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Offline craigus12

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exam prep
« on: November 05, 2016, 01:58:07 PM »
hi there I'm studying for plumbing cert nov 2016 exam only a week away and have come across a question 5 in the june 2013 exam that has me confused.
Its a Q about fully vented modified stack. It has two WC's on a common discharge pipe which can be sized @ 80 mm (which is one of the questions) however when asking for the total FU's of the stack it is saying that the WC's are 4 FU's each when table 6.1 of asnzs 3500 says that WC's discharging from 80mm are 2 FU's.

Any help much appreciated
 

Linkback: https://www.plumbers.nz/study-base/70/exam-prep/2044/

Offline integrated

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Re: exam prep
« Reply #1 on: November 05, 2016, 07:35:20 PM »
I have seen this and remember also reading a technical report out of Australia some time ago how in the real world the wc discharging via 80mm worked better than the wc discharging via the 100mm - and I think this is the reason behind the higher rating for the 100mm because the 80mm works better and to a certain extent was self cleansing - there was a display of it as well where they used a clear perspex pipe to demonstrate it



I would roll with the 2 du's per fixture

Offline craigus12

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Re: exam prep
« Reply #2 on: November 06, 2016, 08:52:29 AM »
Thats what i went with when i answered the question but when i marked it off the answers it would be wrong? but it is correct according to the code.

Offline craigus12

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Re: exam prep
« Reply #3 on: November 06, 2016, 12:15:42 PM »
ALSO if there is three WC's connected are the first two at 2 DU's and the third at 4 Du or are they all 4 DU??

Offline integrated

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Re: exam prep
« Reply #4 on: November 06, 2016, 06:49:39 PM »
ALSO if there is three WC's connected are the first two at 2 DU's and the third at 4 Du or are they all 4 DU??


only a max of 2 wc is allowed at 80mm - so to get three in there you would have to go to 100mm at which point you are now 4du's per wc

see 7.3.4

This also relates to your initial question where if sizing for 2 wc only then 2du's in 80mm dia - more than 2 wc then 4du's in 100mm dia


Depending on what else is connected to the stack then that may determine the correct answer - are there other wc's connected elsewhere?  If so then that would require the use of 100mm dia pipe and hence 4du's - if not then I say the boards exam answer is wrong and it should be 2du's.

Offline craigus12

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Re: exam prep
« Reply #5 on: November 08, 2016, 06:12:24 PM »
thanks for the reply

so if you have 3 WC's can the first two be piped in 80 mm then the pipe size increased to 100mm after the second WC making the first two at 2 du's and the third at 4 du?

or am i just looking into it to much? they always ask to state the minimum pipe size according to the code.

Offline integrated

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Re: exam prep
« Reply #6 on: November 08, 2016, 09:48:07 PM »
I think you are right - b = 100mm, c = 80mm

a - 100
b - 100
c - 80
d - 600
e - 450
f - 2500
g - 600
h - 40
i - 65
j - 50



LOL - how did i do?

Offline craigus12

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Re: exam prep
« Reply #7 on: November 09, 2016, 07:04:41 PM »
all right but the last answer, was 65 mm

so what way do you think i go about it.
I'm thinking stay with the code and 2 wc's = 80 mm and 2 du each,. 3 wc's  = 100 mm and 4 du each


Offline integrated

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Re: exam prep
« Reply #8 on: November 09, 2016, 08:45:13 PM »
well that is interesting because my last answer was based upon total stack du's = 56 which is based on the wc's discharging to 80mm at 2du's for the first two

56 du's is the max permissible for 50mm dia vent

so if their answer is 65mm dia vent then they have allowed for 4 du's on the wc's which means they are sizing them at 100mm dia which then makes the pipe sizes for the discharge pipe (c) in the question wrong

so I think they have definately got the answers wrong

it is either 56du's for the stack + 50mm vent size + 80mm for the first two wc's at 2du's each

or

64du's for the stack + 65mm vent size + 100mm for the wc's at 4du's each



I think the former :)

Offline craigus12

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Re: exam prep
« Reply #9 on: November 10, 2016, 05:40:37 PM »
there answer for total du's is 80 du which is allowing all wc's to be 4 du.
i will answer it how i read it in the code and see how i get on hopefully it doesn't come down to needing 2 marks lol
only 2 days to go ???

Offline integrated

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Re: exam prep
« Reply #10 on: November 10, 2016, 07:51:36 PM »
Yeah I dont think it is anything to worry yourself over - good luck and all the best for the exam!


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