You fellas might be in over your heads here. If you don't know what NPSH is, then you shouldn't be engineering projects with delicate running parameters. There is a gross lack of info here, to include lack of monitoring devices, (thermometers, flow recorders, pressure gages, etc.), unsufficient mention of psi and temp at various points of interest, whether suction pressure is positive or negative, and what is their values, the list goes on and on.
What you need to do is not replace parts, as it will possibly repeat at a cost, but find and correct the problem.
If the owner of this site is compassionate, or has deep pockets, s/he, or they might incur the cost of refinement, as it WILL be their equipment upon completion.
Just my thoughts at this point.
No sweat!
One step at a time, first solve the pressure drop, and he is working on it and I believe pressure drop causing cavitation is what NPSH is all about, correct?
Next, run the boiler and check vitals, and check the barometric.
There's no re-design going on. All specs are being looked at to meet GPM needs to all equipment.
