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  1. #1
    ant0555 is offline Apprentice (new member)
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    Default Choosing a pump - water tank outlet & pump inlet sizes

    Hi,

    I am looking to replace our household water pump with one that has a higher flow rate. The water tank is 5000 gallon above-ground concrete with a 1 inch outlet. Is my choice of pumps limited to only those with an inlet of maximum diameter of 1 inch?

    Thanks,
    Ant

  2. #2
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    watson is offline Soldiers Earned Your Right To Free Speech
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    G'day Ant,
    Our tank has the standard CFA hose connector as well as a 1" coupling for a house pump.
    To keep everything standard as far as fittings and pipe around the house I've reduced that 1" to 3/4" into and out of the pump.
    I know there will be losses associated with doing this.......but, the pump output is far and above what is required for our Instant Gas HWS and shower and any taps we have.
    Currently we are using a Davey XP371 pump with an electronic type of pressure sensor turning the pump on and off. The Pump has been in use for probably 6 years without any dramas so far.

    Just what I've done.
    Last edited by watson; 7th Oct 2011 at 11:56 AM. Reason: Spulling error

  3. #3
    Danny is offline Banned
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    Quote Originally Posted by ant0555 View Post

    I am looking to replace our household water pump with one that has a higher flow rate.

    A pumps flow and pressure rating is different to the flow that is delivered through the attached pipe as that flow has been subjected to energy sapping friction loss.

    Different pumps also have different performance/flow curves and these can vary greatly even for pumps of equal power. Performance curves of different pumps should be studied so as to determine the best pump for your requirement. These can be viewed online by googling varying pumps and their spec sheets.

    The pump's flow and head rating needs to be substracted by the total of the pipes total friction loss to arrive at the pump's total dynamic (or working) head. This sounds complicated and is daunting for the unaccustomed but some simple rules can make it all very simple. These are:

    Bigger pipes have less friction loss.
    Higher flow rates have higher friction loss.
    Long pipes have higher friction loss.
    Doubling the flow rate requires X4 the energy.
    Doubling a pipe's diameter increases the volume X4.
    Doubling a pipe's diameter and maintaining the same pressure increases the flow X6.

    Before you decide on a new pump with a higher flow rate, you firstly need to establish what % flow rate increase you require. Is it 25%, 50% or even 100%. If it is a 100% increase, this would require X4 the energy! Big pumps burn energy and are expensive!

    The easiest way to increase flow rates, particularly through a pipe of reasonable length, is to fit a larger diameter pipe. Many pipes however are sold as a nominal size, this applies to many types of pipe and the actual Internal Diameter (ID) is what needs to be known for calculations. You can easily upsize the volume by changing to another type of pipe but retain the same nominal size. For example, 25 mm Blue Line HDPE has an internal diameter (depending on pressure rating) of about 20 mm but a 25 mm class 12 PVC pressure pipe has an ID of 29.75 mm. This means that each pipe has an internal volume of .314 litres per metre and .698 litres per metre respectively. In other words, changing a 25 mm Blue Line high density poly pipe to a 25 mm class 12 PVC pipe more than doubles the internal volume which will substantially reduce the friction loss! Just a note though that Blue Line is generally used for short distances and it is generally not warranted to replace it when used for short runs. The comparison has been used to give an example of the variances in nominal sizes and the importance of understanding the term.

    If you have a quality pump, maybe an inspection/overhaul could be considered, depending on cost. If a new pump is the favoured option, then you will need to consider the current pump's performance curve and the current pipe configeration, length and size to best judge where friction losses can be reduced and the % flow rate increase you require. This will then determine the pump you need.

    Is my choice of pumps limited to only those with an inlet of maximum diameter of 1 inch?
    Just about all domestic pumps have 1" inlets and outlets but the pipe can be easily increased if needed. If using PVC pressure pipe, always use flexible couplings to connect from the pipe to the pump and the tank. Most domestic pumps I see have been (often unwisely) plumbed with pipes smaller than 1" and many of those pumps are needlessly large, expensive and poorly plumbed.

  4. #4
    ant0555 is offline Apprentice (new member)
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    Quote Originally Posted by watson View Post
    G'day Ant,
    Our tank has the standard CFA hose connector as well as a 1" coupling for a house pump.
    To keep everything standard as far as fittings and pipe around the house I've reduced that 1" to 3/4" into and out of the pump.
    I know there will be losses associated with doing this.......but, the pump output is far and above what is required for our Instant Gas HWS and shower and any taps we have.
    Currently we are using a Davey XP371 pump with an electronic type of pressure sensor turning the pump on and off. The Pump has been in use for probably 6 years without any dramas so far.

    Just what I've done.
    Thanks, I am also looking at a Davey pump as the replacement, just not sure which model yet.

    Regards,
    Ant

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    ant0555 is offline Apprentice (new member)
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    Thanks for your advice and information Danny, I shall consider the pipe work as well to see where we might be able to improve efficiency.

    Regards,
    Ant

  6. #6
    Oldneweng is offline Member
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    My belief is not everyones cup of tea.

    First in answer to the limit of the tank outlet. A 1inch outlet is going to reduce flow slightly but if you increase it to a larger diameter straight away this will be minimal. It is the length which has the most effect. As per previous posts the friction for a certain section is calculated by diameter times length. Keep the small diameter length to a minimum and its overall effect is minimal. I have a 150m suction for my dam water pump. It is 2in poly. Because the lift is minimal the overall friction is very little according to an irrigation/water retailers calculation. I work in a winery which means that my job is mainly operating pumps. I have about 60 to choose from and I think that I have worked out a bit about their operation after 13 years. We mostly use 3in SS fixed lines and connect with 2in or 3in hoses. Over a long run go 3in all the way. Huge difference if parts of the run uses 2in. We have workers who have come from another winery that used 2in lines etc and they like to stick to 2in where possible. 2 setups recently, one by me with all 3in and one by the "others" which had 2in hoses in places along the way. Massive difference in flow rate. I was pushing about 40,000 litres per hour.

    I don't believe that pressure pumps are the best solution. I have two systems. Rainwater and dam water. Both have over head, gravity fed tanks and are filled by pumps that are controlled by float switches which I built and which operates using a max and min level. The rain water supply to the house is fed via a tank about 2ft high. The switch operates at about half the volumn, between full and a foot down. The dam tank is much bigger and operates over about a 2 ft range. This is filled by a pressure pump so I can use the pressure option if I want, to water the lawns and garden but I prefer not to. I have a pressure gauge fitted so when watering lawns etc I just keep turning taps on till the pressure drops to a certain level. About 5 impact sprinklers does the job. The pump develops about 3.6 bar but is more efficient at half that.

    Pressure systems are expesive to run, have reliability issues and don't work if there is no power. I live in a remote rural area which can suffer from bushfires and does often suffer from power failures. I still have water, cooking and hot water capability when the power is out. Not everyone wants gravity feed tanks. Use a big pressure vessel to reduce costs. Pumps with tiny pressure vessels are a con job. I can pump hundreds of litres of water with the power required to draw off a litre of water with some systems. My dam water pump is operated once a week as we run it that way.

    I have a Davey pump which was one of the early electronic sensor models. I had it fixed under warranty twice but the third time they refused to fix it again and just bridged the wires so it is a manual pump. Other than that it has been going for about 20 years and is still fine. I just should have waited for them to sort out all the problems LOL. These early ones leaked water into the electronics and shorted out. I was told several times that the problem was fixed LOL.

    Dean

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