Downdraft Skimmer Design Help

[Travis L. Stevens]

Captbunzo and dugg. This is really something that is up your alley. I'm looking on putting a downdraft skimmer in my 75g. I don't want it overly complicated, but I'm having a few problems making it easy. Here is my first draft:

In the first draft, it seems like it would work out really well, except that I would have no control of my skimmate wetness. I thought about finding a second acrylic tube to fit over the first to make the neck extendable, but it just seems like that would be a lot of trouble and expensive. So, I did a little thinking and came up with my second draft:

I like the second draft MUCH better, but it presents a few small problems. I was hoping to have the skimmer body fully enclosed, but then I would have a problem placing the bulkheads in and getting the 45º piece of acrylic in there to deflect bubbles upwards. I also don't have another 1.5" bulkhead to place on the side with the ball valve. So, how can I install the bulkheads, get the angled piece of acrylic in, and would I be able to use a smaller bulkhead for water to exit the skimmer body? If so, do you think that 1" would do the trick?

Tank Specs
75g Tank
Mag 9.5 Return Pump: Single outlet nearly straight up
1.5" Drain: Single outlet nearly straight down
Skimmer Area in sump holds a constant 12" of water

 

[dugg]

First and most important, use a gate valve Not a ball valve. It is night and day difference in how good you can control things. second, you don't need bulkheads. Just glue the PVC fitting straight to the acrylic. Third, the exit side needs a 90* elbow on the inside, facing down, with about 1/4 inch clearance from the bottom. That will do away with the need for the angled piece. On the exit side just use 2 90's and connect them through the wall with a short piece of pipe. It takes the PVC glue a few extra minutes to dry on the acrylic, but once it dries, it is solid as a rock. The acrylic will break before the joint will fail. Be sure and use the primer, it makes for a better bond on the acrylic. The first issue you will run into, is cleaning. With the sealed box, once it's glued, there is no getting inside to clean. Keeping the inside clean makes a huge difference in production. For the bottom make a double layer acrylic piece, that the top piece fits slightly snug into the base of the skimmer, so it can be pulled off. I pull my skimmer and clean it monthly. Other then the fittings that are glued to the box, dry fit everything else. It takes less then 10 minutes for me to clean and re install my skimmer. Also the exit pipe needs to rise up instead of going straight out. The position of the gate valve, also makes a difference on the internal water level and stability of that level. The top of the Valve should be right around the external water level. When you buy the gate valve, don't forget to grab a stainless screw to replace the one in the knob. I just change that out at the store lol, saves a few pennies. Actually, at ace hardware, they will change it out for you for free if you ask.

 

[Travis L. Stevens]

<a href=showthread.php?s=&postid=8473127#post8473127 target=_blank>Originally posted</a> by dugg
First and most important, use a gate valve Not a ball valve. It is night and day difference in how good you can control things.

I'ld love to use a gate valve, but I can't find any locally, and ordering one would be far too expensive for my taste.

second, you don't need bulkheads. Just glue the PVC fitting straight to the acrylic.

I've already got extra bulkheads handy. I might as well use them for this project.

Third, the exit side needs a 90* elbow on the inside, facing down, with about 1/4 inch clearance from the bottom. That will do away with the need for the angled piece.

Good idea. I don't know why I didn't think of that. I have quite a few things around my place with the same principal to deter bubbles. Thanks for that.

On the exit side just use 2 90's and connect them through the wall with a short piece of pipe. It takes the PVC glue a few extra minutes to dry on the acrylic, but once it dries, it is solid as a rock. The acrylic will break before the joint will fail. Be sure and use the primer, it makes for a better bond on the acrylic.

That is if I go with a makeshift bulkhead. Since I'll probably use my extra bulkheads, I'll probably just move on from this. But, thanks for bringing that up. I already have a few makeshift bulkheads on various tanks.

The first issue you will run into, is cleaning. With the sealed box, once it's glued, there is no getting inside to clean. Keeping the inside clean makes a huge difference in production.

Ah crap! See. That's why peer review is so important. I didn't even think about cleaning! Thanks, dugg. You saved my life there.

For the bottom make a double layer acrylic piece, that the top piece fits slightly snug into the base of the skimmer, so it can be pulled off. I pull my skimmer and clean it monthly. Other then the fittings that are glued to the box, dry fit everything else. It takes less then 10 minutes for me to clean and re install my skimmer.

After reading about cleaning, that was the first idea that popped into my mind. I wouldn't mind being able to remove the neck of the skimmer as well as the bottom. Wouldn't I have to clean the neck of the skimmer more often than the bottom?

Also the exit pipe needs to rise up instead of going straight out. The position of the gate valve, also makes a difference on the internal water level and stability of that level. The top of the Valve should be right around the external water level.

I thought about that, but I have the skimmer body just slightly under the external water to force all bubbles to the skimmer neck. With the valve at the bottom, it won't restrict drainflow as much. When I adjust the valve just slightly, it will force more water into the skimmer neck because of back pressure, thus making the skimmate wetter. Is that a sound theory?

When you buy the gate valve, don't forget to grab a stainless screw to replace the one in the knob. I just change that out at the store lol, saves a few pennies. Actually, at ace hardware, they will change it out for you for free if you ask. [/B]

Cool. Now if I can find an all PVC gate valve. If anyone knows a place let me know.


So, dugg, what exit size do you recommend from the body of the skimmer? Think a 1" exit will work. After all, I'm just using a Mag9.5 as a return. I think I'll only be draining 600-700 gph when it's all said and done.

 

[dugg]

The gate valve is a must really. A ball valve doesn't restrict even close to the same. If you have an Ace Hardware, they will have one. Lowes and HD don't even know what one is lol. It will be well worth the search. The gate valve allows very fine tuning of the skimmate.

For the neck, i use a coupling glued to the top that the riser tube slips into. I clean the riser and cup atleast once a week.

As for exit size, i use a mag 7, and have 1 1/4 exit. If you go bigger the gate valve would be huge, if you go smaller, the gate valve will be harder to find. the 1 1/4 gate valve is a pretty standard one to find on the shelf. Locke supply may also be a place to look, but Ace always has them. If in OKC go to the ACE at SW 44th and western. It should be around $8.

 

[Travis L. Stevens]

I'll keep a close eye out. Thanks Doug. I'll check Locke and Atwoods first since they are here in Stillwater.

 

[cmc0814]

Travis, if you want I can try looking at the Ace Hardware here in Norman to see if they have one.

 

[Travis L. Stevens]

Actually, that would be awesome. Just give me a PM with all the different sizes and prices and we might be able to meet up next saturday at the meeting.

 

[cmc0814]

Well, I found out that I will be babysitting my brother in Texas, so I won't be able to attend. (My parents asked me so they could go to London for their 25th anniversary.) But I will make sure it gets there if you decide to go with it.

 

[captbunzo]

I don't necessarily have time to get into details right now, Travis, but I will personally be VERY selective with the creation of "downdraft" skimmers. In short, I've really decided that I don't think they work all that well...

If I was to build another, I'd design it similar to the spray injections skimmers sold by AquaC. Check your email for a tip there. Anyone else wanting the tip can email me.

 

[Travis L. Stevens]

I got your email and looked it over this morning. It's funny how things work out. I sat down at the drawing board last night after I plumbed the 75g and saw that I won't have enough room in order to do Draft 2. So, it was back to a re-design. I'm going to make a new design and post it up here later, but if I needed a recirculation mod, it was going to be a recirc/spray mod. I'll keep you posted.

 

[Travis L. Stevens]

Okay, here is the next draft. I had to do it like this because of a constraint on space. I can manage it if the drain comes in from the top and the exit goes vertical. It will be a tight fit. Of course, I'll find a way for the skimmer neck, skimmer cup, drain, exit, and skimmer bottom can all come off for cleaning. Let me know what you think.

If it turns out that the return pump just isn't enough flow, I was going to take a MaxiJet 1200 powerhead, plumb it to where it takes water from the bottom of the skimmer, and then spray it through the top. This should keep the bubbles down in the skimmer body longer, create more bubbles, and take some bubbles to be chopped up to make finer bubbles.

 

[pwhitby]

try this bad boy:

this was on my old 225 prior to getting a sump and deltec skimmer.

Its a counter current skimmer with an airstone (wood). Worked really well.

 

[Travis L. Stevens]

Very tempting! So, is that gate valve glued on?

 

[pwhitby]

Talking to me Trav?

 

[Travis L. Stevens]

Yes, sir.

 

[captbunzo]

Yes, it is....

 

[pwhitby]

heres the collection cup (more like barrel)

 

[Keelay]

How do you inject water/bubbles using draft one it's not clear?

 

[Travis L. Stevens]

It's similar to Draft 2's design. The drain from the tank enters on the bottom right side of the skimmer body. The 45º Angle piece of acrylic helps deflect bubbles upwards, and water flows out of all the little holes.

 

[Keelay]

Gotcha. Thought those were bubbles.

I don't recommend Draft 1. You won't have control over the skimmer water level.