Plumbing

[Schnozz]

I'm Baaaaaak!!

Waiting on plumbing parts to arrive. so I started thinking..(BAD IDEA!!). I'd like to add a Vacuum to waste 3-way valve to my Pentair 2HP/2SP Pump & 150sqft Cartridge Filter PNCC0150OP2160 (See attached Image). The pump and filter mount to a base that puts the pump and filter about 6" apart (that connection is screwed connection on both ends and not a glued connection). So, for option #1(see attached image) I would have to cut the base in half and separate them on the equipment pad. For option #2, I may be able to leave the base in one piece, but things would be cramped between the pump and filter. Either way, I have the ability to cut the base in half and add an extension piece in the middle making the base one piece again. I'd also prefer that the outlet from the filter come out on the same side of the pad as the pump rather than from the side of the filter. Or, could I just bolt the pump and filter to the equipment pad and avoid the base all together?? What say you?? Thanks, Bob

 

[kellyfair]

Bob, why are you thinking about a vacuum to waste when you are using the Intex Auto Cleaner? It doesn’t impact the filter at all.

If anything, I would recommend a robot over a vacuum if you do decide to change from the Intex cleaner.

 

[Schnozz]

kellyfair....problem solved. Now that I think about it, I haven't had to vacuum since I started using the Intex supply side robot. (aka Ophelia)

I have a tendency to over think....Thanks, Bob

 

[Schnozz]

No these won't be your last questions.... But that's OK. Keep on asking.




In your case, using 1-1/2 for suction side and return side is more than enough.
There is no way to have a greater VOLUME of water from the pool than back to the pool unless you have a leak. The pipe size will determine the VELOCITY of the water and thus the pressure drop (head loss), but volume remains the same.
Volume is gallons. Velocity is feet per second or some variation of these units.




No, absolutely no need to run each suction and return separately. That is just overkill for your application. For an inground yes, but that is for a different reason than your are alluding too.

As a final note, in all jest... just build it already! no need to over analyze this, lol

For my own knowledge, and if you have a moment...What is the reason, or thinking, for running each suction and each return separately when plumbing an inground pool? Is it the permanence of the install or for maintenance, or efficiency??

 

[Newdude]

For trouble avoidance options. If one leg goes down you can close it off and buy the time it takes to fix it, operating indefinitely with the other line.

if all the eggs are in the one basket and there is a problem, the pool is shut down until it’s fixed.

 

[Teald024]

Running the lines separately also allows you to control the ratio (balance) where water is being pulled from. When a suction side cleaner or vacuum is used, you would typically want to shut off one of the skimmers so the vacuum works properly.
On the return side, you can set up a return to have more flow if necessary in order to prevent dead spots.

 

[Schnozz]

Thank you... Makes perfect sense...While skimming through the forum over the last month, I see that's how cowboy casey set up his 16 x 32 Intex. (2-returns and 2-suctions from the pad)
I see in different threads that pool owners will sometimes plumb the suction side with larger piping (like 2") and return side with smaller piping (like 1-1/2").. What's the reasoning behind that?

For example this post from last year

Starting a new pool build in austin (like everyone else..)

Because of covid it seems like everyone is building a pool in austin. PB are slammed. I built a pool in 2012 and said I would never build another pool. Unfortunately we moved in 2017 and bought a house without a pool so now Im faced with building another pool. Austin is backlogged so it is...

www.troublefreepool.com

 

[Teald024]

The pipe diameter determines the water velocity in the pipe. The velocity causes friction and therefore head (pressure) loss. Rule of thumb for design allows higher velocity on the pump discharge side. Pressure loss on the pump suction side is much more detrimental to the system performance than losses on the pressure side.

 

[Schnozz]

Soooo, smaller size pipe on the return side leads to greater water velocity within the pipe from the pump to the pool. The higher velocity leads to greater friction and increased head loss. I presume this leads to greater pressure at the returns as well?
Larger pipe size on the suction side leads to lower velocity within the pipe from the pool to the pump. As a bonus, the lower velocity generates less friction and therefore reduced head loss.

(The application of that information, as I understand it would be this)

Do I understand correctly, that 1-1/2" returns and 2" suctions amount to a safety feature (???), of sorts, for the pump helping it work efficiently?
It's better (or ok) for a pump to work a little harder to return water to the pool than to suction it from the pool? Smaller return plumbing and larger suction plumbing helps accomplish this.
(I understand there are other considerations that can have an effect this as well, not just pipe size alone)



As always, I appreciate the willingness of TFP members to share their time and knowledge....
Thanks, Bob

 

[Teald024]

Do I understand correctly, that 1-1/2" returns and 2" suctions amount to a safety feature (???), of sorts, for the pump helping it work efficiently?

No safety feature

It's better (or ok) for a pump to work a little harder to return water to the pool than to suction it from the pool? Smaller return plumbing and larger suction plumbing helps accomplish this.

So here’s the deal, the pumps used for pools are centrifugal type. They make pressure and flow by spinning the impeller. Centrifugal pumps can make a certain pressure ratio based on their geometry and how fast they’re spinning. The discharge pressure is based on the available inlet pressure.

assume a ratio of 2:1
If the inlet pressure is 14 psi than the discharge pressure is 28 psi.
now it’s say there’s one psi loss at the inlet. Now 13 psi goes up to 26 psi and consumes a certain power.
alternatively lets say there’s 1 psi loss at the discharge. Now 14 goes up to 28 but then down to 27, but consumes the came power.
so for the same power consumption you get 27 versus 26.
mind you these are all made up numbers with zero calculation behind them, but illustrates the point.

(I understand there are other considerations that can have an effect this as well, not just pipe size alone)

Yes, all components in the system have a head loss and contribute to the pressure.
And the lowest pressure in the system after the pump is just as the water is coming out of the return back into the pool

 

[kellyfair]

Bob, I’m almost afraid to ask - what are you up to?

 

[Schnozz]

Kellyfair.... .....I'm not really up to anything. I purchased and set up my first pool ever in 2015 with the help of TFP (I was pushing 60 years old at the time) My wife asked for a pool and while thinking about it I stumbled upon TFP and realized I didn't have to have special magical powers, or pay a pool guy hundreds of dollars to maintain a pool. Since then I've been fascinated by my pool. Building and set-up, plumbing, filtering, hydraulics, water chemistry, bonding electrical power, everything.
As you know from the thread, I'm finally plumbing my new Pentair Optiflo pump and cartridge filter to my 12 x 24 Intex Ultra Frame. I'm digging up the yard this weekend and want to make sure I'm comfortable with my decisions...I ask questions, and I get straight forward answers, then I do a little research on TFP, ask a couple more questions trying to figure out what I want to do. Even in the same thread, when asking questions I may get two or three different opinions, depending on who responds. They'll all work but it's still up to me to decide. Responders always want to recommend what will be the simplest/wisest/most reasonable approach for my particular setup. Even if I wanted to purchase a Pump and filter worth more than my entire pool, I know I could get the help I needed, even if it was an unreasonable decision.
I asked the last question about two 2" suction lines and two 1-1/2" return lines because in a post from 2020 (I included it a few posts up in #27) one of the responders said that 2" suctions and 1-1/2 returns was a general standard (design rule) in the industry. Like it's a good starting point in plumbing design. I just thought it was interesting and wanted a little information.
TFP is a great site. No matter how many questions I ask, I get some kind of response. Thanks for your interest and the encouragement..B

 

[Schnozz]

No safety feature



So here’s the deal, the pumps used for pools are centrifugal type. They make pressure and flow by spinning the impeller. Centrical pumps can make a certain pressure ratio based on their geometry and how fast they’re spinning. The discharge pressure is based on the available inlet pressure.

assume a ratio of 2:1
If the inlet pressure is 14 psi than the discharge pressure is 28 psi.
now it’s say there’s one psi loss at the inlet. Now 13 psi goes up to 26 psi and consumes a certain power.
alternatively lets say there’s 1 psi loss at the discharge. Now 14 goes up to 28 but then down to 27, but consumes the came power.
so for the same power consumption you get 27 versus 26.
mind you these are all made up numbers with zero calculation behind them, but illustrates the point.


Yes, all components in the system have a head loss and contribute to the pressure.
And the lowest pressure in the system after the pump is just as the water is coming out of the return back into the pool

Thanks for taking the time to answer my question about pipe size by describing the relationship of return line and supply line pressure to the centrifugal pool pump. It's fascinating to me . I'll never remember it all, but I can save it and reference back to it. Since I may increase my pool size to an Intex 16 x 32 in the near future, I'll probably plumb my current pool with two suction lines and two return lines (like Cowboy Caseys build). I realize it's overkill, but it's only a few more bucks. Just trying to make a final decision on pipe size before I dig... Thanks again....Bob

 

[kellyfair]

I’m just joshing with you! I love that your gears are always turning!

 

[Teald024]

Just as an FYI, dual 2” lines on your Intex is definitely overkill, lol.

 

[CrystalRiver]

Having larger piping (low pressure) on the return side and smaller piping (greater restriction) on the suction side can lead to cavitation in the pump. Cavitation is horribly damaging to the parts (tiny sonic booms release a ton of energy very quickly in a very localized area). Having back pressure on the return side, and plenty of supply volume, should make sure cavitation doesn't happen.

 

[Schnozz]

I see...That makes sense, along with the information about how a centrifugal pump works from Teald0024 (post #30). So that's the thinking/reasoning behind the general plumbing design standard that smaller return plumbing (creating greater pressure) combined with larger suction plumbing (creating lower pressure/larger supply volume) is a standard of sorts. Of course, there are other factors to consider. But all things being equal, smaller return plumbing combined with larger suction plumbing will ensure no cavitation at the pump. Do I still understand??

 

[Teald024]

Do I still understand??

Yes mostly, but there is no desire to create a greater pressure with smaller piping. It is just that higher losses are more tolerable. But to be honest, the losses in a pool system are typically low to begin with. There is always a cost/ benefit to engineering & design and at some point the additional cost or complexity outweighs the benefits.
As an absurd example, you could use 4” pipe on both sides. Losses would be lower, price would be higher, BUT, there is not really any significant benefit to warrant the change.

 

[Schnozz]

I don't start digging until tomorrow so I started thinking again and went back to the basics....I went back to the hydraulics sticky. And between the information you've all shared with me in this thread, a few old threads of mine, and refreshing my memory in Hydraulics 101, I had a revelation about pipe sizing . Now I will pontificate....

I understood there should be more pressure on the return side than the suction side. The sticky reminded me that its not greater pressure on the return side that's needed, but greater dynamic head than on the suction side to prevent the pump from cavitating.

From the sticky:
"Also, when designing a plumbing system, it is a good idea to have a separate suction line from each skimmer and/or main drain pair from the pool all the way to the pump. This keeps the suction head low so the pump basket will not draw in air.
However, on the return side of the pump, the head loss of the return side plumbing should always be well above that of the suction side plumbing to minimize the chance of pump cavitation or air leaks. This is more likely to occur when the pool to pump equivalent return pipe runs exceeds that of the equivalent suction pipe runs. This can be determined by summing the diameter squared of each suction run and separately each return run. The return D*D sum should be less than the suction D*D sum. However, there are other methods of equalizing head loss such as throttling valves and smaller eyeballs."

In this reading, I can better understand the reason for larger (or more) suction lines and fittings and smaller (or less) return piping and fittings. So for my circumstance, I could use two 2" suction lines and two 1-1/2" return lines both with the 3-way valves at the equipment pad. From the formula above that would be DxDx2=8 for the suction side and DxDdx2=4.5 for the return side which meets the criteria above. Or I could run two 2" suction lines in conjunction with one 2" return line and split that line at the pool, one for each return. The same formula would apply, DxDx1=4. In place of the3-way valve I could use 2-way valves on each return.

Am I thinking straight??

 

[Teald024]

Am I thinking straight??

sure. definitely in overkill territory though.

If you have a 2 suction points, piped with 1-1/2" pipe to a 3 way valve near the pool. Then 2" back to the pump. Then 1-1/2" pipe back to the pool. Split with another 3 way to the 2 returns. That would be a very robust layout and would not leave you wanting more. Keep in mind you have a 12x20 pool and this layout you are proposing is "better" than 95% of all AGP users since you have 2 suction points and 2 returns.

This may be a fun thought exercise, but you should consider the application of the system. You are trying to design a gokart with a V8 and then trying to squeeze every last ounce of power out if it by adding a supercharger. At some point it just really isn't necessary and you'll just spin your wheels without going anywhere.

And to put the exclamation point on it, you will likely be running on low speed most of the time. Water flows and velocities will be well below the limits and all this will be mute points of design limits.