Kessil

head pressure calculations

jamie

jamie

Supporting Member
BARcard
hi everyone, so i have some questions about head pressure. i have a 108 gallon display with a 30 gallon sump.
water travels 4' up and through 3 90° elbows. then through 1 t fitting with some RFG nozzles. so i think i have 8FT worth of head pressure.
i have a vectra m2 pump currently running at 40%
the pump has a step down to a 3/4 tube since the return line look up has a 3/4 to a 1 inch attachment. i didnt go with the one inch since i would have to cut the 3/4 part off.
i've read a bunch of stuff articles on the matter. i don't know to to calculate the 3/4 tube since the flow chart is set for 1" tubes or pipes.

on the chart 8 feet of head pressure come to about 1200 GPH at 100% im aiming for around 3-5 times the turn over thats why i got it at 40%. is that correct?
anyone got a similar set up or know all about head pressure? any help would be appreciated. thanks
 
Are you just trying to figure out how many gph you're getting? During a water change hold a bucket in front of your nozzle and time how long to takes to fill a gallon
 
I would crank it to 80%, see if the corals can take it, and leave it there. More flow is rarely a bad thing, unless the corals are being ripped apart.
 
H2OPlayar said:
I would crank it to 80%, see if the corals can take it, and leave it there. More flow is rarely a bad thing, unless the corals are being ripped apart.
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On a return pump? I thought the current thinking was it's better to have less flow in the sump to give filtration time to do it's thing?
 
H2OPlayar said:
Less flow in the sump, but the sump is very wide so the flow rate is very low regardless of how fast the return pump is cranked.
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You're mixing velocity and flow rate.

If the flow rate out of your return pump is 2000 g/hr the flow rate into your sump is 2000 g/hr, and the flow rate through your sump is 2000 g/hr (Or at least it better be, or something will overflow.)

I agree, the velocity coming out of the pump is much higher than the velocity of the water through your sump. But the volume being moved is the same.

Volume being moved is what we look at as "turnover". The thought being the more volume (higher turnover) you're pushing through the sump, the less efficient your filtration is.

Whether or not that is true, I don't really know.
 
Your limiting factor is the 3/4". Can't tell from your description but it sounds like you have 3/4" all the way? If so, flow will be severely slowed down by the 3/4" piping.
Most flow charts are with the largest pipe sized at the outlet. So in the case of the M2, I believe that is 1 1/4" or maybe its 1"
 
The low end for turnover is enough water through the sump so your heater and filtration work. So, something over the flow rate of the skimmer.
The high end for turnover is just short of being noisy and causing micro bubbles.

Anything between those 2 points is fine and up to you.
 
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