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\begin_body

\begin_layout Title
Low Flow SRSF Fabrication 
\end_layout

\begin_layout Author
Harrison Gill
\end_layout

\begin_layout Date
December 5th, 2012
\end_layout

\begin_layout Part*
An Overview of the Technology
\end_layout

\begin_layout Standard
Filtration is the final step in water treatment before the clean water is
 chlorinated and sent to the distribution system.
 Stacked Rapid Sand Filtration makes used of a sand bed to remove the remaining
 particles at the end of the treatment process in an efficient manner.
 Unlike conventional Rapid Sand Filters, the SRSF uses multiple layers of
 sand and injection points to enable the filter to be backwashed using the
 same driving head that runs it during filtration.
 This eliminates the need for pumps, elevated storage tanks, and reduces
 the number of filters necessary to treat a given flow rate.
 
\end_layout

\begin_layout Standard
The possible flow rates in a given filter are dictated by the necessary
 backwash velocity to fluidize the sand bed and expand it by 15%.
 The dimensions of the filter are then dictated by the area necessary to
 achieve that backwash velocity at a given flow rate.
 Current filter dimensions are constrained by the area necessary in the
 filter bay for a person to move around to install and service the internal
 parts in the filter.
 This limits area of the filter to something on the order of a box 0.75 m
 on a side.
 The filter requires a backwash velocity of approximately 11 mm/s, this
 means that the lowest flow rate the current filter design can treat is
 about 6 l/s (
\begin_inset CommandInset ref
LatexCommand ref
reference "Adelman et. al."

\end_inset

).
 
\end_layout

\begin_layout Standard
There is a strong demand for plants with flow rates on the order of 3 l/s.
 Because of the constraints on dimensions, it is not possible to build a
 viable filter for that flow rate using current fabrication techniques.
 It may be possible to build a low flow filter inside of a large diameter
 pipe in such a way that it could be assembled by reaching in from the top
 and bottom of the pipe.
 The filter would be limited to 1.5 m in length and the entire vessel would
 need to be kept air tight to ensure that the filter could backwash under
 negative pressure.
 Using such a design a 0.8 l/s filter can be built using 12
\begin_inset Quotes erd
\end_inset

 diameter PVC pipe.
\end_layout

\begin_layout Part*
An Overview of the Design
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename plumbing diagram.pdf

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "fig:Filter schematic"

\end_inset

Picture of Filter
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
The body of the Low Flow Stacked Rapid Sand Filter is built in a section
 of 12
\begin_inset Quotes erd
\end_inset

 schedule 40 PVC pipe capped with 3/8
\begin_inset Quotes erd
\end_inset

 aluminum bulkheads.
 The internals consist of 7 1
\begin_inset Quotes erd
\end_inset

 manifolds which each distribute water to six sections of slotted pipe.
 The layers are arrayed at 20 cm intervals on alternating sides of the filter.
 The side of the filter with the 4 manifolds is for the settled water and
 the side with the three outlets is for the filtered water.
 All the manifolds are connected to check valves except the bottom inlet
 to prevent short circuiting during the backwash cycle.
 The valves then connect to 2
\begin_inset Quotes erd
\end_inset

 pipes which act as manifolds to distribute water to the different layers.
 Water enters the system at the top of the inlet pipe via free fall from
 the sedimentation tanks to hydraulically disconnect the filter from the
 rest of the plant.
 The outlet pipe also allows water to leave via free fall to ensure that
 the filter does not back up and flood.
 Because the filter is a pressurized vessel, in theory, the only elevations
 that matter so long as all of the pipes remain full of water are the relative
 heights of the inlet free surface, the outlet free surface, and the backwash
 free surface relative to each other.
 The backwash exit height will determine the the height of water in the
 inlet pipe during backwash and the height of the outlet pipe will determine
 the height in the inlet pipe during filtration.
 This means that so long as the backwash pipe can be lowered sufficiently
 far, the filter can be placed at whatever elevation is convenient in the
 plant.
 
\end_layout

\begin_layout Standard
The inlet pipe and check valves are all 2
\begin_inset Quotes erd
\end_inset

 diameter PVC pipe.
 The outlet check valves are 1
\begin_inset Quotes erd
\end_inset

 PVC pipe that connects to a 2
\begin_inset Quotes erd
\end_inset

 outlet pipe.
 This is done to help ensure there is even flow distribution across the
 six sand beds.
 The 2
\begin_inset Quotes erd
\end_inset

 piping will help to reduce the headlosses on the inlet side of the filter
 and the 1
\begin_inset Quotes erd
\end_inset

 piping on the outlet side will help ensure that headlosses on the far side
 of the sand beds dominates.
 The even flow distribution is necessary to guarantee good performance by
 the filter.
 
\end_layout

\begin_layout Standard
To backwash the filter, the top three inlet manifolds will be turned off
 via a ball valve, this forces all the flow through the bottom manifold.
 The valve on the backwash outlet is then opened which forces all of the
 flow to exit through the top of the filter.
 The current design also includes a shutoff valve on the top of the exit
 manifold.
 Turning the valve off ensures that the flow will exit through the backwash
 pipe should the hydraulic connection be broken.
 The filter is sized so that the velocity in the main chamber will fluidize
 the sand bed and allow all of the trapped particulate mater to flow out
 of the filter.
 The backwash exit is submerged to ensure that there is a high enough pressure
 across the filter so that no addition head is required in the entrance
 pipe to drive the backwash cycle.
 
\end_layout

\begin_layout Part*
The Filter Design
\end_layout

\begin_layout Standard
\begin_inset Float figure
placement h
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename filter schematic.pdf
	BoundingBox 0bp 1.5in 210bp 297bp
	rotateAngle 90

\end_inset


\begin_inset Graphics
	filename manifold layout.pdf
	scale 25

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "fig:Manifold-top-view"

\end_inset

Manifold top view
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Section*
The internal manifolds
\end_layout

\begin_layout Standard
The manifolds are made of 1
\begin_inset Quotes erd
\end_inset

 PVC pipe which is drilled to accept 1/2
\begin_inset Quotes erd
\end_inset

 PVC pipe along their lengths.
 The manifold pipes are 8-1/2
\begin_inset Quotes erd
\end_inset

 long and the holes are drilled at 1-3/4
\begin_inset Quotes erd
\end_inset

 4-3/4
\begin_inset Quotes erd
\end_inset

 and 7-3/4
\begin_inset Quotes erd
\end_inset

 from the end of the pipe.
 The far end of the manifold is capped and the near end connects to a coupling.
 The holes should be drilled with a 27/32
\begin_inset Quotes erd
\end_inset

 wood cutting drill bit and should be drilled through both sides of the
 pipe.
 It is possible to do this on a drill press but the bit has a tendency to
 grab and pull the pipe out of the vice.
 It is better to drill the holes using a milling machine with an adjustable
 table.
 In either case, it is important that holes are drilled cleanly since the
 slotted pipe will be glued into them.
 The current design utilizes a section of rubber sheet and a hose clamp
 to seal the end of the manifold.
 A shallow glue on cap or rubber cap would make the design cleaner and easier
 to assemble.
 Plastic caps are inappropriate because the need to slide too far onto the
 manifold and run into the last pair of slotted pipes.
 They also have a domed end which takes up too much length across the body
 of the filter and makes them difficult to install.
 
\begin_inset Note Note
status collapsed

\begin_layout Plain Layout
It would be a worthwhile investment of time to figure out a better way of
 drilling these holes/attaching the slotted pipe.
 This method is messy, labor intensive, and is easy to mess up.
 Other ideas should be explored.
 Reducing crosses might be a possibility http://flexpvc.com/cart/agora.cgi?product
=PVC-Crosses
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Each of the manifolds requires 4 sections of 1/2
\begin_inset Quotes erd
\end_inset

 slotted pipe 4
\begin_inset Quotes erd
\end_inset

 long and 2 sections of 1/2
\begin_inset Quotes erd
\end_inset

 slotted pipe 5
\begin_inset Quotes erd
\end_inset

 long.
 The slotted pipe should slotted at 1/8
\begin_inset Quotes erd
\end_inset

 intervals with a 2 mm slot that is 1/2
\begin_inset Quotes erd
\end_inset

 long.
 The slotted pipe needs to be capped so that sand cannot come in through
 the ends.
 The cap needs to be low profile on the end of the pipe so that the manifolds
 will fit inside the filter and not take up much pipe length so that the
 minimal number of slots are covered.
 The lab prototype uses tapered plastic caps that are epoxied on to the
 end of the slotted pipe and then cut down so that the cover one slot or
 less.
 
\begin_inset Note Note
status open

\begin_layout Plain Layout
http://www.mcmaster.com/#4491K66
\end_layout

\end_inset

The slots are then glued into the manifolds using PVC cement.
 They should be oriented such that the strong axis is parallel with the
 central axis of the filter.
 The should be inserted into the manifold just far enough that they will
 remain in place.
 If any PVC cement gets on the slots run a razor blade through the slot
 to remove it.
 
\end_layout

\begin_layout Section*
The filter body
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename inlet side.PNG
	width 6cm

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
The filter body: Made of 6' of 12
\begin_inset Quotes erd
\end_inset

 schedule-40 PVC pipe.
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
The filter body is made of 12
\begin_inset Quotes erd
\end_inset

 schedule 40 PVC pipe which was purchased from flexpvc.com.
 In order for the caps to seal on the ends of the pipe it is important that
 the ends are cut extremely cleanly.
 The cut should be square to the body of the pipe and be smoothed so that
 there is no evidence of teeth marks.
 The inlet and outlet holes are drilled on opposite sides of the pipe and
 should be perpendicular to the surface of the pipe.
 The first inlet is drilled at 3 cm from the end of the pipe the other three
 inlets are drilled at 43 cm, 83 cm, and 123cm.
 The three outlets are drilled at 23 cm, 63 cm, and 103 cm.
 All of the inlets and outlets should be drilled using a 1-5/16
\begin_inset Quotes erd
\end_inset

 forstner bit.
 The holes in the prototype filter were drilled using a milling machine
 however it is likely possible to do on a drill press.
 As with the manifolds, the holes need to be drilled cleanly and accurately
 so that the pipes will seal in them.
 The diameter of the body is determined by the backwash velocity and the
 available flow rate.
 This design is for a filter that can process a flow rate 0.8 L/s but it
 is possible to adapt the design to 8
\begin_inset Quotes erd
\end_inset

, 10
\begin_inset Quotes erd
\end_inset

, and 14
\begin_inset Quotes erd
\end_inset

 pipes.
 
\end_layout

\begin_layout Standard
The caps seal on to the body with rubber gaskets.
 The gaskets are cut from sheets of rubber and are about 1
\begin_inset Quotes erd
\end_inset

 in width.
 In order to minimize the pressure required to seal against the gaskets
 the lip of the 12
\begin_inset Quotes erd
\end_inset

 pipe should be beveled so that the lip is about 3/16
\begin_inset Quotes erd
\end_inset

 thick.
 If there are any sawtooth marks on the end of the pipe they should be filed
 down so that they blend into the lip.
 Once this is done the pipe stubs can be glued into the holes in the walls
 of the pipe for the manifold connections.
 The pipe stubs are 4-1/2
\begin_inset Quotes erd
\end_inset

 sections of 1
\begin_inset Quotes erd
\end_inset

 pipe with a coupling pressed onto one side.
 The pipe stubs should be primed abutting the end of the coupling along
 with the inside of the holes through the filter body.
 The pipe stubs should be inserted into the filter wall from the inside
 so that the coupling protrudes into the interior of the filter and butts
 against the filter wall.
 This should leave several inches of pipe stub protruding from the outside
 of the pipe.
 To glue the stub in place, liberally apply PVC cement to the primed region
 abutting the coupling and then insert the stub into the filter wall from
 the inside of the filter.
 It may be helpful to use a mallet to drive the pipe stubs through the holes.
 
\end_layout

\begin_layout Section*
The filter cap
\end_layout

\begin_layout Standard
The initial design for the caps for the filter called for two 13-3/4
\begin_inset Quotes erd
\end_inset

 diameter 1/2
\begin_inset Quotes erd
\end_inset

 PVC plates.
 They were designed to connect to each other with six 1/4-20 rod and clamp
 on to the filter body.
 The plates were clamped on to the ends of the filter body.
 Unfortunately the PVC tended to deform under the tension required to seal
 the pipe walls against the gasket.
 The decision was made to remake the caps out of 3/8
\begin_inset Quotes erd
\end_inset

 aluminum plate instead.
 
\end_layout

\begin_layout Standard
Several different options were considered for the caps.
 The first was to purchase socket-weld flanges which would be glued onto
 the ends of the filter body and then to manufacture PVC plates that bolted
 onto the flanges.
 This would have made it extremely easy to remove the caps to access the
 internals of the filter and would have eliminated the need for the steel
 rods.
 This plan however was rejected due to the cost of the flanges, about $750
 a piece.
 However if cheaper flanges could be found it might be a viable option.
 
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename caps/topring.jpg
	scale 40

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Top ring
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename caps/bottom cap.jpg
	scale 40

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Bottom Cap
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
The new aluminum caps are 14
\begin_inset Quotes erd
\end_inset

 in diameter and are made from 3/8
\begin_inset Quotes erd
\end_inset

 aluminum plate.
 The same six threaded rods connect the two caps and hold them in compression
 on the filter body.
 The bottom cap requires six clearance holes for 1/4-20 rod arrayed radially
 at 6.684
\begin_inset Quotes erd
\end_inset

 from center.
 The top cap requires the same six holes as the bottom cap for the 1/4-20
 rods.
 It also has a 10
\begin_inset Quotes erd
\end_inset

 hole so that operators can access the internals of the filter should they
 need to.
 To attach the cap for the access hatch six holes tapped for 5/16-18 thread
 are drilled radially around the access port at 5.6525
\begin_inset Quotes erd
\end_inset

 from center.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename caps/top cap.PNG
	scale 40

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Access cap
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
The studs to hold the access port cap cover in place should be fully threaded,
 stainless steel, 5/16-18 bolts which are 1-1/2
\begin_inset Quotes erd
\end_inset

 long.
 They should have a rubber o-ring at the head so that when they are bolted
 into the inside of the top cap, they will seal.
 They should also be coated with locktite so that they will not loosen when
 the cap it tightened on to them.
 The cap is also made from 3/8
\begin_inset Quotes erd
\end_inset

 aluminum plate and is 12
\begin_inset Quotes erd
\end_inset

 in diameter.
 The cap bolts on to the studs and should be drilled with clearance holes
 designed to match with the studs on the top cap.
 The cap should have a 1-1/2 NPT threaded hole in the center to attach the
 backwash pipe.
 The cap should also have a 1
\begin_inset Quotes erd
\end_inset

 NPT threaded hole for the connection for the bed tester.
 (see drawing) A 1-1/2
\begin_inset Quotes erd
\end_inset

 threaded male to male socket weld adapter should be threaded into the central
 hole in the cap for the backwash system.
 A 1
\begin_inset Quotes erd
\end_inset

 threaded male to socket-weld male adapter should be threaded into the bed
 tester hole.
\end_layout

\begin_layout Standard
The bottom, top, and access caps all seal to their respective surfaces with
 rubber gaskets or O-rings.
 The access cap is sealed with a 10-1/2
\begin_inset Quotes erd
\end_inset

 1/8
\begin_inset Quotes erd
\end_inset

 o-ring.
 The gaskets for the top and bottom caps are cut from 1/16
\begin_inset Quotes erd
\end_inset

 rubber sheet such that they cover the ends of the pipe when the caps are
 tightened against them.
 The first design of the aluminum caps called for channels to be cut in
 to them.
 These channels would hold o-rings instead of rubber gaskets which would
 make assembly of the filter easer and eliminate the need to bevel the ends
 of the pipe.
 Unfortunately the channels made the machining of the parts considerably
 more expensive and provided little additional performance benefit.
 
\end_layout

\begin_layout Section*
Attaching the caps and manifolds to the filter body
\end_layout

\begin_layout Standard
The manifolds are relatively easy to insert into the body of the filter.
 To do so, first ensure that all caps are on all of the manifolds.
 Next, take a manifold and reach as far into the filter as possible and
 insert the manifold into the coupling.
 Push the manifold into the coupling as tightly as possible, this will be
 the only thing holding it in place.
 Check that the manifold is square in the body.
 It should be perpendicular to the central axis of the body.
 Continue inserting manifolds in the same manner until the last one is reached.
 At this point turn the filter over and repeat the process with the manifold
 that is farthest inside the body.
 It should be possible to insert all of the manifolds in this manner.
\end_layout

\begin_layout Standard
Attaching the caps to the filter body is a critical step since the connections
 between the plates and the pipe lip are the most likely places to leak.
 Before attaching the caps, ensure that the lip of the pipe is flat and
 free of burrs and dents.
 If there are burrs, gently smooth them out using a fine file.
 If there are dents, it may be possible to fill them with epoxy.
 Once the epoxy dries, file it down until it is level with the lip of the
 pipe.
 
\end_layout

\begin_layout Standard
To ensure the gaskets line up with the lips of the pipe, lay them out on
 the end caps and then tape them to the caps by using small tabs of tape
 that cover the outer edge of the gasket just enough to hold it in place.
 Lay two short sections of 2X4 on the floor and then place the bottom cap
 on them.
 Position the 2X4s such that all of the holes for the threaded rods are
 accessible from below.
 Place the filter body on to the cap.
 Ensure that the body is centered and the entire pipe lip is on the gasket
 and not covering the holes for the threaded rods.
 The gasket will have a tendency to move around on the bottom cap and fall
 of the lip on the top cap.
 This can be prevented by taping the outside edge of the gasket to its cap.
 The top cap is placed on the top lip of the body and oriented so that the
 bed tester will not intersect with the manifolds.
 The holes for the threaded rod should be lined up by rotating the bottom
 cap and then the rods inserted.
 The bottoms of the rods should be threaded with a washer and then two nuts.
 The nuts should be threaded on just far enough that they are on the end
 of the rod, they should then be locked against each other.
 The rods should then be inserted into the top cap and have washers and
 nuts threaded on them.
 The caps should be tightened in a star pattern and the tension should be
 kept even across all rods.
 The rods will have a tendency to spin when tightened.
 This can be prevented by holding the rod below the cap with a set of vice
 grips.
 
\end_layout

\begin_layout Standard
The bed tester is attached to the top cap via a flexible pipe coupling.
 The tester itself is made of a 5' section of 1/2
\begin_inset Quotes erd
\end_inset

 PVC pipe which is glued into a 1
\begin_inset Quotes erd
\end_inset

 to 1/2
\begin_inset Quotes erd
\end_inset

 reducer with the lip removed on a lathe.
 The coupling is attached to the cap by inserting the 1/2
\begin_inset Quotes erd
\end_inset

 pipe into the bed tester port and securing the bushing with the flexible
 coupling.
 Some space should be left between the bushing and the end of the pipe stub
 so that the pipe can be wiggled.
 a 1/2
\begin_inset Quotes erd
\end_inset

 ball valve is connected to the opposite side of the bushing so that the
 bed tester can be used to remove the sand from the filter if necessary.
\end_layout

\begin_layout Section*
The Inlet Manifold
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename manifold sketches/inlet manifold diagram.jpg
	scale 65

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
The Inlet Manifold: (1) 2
\begin_inset Quotes erd
\end_inset

 PVC pipe (2) 2
\begin_inset Quotes erd
\end_inset

 tee (3) 2
\begin_inset Quotes erd
\end_inset

 ball valve (4) 2
\begin_inset Quotes erd
\end_inset

 swing check valve (5) 2
\begin_inset Quotes erd
\end_inset

 elbow
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
The inlet manifold distributes water from the hydraulic disconnect at the
 top of the filter and into the slotted pipe manifolds in the body of the
 filter.
 The manifold must have minimal headloss to allow the sand bed to and downstream
 plumbing to determine the flow distribution.
 It must prevent short circuiting during backwash.
 It must be easy to replace valves should the break or need servicing.
 
\end_layout

\begin_layout Standard
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Filter schematic"

\end_inset

Shows the general piping schematic into the filter.
 The inlet pipe consists of a 2
\begin_inset Quotes erd
\end_inset

 pipe which is slightly taller than the highest point on the backwash system
 and drops to the bottom of the filter.
 There it intersects a 2
\begin_inset Quotes erd
\end_inset

 Tee fitting.
 The Tee connects on one side to a ball valve which is used to drain the
 filter, the other side connects to a second tee.
 The second Tee connects to a short section of 2
\begin_inset Quotes erd
\end_inset

 pipe which connects via a flexible 2
\begin_inset Quotes erd
\end_inset

 coupling to the reducing bushing on the filter body.
 The perpendicular leg of the second tee connects to a 2
\begin_inset Quotes erd
\end_inset

 ball valve and then the rest of the inlet manifold.
 The rest of the inlet manifold consists of sections of 2
\begin_inset Quotes erd
\end_inset

 pipe which connect to tees to distribute water to the remaining three inlet
 manifolds.
 The perpendicular leg of each tee connects to a 2
\begin_inset Quotes erd
\end_inset

 swing check valve.
 These valves prevent short circuiting during the backwash cycle which will
 be discussed below.
 The check valves connect to a 2
\begin_inset Quotes erd
\end_inset

 elbow, then a short section of 2
\begin_inset Quotes erd
\end_inset

 pipe which enables the manifold to connect to the reducer bushings on the
 filter body via flexible couplings.
 
\end_layout

\begin_layout Subsection*
Issues in the manifold design and construction.
\end_layout

\begin_layout Standard
In order for backwash to be successful the full filter flow rate must flow
 through the entire sand bed.
 This requires that all of the flow be diverted through the bottom manifold
 and a single path through the filter bed.
 To ensure that all of the flow goes through the bottom manifold it must
 be on a separate leg the manifold, hence the second tee.
 It must also be possible to shut off flow to the other inlets, hence the
 ball valve on the upper leg of the manifold.
\end_layout

\begin_layout Standard
The lengths of the various sections of pipe in the manifold will depend
 on the specific fittings used and thus are not specified here.
 The important parts of the manifold design are the flow path (down from
 the top and then up to the manifolds), the relative placement of components,
 and the fixed positions of the connections to the slotted pipe manifolds.
 The design used in the AguaClara lab apparatus and in the test filter in
 Honduras uses elbows to position the manifolds closer to the filter body
 to save on horizontal space but there is no reason the elbows could not
 be eliminated and the manifolds be built in a plane instead.
 
\end_layout

\begin_layout Standard
The manifold in the laboratory has the split between the bottom slotted
 manifold and the upper three at the top of the manifold column
\begin_inset Note Note
status open

\begin_layout Plain Layout
need a picture
\end_layout

\end_inset

instead of at the bottom.
 This sets a minimum water height in the filter such that the water get
 distributed to all four slotted manifolds.
 The manifold was redesigned for the prototype filter in Honduras with the
 plans contained in this design report.
\end_layout

\begin_layout Section*
The Outlet Manifold
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename manifold sketches/outlet manifold.jpg
	scale 75

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Outlet plumbing:(1) 2
\begin_inset Quotes erd
\end_inset

 PVC pipe (2) 2
\begin_inset Quotes erd
\end_inset

 tee (3) 2
\begin_inset Quotes erd
\end_inset

 ball valve (4) 2
\begin_inset Quotes erd
\end_inset

 to 1
\begin_inset Quotes erd
\end_inset

 reducing bushing (5) 1
\begin_inset Quotes erd
\end_inset

 swing check valve (6) 1
\begin_inset Quotes erd
\end_inset

 elbow
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
The outlet manifolds are designed to cause more headloss that than the inlet
 manifolds to help even out the flow distribution across the six sand beds.
 The pipe stubs from the slotted pipe manifolds connect to elbows and then
 1
\begin_inset Quotes erd
\end_inset

 swing check valves.
 As with the inlet manifolds, the swing check valves prevent short circuiting
 during the backwash cycle.
 The swing check valves then connect to 1
\begin_inset Quotes erd
\end_inset

 to 2
\begin_inset Quotes erd
\end_inset

 bushing which plugs into 2
\begin_inset Quotes erd
\end_inset

 tees.
 The tees are connected to 2
\begin_inset Quotes erd
\end_inset

 pipe to join them together and create the manifold.
 As with the inlet manifolds, the elbows are there to save lateral space
 around the filter but could be removed to create a 'winged' design.
 
\end_layout

\begin_layout Standard
Above the last outlet on the manifold is a 2
\begin_inset Quotes erd
\end_inset

 ball valve.
 This is there to shutoff the outlet to ensure that the filter goes into
 backwash.
 As long as the backwash pipe remains full, this valve should be unnecessary.
 There is a tee above the ball valve which acts as a weir and sets the water
 level throughout the rest of the filter.
 This should allow filter water to travel to the storage and distribution
 network via a hydraulic jump which will prevent downstream water levels
 from setting the height of water in the filter.
\end_layout

\begin_layout Section*
The Backwash System
\end_layout

\begin_layout Standard
The backwash system is designed to remove the dirt and clay particles from
 the filter bed once it has been filled.
 The system works by fluidizing the sand bed and allowing the particles
 to be resuspended and flow out of the system.
 To do this, the full flow entering the filter must be set through the bottom
 inlet manifold and out the top of the filter bed.
\begin_inset Note Note
status open

\begin_layout Plain Layout
diagram of the system
\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
The backwash system:
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
During backwash there is a significant amount of headloss.
 This is largely due to the sand in the filter bed which causes nearly one
 meter of headloss for every meter of sand that must be fluidized.
 In order to limit the height difference between the free surface in the
 inlet manifold during terminal headloss while filtering, and the sedimentation
 tanks, the exit of the backwash pipe needs siphon water from the filter.
 Based on reports from the Fall 2012 filter team
\begin_inset CommandInset citation
LatexCommand cite
key "key-2"

\end_inset

, the lab filter experienced approximately 200 cm of headloss during backwash.
 This means that the free surface at the end of the backwash pipe needs
 to be more than 200 cm below the point where the influent enters the filter
 system.
 
\end_layout

\begin_layout Standard
Because the backwash exit is lower than the filter, the filter system is
 under negative pressure relative to the atmosphere.
 This means that if the inlet manifold did not drop to the lowest point
 of the filter and then go back up (creating an u-bend) to the slotted manifolds
, the manifolds would suck air into the filter and break the hydraulic connectio
n.
 The negative pressure also sets the maximum distance below the bottom manifold
 the backwash outlet can be set, namely 200 cm before the bottom manifold
 also sucks air into the system.
\end_layout

\begin_layout Standard
The backwash pipe connects to the top of the filter through the 1-1/2
\begin_inset Quotes erd
\end_inset

 threaded hole in the access cap.
 The 1-1/2
\begin_inset Quotes erd
\end_inset

 pipe should connect to the male to male adapter via a flexible coupling
 or other removable connection so that the backwash pipe can be removed
 if the access cap needs to be removed.
 The valve used to turn on and off the filter should be at the lowest point
 on the backwash pipe.
 This is to facilitate the removal of air from the pipe should the hydraulic
 connection be broken.
 There should also be an air bleed valve at the highest point on the pipe
 to allow the air to escape the filter system when the backwash pipe is
 being filled.
 See the Fall 2012 filter team report for more details
\begin_inset CommandInset citation
LatexCommand cite
key "key-2"

\end_inset

.
\end_layout

\begin_layout Standard
It is important that the outlet of the backwash pipe be visible to the operator.
 This is for two reasons.
 The first is to observe the quality of the effluent during backwash to
 determine when backwash should cease.
 The second is to check to see if sand is escaping the filter during backwash.
 If sand is escaping it could cause failure of the filter.
 
\end_layout

\begin_layout Standard
The final component of the backwash system is the bed tester.
 The bed tester is designed to confirm that the sand bed is fully fluidizing
 during backwash.
 The system consists of a 170 cm length of 1/2
\begin_inset Quotes erd
\end_inset

 PVC pipe buried in the sand bed.
 The pipe passes up through the 1
\begin_inset Quotes erd
\end_inset

 threaded NPT adapter and terminates in a 1/2
\begin_inset Quotes erd
\end_inset

 to 1
\begin_inset Quotes erd
\end_inset

 reducer bushing which is machined such that it has the same OD a 1
\begin_inset Quotes erd
\end_inset

 PVC pipe along its entire length.
 The pipe should not be glued into this fitting in order to ensure that
 the cap can be removed without removing the pipe from the sand bed.
 The threaded male adapter in the cap and the bushing should be connected
 together with a flexible coupling so that the pipe can be wiggled.
 The pipe should then be capped to seal the system.
 If it is possible to easily wiggle the pipe during backwash, the bed is
 fluidized.
\end_layout

\begin_layout Section*
Operation
\end_layout

\begin_layout Subsection*
Filtration
\end_layout

\begin_layout Standard
During filtration the valve on the inlet manifold should be open to allow
 water to flow to all of the slotted inlet manifolds.
 The backwash valve should be closed as should the air bleed valve on the
 top of the backwash pipe.
 The shutoff valve on the outlet manifold should be open to allow water
 to flow to the distribution system and prevent the filter from backing
 up.
 During operation unfiltered water will travel through the inlet manifold
 and into the slotted manifolds.
 It will then split and flow through the six sand beds and enter the three
 outlet slotted manifolds.
 It will flow out and up the outlet manifold and leave via the hydraulic
 disconnect at the top of the pipe.
 
\end_layout

\begin_layout Subsection*
Backwash
\end_layout

\begin_layout Standard
Backwash occurs once the filter reaches terminal headloss, roughly 30 cm
 on the lab apparatus although this number will change depending what point
 the filter experiences breakthrough.
 The first step to backwashing is to ensure that the backwash pipe is full
 water.
 If the the water level in the inlet manifold is above the highest point
 in the backwash system the air bleed valve can be opened.
 If the water level in the inlet manifold is lower than the highest point
 in the backwash system, the valve on the outlet manifold should be slowly
 closed until the water level in the inlet manifold is high enough.
 In either case, the air bleed valve should be open until air ceases to
 come out and then closed.
 Next the backwash valve should be opened fully and then the valve on the
 inlet manifold closed to ensure that all of the flow is diverted through
 the bottom manifold.
 This sequence is important because forcing all of the flow through the
 bottom manifold causes much greater headlosses than spreading it over four
 manifolds and if all of the flow is diverted through the bottom manifold
 without the backwash valve opened, the filter will likely overflow.
 Once backwash is complete, approximately 5 minutes based on experimentation
 from the Spring 2012 filter team
\begin_inset CommandInset citation
LatexCommand cite
key "key-3"

\end_inset

, the valve on the inlet manifold should be open and then the backwash valve
 closed.
 At this point the filter will resume filtration.
 It is important that the first minute or so of filter water also be wasted
 since there will be residual backwash water in the slotted pipes which
 could contaminate the clean water in the storage tank.
\end_layout

\begin_layout Bibliography
\labelwidthstring References
\begin_inset CommandInset bibitem
LatexCommand bibitem
key "key-1"

\end_inset


\begin_inset CommandInset label
LatexCommand label
name "Adelman et. al."

\end_inset

Stacked Filters: A Novel Approach to Rapid Sand Filtration, Journal of Environme
ntal Engineering doi:http://dx.doi.org/10.1061/(ASCE)EE.1943-7870.0000562 Michael
 J.
 Adelman, Monroe L.
 Weber-Shirk, Ph.D., M.
 ASCE, Anderson N.
 Cordero, Sara L.
 Coffey, William J.
 Maher, Dylan Guelig, Jeffrey C.
 Will, Sarah C.
 Stodter, Matthew W.
 Hurst, and Leonard W.
 Lion, Ph.D.
\end_layout

\begin_layout Bibliography
\labelwidthstring References
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "2"
key "key-2"

\end_inset

filter team final report.
\end_layout

\begin_layout Bibliography
\labelwidthstring References
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "3"
key "key-3"

\end_inset

filter team spring 2012
\end_layout

\end_body
\end_document
