Enjoy!
J. Charles Delbeek
Honolulu, HI, 1995

Larry Jackson's Skimmer for Dummies

By Larry L. Jackson

Here is a list of parts necessary to build a PVC Foam Fractionator (FF). This will build a unit roughly 54-inches tall. The contact area of the FF is about 48 inches. I have heard it suggested that 30 inches of contact height is necessary to achieve adequate removal of dissolved organics, so making the unit as much as 18 inches shorter would seem to be okay. It is quite possible that adequate function can be achieved with even shorter units since the water takes a tortuous path to the bottom of the unit when sufficient air is being introduced.

Table 1: Parts Needed to Build a Counter-Current Foam Fractionator

Part	Number	Description	Diagram	Universal Part #
1	1	4-inch PVC DWV plug (modified)		450-040
2	1	4-inch PVC DWV adapter (modified)		435-040
3	1	4-inch by 2 inch PVC DWV bushing (modified)		437-420
4	1	6-inch Sch 40 or 80 clear PVC		none
5	1	2-inch PVC male adapter (modified)		436-020
6	1	3-inch by 2-inch SxT PVC bushing		438-338
7	1	3-inch SS PVC Coupling		429-030
8	1	~ 4-inch length of 3-inch diameter Sch 40 PVC		none
9	1	3-inch by 3/4-inch SST PVC tee		402-334
10	1	3/4-inch mpt by 3/4-inch nylon barb fitting		none
11	1	~36-inch length of 3-inch diameter Sch 40 PVC		none
12	1	4-inch PVC countersunk adapter (use a 3-inch to 4-inch bushing adaptor to attach this to the bottom of part 11).		435-040
13	1	4-inch PVC countersunk mpt plug		450-040
14	1	1/4-inch mpt by 1/4-inch nylon barb elbow		none
15	1	3/4-inch PVC Sxfpt 90 PVC elbow		407-007
16	1	~36-inch length of 3/4-inch diameter Sch SDR21 PVC		none
A B C D E	2 1 1 1 1	3/4-inch plastic close nipple (see text) 3/4-inch plastic gate valve 3/4-inch SST PVC tee ~36-inch length of 3/4-inch diameter Sch SDR21 PVC 3/4-inch SS PVC elbow		none none 402-007 none 406-007

Parts A through E are for the outflow of the FF. One close nipple (A) screws into Part 15. The gate valve (B) is screwed onto the other end of thi s nipple. The other nipple (A) connects the gate valve (B) to a tee (C). The tee provides a siphon break for the 3/4-inch thin wall PVC (D) that goes to the sump in such installations. The 3/4-inch thin wall PVC has an elbow (E) at the bottom to reduce splash of water entering the sump. Note in side view that the elbow is near the surface level of water in the sump (SD) to minimize problems associated with bubbling and splashing. I also stuffed a loose piece of plastic DLS material into the exhaust e nd of the elbow to further reduce bubbling and splashing with the added benefit of quieting the exiting flow. Unfortunately, this plastic will collect fibrous material and cause some clogging over time, but is easy to clean. A short piece of 3/4-inch th in wall PVC installed in the upward pointing part of the tee will provide overflow protection and reduce a bit of splash that can occur at this location. I made the upper piece four inches tall.

This parts list assumes use of soft vinyl 3/4-inch tubing connecting the FF to a surface extractor at the tank. I use an Otto 2000 or Hagen 801 (or 802) powerhead to return water from a Rubbermaid deep dishpan to the tank via 5/8-inch soft vinyl tubing. I installed a 1/2-inch plastic boiler drain valve in the return line to balance the FF flow with the return flow from the sump. Note that the return enters the tank at water level so that back siphon problems are avoided when the pump is off. I used a 7 1/4-inch tall 4-inch diameter PVC section to support an inverted 2-gallon water bottle in the sump for evaporation/kalkwasser addition. I drilled a hole in the base of the 4-inch PVC for circulation in the base of the evap/kalk support.

The FF could be easily adapted to gravity feed back to a tank and be supplied by a powerhead. I set the first one I built up in this manner, but prefer the sump-type installation since I found it easier to balance surface skimming with evap/kalk additions. The surface extractor insures maximum removal of surface films, efficient foam fractionation and better light transmission onto th e water. A surface extractor is a prefilter that does no filtering (although filtering can be added easily if desired). I build surface extractors out of 1/4-inch acrylic. Although they are a bit more complicated to build, I would suggest strongly that you build or buy one to feed surface water to any foam fractionator.

The diagram should allow assembly without further explanation. It is best to trial fit parts if there is any question. Vaseline will allow parts to be firmly seated in place and then taken apart, cleaned and glued when satisfied that everything is correct. All these parts are available from well-stocked hardware stores or plumbing-supply houses. If not in stock, most parts can be gotten ve ry quickly, since all are common. The plastic gate valve is the most expensive part of this FF. Although prices will vary, I estimate that this unit will cost about $30 to assemble.

When adjusting the FF, there is a subtle transition in the bubble filled column where mostly water with lots of bubbles changes to mostly bubbles with a bit of water. I have found that adjusting the gate valve so that this transition point is visible in the clear PVC foam throat is where I get best dry-foam production. Since foam production varies with flow rate and the amount of air injected, you will have to find what works for you. Looking down into the foam throat with the cap removed will reveal some information about foam height in the foam throat also.

Charles' Notes

There are, of course, modifications that could be made to improve the efficiency and capacity of any skimmer, and this one is no exception:

1. By increasing the diameter of part 4 to close to the diameter of the skimmer, you could easily double the flow rate and capacity of water the skimmer could handle per hour. This modification would also increase the amount of air that can be introduced .
2. Larry made a further modification in his design just before I made this document. He increased the diameter of parts 12 and 13, from 3 to 4 inches, thereby giving the skimmer a larger, more stable base.
3. The number of airlines could be increased to two to inject more air if you increased the diameter of part 4.
4. Of course one could do away with air pumps and airstones by using a Venturi design instead. This would best be done by devoting a dedicated water pump to circulate water within the skimmer and placing the Venturi injector in-line with
   this pump. T hat way you could still use Larry's passive overflow system.
5. The beauty of this design is that you could easily scale it upwards to create whatever
   size skimmer you wanted, be it 6 or 8 inches in diameter.

For further info and assistance in building this skimmer contact Larry L. Jackson
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