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    ra2457's Avatar
    ra2457 Posts: 5, Reputation: 1
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    #1

    Dec 4, 2013, 02:45 AM
    How much water will flow due to gravity from a vertical pipe 8 ft h & 6 inch dia?
    How much water (in l/m) will flow down due to gravity from a vertically oriented, full flowing, smooth, PVC pipe h 8 feet & dia 6 inches?
    ma0641's Avatar
    ma0641 Posts: 15,675, Reputation: 1012
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    #2

    Dec 4, 2013, 06:43 AM
    First you need to find the volume of a cylinder. Start there. We will help you with homework but you need to do the upfront work. You will need to convert cubic inches to liters.
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    #3

    Dec 4, 2013, 08:00 AM
    Dear ma0641 (Plumbing expert)

    Thank you for your response. I have calculated the answer. Can you please help me to validate if it is correct?

    I repeat the question: How to calculate the quantity of water flowing down due to gravity from a vertically oriented, full flowing, smooth, PVC pipe having height of 8 feet and internal diameter of 6 inches?


    Velocity (metres/second) is square root of 2 times g times head.
    8 feet head= 2.4384 metres, 6 inches diameter is 0.1524 meters. Substituting these numbers in the formula, one gets velocity of 6.9156 metres/second.

    The surface area of the pipe is pi times radius squared. (22/7*0.0762*0.0762) that is 0.0183 sq. meters.

    Therefore, the flow should be 6.9156 times 0.0183 that is 0.1262cubic metres/second.

    1 cubic meter is 35.3147 cubic feet and 1 cubic feet is 28.3168 litres of water.

    Substituting these numbers, one gets a flow of 7572 litres/minute.

    Taking friction loss of? (my guess 5%), one gets a net flow of 7193 litres/minute.

    Please provide your inputs.

    Thank you in advance.

    Rajesh
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    ra2457 Posts: 5, Reputation: 1
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    #4

    Dec 4, 2013, 08:11 AM
    Quote Originally Posted by ma0641 View Post
    First you need to find the volume of a cylinder. Start there. We will help you with homework but you need to do the upfront work. You will need to convert cubic inches to liters.
    Question: How to calculate the quantity of water flowing down due to gravity from a vertically oriented, full flowing, smooth, PVC pipe having height of 8 feet and internal diameter of 6 inches?
    I have attempted the calculation below. Can someone please validate it?
    Velocity (metres/second) is square root of 2 times g times head.
    8 feet= 2.4384 metres, 6 inches is 0.1524 meters. Substituting these numbers in the formula, one gets velocity of 6.9156 metres/second.
    The surface area of the pipe is pi times radius squared. (22/7*0.0762*0.0762) that is 0.0183 sq. meters
    Therefore, the flow will be 6.9156 times 0.0183 that is 0.1262cubic metres/second.
    1 cubic meter is 35.3147 cubic feet and 1 cubic feet is 28.3168 litres of water.
    Substituting these numbers, one gets a flow of 7572 litres/minute. Taking friction loss of? (My guess 5%), one gets a net flow of 7193 litres/minute.
    Is this correct?
    Thank you in advance.
    Rajesh
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    ma0641 Posts: 15,675, Reputation: 1012
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    #5

    Dec 4, 2013, 10:54 AM
    I did not do the math but your logic and formulas are correct. The key here is "vertical " so gravity is considered 100%. Not sure if they asked for volume with friction loss. I would give 2 answers, 100% flow and with friction loss.
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    Rajesh Asher Posts: 1, Reputation: 2
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    #6

    Dec 4, 2013, 11:40 PM
    Dear ma0641,

    Thank you for your inputs. I appreciate the same.
    Another related point, will the formula for flow remain the same if the pipe length was say 100 feet. Or will terminal velocity come into play? If so how to calculate the TV and consequent flow? Please guide
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    #7

    Dec 5, 2013, 06:32 AM
    Formula is the same. Flow resistance may be a bit higher. If you Google "flow resistance in piping " you can read charts. Terminal velocity is not really a case here. Pipe becomes a critical orifice and that is the flow limiter. If my answers were helpful "please click on the green thumb. Thanks
    ra2457's Avatar
    ra2457 Posts: 5, Reputation: 1
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    #8

    Dec 5, 2013, 06:38 AM
    Quote Originally Posted by ma0641 View Post
    Formula is the same. Flow resistance may be a bit higher. If you Google "flow resistance in piping " you can read charts. Terminal velocity is not really a case here. Pipe becomes a critical orifice and that is the flow limiter. If my answers were helpful "please click on the green thumb. Thanks
    Yes, your answer is very helpful. Strangely, this portal's policy does not accept my thumbs up sign for your reply, saying I must spread reputation around!
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    speedball1 Posts: 29,301, Reputation: 1939
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    #9

    Dec 5, 2013, 07:56 AM
    Hey Brian!
    What"flow resistance"are we talking about? The pipe is only a half feet long. Not too much resistance there. Or am I missing something? Regards, Tom
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    #10

    Dec 5, 2013, 08:07 AM
    Quote Originally Posted by speedball1 View Post
    Hey Brian!
    What"flow resistance"are we talking about? The pipe is only a half feet long. Not too much resistance there. Or am I missing something? Regards, Tom
    The pipe is 8 feet long and half foot in diameter
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    jlisenbe Posts: 5,020, Reputation: 157
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    #11

    Dec 6, 2013, 03:41 AM
    This site might be helpful.

    Pipe Friction Loss Calculations
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    #12

    Dec 6, 2013, 06:14 AM
    He also asked if the pipe was 100 ft. Long. My later post referred to that.
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    speedball1 Posts: 29,301, Reputation: 1939
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    #13

    Dec 6, 2013, 09:08 AM
    The pipe is only a half feet long.
    my bad! Sorry for the error. I still don't see any resistance here. Regards, Tom
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