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Swimming pool pump mystery


RonD

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Its the flow rate of the pump, and of course filter has to be rated at least as high as the pump's flow rate

40,000gal pool should have a pump/filter rated at 60-80gal a minute, which would usually use a 2"(73gpm) to 2.5"(120gpm) pipe size
Pump inlet/outlet pipe size must be the same as filter inlet/outlet pipe size

1HP is fine

General speaking you want all the water in the pool to run thru the filter every 8 to 10 hours
40,000gal / 10hours = 4,000gal per hour
4,000gal / 60min = 67gal per minute as minimum flow rate
8 hour full exchange would need 83gpm flow rate

If there are any restrictions, that will cause pressure to build up at the pump impeller/blades and that causes cavitation(air bubbles to form in the pump)
Think of a boat propeller pushing the boat thru the water, when you accelerate the motor to push the boat faster cavitation starts, forming air bubbles behind the boat, but once at speed cavitation should stop unless prop is under size for the boat, lol, the high pressure behind the prop, forcing the boat forward, is gone
 
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RonD

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Yes, if its on the internet it must be true :)

But I did work one summer in high school for a pool "plumber", pretty much all I did was hump around pipe, pumps and filters, but I did watch and listen, I love mechanical stuff, and listen to him bitch about pipe size and flow, and "what the F#!% was that last guy thinking", lol
But in fairness I didn't remember exact flow rates and pipe size, so.........................
 
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Eddo Rogue

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Its the flow rate of the pump, and of course filter has to be rated at least as high as the pump's flow rate

40,000gal pool should have a pump/filter rated at 60-80gal a minute, which would usually use a 2"(73gpm) to 2.5"(120gpm) pipe size
Pump inlet/outlet pipe size must be the same as filter inlet/outlet pipe size

1HP is fine

General speaking you want all the water in the pool to run thru the filter every 8 to 10 hours
40,000gal / 10hours = 4,000gal per hour
4,000gal / 60min = 67gal per minute as minimum flow rate
8 hour full exchange would need 83gpm flow rate

If there are any restrictions, that will cause pressure to build up at the pump impeller/blades and that causes cavitation(air bubbles to form in the pump)
Think of a boat propeller pushing the boat thru the water, when you accelerate the motor to push the boat faster cavitation starts, forming air bubbles behind the boat, but once at speed cavitation should stop unless prop is under size for the boat, lol, the high pressure behind the prop, forcing the boat forward, is gone
Ok this makes sense. the piping I am almost certain is only 1-1/2". It came with those connectors as well as 2". Its all accessible still (under moveable slab), so I can easily plumb in 2" and see if that does the trick. Thanks Ron!
 

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It could be cavitation. It's caused by insufficient head (pressure) on the suction side of the pump for the fluid. There are localized extremely low pressure areas near the impeller that allow the fluid to boil and form small bubbles. When those bubbles move to a higher pressure area, they condense and collapse violently and cause damage to the pump. You can usually hear it when the pump is running. It will sound like ball bearings knocking around inside the pump. Sometimes you can hear it without aids, but a mechanic's stethoscope can pick it up if it's more faint.

There is a minimum suction head dependent on pump design, fluid, flow rate, and impeller speed and when any of those things don't line up there is cavitation. Things to look for would be a restriction on the suction side (plug, throttled valve, suction pipe too small, clogged pump inlet, trying to 'suck' the fluid up too high). If your pump is direct coupled, the only ways to change the speed are a variable drive or changing the motor.

With a centrifugal pump, discharge head and flow are inversely related. Flow up, head down and vice versa. Throttling the discharge is a common way to control flow rate on a pump with constant speed. Throttling increases discharge head and reduces flow, and will actually reduce cavitation. Throttling the suction side is a bad idea. It reduces suction head and makes cavitation happen more easily. If you have a valve or hose, you can induce it by closing the valve off or pinching the hose and listening.

Air ingression can cause a similar sound to cavitation, and can cause a pump to become air bound and quit pumping.
 

RonD

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If pipes are only 1.5" then your pump may be too high a flow rate if it has 2" in and out
 

Eddo Rogue

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If pipes are only 1.5" then your pump may be too high a flow rate if it has 2" in and out
It came with both...I just used the 1.5 because that's what the old brass antique pump had
 

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