Repurposing return lines as suction lines

[texasmax]

I've got a ~32k gallon pool. The lines are smaller than what they should have been when the pool was built 25 years ago. I'm probably going to have the pool resurfaced in the next year and have a spillover spa that we'll probably have filled in and converted to a sun ledge. With a 1.5hpx1.1sf pump and a perfectly clean 60sqft DE filter (with a multiport), I'm pushing 65-70gpm.

On the suction side: 1.5" line from main drain, 1.5" line from 2 skimmers tied together, and 2" line from spa drain.
On the pressure side: 2" line to 5 or so return jets, 2" line to 3 spa jets, and a 1.25" line to 3 "whale hole" returns in the deep end (literally, 3 holes in the side wall of the pool, no eyes/jets/fittings).

These are just the sizes of the pipes as they come out at the pad; who knows what's going on for the lines that split for the jets, etc.

Each of the 6 lines has it's own valve at the equipment pad; partially closing any of the suction side lines drops my flow. On the pressure side, closing off the 1.25" line doesn't affect flow at all. Further, looking up IDs of PVC, my suction side has a total 7.42 sq.in. area and the pressure side has 8.2 (I'm guessing it's not quite as easy as adding cross-sections to find effective total pipe size but FWIW).

All of this tells me my suction side is obviously what's holding me back flow-wise. Here's where I'm going with this if you couldn't tell from the title: I'm debating repurposing pressure-side lines for suction lines. This doesn't need to coincide at all with the pool work, but that's what got me thinking about it (when we fill in the spa, we're going to keep the return jets and T the spa drain through the fill-in and out through the spa wall into the pool so we don't lose any precious line).

I'm thinking the pressure side could stand to lose the 1.25" line (feeding the whale holes)- and that those whale holes might be a better choice for suction than the pool or spa jets. I'd just re-plumb at the pad. That would change my net suction side to 8.9 sq. in. and net pressure side to 6.7. Repurposing a 2" line might be just too much (though I guess I could experiment and see which give the better flow).

Am I thinking straight here?

Thanks for reading!

 

[gwegan]

You can probably do what you want to do. However, since your spa was built the building codes have drastically changed when it comes to pools and specifically regarding suction drains. Your pool may comply with the code when it was built. If you play with the drains at all it probably will not comply with current code.

Today in pool drains have to meet specific safety requirements. California's law set out below is typical. While the California law specifically applies to new installations, many local jurisdictions apply it to retrofits. So before you start doing the work talk to your local building official and ask what you can do with the returns to turn them into drains and if that would require you to comply with current code.

The tough part of the requirement below is the requirement that drains be paired and hydrologicaly balanced. You may be able to do that at the pad, you may not.

The drains would also require anti entrapment covers (you should put those on anyway and your state may actually require this retrofit).

California's law:

115928. Whenever a building permit is issued for the construction
of a new swimming pool or spa, the pool or spa shall meet all of the
following requirements:
(a) (1) The suction outlet of the pool or spa for which the permit
is issued shall be equipped to provide circulation throughout the
pool or spa as prescribed in paragraph (2).
(2) The swimming pool or spa shall have at least two circulation
drains per pump that shall be hydraulically balanced and
symmetrically plumbed through one or more "T" fittings, and that are
separated by a distance of at least three feet in any dimension
between the drains.
(b) Suction outlets that are less than 12 inches across shall be
covered with antientrapment grates, as specified in the ASME/ANSI
Standard A 112.19.8, that cannot be removed except with the use of
tools. Slots or openings in the grates or similar protective devices
shall be of a shape, area, and arrangement that would prevent
physical entrapment and would not pose any suction hazard to bathers.
(c) Any backup safety system that an owner of a new swimming pool
or spa may choose to install in addition to the requirements set
forth in subdivisions (a) and (b) shall meet the standards as
published in the document, "Guidelines for Entrapment Hazards: Making
Pools and Spas Safer," Publication Number 363, March 2005, United
States Consumer Product Safety Commission.

 

[jblizzle]

Why do you need more flow? Dual 1.5" suction lines is not bad feeding a 2" return line. Many people only have a single 1.5" line.

Wondering if you are believing some old minimum turn over requirement myth.

 

[duraleigh]

All of this tells me my suction side is obviously what's holding me back flow-wise.

I'm with jblizzle....70 or so gpm seems perfectly adequate for your 32k pool so I am not sure I understand the goal.

 

[texasmax]

Very, very good point on compliance and safety

I'm not so much concerned about turnover; I'm more concerned with circulation in general (and how I can get there by being more efficient with what I've got). If my Polaris isn't running the entire time the pump is running, I get a lot of build-up on steps and some specific rough patches of plaster. I don't think there's enough push, given jet placement, etc, that running the pump more hours per day will do anything (and certainly not going to a 2-speed and just running it on low 24 hours/day), so my angle on this is to just push more gpm (and want to be smart about it and not just upsize the pump).

 

[jblizzle]

Are you certain the build-up you are seeing is not dead algae building up from a low level bloom? I and many others only run our pumps on low speed certainly moving much less water than you are and have clear water.

Of course if you have a very dirty environment, more flow is not neccesarily going to keep the bottom cleaner. Everyone still has to run a cleaner or robot or manually vaccum to capture the debris that enters the pool.

 

[duraleigh]

I get a lot of build-up on steps and some specific rough patches of plaster

I am not sure what you mean by build up but, taking a guess, I would bet you have a water chemistry issue rather than a flow issue. I think you are likely seeing dead algae.

Can you post a complete set of test results and tell us how you are chlorinating?

I know this veers off from what you asked but I think it will solve your "build-up" problems.

 

[mas985]

The most effective way to increase water movement is by reducing the eyeball size which increases exit velocity. However, I doubt it would solve some of the issues you are having. Also, adding another suction port would probably not change your flow rate very much so the water movement would not be that much better.

 

[texasmax]

There is more than likely some dead algae (late summer I start to get a little lazy), there's also some sediment/dirt from the kids running through the yard and then into the pool. I realize brushing is necessary (to get it to the bottom off the steps so the cleaner gets it) but anything I can do to "help things along" is what I'm after.