Number and spacing of slits in bog manifold?? How to know?

[GBBUDD]

my math is so much simpler a 3rd grader can do that math the fact of what the volume is maters not . the question is do you have the same amount of open flow. the 4,000 plus gph is irrelevant

 

[GBBUDD]

Exactly right! put a plastic pipe for a stream crossing down place 6 inches of stone over it it will support a pickup. place 3 feet over the same pipe and you can drive a loaded mack truck

 

[combatwombat]

40 of those cuts will get me 20 square inches of egress for the water. That seems like a lot, but I still have no clue if that will dissipate 2700 gallons per hour. Hahah! See what I mean with the overthinking?

I've seen the numbers run for under gravel suction grids, which is basically the same idea as a manifold bog, but in reverse. The people who build these like to have openings that equal 5-10x the area of the distribution piping. So, for a 2" pipe, you'd have an area of 12.6 square inches. 5x of that would be 63 square inches. Take that as your minimum and you can figure out what size slits to cut at what spacing.

I'm like you. Always overthinking. I just enjoy understanding why things work as much as seeing them work.

 

[GBBUDD]

I've seen the numbers run for under gravel suction grids, which is basically the same idea as a manifold bog, but in reverse. The people who build these like to have openings that equal 5-10x the area of the distribution piping. So, for a 2" pipe, you'd have an area of 12.6 square inches. 5x of that would be 63 square inches. Take that as your minimum and you can figure out what size slits to cut at what spacing.

I'm like you. Always overthinking. I just enjoy understanding why things work as much as seeing them work.

i had not seen those numbers before but id agree way more is better for even flow

 

[brokensword]

I've seen the numbers run for under gravel suction grids, which is basically the same idea as a manifold bog, but in reverse. The people who build these like to have openings that equal 5-10x the area of the distribution piping. So, for a 2" pipe, you'd have an area of 12.6 square inches. 5x of that would be 63 square inches. Take that as your minimum and you can figure out what size slits to cut at what spacing.

I'm like you. Always overthinking. I just enjoy understanding why things work as much as seeing them work.

thing is, an undergravel filter is different enough to warrant all the openings; a bog doesn't need to worry about that as the water will find it's own way into all the paths upward whereas with undergravel, you're trying to maximize the force pull downward and you want all the substrate to get hit (for bio purposes). There's no way you'd need such sq ft egress out of the bog manifolds. Once out, water will always win; use this to your advantage. There is some bit of support of the idea cutting slits closer together near manifold end runs, but even that I doubt is much advantage. Once out, water will win; just let it out down below the rock. Now, IF you have ALL pea gravel with no space surrounding the manifolds, sure the slits and number/position are more important.

 

[combatwombat]

thing is, an undergravel filter is different enough to warrant all the openings; a bog doesn't need to worry about that as the water will find it's own way into all the paths upward whereas with undergravel, you're trying to maximize the force pull downward and you want all the substrate to get hit (for bio purposes). There's no way you'd need such sq ft egress out of the bog manifolds. Once out, water will always win; use this to your advantage. There is some bit of support of the idea cutting slits closer together near manifold end runs, but even that I doubt is much advantage. Once out, water will win; just let it out down below the rock. Now, IF you have ALL pea gravel with no space surrounding the manifolds, sure the slits and number/position are more important.

It matters in terms of friction loss within the piping. If your slits add up to less than the area of the pipe diameter, you'll be adding back pressure on your pump from the moment you start it up for no apparent gain. More slits = more slits that can get clogged before adding back pressure to the pump. It's easy to add more now. Harder to add more after you dump a few feet o gravel on em'!

 

[brokensword]

It matters in terms of friction loss within the piping. If your slits add up to less than the area of the pipe diameter, you'll be adding back pressure on your pump from the moment you start it up for no apparent gain. More slits = more slits that can get clogged before adding back pressure to the pump. It's easy to add more now. Harder to add more after you dump a few feet o gravel on em'!

oh, for sure; I just meant it seems like 6" between is more than enough if you have any length of pipe/manifold. I cut slits in the 2" distance for my mini container bog, so yep; definitely don't want any back pressure issues to fix down the road!

 

[nimrod]

IF you have ALL pea gravel with no space surrounding the manifolds, sure the slits and number/position are more important.

With 24" depth I am aiming for the first 6" to be larger stone (2" river rock), and the remaining 18" pea gravel. I'm hoping the 40ish slits will be enough!

 

[nimrod]

ah, no; circumference would be 6.28" (2 x Pi x R)

Wow. Embarrassing. I blame my lack of coffee. Using the diameter instead of the radius, what a rookie mistake.

 

[brokensword]

With 24" depth I am aiming for the first 6" to be larger stone (2" river rock), and the remaining 18" pea gravel. I'm hoping the 40ish slits will be enough!

I'd put a layer of 6" stone down first, to give you more open space for water to distribute. The 2" is fine but 4-6 would be better. You'll still have 12" above which is typical for pea gravel bogs.

Also; make sure you have 6" of open wall ABOVE your pea gravel/weir height for when the clogging begins and the water rises on you!

No prob re the math; I saw it and started circling a 2" pipe in my head; got dizzy real fast!

 

[Lisak1]

for when the clogging begins

In our case it was plant roots that caused the water to rise. The things you don't think of! Of COURSE they take up space, but you just don't realize how much water they can displace.

 

[addy1]

In our case it was plant roots that caused the water to rise. The things you don't think of! Of COURSE they take up space, but you just don't realize how much water they can displace.

My pipes are deep enough the plant roots can't clog them. BUT those roots sure do clog up the pea gravel. Every few years I yank a lot of the root matter , a lot! The plants come back just fine. Most of the roots are not deeper than 2-3 inches, some of the plants the roots are just a mat.

During the summer I do one to two purges of plants to allow the water a way to flow back into the pond.

 

[Lisak1]

BUT those roots sure do clog up the pea gravel.

That's exactly what I was talking about! My bog is four feet deep - no roots get down that far - but they do divert and displace a lot of water in the gravel. After year one I added more gravel - it settled a bit over winter. After year two, I was taking that gravel right back out again!

 

[addy1]

That's exactly what I was talking about! My bog is four feet deep - no roots get down that far - but they do divert and displace a lot of water in the gravel. After year one I added more gravel - it settled a bit over winter. After year two, I was taking that gravel right back out again!

I just raised the edge by about 4 inches over the first few years. Now it can handle the different water levels. The bog/pond wall I thought was tall enough to direct all water to the water fall, nope water leaks over it all the time. Which is great, have water movement the entire length of the pond.

 

[nimrod]

I'd put a layer of 6" stone down first, to give you more open space for water to distribute. The 2" is fine but 4-6 would be better. You'll still have 12" above which is typical for pea gravel bogs.

I'll see if my rock delivery service has anything in that size. Thanks for all the help!