Recently one of our clients gave us a copy of their piping standards and said that we are to follow it to the letter unless we can make a case as to why we shouldn't. The problem is that we are installing an HCL purification unit on a very small footprint. The client wants 10 diameters of straight length to the suction of every centrifugal pump. It appears they have copied this standard from a pump manufacturer's design manual. The problem is we do not have the room. The fluids being pumped are cooling tower water, 18%, 22% and 99% HCL. I'm proposing (per your articles and other publications) that I keep the straight length to 5 diameters where space is limited. What is your opinion?
Have an insight or suggestion?
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Re: Suction piping diameters
14 March 2007 at 1:29pmThe rule of thumb for suction piping to a centrifugal pump is 5 to 10 diameters of an uninterrupted straight run of pipe to the suction nozzle. The 10 times the diameter is the safe extreme and is required on small diameters. When you start getting up to about 6 inch diameter or more, you can start cutting it back towards 5 diameters.
You mention that you are installing the system on a small footprint and don't have much room. I would question whose decision that is? If it is the customer's decision, he should be made aware that it is inconsistent to the requirement for 10 diameters. If it is someone else's requirement, this should be discussed with the end user.
The problem is simple. Anything less than 5 - 10 diameters has the possibility of creating turbulence in the suction line with the resulting effect of air entrainment becoming an ongoing problem with the pump operation for years to come.
On my website, there is a complete article on this topic you may wish to review at www.practicalpumping.com.
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