Force & Moment : Discharge Head with Dresser Coupling

[Arline]

What are the forces acts on the discharge head for vertical pump ?

The discharge head is not having flange instead it is coupled to piping system through dresser coupling.

I would like to know how to calculate the forces exerting on the discharge head due to fluid back pressure (at shut-off condition).

Thanks,
Arline

 

[Artisi]

The force will be the area of the discharge pipe or coupling x the presure at shut-off.

Phitsanulok
Thailand

 

[PersianEng]

If you are going to use a dresser coupling for that application make sure to use "harnessed type". Harness is a number of tie rods that bridges over the coupling and takes the thrust loads so that you don't have to be worry for the coupling to come apart.

dresser couplings could tolerate some thrust load before starting to slide relative to the pipe. These load values are usually published by the coupling manufacturers. But again I think using a harnessed coupling makes much more sense.

 

[Arline]

Hi PersianEng,
I am using harnessed type of dresser coupling in my design.

At the time of fluid back pressure (shut-off conditions) does the nozzle sees only axial (Z-direction) thrust load or will we have any forces & moments in X & Y direction also ?

Thanks in advance

Prasad

 

[PersianEng]

Bending moment on discharge pipe may happen due to axial forces in the header transferred to the discharge at a Tee fitting or if there are bends in discharge pipe itself.

At shutdown if there are measures to prohibit transient and pulsating high pressures from happening, the is no problem. However, any sudden closure of valves including check valves triggers pressure spikes even higher than pump sht-off head. The best choice for check valve is a nozzle check valve that gradually closes but is still fast enough to prevent flow reversals.

The header itself shall be well designed and supported. The basic idea is that each spool has to be supported at two points along the pipe as one fix, one sliding type.