Separate and idependent drains needed for two pumps?

JamesW

TFP Expert
Mar 2, 2011
24,208
You have to install two main drain fixtures or a single channel drain if it's listed as suitable for single unblockable use.

You can't just install pipe or a hole.
 

GrandLSU

Member
May 14, 2020
22
Baton Rouge, LA
You have to install two main drain fixtures or a single channel drain if it's listed as suitable for single unblockable use.

You can't just install pipe or a hole.
Thanks for the response. Yes, I'm aware of that, which is why I said this in my post "This would presumably mean drilling a pair of 3" holes (for anti suction entrapment purposes) through the gunite shell sidewall of the pool."

My question is is it a major job to do this at this stage with significant potential downsides, or instead is it no big deal?
 

ajw22

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If the pool builder knows what he is doing then core drilling the gunite for new pipes is not a problem.
 
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JamesW

TFP Expert
Mar 2, 2011
24,208
"This would presumably mean drilling a pair of 3" holes (for anti suction entrapment purposes) through the gunite shell sidewall of the pool."
The holes would be closer to 8" in diameter so that you can install the whole fixtures.

A clean hole should not significantly reduce the structural integrity of the shell as long as the shell is the correct thickness and the concrete is the correct strength.

Round holes are much safer than holes with sharp corners because corners create force focus points that can crack.

This is why windows in ships and aircraft never have sharp corners.

hayward-wg1049avpak2-dimn.jpeg
 
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GrandLSU

Member
May 14, 2020
22
Baton Rouge, LA
The holes would be closer to 14" in diameter so that you can install the whole fixtures.

Really? The pair of existing holes for the main drain in the bottom of the pool are only 2.5" in diameter each. They installed the 2.5" pipes before they shot the gunite, and now that the gunite has been shot, it's just the two 2.5" pipes sticking up through the gunite protruding from the bottom of the pool (ultimately I'm sure there will be some kind of drain cover that goes over the holes, but that hasn't been done yet). So it's 2.5" holes (technically 2.5" pipes) that go through the gunite, certainly not anything close to a 14" diameter hole. You are saying the holes that penetrate through the gunite (and not just the drain covers that go over the holes) should be around 14" in diameter?
 

JamesW

TFP Expert
Mar 2, 2011
24,208
They have to use an approved main drain fixture. You can't just put a screen over the pipe.

I suspect that they might intend to use a channel drain fixture, which can be used as a single fixture if it is listed as unblockable and certified for single drain use.

In any case, the fixture is usually embedded in the gunite and not added after the gunite.

Plaster is only about 1/2" thick. So, I don't know how they plan to get the main drain fixture installed.

You will have to ask them what they intend to do.
 
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JamesW

TFP Expert
Mar 2, 2011
24,208
The grates have to be certified and they certainly can't be 2.5" in diameter.

There's no way that a small grate would be certified due to the water velocity.

The grates need to be certified for the amount of water flow intended to be pulled from the main drains.
 
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JamesW

TFP Expert
Mar 2, 2011
24,208
Below is a channel drain installation manual, which shows the dimensions and it shows how most of the fixture is embedded in the gunite.

 
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GrandLSU

Member
May 14, 2020
22
Baton Rouge, LA
Here is what mine looks like before and after the gunite was shot. As you can see in the picture prior to gunite, of the three white pipes sticking up from the bottom of the pool that form a triangle, the two drains are the white pipes at the rear left and rear right of the triangle. The white pipe at the front and center of the triangle just sticks into the ground, and is just a pressure release valve I believe. The green pipe that you see in the post-gunite picture was added by the gunite people when they shot the gunite, and I believe it is also a pressure release valve. As far as just the construction of this drain goes, does this look okay to you at this stage of construction?
 

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JamesW

TFP Expert
Mar 2, 2011
24,208
As far as just the construction of this drain goes, does this look okay to you at this stage of construction?
No. As shown in the previous picture and in the installation manual, the fixture or fixtures are installed before gunite is shot so that the fixtures are embedded in the concrete.

The channel drain is about 4" deep and the other fixtures are deeper. So, I have no idea what they're planning to do.

Another problem is that the pipe is in the gunite, which creates a control joint type weak line in the gunite.

Pipe should be outside the gunite other than the perpendicular penetration through the concrete.
 
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GrandLSU

Member
May 14, 2020
22
Baton Rouge, LA
Are they already installed? I don't see them.
Yes. If you look at the post gunite picture, you can see one skimmer in the side of the pool that’s closest to the house, about 5 feet before you get to the spa. The other skimmer is a little harder to see, but you can see the top of it. It is in the opposite side wall of the pool (the pool wall that’s furthest from the house), and it’s almost at the end of that wall towards the fence that you can see.

Let me know if you still don’t see them and I’ll circle them on a photo and upload it when I get back to my computer.
 

mas985

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I believe that is one of many standard installation methods for main drains as I have seen it done many times. They do not use a MD bucket/sump but instead just put the pipe straight through the gunite and have a small depression to accommodate a ring for the MD cover that is installed in the plaster.


Here is a picture of one with the gunite:

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JamesW

TFP Expert
Mar 2, 2011
24,208
The ring drain has a premade sump.

You can use a premade certified sump or you can use a field fabricated sump.

For a field fabricated sump, it has to be designed and certified by a qualified professional.

You can't just cut off the pipe and stick a grate over it.
 
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JamesW

TFP Expert
Mar 2, 2011
24,208
Your 20” Unblockable Ring Drain includes the following:
• Drain Sump Body
• Drain Suction Cover


As you can see in the instructions, the sump is embedded in the concrete and only about 1/2" is out of the gunite so that the plaster can finish level with the top of the fixture.
 

JamesW

TFP Expert
Mar 2, 2011
24,208
Another problem is that the pipe is in the gunite, which creates a control joint type weak line in the gunite.
For example, if the gunite is 8" thick, it should be 4" on both sides of the rebar.

A 2.5" pvc pipe has an outside diameter of 2.875".

Behind the rebar, you have 2.875" of pipe, which means that the thickness of the concrete behind the pipe is only 1.125".

It's even less if you take the thickness of the rebar into consideration.

Also, the pipe will block most concrete from getting behind the pipe.

This is called "shadowing".

So, there's a line through the concrete that's really only 4" thick, which is likely to crack if there is any stress at all.
 

GrandLSU

Member
May 14, 2020
22
Baton Rouge, LA
For example, if the gunite is 8" thick, it should be 4" on both sides of the rebar.

A 2.5" pvc pipe has an outside diameter of 2.875".

Behind the rebar, you have 2.875" of pipe, which means that the thickness of the concrete behind the pipe is only 1.125".

It's even less if you take the thickness of the rebar into consideration.

Also, the pipe will block most concrete from getting behind the pipe.

This is called "shadowing".

So, there's a line through the concrete that's really only 4" thick, which is likely to crack if there is any stress at all.

I think (hope) it may not be as bad as it looks in the picture that you are looking at. See the two below pictures. It appears they dug a channel through the dirt for the pipe to go in. It appears the pipe is recessed into that channel, meaning in theory the vertical portion of the the pipe doesn't eat into the 8" thick gunite shell at all.
 

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