Explain the difference between pressure and flow?
Discussion
Can someone please explain the difference between pressure and flow?
I'm specifically interested in how it would affect the "head" i.e. in a shower for example.
This has been bought about by a complaint to my local water board, about the (apparent) loss of water pressure in my house.
For example - if the toilet is filling after a flush, the water pressure (and hence flow!) is really slow - the hot water is particularly bad.
Now, I've lived in this house for 16 years, and the flow / pressure has always been good - until recently (last year) when I complained about it.*
The water board sent a chap around, and he tested the flow with a simple cup type affair, and declared it to be "within specification" (in liters per minute).
Now I'm aware that both my (electric) shower and washing machine specify a minimum and maximum water pressure.
So - how can I easily convey to them that the simple flow test they performed is inadequate? (IMHO of course)
MODS: I realise this is not completely car related - but the technology could apply to cars too! (water / oil pressure etc.).
Please don't move this.
I'm specifically interested in how it would affect the "head" i.e. in a shower for example.
This has been bought about by a complaint to my local water board, about the (apparent) loss of water pressure in my house.
For example - if the toilet is filling after a flush, the water pressure (and hence flow!) is really slow - the hot water is particularly bad.
Now, I've lived in this house for 16 years, and the flow / pressure has always been good - until recently (last year) when I complained about it.*
The water board sent a chap around, and he tested the flow with a simple cup type affair, and declared it to be "within specification" (in liters per minute).
Now I'm aware that both my (electric) shower and washing machine specify a minimum and maximum water pressure.
So - how can I easily convey to them that the simple flow test they performed is inadequate? (IMHO of course)
MODS: I realise this is not completely car related - but the technology could apply to cars too! (water / oil pressure etc.).
Please don't move this.
- there is more to this - it's been going on for several months - but it's of no additional relevance.
A difference in pressure is what causes flow. In the case of your shower, the pressure of water inside the mains pipe is above the air pressure surrounding the shower head. Consequently when the valve is opened in the shower, you get a flow of water from the high pressure to the low.
Same as say, fuel injectors in an engine. The fuel pump raises pressure inside the rail to far above that of the pressure inside the cylinder. This difference gives the exceedingly high flow rate when injection is required.
Same as say, fuel injectors in an engine. The fuel pump raises pressure inside the rail to far above that of the pressure inside the cylinder. This difference gives the exceedingly high flow rate when injection is required.
I'm not a plumber but thought most water comes into the house and goes into a tank in the loft and is then delivered to the rest of the house by gravity ?
Sometimes you take a feed from a rising main for the Kitchen tap or outside tap.
You could always get an electric pump to increase the pressure/flow.
Ex77
Sometimes you take a feed from a rising main for the Kitchen tap or outside tap.
You could always get an electric pump to increase the pressure/flow.
Ex77
Basically as you can't compress a liquid if the pipe is full the only way to get more flow is to increase pressure.
My brother had the same issues after a new estate was built near him - at peak times he couldn't get a decent shower.
The Water Co. idea of satisfactory and yours are completely different.
My brother had the same issues after a new estate was built near him - at peak times he couldn't get a decent shower.
The Water Co. idea of satisfactory and yours are completely different.
Exige77 said:
I'm not a plumber but thought most water comes into the house and goes into a tank in the loft and is then delivered to the rest of the house by gravity ?
That's the old fashioned way - most houses built in the last 20yrs the water comes in a the bottom and is directly fed to the kitchen / bathroomsTheEnd said:
Yea, you need pressure for flow (ignoring gravity here anyway)
Pressure for example would lift it into a tank in the loft.
I guess you have low pressure, but the easy way out for a water company is to say "look, it can fill a cup, what more do you want?" and then leave.
This is exactly what happened.Pressure for example would lift it into a tank in the loft.
I guess you have low pressure, but the easy way out for a water company is to say "look, it can fill a cup, what more do you want?" and then leave.
And oddly enough - the pressure was mysteriously raised late last week, and we had a weekend of good showers, but the pressure was reduced again today.
It's that bad, that if somebody is in the shower and a tap is run in the house, the shower will actually cut out and go ice cold due to the loss of pressure.
The solution offered by the water board has been to replace the pipe running from the boundary water main into my house (which I know is not required).
They couldn't find my stop tap, and have fitted a new one (but without finding the old one - if it even exists!).
redgriff500 said:
The fact it raised at the WE suggests it isn't your problem.
But pop to the neighbours and check.
I checked with the neighbours when I first noticed it.But pop to the neighbours and check.
It has been noticed that it was down.
I also had a chat with a friendly chap from the water board - who told me that the pressure had been reduced to minimise leaks and fines from Offwat...
TonyRPH said:
And oddly enough - the pressure was mysteriously raised late last week, and we had a weekend of good showers, but the pressure was reduced again today.
The pressure may be lower on weekdays simply because every in your area is having showers and baths at the same time. At weekends, it's a bit more variable.LeoSayer said:
The pressure may be lower on weekdays simply because every in your area is having showers and baths at the same time. At weekends, it's a bit more variable.
I'm aware of that - but it's been fine for 15 years or so.It only changed last year...
But I do know it tends to be a little low in the mornings, and sometimes mid evening.
But during the day it's usually fine, but not anymore.
Off topic - I now need to get that afro image and song out of my head lol.
Pressure is force. Think of a punch bag hanging. Apply a little force by hand it'll move a bit. Apply a bigger force it'll move more.
Flow should be thought of as velocity. How fast the water 'flows' in metres/second. You can convert that to any flow you want. m3/hr gallons/minute etc. The way he has tested the flow is acceptable. I'm industry we use calibrated cans which is the same principal. The rate at which the can fills can tell you the flow.
Pressure is directly related to flow but you the size of the supplying pipework also makes a difference.
PS I'm a flow measurent engineer
Flow should be thought of as velocity. How fast the water 'flows' in metres/second. You can convert that to any flow you want. m3/hr gallons/minute etc. The way he has tested the flow is acceptable. I'm industry we use calibrated cans which is the same principal. The rate at which the can fills can tell you the flow.
Pressure is directly related to flow but you the size of the supplying pipework also makes a difference.
PS I'm a flow measurent engineer
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