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Pump Inlet/Outlet Nozzle Erosional Effect
2

Pump Inlet/Outlet Nozzle Erosional Effect

Pump Inlet/Outlet Nozzle Erosional Effect

(OP)
I need to select an ANSI pump for a water treatment plant, with the following problem:

According to the Process data we have calculated, the pump differential and flow rate, we have to select a 1x1.5 pump (outlet x inlet nozzle diameters).

However, due to the nature of the fluid we are handling (water + suspended solids) and requirements of our client, our suction line is 3".

Then, in order to interconnect the pump with this pipe, a 3x1.5 reducer is required and the velocity in the reducer and inlet nozzle is too high (22 ft/s).

According to API14E, the velocity should not exceed an erosional limit (in this case 20.25 ft/s).

Also, this reducer introduces a high pressure drop (due to the kinetic and frictional terms).

We have tried to find a pump with bigger inlet and outlet nozzles, without success.

Is there any harm in the pump and/or these fittings if we maintain this or higher velocities?

Regards,

Alberto

RE: Pump Inlet/Outlet Nozzle Erosional Effect

The change in fitting size, even a drastic change, is pretty common between the suction line and the pump inlet/outlet nozzles that I've seen.  I've also wondered about this but given the pump vendor sizes these nozzles, in light of the potential pump capacity, I've essentially decided they know what they are doing.

As far as the NPSHR, that would also be included when they do their testing and post the NPHSR figures so I have not included the effect of that reducer in my NPSHA calculations.  It's a good question though.  One other reason I don't include the reducer is that when I do these calculations, it's in the early stages of engineering and we have no idea what the pump suction nozzle is for a diameter.

RE: Pump Inlet/Outlet Nozzle Erosional Effect

td2k is right, one thing I would add is to make sure your operating ranges for the pump are within the range for the pump.  If the manufacturer doesnt have them available for you, stay +20 and - 40 percent of bep.  I have seen people design using the pump outside of its range and they get extreme flows, which are beyond the nozzle design for the pump as designed by the manufacturer.

BobPE

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