1. #1
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    Default Advise on low level strainer

    I need advise on low level strainers. What is good or bad? Foot valve or no?

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    SK, I hate to reply to a question with another question, but Socraties did it so I guess it is a good example to follow. What size low level strainer & what amount of water (max flow) are you considering? Will it be used to transfer between drop tanks? Most low level strainers are a compromise between how low you can get before the prime breaks due to air getting into the suction, and the maximum flow rate that can be achieved with that particular strainer. As a good rule of thumb, the area of the intake (openings in the screen) should be around 5 times the area of the suction tube. Most low level strainers do NOT meet this suggestion, and will be a restriction to the flow. If your intent is to supply hand lines on rural, single family dwellings, then the standard low level strainers with a 2" opening will supply most of your needs. However; if you think that you might want to occasionally supply a deck gun or aerial at 1,000 gpm +, then it might be necessary to ask the supplier for some flow data. Likewise with a drop tank to drop tank transfer. Using 6" suction, Flows of 500 to 800 gpm are easy, but keeping up with 1,000gpm+ require some strainer modification... Like raising the opening to 3" instead of 2" standard supplied. Cross section of 6" hard sleeve is 28.3" so the strainer opening needs to be around 140 sq in. 12 x 2 x 4sides = 96 sq in. A 12 x 3 x 4 sides is 144 sq. in. A little bit of in house engineering can open up this slot. If the question concerned a 3" low level strainer, (like the two we routinely use for SFD fires) used in pairs, then a "Turbo Draft" on one will help keep the pump cool while supplying enough water for 4 - 1 3/4" hand lines at 720 gpm total.
    Last edited by kuh shise; 04-30-2014 at 03:39 PM.

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    6" in folding tanks is standard operation. We do supply master streams at times, the style we use has given us capacity. We are getting a new one and I was wondering about using a foot valve?

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    sklump,

    If what you have give you capacity then why are you looking at something different than the tried and true? Just had to ask.

    Do you use a low level strainer with jet assist? That can make quite a difference on both initial prime and overall flow.

    Walt
    Train like you want to fight.
    www.kvfd.net

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    Foot valve will almost double the friction loss in one 6" hard sleeve due to turbulence. 1.15 psi at 1500 gpm to 2.3 psi with the foot valve. If you will always be working from a drop tank with 4 ft. or less lift, then the foot valve won't make much difference unless you try to get flows closer to 2,000 gpm which you are not supposed to do using only one 6" inlet. (1750 & up need two separate sleeves to test engines) It could restrict your flow when pulling 10 ft. + lifts through 2 sections of 6" hard sleeve. You will be able to determine just how much by putting one of your present LL strainers on the suction and adding flow until you cavitate (max out) your flow. Then replace that strainer with the strainer that has a foot valve and take it to cavitation and compare the flows. If the reason you are considering using a foot valve, is because of loosing prime when operating at low flows, this might not solve your problem. Grass, algae, leaves and sticks will all affect the seal of the clapper, allowing the water in the tube to slowly leak back into the water source and drawing air into the impeller eye requiring you to pull the primer. If your desire is to "drop your tank" to pull a prime, this can be a very effective solution to a failed primer. A better and less expensive solution to repeatedly lost prime during low flow operations (like mop-up) is to put a circulation line back into the source thus blowing the air through the pump with the return flow and keeping the prime solid. Good luck in your tests. Might have the opportunity to do a test with a clappered strainer later this year in a Rural Fireground Water Movement class up here in the Big Woods. Will try to remember to report the results.

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