Spa jets + booster on = increase in filter pressure. Why?

[thehowheels]

Please help me understand why this is true.

To the best of my knowledge, the spa jet pump and booster pump are plumbed separately from the returns and drain. I have 2 drains in my spa: one on the floor and one on the wall. I've concluded that the drain on the wall goes to the circulation pump / filter, and the other goes to the spa jet / booster pumps.

With the valves set to spillover mode (drain from pool, return to spa), my filter shows 11 PSI (10 PSI baseline when I cleaned the filter last month). When I flip on the spa jets and booster pumps, my filter pressure climbs to 16 PSI.

How can this be? The only explanation is that the two systems must be connected somewhere, right?

 

[jblizzle]

Re: Spa jets + booster on = increase in filter pressure. Why

That is a little puzzling as I too would have thought the systems were independent.

My initial thought (before reading all your post) was that if the booster pump was fed from the return water after the filter, then that could reduce the main pump pressure side head loss and allow the pump to move more water and give the higher pressure ... but now that I wrote that, I am not sure it actually makes sense. And if you have separate drains for the 2 pumps, then it certainly does not make sense.

 

[mas985]

Re: Spa jets + booster on = increase in filter pressure. Why

Maybe it would help to post a picture of your pad plumbing/equipment.

 

[Richard320]

Re: Spa jets + booster on = increase in filter pressure. Why

I'd do some experimenting. Turn on the booster alone and see which returns spew water. Also see if that makes the pressure rise on the filter. If yes to either, the returns are teed together and the flow is greater than the pipes can accommodate without the pressure climbing.

 

[thehowheels]

Re: Spa jets + booster on = increase in filter pressure. Why

Here's the pad and equipment. Sorry about the shade!

The bell-shaped thing on the stick is the booster pump (which is LOUD! I wonder if there's a problem with it ...)

The black pump is the spa jet.

The white pump is the circulation pump.

I did some testing, and sure enough, the returns and spa jets are plumbed together. I can feel water flowing out of all of the returns in the spa, and when I flip the spa jets on, I feel increased pressure again on all returns.

Is this typical? Where do you think it's more likely they are teed together? Before or after the filter?

For what it's worth, turning the booster pump on made no difference in filter pressure.

 

[msumoose]

Re: Spa jets + booster on = increase in filter pressure. Why

The thing you are calling the booster pump is an air pump for the spa air. There would have to be a water in and a water out for it to pump water. That model is made by Polaris and is a 1.5 HP, 110v model.

And yes, they are loud. It is a strong fan.

It would make sense that if it is connected to the spa jets that it would raise your pressure...

 

[thehowheels]

Re: Spa jets + booster on = increase in filter pressure. Why

The thing you are calling the booster pump is an air pump for the spa air.

Got it. I just found the product literature, they call it a blower.