Best Return Pump?

[ben1987]

ocean runner is a good solid pump ui doubt you will be dissapointed

 

[Stampos]

ocean runner is a good solid pump ui doubt you will be dissapointed

I hope so as well

 

[rabbut]

Actually, restrictive losses are a big issue if you are pushing water under pressure though the pipe. Think about external filters. Aff 6ft of hose and the flow from most motors will half as a result. We are pushing more flow at more pressure though the same size pipes, so resistive losses will be greater here...

I'd have personally had the OR6500, but that OR3500 should be ok for most set-up's that don't require heavy duty skimming from a skimmer in the sump (pred tanks or ULNS set-up's for example)

All the best
Rabbut

 

[ben1987]

pretty much bang on for the 5 or 6 X sump turnover for an average set-up if my maths is right

 

[rabbut]

Aye, without allowances for a long return run....

Flow at 110cm head height = 3500lph

Allowance for resistive losses from a 5ft run of pipe to the outlet and a 90 degree elbow, and you a looking at something more like 2500-2000lph

The tank is 425l

best flow scenario, would be something like

2500/425 = ~ 6.8X an hour

Worst flow scenario

2000/425 = ~ 4.7X an hour

That's adequate for most set-up's. Personally, I've always liked to "overcook" my filtration and work on an idea of more is better, so more flow than recommended for me is always desirable. However you have the minimum required flow there and the pump will do the job you want it to do perfectly well unless you have a set-up where you require a heavy filtration system

All the best
Rabbut

 

[jtnova13]

I guess also it depends on what size piping you are running. I run 3/4" return lines. Based on bernoulli's principle, you will still move the same volume of water, just the velocity and pressure will differ. Pv/T = Pv/T

I think ,though, that when you are calculating head loss... unless the horizontal runs are like 60 feet, you will run into negligible losses from horizontal runs. Valves also have some pressure drop, also negligible.

 

[Stampos]

Hey guys,

I just wanted to thank you all for your advice

I set the tank up today (took 12 hours!) And started it up a little while ago. The piping that came with the tank could use some adjustments but for now its running fine with polywool in the sump to clear up the murkiness from the sand.

The pump itself seems pretty powerful, it comes out of the outlet and can move the sand 2' below (again, needs adjusting) but on the whole I am over the moon, so thank you

Simon

 

[rabbut]

I guess also it depends on what size piping you are running. I run 3/4" return lines. Based on bernoulli's principle, you will still move the same volume of water, just the velocity and pressure will differ. Pv/T = Pv/T

I think ,though, that when you are calculating head loss... unless the horizontal runs are like 60 feet, you will run into negligible losses from horizontal runs. Valves also have some pressure drop, also negligible.

Well, no, the roughness of the pipe though which the water is flowing will affect how freely the water will flow and how much resistive loss there is. Resistive losses for kinetic fluid flow calculations must involve a frictional constant for the pipe being used to move the water. Any equation without that isn't tanking into account resistive losses due to friction in the pipe, the main cause of the pressure and velocity of flow drop

Taken from pipeflow.co.uk

Calculating the fluid head resistance

Fluid head resistance can be calculated from h = f (L/d) x (v ²/2g)

where
h = head loss (m)
f = friction factor
L = length of pipe work (m)
d = inner dia of pipe work (m)
v = velocity of fluid (m/s)
g = acceleration due to gravity (m/s ²)

Effect of the inner roughness of the pipe

The inner roughness of the pipe can create eddy currents. This increases the friction between the pipe wall and the fluid. The relative roughness of the inside of the pipe is used in determining the friction factor to be used.

Relative roughness = Inside pipe roughness/Inside pipe diameter


The average inner roughness of commercial pipes:

Rigid P.V.C. 0.0200 mm

So, we have a 35mm pipe, so, the frictional constant is as follows;

relative resistance = 0.0200/35 = 0.005...

you trace the frictional constant off the chart, to get about 0.03 (note logarithmic chart)

Now, resistive losses are calculated as follows

h = f (L/d) x (v ²/2g)
= 0.03 (1.5 / 0.035) X ({1.2*1.2} / {9.81*9.81})
h = about 19cm

A 19cm head height will make a hundred to a couple of hundred litres an hour difference in flow rates... You can then kill a few hundred lph more with a 90 degree elbow. Granted, the long length isn't too much of an issue, but elbows are a major flow killer.

It's late at night, and I didn't want to do too much typing, so I hope you know how to calculate pipe area and the velocity though the pipe given the volume per unit time and the area of the pipe. Also, I'll assume you can convert between units to get what is needed for the maths

All the best
Rabbut

Edit, woops, one too many zero's here and there in copying from paper to typed text