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.

 

[secret squirrel]

Plumbing at college is like everything you learn at college no matter what the subject!

The first real job you go to, you'll look at it and say "what the .... what muppet did this" If it wasn't me it was Tamz...........(couldn't resist)

Then you'll make the best of a bad install and change what you need to, valves that don't work, valves and pumps around the back of a cylinder,

The analagy I use is its like your driving test, you know how to drive but you really learn when your out on your own, same with plumbing.

Don't worry, if you get the chance to go out with an experienced plumber ask all the questions you can, he may look at you laugh but will tell you the college answer and how to do it the easiest way........

 

[AWheating]

Installation Tips Contents List

plenty hear to help with your learning.

 

[fuzzy]

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

standing pressure equal, flow rate different

 

[tamz]

^^ A good place to start if you want to learn a bit more theory^^

Jump up past Fuzzy

 

[tamz]

valves and pumps around the back of a cylinder,

Makes it look neat and creating work for the boys :lol:

 

[pioneeruk]

thanks for everything guys i really do appreciate all the help.i got another question,
in my nvq & technical certificate level 2 book theres an example for calculating the intensity of pressure and total pressure:

ive attached the pic not sure if its showing up, but anyways can someone explain this? i kinda get it, only thing thats got me is the head x 9.81kPa is that the gravitational pull?



thank you very much

 

[TGor]

In theory (and in practice) the un-reduced pipe run would give a higher dynamic flow pressure for the same flow rate because, as was pointed out the smaller pipe would have a greater velocity which would increase the friction head loss .. this is not easily seen in short pipe runs but can be a major issue with long runs.

Lamonts smooth pipe formula is commonly used for these calculations.(there are few more formulae which are thought to be more accurate)

P = (V/.5545 x d[SUP]0.6935 [/SUP])[SUP]1.7715[/SUP]

Where:
P = pressure loss (KiloPascals)
V = velocity (metres per second)
d = Internal diameter (millimetres)


The velocity in a pipe system is a function of the actual flow rate and the internal diameter of the pipe V= Q/A where V= Velocity Q= Quantity of Water flowing and A= cross sectional area of pipe (Internally)

One of the benefits of getting to grips with the mathematics of plumbing is to gain an understanding of how water flows in pipes and what effect different pipe diameters can have on flow rate and pressures. For examle a 22mm copper pipe has a larger internal diameter than an equivalent pipe of Poly or PEX etc .. so in practice a copper pipe gives a lower velocity which in turn gives less pressure loss due to friction and the practical result maybe that you might need to go to the next larger size in plastic to get the same result .. meaning that copper might work out cheaper. This might give you an advantage over your competitor who might not know how to calculate the correct pipe size for a particular project.

Another benefit is being able to design pipe systems in buildings that meet the following criteria:
To ensure that connected fixtures and devices have sufficient pressure to operate satisfactorily at all times and comply with any code requirements for pressure
To ensure that the pipework is of sufficient size that the velocity in the system does not exceed a level where problems of noise and possibly corrosion are a result and that code requirements for velocity are complied with.
To ensure the most cost effective installation

Hope this helps ..

 

[tamz]

9.81 is gravity and can be taken as a constant (unless you want to get really serious).
What they are asking / showing in example 1 is with a head of 3m above the base of the lower tank the pressure is 29.43kPa/m2.
The base of the lower tank is 2m x 1.5m (3m2) so the total pressure exerted upon the base is 3 x 29.43 = 88.29kPa.

 

[kel4783]

Greater the head the greater the pressure (head gives pressure not volume)

 

[dontknowitall]

The answers above are correct (I assume) but what annoys me is that courses and training colleges spend so much time on miniscule physics theories and not enough time on the practicals and diagnosis of problem finding, a point mentioned by Secret Squirrel.

So, for some real, practical knowledge which will be used out in the jungle:

A pressure gauge will tell you what the water pressure is.
If it's below 0.5 bar there are issues to consider when it comes to fitting mixer taps and showers. If it's above 3 bar you should be thinking of fitting a pressure reducing valve. A few jobs require knowledge of pressure but for most jobs you don't need to think about it.

A weir gauge will tell you what the flow rate is. If it's very low there might be a blockage, and other times its measurements are used when you're fitting a combi boiler or unvented cylinder. Again, for most jobs you won't use it.

Generally ...
28mm will be the primary heating flow and return (usually only from large boilers or cooking stoves (Agas, etc))
22mm = hot water, central heating circuit or gas
15mm = cold water, hot water from a combi, the run to a radiator off the central heating circuit or gas
10mm will be heating or oil

To find out which pipes are hot water, turn on a hot water tap. The pipe will be hot. To establish which are the heating pipes, turn on heating then feel which pipes are hot. The flow warms up faster than the return.

 

[pioneeruk]

thank you so much guys really apreciate your help

 

[garykelly123]

lol dont forget the 9.81 as it comes up in the exams

 

[Ged Simpson]

The theory for the example given is a little erroneous, so I have laid it out that may be easier to understand.

Intensity of pressure is the force per unit area and in metric language, this is newtons per square metre and is written as n/m[SUP]2[/SUP].
The example you give with two tanks is actually incorrect, because it does not include the density of the liquid.
The force of the liquid at the lowest point is given by the formula
Force = ρ x g x h (newtons), where ρ is the density in kg/m[SUP]3[/SUP] (1000kg/m[SUP]3[/SUP] for fresh water) g is acceleration due to gravity (9.81m/s[SUP]2[/SUP]) h is the height of liquid from highest to lowest point
It would seem from your given example that the definition of Intensity of Pressure is the force due to the head of liquid at a given height, so for the example
Force (Intensity of Pressure) = 1000 x 9.81 x 3.0 = 29,430 newtons
So Intensity of pressure = 29,430 newtons
But 1n/m[SUP]2[/SUP] = 1Pa, so Intensity of Pressure is 29,430Pa/m[SUP]2[/SUP] or 29.43kPa/m[SUP]2[/SUP]
Total Pressure is the intensity of pressure at any point multiplied by the X-sectional area at that point. In the example given, this is supposedly the base of the small tank
Total pressure = Intensity of Pressure x Area of base of tank
= 29.43 x 1.5 x 2.0
= 88.29kPa

 

[pioneeruk]

A pressure gauge will tell you what the water pressure is.
If it's below 0.5 bar there are issues to consider when it comes to fitting mixer taps and showers. If it's above 3 bar you should be thinking of fitting a pressure reducing valve. A few jobs require knowledge of pressure but for most jobs you don't need to think about it.

A weir gauge will tell you what the flow rate is. If it's very low there might be a blockage, and other times its measurements are used when you're fitting a combi boiler or unvented cylinder. Again, for most jobs you won't use it.

so if the water pressure was below 0.5 bar what would you consider in fixing this?

 

[tamz]

If it is below 0.5 bar it will be tank fed. You need the proper low pressure taps with bigger openings. Pressure and flow.

 

[student plumber]

I remember asking the tutors about this one.
It talks about the intensity of pressure on the 2m x 1.5m base, the weight of water in the upper tank exerting itself on the area below which is where the 9.81 newtons comes in.

If the diagram was on the moon there would be less pressure because the gravitational pull is not so strong, so it would be less than 9.81, and when you go for a jog you'll make big jumps in the air.

But if it was on jupiter the pressure would be greater because the gravitational pull iss stronger, so more than 9.81, and a short jog will make you feel like you ran a marathon as your legs would have been heavier.

But the water in the tank and your legs are constant which is mass (kg).
9.81 newtons is the weight and coming from a height gives the pressure, more height = more head = more pressure.

It's in the book but they could have simplified the teaching it's a bit heavy going, and I'm a bit tired so I hope this is right.

If I rightly remember the example was of a tank of water exerting pressure on a boiler that it goes into.
But my question was what about the weight on the 2m x 1.5m base from the boiler itself, it's made of metal so it would be heavy, but it is not a solid lump of water and metal, and I'm sure it wasn't as light as a feather when the plumber carried it in.

But couldn't get an answer, so if someone here can much appreciated.

If there was no gravitational pull on earth then you wouldn't weigh anything.

 

[TGor]

It used to be a lot easier when we had different water i.e. one foot hieght of water = .434 pounds per square foot, now that was a lot more understandable

 

[pioneeruk]

how many types of testing equipment does a plumber need to have?
is it 3?
1. Dry test gauge
2. water pressure gauge
3. weir gauge

am i right?

 

[fuzzy]

so if the water pressure was below 0.5 bar what would you consider in fixing this?

you can raise the cistern or boost the supply, only allowed to boost 12l/m from mains supply though

 

[pioneeruk]

what are the plumbers main testing equipment?
are they:

1. water pressure gauge?
2. Dry pipe test gauge?
3. weir gauge?

cheers guys