Plumbing knowledge

[Jaymo]

Evening all

 

Have some 100mm polypipe with a length of 11.5m to lay in some trenches.

Thing is that it needs to be a max slope of 1%

What does this equate to in real angles as every online calculator seems to give a diff answer.

 

Thanks in advance for any help

[grrclark]

A 1% slope would be 1m of drop for every 100m of run, so 11.5cm drop to your 11.5m runs.

 

I'm not a plumber so feel free to ignore

[Pie]

If it's for drains it used to be 1" drop in a 4 m length

[robbiep]

Just ensure you've got a drop of 1 cm per metre - when I used to lay drainage we would put a shim of timber on top of the pipe at the lower end, and spirit level from that to the top end. Level bubble = correct drop.

IIRC, we used to use something like 20mm drop on a 120 cm pipe

[Jaymo]

Its for a Septic tank drainfield.

 

The natural fall of the land is 2 to 2.5 percent giving a fall of 2cm per 100cm.

But the prob is that although I can shim the pipes to the max of 1%, really need the angle.

Not only that, if I do get them level to the max tolerance then the next prob is that the depth from top of the pipe to the surface must be acregular 20cm which on downwards sloping ground with a levelled of pipe means this 20cm cannot be maintained.

Was thinking of shorter runs with some 15degree bends to mainttain this constant depth.

[delburt0]

11cm for the 11.5 mtrs would equate to just under just break it down..ie 1.15 cm per mtr.= 11.5. Mtrs..

[apache]

If you say flat is 0° and 90° in a 1 in 1 fall - ie vertical then it's the percentage multiplied by 0.9

 

I think.

[figgy]

Your over thinking it, it's only drainage into a field. If you already have a 2-2.5% slope with the land just maintain your required depth and it will be fine.

 

All this need an angle carp, you couldn't work it to an angle as the pipe will not be perfectly straight. Better to go with measurement over distance and use your inverts and a laser or dumpy level.

 

If you need 11cm over he length then that's all you need if it works out at more because of the land your working so what, either go withit or dig deeper at one end to maintain correct fall.

 

Figgy

[Jaymo]

Its not me, I would be happy for the nominal 2% fall.

 

Its in the regulations that I'm having to conform too.

They come out and inspect, even checking the consistsncy of the 20cm of space ro put the soil back over.

Can always grade the topsoil to give this required 20cm.

[figgy]

You will have to dig deeper one end to achieve the required fall.

 

Still use measurements to attain your correct fall percentage, it's more consistent over a distance of it perfect pipe.

 

The 20cm above the pipe, is than not a minimum? If so it can go deeper.

 

Figgy

[Aaz]

11.5mtrs is very strange figure for a leakage field on a septic - where did this come from?

 

As for fall, I'd keep it almost level throughout the run, get yourself a laser if it helps you, they can hired for less the £40 a day. The regs are there to stipulate where and how the soakaway should be installed but sometimes a bit of common is called for especially with the effluent from a septic tank - just ask the inspector why you need so much fall and if he's in a good mood he'll shrug his shoulders and tick the box, too much fall on this effluent will have a negative effect, its normally no deeper than 700mm below ground so not sure what the 200mm is you are referring to? Is the inspector saying how deep you have to be to the top of the the pipe or the stone thats around it?

 

Where are you based - this what i do so maybe I can be of more help, just pm me?

[robbiep]

If you say flat is 0° and 90° in a 1 in 1 fall - ie vertical then it's the percentage multiplied by 0.9

 

I think.

1 in 1 is 45 degrees. 1 fall in 0 length is 90 degrees (vertical)

[Jaymo]

Aaz

You have PM thanks

[Fisherman Mike]

Normally the trench would be dug level and the fall adjusted in the sand or peas shingle bed under the pipe. Much easier than trying to dig a trench to a gradient.

 

Is the pipe not perforated.?

[shootnfish]

As FM says dig your trench flat then knock pegs in every meter or so for your fall then put shingle in to the top of your pegs then lay your pipe on that then put your shingle around and over the pipe.

[STOTTO]

About .575 degrees, (tan .575 = 0.010035 x 11.5 = 0.115) metres or 11.5 centimetres drop over your 11.5 metre run or 1%. I’m going to lay down now!

 

Regards

[Aaz]

Normally the trench would be dug level and the fall adjusted in the sand or peas shingle bed under the pipe. Much easier than trying to dig a trench to a gradient.

 

Is the pipe not perforated.?

 

So over 100mtrs your shingle depth would be??

 

Always have the trench with the desired fall and the shingle depth will remain constant and as this is a leakage field for a septic no real fall is required, based on this you are correct

[TIGHTCHOKE]

 

So over 100mtrs your shingle depth would be??

 

Always have the trench with the desired fall and the shingle depth will remain constant and as this is a leakage field for a septic no real fall is required, based on this you are correct

 

Where do you get 100 Mtrs from?

[figgy]

That's the standard length of the soak away pipe for a sceptic tank for a average house. Can be double or more for a bigger system.

 

Probably why people are questioning the 11.5 meters length.

 

 

Figgy

[TIGHTCHOKE]

Thank you

[Jaymo]

Wow guys.

Some great knowledge and poss some dodgy maths but as Carol Vorderman is not a relative I can neither confirm or deny this.

 

The pipe we are using is 100 pvc pipe that has slashes pre cut on the underside and the drainfield as approved by the local authority after a soil test was deemed to be 42m divided into four trenches, but the digger went over this and so total length is now 46 m

According to my mrs she says longer is always better? Dont know what she is on about or implying.

 

Anyway thanks once again.

 

Jay

Edited November 13, 2014 by Jaymo

[Aaz]

That's the standard length of the soak away pipe for a sceptic tank for a average house. Can be double or more for a bigger system.

Probably why people are questioning the 11.5 meters length.

Figgy

There is no standard length for any size house I'm afraid figgy, the length of any soakaway/ leakage field is determined by the results of percolation tests. I questioned the 11.5mtrs as on a septic this would be rarely sufficient for any drainage to have any longevity, unless you had extreme drainage in the area required, nothing I've ever come across.

 

My figure of 100mtrs was plucked out of the air to highlight that if you kept a trench level and use the aggregate to create fall then by the time you got to 100mtrs (can't be bothered to do the math) you'd have negative shingle in the trench based on the falls required for 'most' drainage situations.

[STOTTO]

Wow guys.

Some great knowledge and poss some dodgy maths but as Carol Vorderman is not a relative I can neither confirm or deny this.

 

The pipe we are using is 100 pvc pipe that has slashes pre cut on the underside and the drainfield as approved by the local authority after a soil test was deemed to be 42m divided into four trenches, but the digger went over this and so total length is now 46 m

According to my mrs she says longer is always better? Dont know what she is on about or implying.

 

Anyway thanks once again.

 

Jay

Dodgy maths? Check this out; http://www.carbidedepot.com/formulas-trigright.asp

 

First box, side a: type in .115 = (1% in metres) over your 11.5 metre length.

 

Second box, side b: type in 11.5 (metres length of your run)

 

Hit: calculate

 

Third box: Ignore

 

Fourth box, angle A: Observe the angle; 0.5729⁰ (I was pretty close @ .575⁰)

 

Regards

Edited November 14, 2014 by STOTTO

[mark@mbb]

Drainage didn't come in 4mts lengths it came in 3' or a yard and the flu was 1 in 1 length of pipe which as a rule of thumb was one in 4 as the collars were pointed with soft hessain rope and sand and cement not plastic collars so a 4mt menthe would need a 4" fall at least and be laid on soft sand

 

Plus drainage was a bricklayers job not a plumbers as drains all started off as brick culverts

Edited November 15, 2014 by mark@mbb

[Fisherman Mike]

There is no standard length for any size house I'm afraid figgy, the length of any soakaway/ leakage field is determined by the results of percolation tests. I questioned the 11.5mtrs as on a septic this would be rarely sufficient for any drainage to have any longevity, unless you had extreme drainage in the area required, nothing I've ever come across.

 

My figure of 100mtrs was plucked out of the air to highlight that if you kept a trench level and use the aggregate to create fall then by the time you got to 100mtrs (can't be bothered to do the math) you'd have negative shingle in the trench based on the falls required for 'most' drainage situations.

Yes true but the drainage fall normally follows the relief of the land ....in short runs as in this case.."the bed and peg" method is the best way to maintain the shallow fall required..As the pipe is perforated I would be very surprised if the fall was that critical in any event. I too was surprised at the length of 11.5 m for a leach pipe on a septic system...would have expected it to be much more unless its going to a soakaway.