I am eager to find out whether there is a conservative standard rule for sizing a header, that either collects the deliverly lines of a number of pumps to a single delivery line or that branches a single suction line to individual suction line of the pumps. When I look at existing installations I get the impression, that the header diameter is relatively small in order to be able to digest the total flow without influencing the heads of the individual pumps. I can imagine that the number of pumps is of significance. Obviously there are CFD programs, that can enable one to find out what minimum diameter is required to minimize the mentioned influence. But as I am not in the position to do that I would like to find out if there are any safe conservative guide lines. 
 

For the suction header: Make sure that the lengths between the header/suction pipe connection and the header/pump connections is not only as short as possible but also of the same lengths (if possible). Magnetic pumps Your suction pipe has a certain diameter which must consider the total flow of all pumps that can run in parallel in respect of fluid velocity. Your header should be of the same size (diameter) than the suction pipe is, assuming that the suction pipe diameter is properly selected. That is only my rule of thumb, not more! Your suction header can be of smaller size but then we need to know a little bit more of pump flows, no. of pumps etc. As you wrote the number of pumps is of significance. 
 

Yobbo, my suggestion is you read a few basic pump hydraulic books so you understand the influence of pump installations and the overall system and pipe friction losses on pump performance, both inlet and discharge side. It is not a black science and not all that complicated for simple everyday pump installations. The flash wizbang bells and whistle all singing and dancing computor programme are Ok but not necessary for simple pump layouts like 3 or 4 pumps on a common suction or discharge line. 
 

Without going into the fluid mechanics, and assuming don't have an unnecessarily long header, a simple method might be to find a pipe diameter that equals the sum of the areas of all individual pump discharge nozzles, then increase by one pipe size.If you had a balanced configuration that would tend to combine flows as equally as possible (the header discharge is located near center of the header and the center of all pump discharge entry points), increasing by one size might be optional.At least it looks like it will give reasonable sized headers in most situations.  Breakeven point between throttling and VFD

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2011-11-02

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