I calculated the line resistance and matched the system curve with the pump curve, but I found a mysterious 20 psig drop in the system that cannot locate.  I'm guessing it is at the junction with the other pipe the line discharges into but I can't find a good equation to calculate the drop.

The line looks like this

-------------------------------> 8", Pstat = 32 psig, 5 ft/s, water
       ^
       |
       |
       |
     3", Pstat = 24 psig, 5 ft/s, water, Velocity pressure ~ 26 psig

Can this junction create a 20 psig resistance in the 3" line?  The 3" line comes into the 8" line at a right angle.

Made a mistake...

The pump discharge is 148'head at 120 GPM on the 3" line.  After 114' of pipe, a check valve, butterfly valve, a globe valve, 6-90 bends, and a 20' elevation, the pressure drop is 11.1 psig (25.6 ').

-------------------------------> 8", Pstat = 32 psig, 5 ft/s, water
       ^
       |
       |
       |
     3", Pstat = 52.9 psig, 5 ft/s, water, Velocity pressure ~ 26 psig.

The velocity pressure I had to take into account since the flow is going perpendicular to the 8" pipe.  Did I do this wrong or am I on the right track?

The new 2009 edition of the Crane TP410 addresses Tees and Wyes in a much more comprehensive method that takes into account the flows in each leg and the sizes of the pipelines in the tee. The method was developed from the Idlechick book with comparison to Don Miller's "Internal Flow Systems" book. The 2009 edition should be released within a few weeks.

You can also model your system in software such as PIPE-FLO or Crane Flow of Fluids to help troubleshoot.

An extra 20 psi drop is pretty large, so you may have a problem with partial pluggage. I once found a large bolt lodged between the seat and disc of a 150# steam pressure control valve at the mill I used to work at, and massive pluggage of orifices on a steam dryer that reduced steam flow by 25%.

You get what you inspect, not what you expect.

The 3 inch line tee into an 8 inch line would not normally account for any significant pressure drop for this case.

However, the installation may have been bad, for example, if the 3 inch pipe protrudes into the 8 inch pipe by 7-1/2 inches, then you have a big restriction there, and all looks well from the exterior.  There are numerous other errors that could cause high pressure drop in the line, about as many as you can imagine.  This kind of poor installation work should be rare, but I have seen worse.

Physically what was used for the junction between the 3" and 8" lines? Was it a reducing tee,an O-Let type connection, or a fabricated stub in connection?

The pressure drop seems high for a tee or stub in connection but if the cut-out on an O-Let was much smaller than the nominal 3" size (which is not uncommon) then that might be a possible source of the problem.

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