Brake Pipes

[Daveg]

Something to do with "excessive" wanting to do something with 1/3 of a brake pipe or something like that

Knock yourself out Jock and put us right LOL ;D

Daveg

[aylesburyjock]

Not a problem Daveg , it's wall thickness which has to be depleted by a third for the rfr, rather than pipe diameter.

[Daveg]

Do you know how thick the actual wall of a brake pipe is Jock?

Daveg

[Admin]

For a 4.75mm diameter brake pipe to have its wall thickness (0.70mm) reduced by a third at one point, the diameter will be 4.517mm.

If it's wall thickness is reduced by a third around the whole circumference, the diameter will be 4.283mm.

[wally]

When all is said and done it is a reduction of around 0.25 mm which is around10 thou. If you look at and feel a 10 thou feeler gauge you realize that it aint much of a reduction at all.

Wally

[Daveg]

This is by no way an exact science, and I must point out that the internal measurement of the brake pipe will not be exact, but on a practical application using a pipe and mathematically working to it, a good guide can be seen.

Picture 3 records the OD of the brake pipe. This is shown as 4.80mm.

Attachments:

[Daveg]

Picture 4 shows a inaccurate method of measuring the internal diameter of pipe.

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[Daveg]

Picture 5 shows the wall thickness being measured.

Attachments:

[drivewasher]

I'm sure I have read that the wall thickness of new pipe is aprox 0.91mm

[Daveg]

OK the maths from memory.

Pipe OD = 4.80
Pipe id = 2.28
Dia(wall)= 1.18

CSA = OD^2 - (OD^2 - id^2) / 4

CSA = 4.31

d = 2.34

Wall thickness

4.80 - 2.34 / pi = 0.78 + 0.25

= 1.03mm

Like I said not an exact science and the method used to determine some areas of calculations are not exact although I could if necessary get the tolerances of 0.15 in line.

Daveg

[nitros44]

Brake pipes are very difficult to judge as different makes of vehicle seem to have better or poorer pipes.

Some are easy to examine and some extremely difficult due to positioning on the vehicle and covers which don't help.

Now for me were corrosion is concerned this is where a testers experience is important.

Now the manual says;
A visual and physical check must be carried out on all mechanical components that are visible and accessible

and

That light scraping of the brake pipe to remove any surface dirt is permissible.

But we all have different levels of what we might consider as light scraping so i can only comment on my level of effort applied to the corrosion assessment tool and in my opinion when i inspect brake pipes the only way to properly examine a suspect pipe is to give the effected area a light scraping(without causing further damage) to remove dirt,as well as the loose fragments of corrosion which also contain dirt need to be removed to see the true condition of the pipe.If i can see that the pipe has been necked or black pitting(deep)which is evident,these are signs which indicate excessive corrosion has taken place and reduced the wall thickness.

On the other hand how many of us at 1st glance looked at a pipe and said that looks like a fail,however after removing the debris off the pipe it turned out that it was not that bad.

At the end of the day it comes down to the testers experience and what he considers by how much the wall has been reduced.

Where corrosion is evident around body clips and it cant be proven that the pipe wall has been reduced , and i would say most NT"s do this,and for me its always best practice to issue pass/advise and let the presenter make the choice

I witnessed a vehicle not to long ago which was reinspected at our place from another test station and bit more then light scraping was applied to the rear brake pipes on Vauxhall Astra

[drivewasher]

Aug 18, 2012 16:14:37 GMT Daveg said:

OK the maths from memory.

Pipe OD = 4.80
Pipe id = 2.28
Dia(wall)= 1.18

CSA = OD^2 - (OD^2 - id^2) / 4

CSA = 4.31

d = 2.34

Wall thickness

4.80 - 2.34 / pi = 0.78 + 0.25

= 1.03mm

Like I said not an exact science and the method used to determine some areas of calculations are not exact although I could if necessary get the tolerances of 0.15 in line.

Daveg

Why not simlpy subtract the inside dia from the outside dia, that gives you total material thickness. Then divide by 2 to give single wall thickness

IE
2.28 from 4.80 = 2.52

2.52 divided by 2 to give single wall thickness 2.52/2 = 1.26

[drivewasher]

Copper pipes are 22 gauge thick walls that equates to 0.64mm

Some thicker gauge is 20 thats 0.81mm

Thinking about it now the read I was reading (lol.. ) was about 0.8mm walls for most common brake tube

[Daveg]

Aug 18, 2012 17:19:58 GMT drivewasher said:

Aug 18, 2012 16:14:37 GMT Daveg said:

OK the maths from memory.

Pipe OD = 4.80
Pipe id = 2.28
Dia(wall)= 1.18

CSA = OD^2 - (OD^2 - id^2) / 4

CSA = 4.31

d = 2.34

Wall thickness

4.80 - 2.34 / pi = 0.78 + 0.25

= 1.03mm

Like I said not an exact science and the method used to determine some areas of calculations are not exact although I could if necessary get the tolerances of 0.15 in line.

Daveg

Why not simlpy subtract the inside dia from the outside dia, that gives you total material thickness. Then divide by 2 to give single wall thickness

IE
2.28 from 4.80 = 2.52

2.52 divided by 2 to give single wall thickness 2.52/2 = 1.26

With reference to the diagram and the area shaded blue, if you take the diameter of the whole pipe, then subtract the central diameter from it you would indeed end up with 2.28, if then you divide this by 2, you end up with 1.14, which is very close to my 1.18 as measured, so the question becomes, if dividing by 2 is an average reading taken, what is the reading taken by the caliper?

If I say 4.80 - 2.52 = 2.28 / pi = 0.78 + 0.25 = 1.03

The only area I see here as inaccurate is the caliper measurement of 2.28?

Daveg

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[drivewasher]

either clliper is out OR the tube is slighty squashed/oval and the inside outside measurements were not taken in the same place OR there are burs on the inside cut edge of tube

[phaetonott]

You know what? I just look at them and decide pass, P&A or fail.

I tend to be a little harsh (in my opinion) so if they look pretty bad I fail them, The only people who have ever argued are traders, and one of those broke a rear brake pipe on a Fiesta while he was "proving" to me that it was only surface rust.

The responsible customer would rather replace a pipe than kill his family, and if they want to protest to VOSA I'll explain my reasons to them and rely on their common sense.

[Daveg]

There reads a lot of if's,but's and or's there to me lol ;D, however the pipe in question is brand new and the centre hole is as round as can be

I think it is something to do with the branch of mathematics used ,where maybe I should have thought more along the lines of hydraulics and their equations and formulas to solve it

Then again at the outset I did say the maths on this thread were not exact science

In regards to the mot test as others have said it is a visual inspection with careful scraping of surface dirt to be removed if necessary, but I don't think it says anything about surface corrosion to be removed prior to making a decision does it

I personally don't fail many brake pipes but I do whether it is acceptable or not scrap off light surface corrosion before making a decision, if I can reach it, or I just pass and advise if I can't, then if the pipe(s) leak under pressure then I just fail the brake system for a leak

There is however some thought provoking questions go on in my mind regards the trade idea about all this passing and advising, where I know VOSA started all this off about elements of doubt about compoents and all that, but the Road Traffic Acts don't give discression for driving vehicles with faults on them, and there is no legal requirement to issue any advisories, and VOSAs senior personell have been asked about this at seminars, the answer coming back was well it shows us you are doing a good test!

Interesting stuff

Daveg

[wally]

Aug 18, 2012 18:58:36 GMT Daveg said:

Aug 18, 2012 17:19:58 GMT drivewasher said:

Why not simply subtract the inside dia from the outside dia, that gives you total material thickness. Then divide by 2 to give single wall thickness

IE
2.28 from 4.80 = 2.52

2.52 divided by 2 to give single wall thickness 2.52/2 = 1.26

With reference to the diagram and the area shaded blue, if you take the diameter of the whole pipe, then subtract the central diameter from it you would indeed end up with 2.28, if then you divide this by 2, you end up with 1.14, which is very close to my 1.18 as measured, so the question becomes, if dividing by 2 is an average reading taken, what is the reading taken by the caliper?

If I say 4.80 - 2.52 = 2.28 / pi = 0.78 + 0.25 = 1.03

The only area I see here as inaccurate is the caliper measurement of 2.28?

Daveg

Daveg - I think you mentioned on one of your other many threads about you possibly getting people to look at something with a different view and creating an interest in learning more.

You got me thinking

I am not going to argue about the true wall thickness of brake pipe, just the example you have given.

Using your own initial figures - If the outside diameter is 4.80mm and the inside Diameter is 2.28mm then as Drivewasher has already said, the wall thickness must be 4.80 minus 2.28 which equals 2.52 divided by the 2 walls which then must equal 1.26mm each.

Now for the life of me I can not see why you need to use all that complicated maths to come to the answer you got of 1.03mm in your first calculation (at 5:14) and then you stated "you end up with 1.14, which is very close to my 1.18 as measured" (at 7:58)

You also stated "Then again at the outset I did say the maths on this thread were not exact science "

All I can see is Outside dia minus inside Dia dived by two as being exact.

Another statement you made is "maybe I should have thought more along the lines of hydraulics and their equations and formulas to solve it " What has hydraulics got to do with it?

The wall thickness is wall thickness irrespective of if there is anything in the pipe or not, if it is empty hydraulics don't/can't come into it, can they?

Also what is CSA as used in your calcs? Why does this come into the equation?

I have always thought I was quite good at straight forward thinking maths, so I am truly interested (and I am sure Drivewasher would also be interested) in an explanations as to why your calcs do not show the wall thickness as 1.26mm.

Wally

[drivewasher]

CSA is "Cross sectional area"

Easiest way is simplest way IE outer dia minus inner dia divided by 2

But then again, I'm not fluent in Klingon lol...

www.youtube.com/watch?v=_vPWE2Ebz48

[Daveg]

Aug 19, 2012 0:21:37 GMT wally said:

Aug 18, 2012 18:58:36 GMT Daveg said:

With reference to the diagram and the area shaded blue, if you take the diameter of the whole pipe, then subtract the central diameter from it you would indeed end up with 2.28, if then you divide this by 2, you end up with 1.14, which is very close to my 1.18 as measured, so the question becomes, if dividing by 2 is an average reading taken, what is the reading taken by the caliper?

If I say 4.80 - 2.52 = 2.28 / pi = 0.78 + 0.25 = 1.03

The only area I see here as inaccurate is the caliper measurement of 2.28?

Daveg

Daveg - I think you mentioned on one of your other many threads about you possibly getting people to look at something with a different view and creating an interest in learning more.

You got me thinking

I am not going to argue about the true wall thickness of brake pipe, just the example you have given.

Using your own initial figures - If the outside diameter is 4.80mm and the inside Diameter is 2.28mm then as Drivewasher has already said, the wall thickness must be 4.80 minus 2.28 which equals 2.52 divided by the 2 walls which then must equal 1.26mm each.

Look at the measured value of the thickness of the wall of the brake pipe, recorded at 1.18mm as I posted. The maths Drivewasher has used are my measurements and has just divided by 2 to get his answer of 1.26mm, which is clearly different to my measurements recorded. My whole point of everything I have said is to say that the maths MUST be exact to any meansurements taken, otherwise inaccuracy is the result, which is why I said it was not an exact scienceDrivewasher can't really use the maths I posted as he cannot account for any inaccruacy of any measurements taken

Now for the life of me I can not see why you need to use all that complicated maths to come to the answer you got of 1.03mm in your first calculation (at 5:14) and then you stated "you end up with 1.14, which is very close to my 1.18 as measured" (at 7:58)

You also stated "Then again at the outset I did say the maths on this thread were not exact science "

Exactly my point Wally, the maths is exact only when the produced used is also exactly accurate, so if maths is used to design some specifications of a compoent, then the compoent made to those tolerances will be right, but if maths is used the opposite way round as in my example on this thread, then inconsistances in the solutions are recorded, and the interpreter is then left to find out why?

All I can see is Outside dia minus inside Dia dived by two as being exact.

The Outside diameter and the inside diameter are not exact Wally, which is why problems in the maths showed up.

Another statement you made is "maybe I should have thought more along the lines of hydraulics and their equations and formulas to solve it " What has hydraulics got to do with it?

Hydraulics has everything to do with it, in industry different mathematical techniques are used to establish a standard way of reaching a solution to a problem. Many students who have studied maths and science will agree with me here, even though you may not understand.

The wall thickness is wall thickness irrespective of if there is anything in the pipe or not, if it is empty hydraulics don't/can't come into it, can they?

This is not true at all Wally. Accuracy of the diameter outside and inside along the length of the pipe will change. By understanding how to determine the internal diameter of a pipe and using hydraulics to work out fluid areas and pressures, the minimum diameter of the pipe wall can be established with a built in safety factor to ensure minimum costs and safety to the end user. College maths will not cover specalised areas of expertise like this.

Also what is CSA as used in your calcs? Why does this come into the equation?

This is a prime example Wally, no disrespect intended whatsoever. You would like me to believe that you have a straight forward way of thinking and even if you like Drivewasher thought had concluded the issue, you both could be miles away from the correct answer purley by misunderstanding something you have never had training in, which in this day and age is more important now than ever before, i.e. like vehicle electrics on hybrids, they can kill immediately but 12 - 14 volts was never really a problem was it, if you understand what I mean.

I have always thought I was quite good at straight forward thinking maths, so I am truly interested (and I am sure Drivewasher would also be interested) in an explanations as to why your calcs do not show the wall thickness as 1.26mm.

Read on below

Wally

The brake pipe in question I took one measurement of the Outside Diameter, which recorded 4.80mm. I took one measurement of the internal diameter of the pipe using a vernier caliper, correctly calibrated, which gave a recorded internal diameter of 2.28mm. This was my first mistake, where later I advised the accuracy of the measurement was suspect..

I have now taken more measurements and have an average outside diameter of 4.74mm. This time as I should have completed last time I used a drill bit to measure as accurately as I can the internal diameter, which records a result of 2.37mm.

This measurement of 2.37mm is only accurate at the point of entering the pipe. Moving the drill bit leftwards and rightwards produces a swing of 5mm, therefore the Mean diameter of the internal pipe based on this method is 2.50mm.

Why use all that complicated maths, well because it appears that somebody somewhere decided that it was the right thing to do so I am not guilty of that, I just follow the rules and try to interpret them as clearly as I can.

CSA = OD^2 - (OD^2 - id^2) / pi

CSA = OD^2 - (OD^2 x 4) / pi

CSA = 28.61 - 22.47

= 6.14
d = Sqrt 6.14

d = 2.47mm

(If you trucate the figure you get 2.50 as the Mean above I calculated with the drill bit)

Now using my average figures above.

4.74 - 2.37 = 2.37

2.37 / 2 = 1.18 mm

The vernier caliper records the average reading, so the wall thickness is the average, and by using the average readings of the pipe diameter the average result concludes that the wall thickness is indeed as measured 1.18mm.

As can be seen above, the maths is just another tool in your mental tool box to allow you to understand things that your eyes cannot see. So working out the internal diameter of the brake pipe above is accurate enough for the tolerances of the brake pipe in question is it not.

2.47 (2.50) = 2.50.

Just like the thread I wrote in Vehicle Repairs, although the maths is very much more complicated, the internal working specifications of the engine can be established without dismantling the engine.

Just another tool in the tool box as I see it saving money and workshop time.

Daveg