply lines near 2 of our highest risk locations and if necessary relay pump to supply a good portion of our community through a ldh relay.

    Honestly the reality is in most circumstances a 500 gpm pump would suffice for the everyday SFD fire. But we don't buy 500 gpm pumpers do we?
    Um, I think we're making the same point...

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    Quote Originally Posted by johnsb View Post
    Um, I think we're making the same point...
    Could be.
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