Dirty water tank not getting filtered?!

[limey1]

Im puzzled at the filtration system in place. The tank capacity is around 10,000 U.S gallons. There is a 1/2 hp pump with a 1 1/2 inlet and outlet, drawing water from the bottom of this tank.(7ft head)To complicate matters, this is then going through a single stage, 5 micron filter and then returns to the tank through 70ft of 1 1/2 pipe. Im a complete novice at this kind of thing but my numbers tell me the rating on this pump is incorrect. p.s there is a gauge on the outlet side reading 10-20 psi. Im trying to research this more but any assistance would be appreciated

 

[BigInch]

What's the flowrate?

How far from tank to pump and pump to filter?

What is the pump height in relation to the tank? Is the pump at the same bottom of the tank elevation, higher or lower? How many feet?

How high is the highest point on the return line (in relation to the pump, as in feet higher than the pump elevation?

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[limey1]

Flowrate is 36 gpm, new filter, tapering off to 18 gpm (reading 25psi differential pressure). Distance from tank to pump/filter is 6'. Pump is 4' higher elevation in relation to bottom of tank. Return pipe has max elevation of 3'above the pump and is approximately 65' away.

 

[BigInch]

Yup, looks like not enough pump power for that filter, possibly not enough pump differential head too. I explain..

For that 25 differential pressure (loss) at the filter, plus another 10 psi or so for pipe losses, you'd need at the least a 1 HP with very good pump efficiency. I'd suggest a minimum of 1.25 HP (allowing for somewhat lower efficiency).

While you're at it, be sure the pump has a rated differential head of at least 80 feet at that flowrate of 36 gpm, which indicates a discharge pressure in the range of 40 absolute minimum to 50 psig will be needed.

http://virtualpipeline.spaces.msn.com

"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein

 

[limey1]

Thanks for the info BigInch. I found a 1 1/2 hp pump through AMT pumps which seems to fit my requirements. Im going to do a trial with a 50 micron filter vs 5 micron as the latter is kaput after 2 1/2 hrs. Im thinking maintaining flow to be more important in this application than level of filtration. Multi stage is the future plan but Im hoping to see some benefit from at least trying this approach in the meantime.