Flow rate

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Hiya

Quick basic one....

If you're measuring your flow rates and kitchen tap says say14l/min and outside tap says 18, is it valid to just use the highest number and assume some sort of restriction on the kitchen tap?

Nothing else can increase flow to one specific tap without pumps etc can it? So must be mains rate
 
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I understand some restrictions will increase pressure on a system but not flow am I right?
 
When liquid flows through a restriction there will be a pressure difference across the restriction.

The greater the restriction the higher pressure for the same flow rate

or

The greater the restriction the lower the flow rate for the same pressure.
 
You still need to do some study Phill.

To understand dynamic flow rate and why residual pressure is required to operate showers.

Tap outlets should ideally be restricted to want is required. WC hand wash basin 4 li/min. Kitchen and bathroom wash basin 6 li/min.

Limiting the flow reserves flow for other outlets and prevents splashing.

Tony
 
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You still need to do some study Phill.

To understand dynamic flow rate and why residual pressure is required to operate showers.

Tap outlets should ideally be restricted to what is needed. WC hand wash basin 4 li/min. Kitchen and bathroom wash basin 6 li/min.

Limiting the flow reserves flow for other outlets and prevents splashing.

Tony
 
Limiting the flow reserves flow for other outlets and prevents splashing.

There is still the need to limit the static pressure ( when the tap is closed ) to prevent a spurt of water under pressure when the tap is opened. A flow limiter will not reduce the pressure at the tap until there is flow through the flow restrictor.
 
I see, cheers guys.

Is there a specific theory course you might recommend to help me? I find this fascinating as an area and I feel like I need to understand it.

So if you remove all talk of boilers etc and just think of flow and physics.....if my outside tap is 18l/min at say 3 bar that will be what's left over on both counts from what came in the front door before flowing through stop taps valves elbows etc and appearing on the back wall? All of which will have reduced pressure AND flow to a theoretically calculatable degree based on size of restriction?
 
And Tony if I understand you correctly the 3 bar is all fine well but if you open the tap it's no longer 3 bar as that pressure is not when the tap is open?

So a tap earlier in the system being open would reduce considerably what's left I.e making it theoretically a new system with entirely different pressure and flow?

So you are calculating for exam conditions as well as practical conditions?
 
Interestingly I have a stop tap under my sink which is currently seized in a position. It may be that this is restricting the flow intentionally to the sink or it may be that it is fully open......it is currently Schroedinger's stop tap.......needs replacing either way!
 
I see, cheers guys.

Is there a specific theory course you might recommend to help me? I find this fascinating as an area and I feel like I need to understand it.

So if you remove all talk of boilers etc and just think of flow and physics.....if my outside tap is 18l/min at say 3 bar that will be what's left over on both counts from what came in the front door before flowing through stop taps valves elbows etc and appearing on the back wall?


Even a full degree in hydraulics might not help. We had a lecturer here about five years ago annoy a few people because he was unable apply his theory to practical plumbing.

You must first try to understand what static pressure means. Then how flow resistances affect flow rates. It has never been a problem for me but I am aware that others seem to find it difficult to follow.
 
I shall do just that Tony. I think I need to invest in a pressure gauge and flow cup and just measure some stuff under different conditions.

Once I understand what changes affect what I'll be better off to start learning!
 
Not that this applies to me but if your flow rate is say 20l/min and your mains shower was say 15l/min would that mean you had 5l/min left for another appliance to run simultaneously? Assuming the other appliance was cold only feed I.e washing machine electric shower etc.

Would that situation reduce the flow to the boiler or would the mains flow account for the uplift?
 
I cannot give you a meaningful reply when you don't understand the relationship between pressure and flow.

They are similar to voltage and current in electronics which many find easier to understand.

You need a pressure gauge but just a saucepan or measuring jug and a stopwatch to measure flow.
 
This might help to understand how flow out of one tap will affect floe out of other taps.

The flows at taps will depend on how far the tap is opened and the pressure at the tap.

With no water flowing at F 1 the pressure for F 2 will be P mains - (R 1 + R3) x F 2

With water flowing at F 1 the pressure for F 2 will be P a - (R 3 x F 2 )

Substituting for P a


The pressure for F 2 will be P mains - ( R 1 x ( F 1 + F 2 ) +( R 3 x F 2 )

water flow.jpg


At least I think that is correct mathmatically
 

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