DESIGN : DEAR MR PLUMBER
17
Art of knowing
They say a good engineer is one who knows what he doesn ’ t know , but one who knows where to find the information that he doesn ’ t know .
By
Vollie Brink , Pr Eng
One important element is still necessary : selfstudy , also called research .
I don ’ t think many plumbers and engineers know the ‘ power ’ that they have available to seek and find information .
I received a call from a person who wanted to talk to me about SANS 10252-1 . This person is an architect and he is involved with lecturing , but said that he finds SANS 10252-1 difficult to understand . I told him that SANS 10252-1 was not intended as a document for architects ; it was developed by engineers as a design manual for engineers .
I also told him that we register engineers in terms of the Engineering Profession Act , and that our Code of Conduct does not allow us to venture into the work of other professions ; therefore , we don ’ t do architectural design and so forth . However , we agreed that you don ’ t need an engineer to design the services of a house or for straightforward installations — for these , the plumber should be able to do the design and installation , for which his or her training and competency should be sufficient .
The deem-to-satisfy rules have been developed since 1977 to be the guide for the plumber to do the design and installation . The problem is that the boundary between the deem-to-satisfy rules and the engineering design has been eroded , and with the last few revisions , it has become even vaguer , such as that a deem-to-satisfy design shall not allow a gradient of less than 1:60 .
The latest revisions still to be approved and promulgated will hopefully solve the boundary issue and serve the plumber and the architect with better information in relation to the deem-to-satisfy design .
In another case , I was contacted for advice on the installation of a few small pumping systems in a building that is being refurbished . The new layout required new toilets and kitchens in positions that are not near to a services duct . Therefore , the solution was to provide small pump systems with a pump discharge pipe from the pump to the ceiling and then horizontally in the ceiling to an existing stack pipe , which was on a lower floor .
The pump had to ‘ lift ’ the effluent to the ceiling , run horizontally , and then drop again to a connection . The total horizontal length of the discharge pipe , which we call a pumping main or a rising main , is about 30 – 40m and the supplier of the small pump system presented the diameter of this pipe as 50mm diameter .
Another experienced plumber argued that the pipe size is wrong and that the 50mm diameter pipe must be enlarged to 100mm diameter after 6m from the pump .
I thought that this is a good example from which to learn . The 6m length is irrelevant in this case : the 6m refers to the maximum length of a branch pipe that does not require ventilation and is only relevant in the case of a gravity drainage system — not a pumping main .
In a pumping system , the discharge pipe has the same diameter all the way from the pump right up to the position where the pumping main discharges into a sump or a stilling chamber before it connects to a manhole and discharges into the sanitary drainage system .
The pipe system designer must calculate the duty point of the pump , which includes the static head ( lift ) and all the friction losses along the pumping main ( the diameter must be calculated to suit the flow rate of the pump ), right up to the discharge . This will be the hydraulic head , and the duty point can then be plotted on a pump flow chart and the appropriate pump selected .
The pipe diameter will be the same from the pump to the discharge point and the 6m has no bearing on this situation . The design of a sanitary pumping system is fully described in SANS 10252-2 . I just want to caution my plumber friends to be careful when installing a pumping system that must pump soil water ( raw sewage ) in a building that does not have a sump as prescribed in SANS 10252-2 , but which has a soil pipe containing sewage in a ceiling that runs above the workers in an office . I would not recommend it for sewage , but it could be considered for grey water . Happy plumbing . PA
Vollie Brink
Vollie Brink is one of the industry ’ s longest serving wet service engineers . He continues to serve on SABS committees and has been involved in the Green Building Council Star rating system . Brink continues to consult for various organisations while enjoying a wellearned retirement .
One important element is still necessary : selfstudy , also called research .
www . plumbingafrica . co . za June 2017 Volume 23 I Number 4