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RedR TSS gravatar image
RedR TSS

We are getting onto dangerous ground here, and the short answer is no. In theory one could design a system in which the frictional losses “burnt off” the excess head – but this I suspect would need a far smaller pipe diameter, may well give rise to excess velocities leading to scour, and would in practice almost certainly self-destruct for a whole host of reasons (air-locks, human error, water hammer etc.). This is an excellent example I am afraid of where advice at distance is possibly dangerous. Our colleague in Kyrgyzstan needs an experienced engineer on site. That has a cost – but so does 6km of 90 mm pipe. I will try to find time to play with the limited figures we have received, but would really need the full pipe run profile to give more definite suggestions. I also have difficulty understanding why there are problems with break pressure tanks.

Also given it a bit more thought. The preferred option would always be a properly designed system with break pressure tanks etc... Such a system would be designed to have pipes running full with velocities in the safe range (no deposits, no scour). If they really can not have break pressure tanks and need to use 90 mm pipe, they will have to design the system to run almost like an open channel – with the pipe never running full and frequent tees in the pipe with say 2 metre lengths of open ended pipe sticking up at high points to ensure that there is some guarantee that the pipe will be destroyed by excess positive or negative pressure. Another alternative would be to use a smaller diameter pipe – but having looked at the figures while 90mm is too big, 63mm is too small. I do not know if there is an intermediate size available there. But relying on pipe friction to keep the pressure in the pipe within limits is dangerous in my view – one blockage, severe water hammer etc and the pipe could explode.# Hope they find a good solution which addresses their needs safely. Regards Tim Foster

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No.2 Revision

We are getting onto dangerous ground here, and the short answer is no. In theory one could design a system in which the frictional losses “burnt off” the excess head – but this I suspect would need a far smaller pipe diameter, may well give rise to excess velocities leading to scour, and would in practice almost certainly self-destruct for a whole host of reasons (air-locks, human error, water hammer etc.). This is an excellent example I am afraid of where advice at distance is possibly dangerous. Our colleague in Kyrgyzstan needs an experienced engineer on site. That has a cost – but so does 6km of 90 mm pipe. I will try to find time to play with the limited figures we have received, but would really need the full pipe run profile to give more definite suggestions. I also have difficulty understanding why there are problems with break pressure tanks.

Also given it a bit more thought. The preferred option would always be a properly designed system with break pressure tanks etc... Such a system would be designed to have pipes running full with velocities in the safe range (no deposits, no scour). If they really can not have break pressure tanks and need to use 90 mm pipe, they will have to design the system to run almost like an open channel – with the pipe never running full and frequent tees in the pipe with say 2 metre lengths of open ended pipe sticking up at high points to ensure that there is some guarantee that the pipe will be destroyed by excess positive or negative pressure. Another alternative would be to use a smaller diameter pipe – but having looked at the figures while 90mm is too big, 63mm is too small. I do not know if there is an intermediate size available there. But relying on pipe friction to keep the pressure in the pipe within limits is dangerous in my view – one blockage, severe water hammer etc and the pipe could explode.# Hope they find a good solution which addresses their needs safely. safely.

Regards Tim Foster Tim