Pump input location?

[Lavoisier]

Does anyone know what the minimum distance should be from the water level and a pump (Hammerhead Gold) input location. I want to keep the closed loop pump as high up the tank as possible without sucking air into the pump from the surface. Here is the design:

Thanks, ahead of time.

 

[JonnyQuest]

An equation to determine minimum submergence to prevent vortex formation is

S = D + 0.574 x Q / D^1.5

S - Minimum submergence (inches)
D - Diameter of pipe (inches)
Q - gpm

Use with caution. Experimentation would be preferred before you drill a hole in your tank.

I assume you will have a strainer on the inlet? This should help reduce vortex formation. Can you put an elbow facing down on the inlet? Any reason why you want the pump suction as high as possible?

 

[Lavoisier]

I must be misplacing a decimal somewhere!

D=1.5 inches
Q=91 gpm (Hammerhead at 5500 gph/60)

gives me 29.93 inches. I hope I should be at 3"

I will have a strainer and can use an elbow facing down. I want it high for two reasons. First, is safety--if a leak occurs (I only drain down to the bulkhead). Second, is less head loss, so more efficient use of the pump.

 

[JonnyQuest]

I think the correlation is only good for inlet velocities between 2-8 ft/s, which you are more than twice that. At 3 inches from the surface, at your velocity, a vortex is almost certainly going to form.

Placing the pump inlet much lower, the head loss should be minimal as it will be only the frictional loss of 1-2 feed of pipe (not 1-2 feet of head). For a closed loop system there will only be frictional losses, there is no static head (the pump inlet and outlets are under the same water level).

You should consider increasing your pipe sizes as the velocities are very high using 1.5" PVC pipe and therefore frictional losses are expected to be high as well.

As far as leaks, I would assume you would catch them before the tank drained too far. Just make sure you have a valve on the inlet (I think you do) so you can service your pump if necessary without draining your tank.

 

[Lavoisier]

Would there be a disadvantage to keeping the pump up higher and using the 90 degree elbow with 3 or 4 inches of pipe downward? or would that just create a siphon to the bottom of the pipe?

I was thinking of 2" pipe?

 

[Jeff000]

With so much pipe above your tank it's going to be a nightmare to work in.

 

[JonnyQuest]

The one disadvantage that I can see is a potential lower flow rate with the pump placed closer to the top fitting (sharp change in direction). You need to keep in mind that a high velocity discharge region will occur at the outlet of the pump. It will take some pipe length before it slows down and utilizes the entire cross-section of the pipe. In other words, the water velocity does not instantly get reduced at soon as the pipe diameter increases. To have a turn so close to the this high velocity jet from the pump outlet may restrict the flow more as compared when the velocity profile is more uniform across the full cross-section of the pipe further away from the pump outlet.

 

[Lavoisier]

That is helpful. How much distance do you think I will need with a 6000 gph flow? A broken seal in a pump is a real risk and I do some traveling so it could happen with me gone. The higher my pump the less chance of a catastropic event. I have had two in the 40 years I've been in the hobby. I do not want another. I will accept less flow for less risk. I am interested in your thoughts.

 

[JonnyQuest]

General rule of thumb is 10x pipe diameter to achieve a more or less uniform velocity profile.

I know one time is one too many, but 2 in 40 years is a relatively small risk. Does the failure cause a slow leak or is it major leak when it occurs? Does the pump stop when a failure occurs or does it continue to pump while leaking water?

Would you consider a preventive maintenance schedule of replacing the pump seals every 5 years to reduce the risk of failure?

 

[Lavoisier]

General rule of thumb is 10x pipe diameter to achieve a more or less uniform velocity profile.

I know one time is one too many, but 2 in 40 years is a relatively small risk. Does the failure cause a slow leak or is it major leak when it occurs? Does the pump stop when a failure occurs or does it continue to pump while leaking water?

Would you consider a preventive maintenance schedule of replacing the pump seals every 5 years to reduce the risk of failure?

Actually, the two different catastrophes were two glass joints that sprang leaks, not a pump seal. (The last one was the impetus to for my current build--the seams will not give out on this tank!!). I do understand that the risks are small but as you said one is too many and if I do not have to take the risk I'd rather not.

Having said that, I believe I can keep the pump at 3-4 inches below the water level and run the supply pipe up another foot to smooth the flow then go over and down to the SeaSwirls. Does that plan sound like it might solve my problem and my paranoia?!

Thank you for input...alot! (I never saw this info or warning from Reeflo).

Yes, I do believe in and will continue to do annual pump maintenance and five years sounds pretty good to replace the seals.

Regards