Rated Capacity for a Pump.

Rated capacity is the load you can place on a pump and have it last for it's design life.

So a pump rated for 100 GPM, with a certain fluid, with a 2 year warranty will, on average, last for 2 years. So 10,000 pumps, some will last longer and some shorter than 2 years. maker replaces those that break, so he tries to make sure he overdesigns the pump so the highest possible % endure.

Let us say you need 200 GPM, simple, run the pump faster. You may have to run it 2.4 times as fast to get 2 times the output. So will it now last 2 years? Probably nor, bearings are runing at 2.4 times rated speed, pasrts are stressed. You may have excess cavitation by the occurance of negative pressure in some places, this can cause pitting as cavities collapse with a focussed spherical collapse wave.

so you should get a 200 gpm rated pump, as the 100 might breal in 2 weeks and warranty will be voided

So you get what I mean

don't want to run pump faster to get more gpm, change the impeller. increasing speed will cause cavitation if increased beyond designed operating parameters. design capacity is what it calculates to on paper when the engineer designs it, rated capacity is what it will deliver under certain condition, i.e; suction lift and head pressure. normal operating capacity would be pretty close to it's rated capacity but given variance for the conditions under which it operates when installed in whatever system you're installing it in. I'm not an engineer per se but have turned wrenches and worked on stuff like that for 30+ years. know what you're requirements are then find a website or book with different pumps and pick what you need. better to have a little more (oversize) than not enough. this will allow for future additions/modifications.

Very late response.

The manufacturer guarantees performance at one point on the curve for the pump. This is the rated point and includes the rated capacity, differential head, NPSHr (if requested), power and efficiency.