Help me understand spa plumbing.

[bigdav160]

With a little luck I'll be in gunite by next weekend.

Since I'm owner/builder this pool, I want to make sure I have a keen understanding of the plumbing of the 18" elevated spa with a wide spill over.
I'm going to be using a single pump (pentair 3050VS).
Following this drawing, it appears the returns for the make-up and the jets are the same:
[attachment=1:3gv237aq]Pool_Spa_Plumbing.jpg[/attachment:3gv237aq]

But looking at builds on this forum I see spa with extra returns, like this:
[attachment=0:3gv237aq]plumb1.jpg[/attachment:3gv237aq]

In that pic I see lines for the water and air for the jets, lines for the spa drains and another at knee level.
Is this because there is a separate pump for the jet returns? Or is there another reason?

TIA
Dave

 

[Qwaxalot]

The extra plumbing loop around the spa is for an air blower. It pushes air that mixes with water at the "T" fittings. Besides the air being introduced, the blower adds significantly more pressure to the jets.

 

[bigdav160]

I know it's hard to see but it appears there are four lines in that spa pic.

Blower air
Spa jet
Spa drain
?????

My question is why the fourth. It looks like a water return and isolated.

Here's another one from a TFP thread

I see the drain, jet, air (not finished) and another 2" line with a tee at the end. Why?

 

[Qwaxalot]

I suspect that that extra line is the spa bypass. There to keep the spa water fresh, and have the spa overflow on all the time. Slightly different from your original diagram, which controls the spa bypass with a valve (the way I would do it).

 

[bigdav160]

So a separate line to the spa is called a "bypass"?

I just need another valve, check valve and piping (of course).

At the pad, could I not just tie this in after the pool returns?

Thanks.
Dave

 

[JasonLion]

I call the extra line a spa return, distinct from the spa jets. In a single pump system it is rare, but when there it is used so you can run the spillover or heat the spa without running the jets. It requires another three way on the spa return line.

That same return line is used differently, and is required, when using a separate jet pump. The regular return line comes from the heater, which is on the pool/spa shared circuit, while the jets would then be on a separate jets only circuit.