A Dynamics of Water Question

[rossco]

Thinking about the design of a new tank in the future, I intend to have an overflow/sump/return pump, closed loop, and a couple of streams.

I have noticed a few top entry water sources (pipes squirting into the tank from the top). :-?

Question - if you have a below-the-tank sump and want to reduce the head pressure as much as possible from the sump to tank to increase the throughput of water, where should the exit of sump return pipe be in the tank - squirting into the tank at the top or can it be through the bottom increasing flow around rockwork?

I guess the physics question is - does it make any difference whether it is atmospheric/gravity pressure (top) or water pressure (bottom) resistance ie is the head height similar regardless of where it exits if the top of the respective water levels (main tank and sump) is the same?

[slappers]

where should the exit of sump return pipe be in the tank - squirting into the tank at the top or can it be through the bottom increasing flow around rockwork?

if you put the return from the sump to the bottom of the tank ??

say you have a power cut your whole tank will empty into your sump

[rossco]

Yup, is a risk but I was going to rely on a non-return valve...

[chimera]

no difference, it all depends where you put your sump (in relation to the display) as opposed to where the return is fed back into the display. two main things to consider, static head (gravity) and dynamic head (friction). what you're interested in (in regards to the amount of flow you require) is the combined value of both or total dynamic head. static head is from the top of the sump water level to where the water is being pumped in (gravity plays its role here) so no difference where the return goes as it has gravity to the surface of the display no matter what. dynamic head includes resistance/friction based on things like 90 degree elbows, valves etc. total dynamic head is kind of both - the total resistance to flow caused by gravity and friction. at least thats how i understand it.

personally i would always go up and over. that way you can do away with worrying about reverse syphoning and easily add a small hole to break the syphon should the return pump be switched off or fail.

[KP]

In theory there is exacty the same amount of work required to pump the water in either case. The extra friction in the pipe and additional bends would mean a pipe going to the top needs more energy.

[chimera]

thats what i said oh and up and over also means its easier to change the location of where flow enters back in the tank if you ever wanted to change. for example, say you increased flow, you might then decide to T it off and use to inlets to the tank (or 2 x sea swirls if you're game )

[KP]

haha, I was too slow :lol:

[chimera]