This maybe my dumbest question yet. Has any body ever tried putting a pump after the filter? So that the pump is pulling water through the filter instead of pushing it. Besides the the obvious problem of backwashing is there other reasons this should not be done?
Pump Positioning
- Thread starter bg458
- Start date
It's hydraulically more difficult for your pump to pull water than push it, so it makes more sense to put large strains like a filter on the pressure side. It's also less finicky as your filter accumulates debris for the same reason.
That being said suction side filters are used regularly, just in hot tubs, not pools. The hydraulics are not so demanding in a tub because of the relatively small amount of water, the debris load is low because they're covered 99% of the time, and using suction side filters allows you to connect the cartridge to a simple PVC fitting rather than building/buying a pressurized housing for it.
That being said suction side filters are used regularly, just in hot tubs, not pools. The hydraulics are not so demanding in a tub because of the relatively small amount of water, the debris load is low because they're covered 99% of the time, and using suction side filters allows you to connect the cartridge to a simple PVC fitting rather than building/buying a pressurized housing for it.
This may or may not be an issue with modern filters, but I would imagine another issue would be structural. When they are designed, the concern is their ability to contain rather high pressures without exploding. I don't think they are designed to withstand high vacuum, and could potentially implode at such vacuum levels that could be experienced at the inlet to the pump. This would probably not be a problem if the filter was full of water, but if it were partially filled with air, the vacuum could be enough to cause problems. I'm just not certain that filters would be designed to deal with that sort of stress (unless the engineers anticipate some hooking up the system backwards!).
Rather than being in any kind of sealed chamber, a suction side cartridge is usually just in a "well" for lack of a better word. Sometimes directly under a skimmer basket, but often just behind a weir like you see here. Collapse can be a problem if the filters get clogged up, but no more so in my experience than a clogged pressure side filter since a pool/spa pump is capable of creating much more positive pressure than vacuum force.
I'm not sure how this would change if you were to just hook a sealed pool filter housing up on the suction side of your pump, aside from making the system difficult to prime.
I'm not sure how this would change if you were to just hook a sealed pool filter housing up on the suction side of your pump, aside from making the system difficult to prime.
- May 3, 2007
- 16,828
- Pool Size
- 20000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
Assuming that the head loss and flow rate through the filter is the same on the suction vs return side of the pump, which it should be, then the differential pressure between the input and output ports of the filter will be the same on either side of the pump as well. Absolute pressure will be different but that is irrelevant to the filter media.
However, the biggest problem with moving the filter from the return side to the suction side is the head loss of the filter moves as well. So even though the operating point of the pump should remain the same, having more head loss on the suction side while reducing the head loss on the return side will make the pump much more prone to cavitation especially when the filter gets dirty. A spa can get away with this because there is high head loss in the jets so moving the filter to the suction side is not such an issue. Plus stand alone spas use cartridges which have much less head loss than other filter types.
However, the biggest problem with moving the filter from the return side to the suction side is the head loss of the filter moves as well. So even though the operating point of the pump should remain the same, having more head loss on the suction side while reducing the head loss on the return side will make the pump much more prone to cavitation especially when the filter gets dirty. A spa can get away with this because there is high head loss in the jets so moving the filter to the suction side is not such an issue. Plus stand alone spas use cartridges which have much less head loss than other filter types.
Similar threads
