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#1
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Water pressure out of kitchen tap - calculation
Can anyone show me how to convert static head of water pressure into delivery of water at the tap - or even better, please do it for me because I never was any good at maths :-( First the numbers, then the explanation - it was taking 58 seconds to fill a 1-litre jug, so how many metres static head is that? Explanation - United Utilities have fixed a problem on their "communication pipe" (whatever that is) that was causing us to have very low water pressure. According to their 'standards of service' (as pointed out to me by their own inspector), we may be eligible for 50 quid compensation and, given these tough economic times I thought "great", whereas in the past I may not have bothered. Anyway, I digress... There wasn't enough pressure to open the solenoid valve of the shower and because there's always a slug of cold water in the pipes that has to come through first, it was taking seven minutes to get enough hot water from the combi boiler in the loft to fill the bathroom wash basin. We then had to stand in the bath and scoop the hot water out of the basin with a jug and pour that over ourselves every morning for 10 days. So their 'standards of service' wording is: "If the water pressure in our communication pipe falls below 7 metres static head twice within a four week period (each time for longer than one hour) we will automatically pay you £50 once per annum" From first reporting low water pressure to UU, it took 5 days for an inspector to come out and have a look, and then another 5 days before the guys arrived to dig the hole and fix the problem - a total of around 240 hours. Having just rung UU to see about this compensation, they first tried to weasel out of it by saying that we'd only had one period of low pressure within four weeks but to qualify for compensation we need two periods of more than one hour each - seems that one continuous period of 240 hours doesn't qualify, or so they are trying to say!!! |
#2
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Water pressure out of kitchen tap - calculation
John wrote:
First the numbers, then the explanation - it was taking 58 seconds to fill a 1-litre jug, so how many metres static head is that? Flow and pressure are two different things. You can't tell one from the other (tho I presume some rules of thumb might be used to take average uses of pipework, stopcocks & taps in a domestic environ and calculate an average flow restriction. From that you could have a stab at working a pressure from a flow rate.) Anyway, the most useful thing you need to know is 1 bar (14 psi) pressure = 10m head. So their 7m head is 0.7bar which is Not Very Much. Also, one litre / minute is Very Poor. IIWY I wouldn't bother with numbers and just fight your corner that the water supply was unusable for long periods. -- Scott Where are we going and why am I in this handbasket? |
#3
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Water pressure out of kitchen tap - calculation
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#4
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Water pressure out of kitchen tap - calculation
"John" wrote in message m... Can anyone show me how to convert static head of water pressure into delivery of water at the tap - or even better, please do it for me because I never was any good at maths :-( First the numbers, then the explanation - it was taking 58 seconds to fill a 1-litre jug, so how many metres static head is that? Explanation - United Utilities have fixed a problem on their "communication pipe" (whatever that is) that was causing us to have very low water pressure. According to their 'standards of service' (as pointed out to me by their own inspector), we may be eligible for 50 quid compensation and, given these tough economic times I thought "great", whereas in the past I may not have bothered. Anyway, I digress... There wasn't enough pressure to open the solenoid valve of the shower and because there's always a slug of cold water in the pipes that has to come through first, it was taking seven minutes to get enough hot water from the combi boiler in the loft to fill the bathroom wash basin. We then had to stand in the bath and scoop the hot water out of the basin with a jug and pour that over ourselves every morning for 10 days. So their 'standards of service' wording is: "If the water pressure in our communication pipe falls below 7 metres static head twice within a four week period (each time for longer than one hour) we will automatically pay you £50 once per annum" From first reporting low water pressure to UU, it took 5 days for an inspector to come out and have a look, and then another 5 days before the guys arrived to dig the hole and fix the problem - a total of around 240 hours. Having just rung UU to see about this compensation, they first tried to weasel out of it by saying that we'd only had one period of low pressure within four weeks but to qualify for compensation we need two periods of more than one hour each - seems that one continuous period of 240 hours doesn't qualify, or so they are trying to say!!! What they seem to be saying there, is that if there's a problem, and their first attempt at fixing it doesn't work, to the extent that you can report two separate incidents of pressure loss or whatever then and only then do you qualify for compenation. As worded there there is no compensation payable for any delay in their rectifying a problem. Although that may be covered in a separate clause. michael adams .... |
#5
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Water pressure out of kitchen tap - calculation
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#6
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Water pressure out of kitchen tap - calculation
Scott M wrote:
John wrote: First the numbers, then the explanation - it was taking 58 seconds to fill a 1-litre jug, so how many metres static head is that? Flow and pressure are two different things. You can't tell one from the other (tho I presume some rules of thumb might be used to take average uses of pipework, stopcocks & taps in a domestic environ and calculate an average flow restriction. From that you could have a stab at working a pressure from a flow rate.) Anyway, the most useful thing you need to know is 1 bar (14 psi) pressure = 10m head. So their 7m head is 0.7bar which is Not Very Much. Also, one litre / minute is Very Poor. IIWY I wouldn't bother with numbers and just fight your corner that the water supply was unusable for long periods. While you're at it, shoot the bozo who fitted a combi in a house with such poor supply pressure. If ever there was a case for a storage tank system, you've got it! Thinking about it, it's hard to believe that any plumber would have fitted a combi in those circumstances so have circumstances changed? Did your house ever receive a better supply pressure? Are your neighbours affected? If they're not, you may have a problem with you plumbing. Have you checked that the mains water cock is fully open? Do you have a stopcock in the street that you can check? Another simple test you could do is to hold your thumb over the cold tap. If the pressure builds to the point of forcing past your thumb then it's a flow restriction you've got rather than a lack of supply pressure. Tim Tim |
#7
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Water pressure out of kitchen tap - calculation
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#8
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Water pressure out of kitchen tap - calculation
On Jul 18, 1:18*pm, John wrote:
Can anyone show me how to convert static head of water pressure into delivery of water at the tap - or even better, please do it for me because I never was any good at maths *:-( First the numbers, then the explanation - it was taking 58 seconds to fill a 1-litre jug, so how many metres static head is that? Explanation - United Utilities have fixed a problem on their "communication pipe" (whatever that is) that was causing us to have very low water pressure. According to their 'standards of service' (as pointed out to me by their own inspector), we may be eligible for 50 quid compensation and, given these tough economic times I thought "great", whereas in the past I may not have bothered. Anyway, I digress... There wasn't enough pressure to open the solenoid valve of the shower and because there's always a slug of cold water in the pipes that has to come through first, it was taking seven minutes to get enough hot water from the combi boiler in the loft to fill the bathroom wash basin. We then had to stand in the bath and scoop the hot water out of the basin with a jug and pour that over ourselves every morning for 10 days. So their 'standards of service' wording is: "If the water pressure in our communication pipe falls below 7 metres static head twice within a four week period (each time for longer than one hour) we will automatically pay you £50 once per annum" From first reporting low water pressure to UU, it took 5 days for an inspector to come out and have a look, and then another 5 days before the guys arrived to dig the hole and fix the problem - a total of around 240 hours. Having just rung UU to see about this compensation, they first tried to weasel out of it by saying that we'd only had one period of low pressure within four weeks but to qualify for compensation we need two periods of more than one hour each - seems that one continuous period of 240 hours doesn't qualify, or so they are trying to say!!! There is 0.4336 psi in every foot head. So,If you have 10ft head you have 4.336psi when there is no flow. (ie the tap is closed) As flow in your pipe. increases,the pressure at your tap will fall. By how much depends on the amount of flow and the size/resistance of your pipe. It works in exactly the same way as Ohms law (electrcity). Only non- linear, you have to use a chart. You have pressure/ft head=volts. You have resistance (pressure drop per unit lengthf or size of pipe derived from the chart)=ohms You have flow (gallons/liters perminute) = amps There are tables that give pipe resistances either in ft hd, psi or bars for each size of pipe per unit length for the maximum recommended flow for the pipe. The table also gives resistances for pipe bends and elbows. Best source of tables is pipe/pipe fitting manufacturers. It's all about finding the minimum pipe size for a given flow, pressure and length of pipe. |
#9
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Water pressure out of kitchen tap - calculation
On 18/07/2011 17:13, harry wrote:
On Jul 18, 1:18 pm, wrote: Can anyone show me how to convert static head of water pressure into delivery of water at the tap - or even better, please do it for me because I never was any good at maths :-( First the numbers, then the explanation - it was taking 58 seconds to fill a 1-litre jug, so how many metres static head is that? There is 0.4336 psi in every foot head. So,If you have 10ft head you have 4.336psi when there is no flow. (ie the tap is closed) As flow in your pipe. increases,the pressure at your tap will fall. By how much depends on the amount of flow and the size/resistance of your pipe. It works in exactly the same way as Ohms law (electrcity). Only non- linear, you have to use a chart. You have pressure/ft head=volts. You have resistance (pressure drop per unit lengthf or size of pipe derived from the chart)=ohms You have flow (gallons/liters perminute) = amps There are tables that give pipe resistances either in ft hd, psi or bars for each size of pipe per unit length for the maximum recommended flow for the pipe. The table also gives resistances for pipe bends and elbows. Best source of tables is pipe/pipe fitting manufacturers. It's all about finding the minimum pipe size for a given flow, pressure and length of pipe. Up to a point, Lord Copper. As Tim says above, this all *assumes* you don't have a serious restriction somewhere. And from your flow rate, I bet that you have. Think volts, amps, and ohms (if you can do electrics). |
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