[FirlandsFarm]

Hi everybody, first post so apologies if wrong forum etc.

I have a swimming pool with a floor cleaner that is powered by using the pump output return flow to create a thrust jet that propels it around the floor. I have a spare pump (identical subject to w&t) and want to increase the thrust but cannot decide if I should plumb it in series or parallel. I understand that series increases the pressure and parallel increases the flow but I find that difficult to visualise in my tiny mind!

Is more thrust more flow or more pressure? Only the design of the pipe/pumping layout is variable, everything else such as all pipes used etc. are determined by existing union sizes.

[kaya]

i didn't know how to explain so made a rough plot

say black curve is the pressure vs. flow rate curve for your pump. red line would be the combined one if you connect two similar pumps serial(togather they will pump the water higher), and blue dashed line would be the parallel configuration(togather they'll pump more water).

since Thrust is ~ velocity^2, you would like to have more mass flow, and to increase this you have to know at what operation condition you're operating.

say you current system pressure is a, and flow rate is â, then connecting them in serial perhaps would be a better idea because you're pumping the water high(there is a lot of pressure in the system already). if your pressure is b(you pump is connected to a hose thats at the same level, not much height difference between inlet and outlet), then you would benefit more from combining them in parallel way. that won't double the flow rate becuase system pressure will increase but you'll surely gain more.





edit: ps. jet nozzles often create a lot of pressure when they are loaded.

[FirlandsFarm]

Thanks for your reply Kaya but I'm still not clear.

Height is between zero and insignificant. The pumps will be at ground level, the outlet feed from the pool to the pump is approx 2ft above the pump so gravity provides the supply. The end of the return pipe is effectively also at ground level but rises and falls approx 4ft to gain access over the side of the pool so I am assuming it is effectively neutral.

To me thrust (and I'm using the term as a layman i.e. simply as a force to move a body) is a combination of flow and velocity. I have no flow target nor pressure/height target, my only target is to move the body (the pool cleaner) as fast as possible (if it moves it too fast I will fit a by-pass circuit to regulate it).

All pipework is of identical diameter in either set-up.

Once the two flows of the parallel set-up have merged back into the one pipe leading to the cleaner would there be much difference in characteristics of the flow back to the cleaner than in the series set-up?

Thanking you for your continued help

[kaya]

ok give me the exact model of the pump and measure the flow rate with a bucket or something at the cleaner exit [i.e. 10 liters per 10 sec sth like this] then I'll give your answer