Pressure

[Dannyparty92]

I know that 1 metre = 0.1 bar so say if you have a cistern in a loft and a straight drop of pipe down 10 metres the pressure at that outlet will be 1 bar of pressure assuming its a straight drop with no fittings restricting the flow. Is this the same as working the pressure out at a point and if there's three metres of pipe going up then will the pressure be 0.3 bar below the pressure originally. Also is this rule the same for 15/22 mm pipe sizes. And also do you increase the distance of a pipe run by what fittings Are including in the run for the purpose of working the pressure out? Thank you in advance for any answers .

 

[erpkid]

Pressure is determined by head as you have described. Flow is influenced by fittings and the run of the pipe work.

 

[Dannyparty92]

So the 1 metre = 0.1 bar rule applies with pipe work going up and horizontal pipe work aswell?

 

[zzzjim]

Head is all about vertical height .

Static pressure (nothing moving) does not care about pipe size.

 

[MrMeek]

your doing it wrong, its 0.1 bar per meter head to the outlet. so measure the bottom of the tank to the outlet point

 

[Megaflo-Experts]

So the 1 metre = 0.1 bar rule applies with pipe work going up and horizontal pipe work aswell?

It is the vertical distance that matters; so if you drop 1m and across 3m, the (static) pressure is still 0.1 bar.

Pipe size doesn't affect static pressure, so 15mm or 22mm pipe will have the same static pressure.

Dynamic or working pressure is different, and this is affected by pipe runs, pipe size and fittings (as well as horizontal runs) due to pipe resistance.

Hope that helps.

 

[MrMeek]

this is what I think your asking.

 

[Dannyparty92]

Aw ok thank you everybody I assume to work out the flow rate at any given outlet is quite hard?

 

[MrMeek]

Aw ok thank you everybody I assume to work out the flow rate at any given outlet is quite hard?

flow cup lol

 

[zzzjim]

Each fitting reduces flow (sudden change in direction)

pulled (gentle) bends should reduce flow less .

 

[dancinplumba]

each fitting also reduces dynamic pressure

 

[MrMeek]

Aw ok thank you everybody I assume to work out the flow rate at any given outlet is quite hard?

this answers everything from pressure to flow
http://www.ukcopperboard.co.uk/literature/pdfs/Installation-Tips/Pipe-sizing-basic-principles.pdf

 

[Dannyparty92]

So say your adding an additional bathroom to a property? How would you work out that there will be enough flow to supply say a WC basin and shower?

 

[MrMeek]

but you wouldnt work out if there is enough flow, you would try to estimate if the tanks could supply the bathroom first or upgrade them to larger tanks, then tap into the hot pipe work and tank (shortest runs possible if you can) and you should be ok then work out what pressure the bathroom will have if its two low pump it.

thats what I would do anyway someone may have a better way
+ that link what i sent you tell you how to size pipes......

 

[Dannyparty92]

Thanks Mrmeek .

 

[R1CKY]

Don't forget to consider diversity if you're adding an extra bathroom. No need to spec the system to supply all appliances at once, as chances are they won't all be used at the same time.

 

[Dannyparty92]

So are the total loading units for each appliance based on how much they might be used?

 

[stevetheplumber]

am i too old for this but i thought head was from water level not bottom of tank preausre is basically the weight of water above a point (if you realy want to be technical its the gravity thats acting on it) therefore its taken from the higher point

 

[Howsie]

am i too old for this but i thought head was from water level not bottom of tank preausre is basically the weight of water above a point (if you realy want to be technical its the gravity thats acting on it) therefore its taken from the higher point

It's the atmosphere or so I thought. Too much wine... She's got the dinner cooking time wrong. Fecking starving.

 

[stani]

am i too old for this but i thought head was from water level not bottom of tank preausre is basically the weight of water above a point (if you realy want to be technical its the gravity thats acting on it) therefore its taken from the higher point

I agree with this train of thought, otherwise if you had a 10 metre deep tank you would be thinking of starting at 0 bar when in fact it is 1 bar.

 

[Mike Jackson]

You need to measure the head from the lowest point of the cistern. Suppose you had the 10m deep cistern as above and had a tap that required 1 bar 5m below it. If there was a large draw off the tap would stop working when the cistern was half empty.

 

[stani]

Unless your an optimist in which case it would be 1/2 full

 

[R1CKY]

You need to measure the head from the lowest point of the cistern. Suppose you had the 10m deep cistern as above and had a tap that required 1 bar 5m below it. If there was a large draw off the tap would stop working when the cistern was half empty.

The tap would be subject to 1.5bar when the cistern is full, as it empties half way, it would still have 1 bar of pressure being exerted on it.

If you imagine a tall cistern, with taps positioned one at the top, one at the bottom. Which tap would spray the furthest?

 

[stevetheplumber]

if you had a preasure relief valve set at 3 bar and the metre high tank gave 2.9 bar to the base when it was full the valve would discharge i was more in the mathmatically correct mode than practical

 

[R1CKY]

Actually, just re-read what you've said and I see the point you're trying to make! D'oh! For the case of designing a system, assume pressure from the bottom of the cistern as you can't guarantee the cistern will always be full! Not that your likely to find a cistern deep enough in a domestic property for it to make a noticeable difference!

 

[Howsie]

You need to measure the head from the lowest point of the cistern. Suppose you had the 10m deep cistern as above and had a tap that required 1 bar 5m below it. If there was a large draw off the tap would stop working when the cistern was half empty.

It's directly related to the existing 'head' in the tank. Diminishing returns or something!

 

[stani]

Just been on to Wikipedia for a definition of pressure and head, even tried the translate to Chinese keys at the bottom it made exactly the same sense, think this may go on for some time.

 

[Mike Jackson]

Actually, just re-read what you've said and I see the point you're trying to make! D'oh! For the case of designing a system, assume pressure from the bottom of the cistern as you can't guarantee the cistern will always be full! Not that your likely to find a cistern deep enough in a domestic property for it to make a noticeable difference!

If you're designing systems to that close a tolerance you're asking for trouble anyway.

 

[stevetheplumber]

If you're designing systems to that close a tolerance you're asking for trouble anyway.

i agree but the preasure at the tap if you fitted a guage it would equate to the head including the tank level but as youi say the difference would be negligable on domestic but noticable on something like a water tower