newbie question about pipe sizes

[pioneeruk]

hi guys,

i have a question which is really bugging me, ive just started the 6129 city and guilds so please be nice, im not the brightest of guys however i do wanna learn, anyways the question:

lets say on oneside i had a pipe of 22mm coming down vertically then horizontally in 15mm to a tap
and on the other side
i had a pipe of 22mm coming down vertically then horizontally in 22mm to a tap
now which of the 2 examples above would give me more pressure? lets say there both coming down equal height etc.

Reason am asking this is i just want to know if the reduction of the pipe diameter will make any difference in the pressure of the water coming out of the tap.

i hope ive made sense :S


thank you

 

[secret squirrel]

You've made sense well to me anyway, don't know whether thats a good or bad thing!

Keep it simple, 50 gallon tank. 1 metre high is 0.1 bar. This is fixed, pressure will always be 0.1 bar. Run a 22mm pipe from the tank to a tap it will be 0.1 bar as will the 15mm pipe BUT the flow will be greater from the 22mm pipe.

Don't please please ask what the flow difference is I'll have to look it up....

 

[tamz]

The pressure would be slightly greater on the 22mm pipe but not for the reasons you are thinking.
It would be due to slightly lower frictional losses but nobody would ever detect it as we are talking minuscule on a domestic situation.

Flow is a different thing to pressure. You would have a larger flow rate as more water can pass through the bigger pipe.
In reality there would be very little difference here either as the tap would restrict the flow anyway.

Velocity is another thing. The smaller pipe would have the water flowing at a greater velocity (think what happens if you squeeze the end of a hose).
Same pressure, lower flow but higher velocity.

I'l not explain it any more because the sums would do your nut in (and mine).

 

[pioneeruk]

thanks for the reply guys,

so if the tank was a different size not a 50gallon would 1 metres head still be 0.1 bar?
So if i started with a 22mm pipe but reduced to a 15mm pipe the velocity would be greater right? because the water is being forced through a 15mm pipe from a 22mm?

arrghh lol this is hard, i really wanna get my head around the science of plumbing then am guessing the rest will follow.

 

[secret squirrel]

The pressure would be slightly greater on the 22mm pipe but not for the reasons you are thinking.
It would be due to slightly lower frictional losses but nobody would ever detect it as we are talking minuscule on a domestic situation.

Flow is a different thing to pressure. You would have a larger flow rate as more water can pass through the bigger pipe.
In reality there would be very little difference here either as the tap would restrict the flow anyway.

Velocity is another thing. The smaller pipe would have the water flowing at a greater velocity (think what happens if you squeeze the end of a hose).
Same pressure, lower flow but higher velocity.

I'l not explain it any more because the sums would do your nut in (and mine).

and mine!

 

[secret squirrel]

thanks for the reply guys,

so if the tank was a different size not a 50gallon would 1 metres head still be 0.1 bar?
So if i started with a 22mm pipe but reduced to a 15mm pipe the velocity would be greater right? because the water is being forced through a 15mm pipe from a 22mm?

arrghh lol this is hard, i really wanna get my head around the science of plumbing then am guessing the rest will follow.

Yes, even if it was a 100 gallon tank but 1m still be 0.1 bar agai may be a miniscule difference but not anything to take into account.

yes. velocity would be increased, by using 22 reducing to 15.

But on a tank system when going from 22 mm to a bath tap by a flexi hose (reducing the bore) the flow is reduced considerably.

This will do your head in completely if you let it.

 

[pioneeruk]

i didnt know there was so many formulas in plumbing, do you guys who have experience in the plumbing trade know all your formulas etc? does it ever get easy? am worrying i will screw up.

 

[Plumbstar Tom]

you tend not to need it all in depth to be honest it just helps to know it

If your on a low pressure system then you just have to make sure that you do not reduce the performance any more by adding elbows and flexis etc

Plumbing all makes logical sense when you understand it

Water will always find its own level

I remember when i created my first syphonic action on a house to empty a washing machine that wouldnt drain! amazing!

 

[tamz]

There are hundreds of formuli, some you remember others you know how they work but have to get the books out. Most times you won't have to know any as it has all been done for you. Depends how in depth your course work gets regards what you are expected to learn and how much into design you want to get.
I don't know what they teach these days as i did mine a long time ago when things were done differently.

 

[AWheating]

unless you are using a calculation on a weekly basis you will not remember them, which is what books/notes are for.

Some gas safe engineers have gas rate calculations imprinted on the brain, some use a table and cant remember them without getting a book out..... its knowing where to find and how to use it correctly that matters not memory.