Valve between pump and filter.

Like many, my pump is too big and I have a sand filter, which doesn't filter much at all. I am using DE in my filter, and that helps, but I also installed a ball valve between my filter and pump. The intention here is to restrict flow and decrease the filter PSI, hopefully allowing it to filter better.

What I have found is it works well, and I have very precise control over the pressure and flow at the returns. I also have great control of my suction side auto pool vacuum, which tends to want to climb out of the pool and cause the pump to cavitate. I have noticed the filter actually capturing the finer dirt and silt that used to get pushed through before.

My question is can I cause damage doing this to the pump or something else? Is this a good idea? I have also considered replacing the pump impeller, but with this setup I have a lot of control, like a variable speed pump. Thoughts?

I suspect you're going to burn out your pump motor faster and possibly increase your electrical usage. A lower capacity impeller or a two-speed motor would be a better solution.

Or a bigger sand filter. If it's a 1.5 hp Superpump or other IG pump you probably should have a 250-300 lb sand filter.

Ok, that's what I was wondering. My filter normally runs at 16 PSI, and with the ball valve I drop that to about 12 PSI and that seems to work well, but if I burn out my motor I'll be wishing I had upgraded the pump or filter. I was looking for the cheap fix.

I dunno. But you MAY be able to lower the speed of the motor with a transformer. I don't know how well or safely that would work, but that would be like a 2 speed pump. Still, it could burn it out as well. Have to find an expert on electrical motors.

I have often wondered if you could use a simple rheostat to control the speed of the motor, like any other electric motor used in electronics. Heck, even my electric chain saw runs faster or slower depending on how far I pull the trigger.

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Originally Posted by swimdaddy

My question is can I cause damage doing this to the pump or something else? Is this a good idea? I have also considered replacing the pump impeller, but with this setup I have a lot of control, like a variable speed pump. Thoughts?

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Throttling valves are common in the water distribution industry and are not a problem for the pump or motor as long as there is some flow rate. A pump motor actually uses less energy and runs cooler when you restrict the flow (i.e. higher head loss). The down side is it is less efficient in terms of GPM/Watt-hr.

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Originally Posted by swimdaddy

I have often wondered if you could use a simple rheostat to control the speed of the motor, like any other electric motor used in electronics. Heck, even my electric chain saw runs faster or slower depending on how far I pull the trigger.

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However, that can potentially burn out an induction motor. Reducing the voltage on an induction motor increases current and slip so it does slow down the motor but at a higher current use so it can burn out the windings.

That is interesting that the pump actually uses less energy and runs cooler with restricted flow. I do find that the filter, for what it is worth, does a better job with less flow. Its an intersting game I play, dropping the PSI with the control valve and then raising it some with DE. I think I learned this year that I probably backwash too much. I got in the habit of backwashing once a week but if the pool looks good and the PSI hasn't risen there is probably no reason to do it.

I have abandoned the idea of the rheostat or step down transformer, sounded good though.

The valve works really well, small movements change the PSI a lot, very fine control. Is there an ideal PSI to shoot for for efficient filtering? I don't know what my flow rate is, but the return jet is strong, kids can use a noodle to shoot water a good 15 feet. At fully open, 16psi, with DE 17psi, I have been throttling that down to 10 or 12psi.

Mark knows more about pumps than I do, so his advice takes precedence over mine.

We've well-documented over the years what you have found: A sand filter filters better with less flow. Something about the dirt not being forced past the sand as easily. That's why I'd rather run it on Low (2spd pump) than High pretty much all the time. Thus a bigger sand filter does better for the same reason: More capacity for the same flow.

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Originally Posted by swimdaddy

Ok, that's what I was wondering. My filter normally runs at 16 PSI, and with the ball valve I drop that to about 12 PSI and that seems to work well, but if I burn out my motor I'll be wishing I had upgraded the pump or filter. I was looking for the cheap fix.

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I would recommend buying another filter, the same filter you have now and connecting them both into service. This will double the surface area of filtration whilst keeping reasonable sized plumbing into each. This is preferable to have to try and sell off your filter and buy a single one slightly larger. I would have put that down as the cheapest fix.

I must admit I am baffled by how you would plumb in 2 sand filters unless they are both side-mounts and you use a single multi-port valve for both, and then it would probably need to be a larger and more expensive one. Otherwise I don't see how you could do it with 2 top mounts because of the multi-port valves. I guess they could be parallel, but then EVERY function would need to be duplicated on each, especially back-washing and you'd need to shut one down, than the other.

Comparing Hayward top-mount sand filters (Pro-Series):
An 18" (150#) filter runs about $230.
One with 22" (200#) runs about $250.
And a 24" (300#) runs about $380.

So I fail to see how a second 18" filter is cheaper than replacing it with a 22" or 24" filter. Plus if the 18" can be sold, even for far less, it offsets the cost of the bigger filter.