cistern howto

8/10/2019 Cistern Howto

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Water is perhaps the most important requirement for your property. And storage is the most costly part of any watersystem.

Plastic tanks are easy to set up, but they are very expensive in larger sizes. Concrete ones are durable, but ill advisedfor any beginner, as they are prone to leaks if not done correctly, especially where the walls and floor meet. We havefound that the shell and liner system described in this article is by far the best option for us. It's cheap, easy (even for

just two people), and quick.

rn Howto http://velacreations.com/component/k2/313-cistern-howto.html?

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Materials

50 bricks (Compressed Earth or similar)

5 pieces 10ft x 4ft pieces of 18 gauge sheet metal

60 x 3/8" X 2" bolts, nuts and washers

50 ft of 2" angle iron

50 ft of 2" metal strip

12 x 3/4" PVC Ts

9 pieces of 20 ft 3/4" PVC

6 pieces of 20 ft 1/2" rebar

18 ft x 18 ft vinyl tarp

18 ft x 18 ft mesh (hail screen)

2x 5 gallon buckets of acrylic

3 bags cement

1x 1 " bulkhead

1x 1 " nipple, 3" long

1x 1 " valve

Silicon

Pond liner potable if needed 16 ft diameter, 5 ft tall

Overflow Parts (for this tank, we used 3" overflow)

1x 3" bulkhead

2x 3" male thread to PVC adaptors

3x 3" Elbows

1x 3" T

1x 3" cap

20ft X 3" pipe

Tools

Dirt-working tools (shovel, pic, etc.)

String

Tamper or Compactor

Level

Marker

Measuring Tape

Drill

Circular Saw

Welder


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1/8" drill bit

3/8" drill bit

Crescent wrenches

Hole saws

Saw (for PVC)

Concrete mixing tools

Large brushes with long handles

Step by Step

Sizing

This article is based on a 16ft diameter, 4 ft tall tank, holding6,000 gallons. However, you can alter the dimensions to fit yourneeds.

Round tank:

(3.14) x radius x radius x height x 7.5 = gallons

(e.g. 3.14 x 8ft x 8ft x 4ft x 7.5 = 6028.8 gallons)

Square tank:

length x width x height x 7.5 = gallons

(e.g. a 18ft square that is 4ft tall will hold 9,720 gallons)

Liner Dimensions:

You want to make your liner a little larger than the tank'sdimensions, so that it has some slack. Also make it 1ft taller than your tank's walls.

Even though a square tank is more efficient with space and thus your liner, we would unequivocally recommend goingwith a circular design. We have done both and the round one is far stronger and requires less work. Any money youmight save on the liner for a square tank is negated by the extra strength you will have to add to the frame. If youdecide to go square, bury the bottom 1/3 of the tank.

Site

Mark out the area where you wish to build your tank, andlevel it. You can dig down or fill in, though a combinationof the two is often the least labor intensive.

1.

Put a layer of sand, about 6" deep over the whole areaand compact it well.

2.

Place a rebar or post in the center of the area and attacha string to it.

3.

Tie the other end of the string to a stick or piece of metal,so that the distance between the stick and the centerpost equals the radius of your tank, in this case 8 ft.

4.

Keeping the string taut and the stick upright, mark thesand in a circle around the central post.

5.

Center bricks over this line all the way around thecircumference, leveling them with each other.

6.

Fill your circle with sand, then compact it well, so that the sand is an inch or two below the top of the bricks.7.

Fill that inch or so with finely screened sand and compact again.8.


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Walls

Drill 1/8" holes every 6" on a 4ft long strip of metal (therewill be 7 holes in total). This will be the jig that you use todrill the sheet metal, so that all your holes line up exactly.

1.

Clamp the jig onto one 4ft side of sheet metal and thendrill through the jig's holes into the metal. Make sure thatthe edges of the metal jig line up well, so that you will geta precise position on each sheet of metal. Repeat thisprocess until all five pieces of sheet metal have holes onboth 4ft sides.

2.

Using a 3/8" drill bit, drill out all these holes so that your3/8" bolts pass through easily.

3.

Stand up two pieces of sheet metal, so that their bottomedge is centered on the ring of bricks, and the holes onthe sides line up with each other.

4.

Bolt them together, making sure the bolt heads are on the inside of the circle and the threads on the outside.Start from the bottom bolt to the top.

5.

Continue bolting together the sheet metal until you have completed the circle.6.

Drive in small pieces of rebar at the base of the walls periodically. These rebar should go in the cracks betweenthe bricks. This will make sure the structure doesn't shift and fall off the bricks.

7.

Paint the metal walls, inside and out, with a quality metal primer and finish paint.8.

PlumbingPt1

There are three sets of plumbing to consider: the intake (whichcan go into the tank roof and will be addressed in the roofsection of these instructions), the outlet and the overflow.

Outlet:You can make this any size you wish. The larger it is, the

faster water will come out, but the more expensive your pipeswill be. Generally, pipes to a house are either 1/2" or 3/4". Youwant the outlet to be as low to the floor as you can get, and in alocation that is convenient to wherever you want to use thewater. On our tanks, we use 1 1/2" outlet sizes, to be able tohook multiple tanks together.

Overflow:The size of the overflow depends on the source ofwater that will be filling the cistern. For a rain catchment system,your overflow wants to be able to match or exceed the size ofpipes going from your gutters to the tank. At least 3" isrecommended, although more if the catchment area is very largeand you experience heavy, fast rains. The overflow point willwant to go as close to the top of the walls as you can make it. Think about where you want the overflow to go - whether

to another cistern, an orchard, or somewhere else that can safely handle the excess water - and place it accordingly.

Please note, that in this system the overflow point and the overflow pipe are 2 different things. Because we have a selfcleaning overflow design, the overflow point is actually higher than the pipe hole in the metal wall.

To position the overflow hole (where the overflow pipegoes through the wall), hold a 3" T against the side of thewall. The T should be on it's side, so that the long part isvertical. The bottom of the small side part is the overflowlevel. Make this about 4 inches below the top of the tank.This is the overflow point. Mark this spot with a marker.

1.

Cut a 4" piece of 3" PVC. On one end of this piece, put a3" elbow. On the other end, place another elbow, but turn

2.


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it 90 degrees compared to the first elbow.Line the top elbow up so the bottom of its side hole islined up with your overflow point. The bottom elbowshould be facing the wall. Draw a circle around theelbow. This marks your overflow hole.

3.

Now, position the bulkhead fitting over this hole, anddraw a line around it so that the line is slightly bigger thanthe threads on the fitting. Cut out this hole.

4.

For the outlet hole, hold the 1 1/2" bulkhead in place, about 1" from the bottom of the tank. Draw a line aroundthe threads of the bulkhead. This is the outlet hole.

5.

Drill out each hole with a metal hole saw. If you don't have a hole saw that fits the size perfectly, use a jigsawwith a metal blade. Drill a 3/8" hole on the inside edge of your line, and then use this hole to start cutting alongthe line.

6.

Liner

Fold five strips of vinyl tarp, 4.5ft long and a couple ofinches wide.

1.

Line these strips over each set of bolts, to protect theliner from any rough edges of the bolts. Tuck the bottomof each strip under the sheet metal walls and fold the topover the top of the sheet metal and attach it temporarily

to the highest bolt.

2.

Also put a strip of tarp on the top edge of the walls.3.

Place another piece of vinyl tarp on the floor of yourcircle, so that your liner will be protected from any littlerocks in the sand.

4.

Get out your liner somewhere outside of the tank and foldit in a way that will be easy to unfold in place. This is bestdone by unfolding completely, then folding the sidestowards the center, then rolling the whole thing up from one side to the next. Lift the liner inside the cisternwalls.

5.

Position the liner on one side of the tank, then unroll it.Position the bottom of the liner on the floor, so that itmeets the walls evenly, then lift the sides of the liner upagainst and over the metal walls. There should be abouta foot of extra liner on the outside of the walls, and onceit is all in place, it will hold itself. Make sure to leave a bitof slack on the sides.

6.

PlumbingPt2


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From the outside, draw a circle through the outlet and overflow holes in the metal onto the liner.1.Cut out each circle, but not all the way to what you marked. Make the liner hole about 1/8" smaller on all sides.2.You want the flat part of the bulkhead on the inside of the tank. Unscrew a bulkhead, but leave the grommet inplace. From the inside of the tank, push the bulkhead through the liner hole, and then through the hole in themetal. Screw the bulkhead nut in place. Tighten it well and put a bead of silicon around it where it meets theliner.

3.

For the overflow fittings, you don't need PVC glue, especially for the fittings on the inside of the tank. Just pushthem together.

4.

On the inside of the overflow bulkhead, screw a malethread to PVC adaptor. Cut a 4" piece of 3" pipe, andinsert it into the adaptor. Now, take your elbow assemblyfrom step 4, and push the bottom elbow on the pipe.

5.

Cut a 4" piece of 3" PVC and insert it into the top elbow.On the other end of this pipe, push on the T, with the longpart vertical.

6.

Measure from the bottom of the T to the bottom of thetank. Subtract the height of an elbow from thismeasurement. Now, cut a piece of 3" PVC to fit thismeasurement.

7.

Put an elbow on one side of this pipe, and the other endshould go up into the bottom of the T.

8.

With the remaining 3" PVC, lay it on the ground andmake a line of 3/8" holes for the entire length of PVC.These hole should be about 4" apart. On the other side of

the pipe from this line make a few 1/8" holes, maybe 6holes for the entire length of the pipe.

9.

Place the 3" cap on one end of this pipe, and the other end can insert into the elbow on the overflow assembly.Make the 3/8" line of hole face the tank bottom. The pipe should lay on the ground, and try and make it gotowards the outlet bulkhead as much as possible.

10.

On the outside of the overflow's bulkhead, screw a male thread to PVC adaptor. You can then attach PVC pipeto this to take the overflow's water to where you want it to go.

11.

On the outside of the outlet's bulkhead, screw in a threaded nipple and then a valve. From the valve, you canattach pipes to take the water to wherever you want to use it.

12.

Roof Support

Lay out two 20 ft and one 10 ft pieces of 2"angle iron. On

one side of the angle iron, drill 3/8" holes, one foot apart,about 3/8" from the edge.

1.

On the other side of the angle iron, cut the metal every 6inches with a chop saw. This will allow the angle iron tobend easier.

2.

Using a small strip of metal as a bridge, weld the fivepiece of angle iron together.

3.

Paint the angle iron and metal strips with a high qualitymetal primer and finish paint.

4.

Bend the continuous piece of angle iron to snugly fit theinside of the tank, so that the horizontal part is about aninch below the top of the walls. Mark where it joins itself,remove it and weld it together so that it is a circle.

5.

Put the circle back inside the tank, so that the horizontal

part is about an inch below the top of the walls, andclamp it in place.

6.

Hold the 10ft x 2" strips of metal on the outside of thetank walls, level with the angle iron. Through the holes of the angle iron, mark the strips of metal. Remove thestrips and drill out the holes using a 3/8" drill bit.

7.

Bolt the strips to the angle iron, removing the clamps as you go. These two pieces of metal not only clamp theliner in place, but the angle iron also serves as a support for the roof.

8.

This roof is designed to allow any rain that falls on it to enter the tank.

Roof


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You need to make a ring of 3/4" PVC that sits on theangle iron support. Within this ring, place twelve 3/4" Tsalternatively at 37" then at 63". The Ts want to be angledup at about a 30 degree angle. None of this PVC needsto be glued together, which helps to make minoradjustments as you go along.

1.

Cut 6 pieces of 17ft long 3/4" PVC.2.Cut 6 pieces of 17ft long 1/2" rebar.3.Feed the rebar intoeach piece of PVC andthen place each pieceof reinforced PVC intothe Ts on the outercircle according to thediagram. As eachpiece goes into place,the structure will getincreasingly strong.

4.

Put a piece of vinyltarp over your frameand tuck it under thePVC circle. Cut off anyexcess from the inside.

5.

Do the same with a mesh like hail screen.6.From the inside of the tank, screw the tarp and screen to the PVC circle, every 6". Now you can screw the PVC

circle into the angle iron.

7.

Cut out a hole for your access door. It wants to be big enough for you to comfortably fit through. Add some extraPVC around the door opening for added support. You can make the door out of any material later, so long as itfits over the opening and is either removable or hinged.

8.

Cut a hole out of the tarp and mesh where you want your inlet pipe to go. Place a PVC elbow (already attachedto your inlet pipe if you wish) into the hole.

9.

(NOTE: If you are using the tank for fish, use greenhouse plastic instead of the tarp and mesh, and you are done).

Concrete

With large brushes on long handles, paint the whole roofwith a layer of acrylic, cement and water. You want the

consistency to be like sour cream. It will not completelycover all parts of the mesh.

1.

Once the first coat is dry, you can apply the second coat.The second coat wants to be a mix of acrylic, cementand water with sifted sand added. Try and cover themesh completely with this coat.

2.

For the third and final coat, do not put sand in, justcement, acrylic and water.

3.

Each coat dries fairly quickly. You can add more coats ifyou wish, but three are sufficient for this purpose. As itcures properly (over a week or two), it will getincreasingly hard.

4.

Paint the roof with a white, waterproof paint.5.

Sweep out the interior of the tank, and clean up any acrylic concrete that may have spilled inside. The tank cannow be filled with water and used.

6.


2/11/2014

cistern howto

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