Another big becket skimmer

[hahnmeister]

Im worried about the large diameter of the downdraft pipe on that skimmer. MarkS had 4 becketts on his, and was using individual 1.5" PVC for each injector. The problem was that the downdraft wasnt fast enough due to a large diameter of pipe, so the pressure was building up in the pipe, causing bubbles to combine and not come out of the bottom as intended. Mark decided to only use 1" for the downdraft tubes for 'next time'.

Now, if I do the math, a 1.5" pipe has a cross sectional area of 1.7 square inches...and a 1" pipe is .785 sq. in. Now, even 1.5" pipe x4 (for 4 injectors) is only about 7 square inches.

A 6" pipe is 28 square inches. That diameter is just out of the ballpark for what you should use.

What this means is that your downdraft tube wont be able to get much of its bubble mix out of the bottom before they combine and rise back up to the top of the downdraft pipe where they will sit until the skimmer chokes on the air pocket that it makes.

The largest pipe diameter you would really want to use on a 4-injector unit like that is a 3" diameter...and a 2" would even work better. You have to keep the velocity of the downdraft pipe at about this rate to keep it from choking itself.

 

[Cuby2k]

<a href=showthread.php?s=&postid=7543398#post7543398 target=_blank>Originally posted</a> by hahnmeister
Im worried about the large diameter of the downdraft pipe on that skimmer.

Wow, this is exactly the problem that I feared with my DIY beckett skimmer. I used a 3" dia downtube albeit it with a single beckett (like) nozzle and in test trials could not get it to flow very well.

At first I used an Iwaki 30 then switched to an Iwaki 70. I think in the near future I am going to replace the 3" downtube with a 1-1/2" in an effort to get the velocity up enough to carry the bubbles to the up side.

I haven't set mine into real use so I would love to see this baby in action or if anyone has a similar setup going.

Sure a nice looking unit.

 

[blfuller123]

I am trying to maxamize the contact time as much as possible. Yea it is a 6 inch tube with four beckets, but remember it will have over 5000 gph running though the four injectors. I am going to be using a sequence mantaa ray pump.

 

[hahnmeister]

5000gph is the pump rating...keep that in mind (not to mention his was also recirculating so head pressure due to height was almost none). MarkS had a large pump on his 4 beckett monster as well and still had problems. As you go up in pump rating, the restriction becomes greater as well...so going larger in pump size doesnt always mean a proportional addition in flow.

While 5000gph sounds good, its what...something like 1250gph per injector (in not calculating actual rates due to restriction, air, etc)? Just a quick look, your flow might be what...25% more than usual for a beckett per injector? But your downdraft tube is more than 400% larger. I dont think that 2000gph per injector would be able to keep up with that. But like most things...we shall see...

The downdraft pipes on a beckett rely heavily on Newton's conservation of energy equasions...the faster the velocity of the liquid/mixture, the lower the pressure. The more that the water slows down (by making the pipe wider) the higher the pressure becomes with depth...causing bubbles to combine and stagnate in the downdraft tube(s).

 

[billyzbear]

If you look at this skimmer, http://reefcentral.com/forums/showthread.php?s=&threadid=151956&perpage=25&pagenumber=3
He says he would down size the inj tubes to 2 1/2".
I have done some testing with a PCX55, 1 1/2" inj. tubes first with one then two. I never had choking problem. Was the Beckett above the water line? With mine I run into a problem with turbalance. I added a 6" section of 3" pipe to the inj tube which did help a little. This lowered the velocity but I still can't add much air. I'm using big valves not the 1/4" valves a lot of people use. I still have more testing. I added a Sedra 9000 to my skimmer now and it's way better. Next I want to step up to 10" pipe with the Sedra on close loop with one beckett inj with 2" inj tube going into a 6" tube with defuser and see how that works. I can't wait until the dart needle wheel comes out.

 

[blfuller123]

I am going to divide up the downdrafts into four areas using baffles. I will get some pictures up of my idea when I get it done. I need to get another piece of acrylic. Thats right, I am going to listen to someone else for once (mark your calanders).

 

[blfuller123]

Here is the modified injector and down draft. Its kinda hard to tell from the picture but all of the beckets are seperated in the top (still need to put the valves in) and the down draft tube is sectioned off internally. I used clear and black acrylic in the tube. Still need to work on the box and the collection cup. I did get the gaskets put on the injector and downdraft tube.

 

[hahnmeister]

Seperating the becketts is a good idea for individual air control...but I dont see the point in seperating the downdraft tubes...the problem that you see as turbulence is really just pressure rearing its ugly head and making the the bubbles try to rise back up...causing all the turbulence. A smaller pipe diameter would be the easy cure...maybe a 3" pipe for all 4 becketts to flow through.

 

[Cuby2k]

Vert nice looking work.

 

[blfuller123]

Seperating the tube was alot easier than re making the tube.

 

[blfuller123]

I ended up redoing the whole injector and downdraft tube. I kept the other injector just to play around with, but maintenance wise, it was going to be a pain to take apart and clean the injectors. Getting the flanges apart was tough because you really need jack screws to get them apart. Putting them back together was kind of a pain as well becuase trying to get four beckets lined up (they fit really tight) into the corresponding holes.

The smallest diamater tube I could squeeze four beckets in was a four inch tube. These have there own chambers. I still have to get the airvalves installed. My gate valve is suppose to be in this week so maybe this next weekend I can get some water running through it.

 

[AnnArborBuck]

Now that looks awesome!

 

[blfuller123]

I havent got much done. I have to go out of town tomorrow so doing some testing this weekend is probabaly not going to happen. I got the bottom flange done on the down draft tube and put it on the box to make sure it would work. I still have to get the air valves installed and finish up the plumbing to the inlets. I want to do all of my testing before I get everything polished up. It measures 60 inches at the tallest point and the box will hold just over 16 gallons of water. It is going to be a couple of months before my tank is ready for water.

 

[crazyboy]

DAMN!!! Extremely nice work!

 

[exmt]

All I can say right now is......Damn! Holy ****! I always wished I could do stuff like that.

 

[blfuller123]

Thanks for the nice words!

 

[RGibson]

blfullert you will need valves on the in put of becketts to make the water flow even on each one .Gate valves are the best to used to do this.

 

[Beenalongtime79]

Looks really cool man.

 

[blfuller123]

RGibson, thats why I said "I still have to get the air valves installed and finish up the plumbing to the inlets. "

 

[RGibson]

Is not air valves it water valves you need allso.