Pro/Forums - View Single Post - Two pumps config

myv65 · 10-26-2002, 10:25 PM

This is not that difficult a situation. You can think of pumps as devices that add pressure to a system. The amount of pressure they add varies with the flow rate produced. If you put two identical pumps in series, the maximum possible pressure you can develop essentially doubles while the maximum possible flow rate remains the same as for a single pump. If you put two identical pumps in parallel, the maximum possible head remains constant while the maximum possible flow rate doubles.

In real-life systems, you always have some flow resistance. This means that a pump will never produce its peak flow (which only exists at zero head). In a typical system, you'll normally not see much performance difference between the two options. In restrictive systems you may see a nice boost from running in series. In rare instances, the difference may be dramatic. Heck, in open systems with enough vertical lift, you routinely see multiple pumps in series (lift stations). I'm now talking more on the industrial side of things.

For simplicity's sake, series piping is easiest. The impellers in these pumps are open enough that if a pump fails, you'll still generate enough flow to protect a system. The "dead" pump becomes just another resistance in the system at that point. In parallel systems, you really ought to have check valves on the pump outlets otherwise a dead pump will allow a short circuit and effectively kill the flow going through your radiator and block. This setup handles a failed pump better because the failed pump doesn't restrict the flow of the working pump. Check valves are not zero resistance either, though, so also impact overall flow a little.

Airspirit's comment about working better pushing than sucking only really applies if the suction pressure drops to the point of cavitation. So long as cavitation is avoided, a pump merely adds head to a system irrespective of its location within that system. Ultimately most of the energy consumed by the pump shows up as thermal energy in the fluid, so keeping all pumps ahead of the radiator offers some slight benefit. This point pales versus air temperature fed to a radiator. If putting the pumps both ahead of the radiator means using warmer air for the radiator fan, don't do it. Keeping the coolest possible air feeding the radiator takes priority.

Here's a link to a file explaining the stuff in a little more detail. Head on down to page 7 for more info on series vs parallel operation.

10-26-2002, 10:25 PM	#6
myv65 Cooling Savant Join Date: May 2002 Location: home Posts: 365	This is not that difficult a situation. You can think of pumps as devices that add pressure to a system. The amount of pressure they add varies with the flow rate produced. If you put two identical pumps in series, the maximum possible pressure you can develop essentially doubles while the maximum possible flow rate remains the same as for a single pump. If you put two identical pumps in parallel, the maximum possible head remains constant while the maximum possible flow rate doubles. In real-life systems, you always have some flow resistance. This means that a pump will never produce its peak flow (which only exists at zero head). In a typical system, you'll normally not see much performance difference between the two options. In restrictive systems you may see a nice boost from running in series. In rare instances, the difference may be dramatic. Heck, in open systems with enough vertical lift, you routinely see multiple pumps in series (lift stations). I'm now talking more on the industrial side of things. For simplicity's sake, series piping is easiest. The impellers in these pumps are open enough that if a pump fails, you'll still generate enough flow to protect a system. The "dead" pump becomes just another resistance in the system at that point. In parallel systems, you really ought to have check valves on the pump outlets otherwise a dead pump will allow a short circuit and effectively kill the flow going through your radiator and block. This setup handles a failed pump better because the failed pump doesn't restrict the flow of the working pump. Check valves are not zero resistance either, though, so also impact overall flow a little. Airspirit's comment about working better pushing than sucking only really applies if the suction pressure drops to the point of cavitation. So long as cavitation is avoided, a pump merely adds head to a system irrespective of its location within that system. Ultimately most of the energy consumed by the pump shows up as thermal energy in the fluid, so keeping all pumps ahead of the radiator offers some slight benefit. This point pales versus air temperature fed to a radiator. If putting the pumps both ahead of the radiator means using warmer air for the radiator fan, don't do it. Keeping the coolest possible air feeding the radiator takes priority. Here's a link to a file explaining the stuff in a little more detail. Head on down to page 7 for more info on series vs parallel operation.