...
Installing
...
a
...
Chemical
...
Doser
...
Getting
...
a
...
new
...
chemical
...
doser
...
(CD)
...
ready
...
for
...
operation
...
requires
...
three
...
steps:
...
sizing,
...
assembly,
...
and
...
calibration.
...
The
...
information
...
under
...
the
...
general
...
headings
...
is
...
applicable
...
to
...
chemical
...
dosers
...
for
...
any
...
AguaClara
...
plant.
...
There
...
are
...
subheadings
...
for
...
Tamara
...
specifics
...
that
...
describe
...
dimensions
...
for
...
the
...
CD
...
that
...
are
...
unique
...
to
...
the
...
turbidity
...
range
...
and
...
flow
...
rate
...
of
...
the
...
Tamara plant. Further information on the theoretical modeling behind the Tamara design can be found here and general information about the AguaClara chemical doser can be found here.
Sizing
Sizing refers to both the CD design in MathCAD and the proper scaling for the plant. The MathCAD sheet that can be used to design a CD is attached to the main Linear Chemical Doser wiki page. The main constraint used in designing a CD is for it to deliver enough chemical (mg chemical per L plant flow rate) for the maximum plant requirement while making sure that the flow controller is not going to exceed the turbulent transition flow rate. The length of the lever arm can also constrain design depending on available space in the plant, therefore lever arm length is a required design input for the MathCAD design sheet. The lever arm is equal length on both sides of the pivot, and lever arm length is given in cm on either side of the pivot point (i.e. it is the effective length of the arm for dosing and calculations). To find the length of pipe required for the entire lever arm, multiply the lever arm length by 2.
The CD is designed to operate with the LFOM with a maximum head loss of 20 cm. The constraints are input to the MathCAD sheet to find a combination of FC outflow tubing length and inner diameter that matches the plant chemical dosing needs.
Another scaling issue that needs to be addressed before installation is the vertical relationships between the FC and the chemical stock tanks. The FC fill line cannot be located above the level of the stock tank exit, or else the FC will not maintain a constant head.
Sizing specifics for Tamara
| Wiki Markup |
|---|
{float:left plant. h2. Sizing Sizing refers to both the CD design in MathCAD and the proper scaling for the plant. The MathCAD sheet that can be used to design a CD is attached to the main [chemical doser] wiki page. The main constraint used in designing a CD is for it to deliver enough chemical (mg chemical per L plant flow rate) for the maximum plant requirement while making sure that the [flow controller] is not going to exceed the turbulent transition flow rate. The length of the lever arm can also constrain design depending on available space in the plant, therefore lever arm length is a required design input for the MathCAD design sheet. The lever arm is equal length on both sides of the pivot, and lever arm length is given in cm on either side of the pivot point (i.e. it is the effective length of the arm for dosing and calculations). To find the length of pipe required for the entire lever arm, multiply the lever arm length by 2. The CD is designed to operate with the LFOM with a maximum head loss of 20 cm. The constraints are input to the MathCAD sheet to find a combination of FC outflow tubing length and inner diameter that matches the plant chemical dosing needs. Another scaling issue that needs to be addressed before installation is the vertical relationships between the FC and the chemical stock tanks. The FC fill line cannot be located above the level of the stock tank exit, or else the FC will not maintain a constant head. h4. Sizing specifics for Tamara {float:right|border=2px solid black|width=500px350px} [!CD Calibration^FloatArmClearanceNoCaption.PNG|width=500px350px!|CD Calibration] {float} |
The
...
CD
...
fits
...
conveniently
...
on
...
the
...
wall
...
of
...
the
...
plant
...
entrance
...
tank
...
in
...
Tamara.
...
The
...
base
...
of
...
the
...
CD
...
will
...
be
...
attached
...
to
...
the
...
wall
...
via
...
a
...
saddle.
...
The
...
geometric
...
constraints
...
of
...
the
...
plant
...
should
...
not
...
interfere
...
with
...
the
...
chemical
...
doser
...
functioning
...
properly.
| Wiki Markup |
|---|
\\ {float:right|border=2px solid black|width=500px} [!CD Calibration^PerspectiveWAlumTank.PNG|width=500px!|CD Calibration] {float} |
In
...
Tamara
...
the
...
CD
...
lever
...
arm
...
can
...
be
...
no
...
longer
...
than
...
37
...
cm
...
(on
...
the
...
outer
...
side
...
of
...
the
...
pivot)
...
because
...
of
...
the
...
layout
...
of
...
the
...
plant.
...
AguaClara
...
Engineers
...
in
...
Honduras
...
asked
...
that
...
the
...
CD
...
stick
...
out
...
no
...
farther
...
than
...
the
...
rapid
...
mix
...
pipe
...
so
...
as
...
to
...
not
...
interfere
...
with
...
the
...
walkway
...
that
...
plant
...
operators
...
use
...
between
...
the
...
entrance
...
and
...
exit
...
tanks.
...
The
...
CD
...
for
...
Tamara
...
has
...
been
...
designed
...
to
...
require
...
a
...
lever
...
arm
...
with
...
35
...
cm
...
of
...
length
...
out
...
from
...
the
...
pivot.
...
The
...
full
...
range
...
of
...
chemical
...
dosing
...
is
...
accomplished
...
in
...
a
...
35
...
cm
...
span
...
by
...
using
...
3.25
...
m
...
of
...
3/16"
...
inner
...
diameter
...
tubing
...
for
...
FC
...
outflow
...
as
...
discussed
...
in
...
the
...
...
...
...
...
below.
...
There
...
is
...
13
...
cm
...
of
...
vertical
...
space
...
between
...
the
...
stock
...
tank
...
exit
...
and
...
the
...
plant
...
entrance
...
tank
...
wall.
...
This
...
means
...
that
...
the
...
FC
...
must
...
be
...
positioned
...
in
...
that
...
vertical
...
window.
...
The
...
steps
...
for
...
doser
...
frame
...
assembly
...
below
...
take
...
these
...
constraints
...
into
...
account.
Assembly
Not all parts for the CD can be purchased in Honduras. Fittings and UV-resistant tubing for use with chemicals need to be brought in. Please check the parts list to determine what is needed for assembly.
Doser frame
The first step in assembling the CD is to build the doser frame. This involves cutting the 1 ½" PVC pipe for the stand and the 1" PVC pipe for the lever arm.
| Wiki Markup |
|---|
h2. Assembly Not all parts for the CD can be purchased in Honduras. Fittings and UV-resistant tubing for use with chemicals need to be brought in. Please check the [parts list|CD parts list] to determine what is needed for assembly. h3. Doser frame The first step in assembling the CD is to build the doser frame. This involves cutting the 1 ½" PVC pipe for the stand and the 1" PVC pipe for the lever arm. {float:right|border=2px solid black|width=500px400px} [!CD Calibration^CuttingSaddle.png|width=500px400px!|CD Calibration] {float} |
The
...
1
...
½"
...
pipe
...
should
...
be
...
cut
...
with
...
a
...
circle
...
saw
...
followed
...
by
...
cuts
...
down
...
to
...
the
...
circle
...
in
...
order
...
to
...
create
...
a
...
saddle
...
shape.
...
The
...
bottom
...
of
...
the
...
saddle
...
must
...
be
...
at
...
least
...
3.9
...
cm
...
below
...
the
...
pivot
...
in
...
order
...
to
...
allow
...
a
...
full
...
20
...
cm
...
range
...
of
...
motion
...
in
...
the
...
lever
...
arm.
...
The
...
cut
...
must
...
be
...
wide
...
enough
...
to
...
allow
...
the
...
lever
...
arm
...
to
...
move
...
without
...
rubbing
...
on
...
the
...
stand.
...
The
...
1"
...
PVC
...
pipe
...
must
...
be
...
at
...
least
...
twice
...
as
...
long
...
as
...
the
...
lever
...
arm
...
length
...
parameter,
...
because
...
that
...
value
...
is
...
only
...
equal
...
to
...
the
...
effective
...
length
...
of
...
chemical
...
dosing
...
away
...
from
...
the
...
pivot
...
and
...
the
...
lever
...
arm
...
extends
...
equal
...
distance
...
in
...
both
...
directions
...
away
...
from
...
the
...
pivot.
...
Next
...
the
...
notches
...
for
...
chemical
...
dosing
...
increments
...
should
...
be
...
cut
...
along
...
the
...
lever
...
arm.
...
Each
...
notch
...
represents
...
an
...
increase
...
in
...
alum
...
dosing
...
of
...
a
...
constant
...
number
...
of
...
milligrams
...
of
...
alum
...
per
...
liter
...
of
...
plant
...
flow
...
rate,
...
for
...
example
...
each
...
notch
...
in
...
Tamara
...
is
...
for
...
an
...
increase
...
of
...
2
...
mg/L.
...
The
...
distance
...
between
...
notches
...
is
...
a
...
function
...
of
...
the
...
CD
...
design,
...
and
...
is
...
a
...
calculated
...
parameter.
...
The
...
notches
...
need
...
to
...
be
...
cut
...
deeply
...
enough
...
that
...
the
...
dosing
...
tube
...
ring
...
can
...
stay
...
in
...
the
...
notch
...
at
...
the
...
full
...
range
...
of
...
motion
...
without
...
slipping
...
out.
...
A
...
hole
...
should
...
also
...
be
...
drilled
...
straight
...
through
...
the
...
opposite
...
end
...
of
...
the
...
lever
...
arm
...
to
...
provide
...
somewhere
...
to
...
tie
...
the
...
float
...
to.
...
To
...
attach
...
the
...
lever
...
arm
...
to
...
the
...
stand,
...
a
...
hole
...
gets
...
drilled
...
through
...
both
...
pieces
...
(stand
...
and
...
lever
...
arm)
...
that
...
line
...
up
...
to
...
form
...
the
...
pivot.
...
Make
...
sure
...
the
...
lever
...
arm
...
is
...
being
...
drilled
...
exactly
...
in
...
the
...
center
...
of
...
the
...
pipe.
...
A
...
screw
...
or
...
pin
...
gets
...
inserted
...
through
...
the
...
holes
...
to
...
act
...
as
...
the
...
pivot.
...
Move
...
the
...
lever
...
arm
...
up
...
and
...
down
...
to
...
make
...
sure
...
there
...
is
...
little
...
friction
...
between
...
the
...
two
...
pipes.
...
The
...
final
...
aspect
...
of
...
the
...
frame
...
to
...
construct
...
is
...
the
...
base.
...
The
...
1
...
½"
...
PVC
...
pipe
...
stand
...
fits
...
into
...
a
...
flange,
...
which
...
then
...
should
...
be
...
bolted
...
to
...
a
...
wall
...
saddle.
...
The
...
entrance
...
tank
...
wall
...
may
...
not
...
be
...
strong
...
enough
...
to
...
support
...
drilling
...
so
...
the
...
team
...
in
...
Honduras
...
can
...
use
...
local
...
materials
...
to
...
create
...
a
...
saddle
...
that
...
holds
...
the
...
CD
...
firmly
...
in
...
place
...
on
...
the
...
wall,
...
without
...
drilling
...
into
...
it.
...
Frame
...
assembly
...
specifics
...
for Tamara
| Wiki Markup |
|---|
Tamara {float:right|border=2px solid black|width=500px350px} [!CD Calibration^CDTamaraFrameDims.png|width=500px350px!|CD Calibration] {float} |
Each
...
lever
...
arm
...
notch
...
represents
...
an
...
increase
...
in
...
alum
...
dosing
...
of
...
2
...
mg/L.
...
For
...
Tamara
...
a
...
maximum
...
of
...
50
...
mg/L
...
alum
...
dosing
...
(mg
...
chemical
...
per
...
L
...
plant
...
flow
...
rate)
...
was
...
designed
...
for,
...
so
...
the
...
35
...
cm
...
lever
...
arm
...
can
...
be
...
divided
...
up
...
by
...
25
...
equally
...
spaced
...
notches
...
for
...
2
...
mg/L,
...
4,
...
6...50
...
mg/L
...
where
...
0
...
mg/L
...
is
...
the
...
pivot
...
and
...
50
...
mg/L
...
is
...
the
...
far
...
tip
...
of
...
the
...
lever
...
arm.
...
Because
...
the
...
farthest
...
dosing
...
notch
...
must
...
be
...
located
...
at
...
the
...
35
...
cm
...
mark,
...
the
...
lever
...
arm
...
should
...
be
...
made
...
an
...
extra
...
centimeter
...
longer
...
(i.e.
...
36
...
cm
...
on
...
both
...
sides)
...
so
...
that
...
there
...
is
...
room
...
to
...
cut
...
the
...
farthest
...
notch.
...
Placing
...
25
...
equally
...
spaced
...
notches
...
means
...
that
...
there
...
must
...
be
...
exactly
...
1.4
...
cm
...
between
...
the
...
center
...
of
...
each
...
of
...
the
...
notches.
To assemble the CD stand for Tamara it is important to keep the FC water level below the stock tank outflow. Cut the 1 ½" PVC pipe for the stand so that it will be 13 cm tall when attached to the saddle and flange. The wall saddle will be constructed locally, so simply subtract the thickness of the saddle and flange from 13 cm and then make the stand that tall.
Dosing tube system
A flow controller (FC) is already in place in AguaClara plants, and that existing FC can be clamped onto the CD. Use two hose clamps with a strip of metal connecting them so that the FC is firmly in place. The exact height of the FC on the CD is very important with respect to two parameters. The alum level in the FC cannot be above the height of the stock tank outflow, but this constraint should be met automatically by keeping the height of the CD frame as tall as the outflow while ensuring that the FC is not sticking up above the pivot. The second parameter is that there should be no alum flow when the lever arm is exactly horizontal. This means that the FC must be placed at a height where the pressure break tee is even with the alum level in the FC. Temporarily attach the FC and continue to assemble the tubing before moving onto the section on calibration for more detail on FC height.
The length and inner diameter of the FC outflow tubing are calculated parameters based on the CD MathCAD sheet. This is designed to give the plant the correct dosing response for the desired dosing increments.
The ½" outer diameter tubing from the pressure break tee is designed to be long enough to allow some alum to always remain in the tube, while not overflowing when the highest dosage and flow rate are used. It is 25 cm long to hold 2 cm of alum in it at a plant flow rate of zero, while containing 22 cm of alum when the lever arm moves down by 20 cm at full plant flow.
The ¼" outer diameter tubing leaving the ½" tube needs to plug into the rapid mix 2 cm above the bottom of the ½" tube at the zero plant flow rate. This is what keeps 2 cm of alum in the ½" tube at all times. The length of the ¼" tubing depends on the distance between the rapid mix and the CD. Make sure the tubing is long enough to reach at the full lever arm range of motion (20 cm).
A series of connectors are required to switch between ¼" and ½" tubing and fittings. A ½" pressure break tee is used, with two reducer stems (1/2" to 3/8" and 3/8" to ¼"). At the bottom of the ½" tube a ½" to 3/8" reducing union and a 3/8" to ¼" reducer stem are used to connect tubing.
The ½" pressure break tee is also used to attach the dosing tube system to the lever arm. A dosing ring (loop that can be made from any type of rigid wire) is threaded through small holes drilled through the open top of the tee. The ring should be designed so that it fits into the lever arm notches well without slipping out because it will be the only thing used to set the dosing tube position.
Dosing tube specifics for Tamara
Make sure for Tamara that 3.25 m long 3/16" inner diameter tubing is used to connect the FC to the pressure break tee. The rest of the general tubing specifications above are correct for the system but the FC outflow tubing is a plant-specific parameter.
Float assembly
The main factors governing float assembly are diameter of the float and its center of mass. The minimum outer diameter for a float being used with this chemical dosing tube system is 6.3 inches, based on the weight of the dosing tube system. This is designed to give no greater than 5 mm of variation in float height as the dosing tube system is moved toward and away from the pivot across the entire range of plant flow rates. The height of the float is not designed for quantitatively, but the following conditions must be met:
- When filled with sand the float's center of mass is below the water line
- This ensures float stability
- The float is not so short that it is light enough to be pushed around the entrance tank by turbulence
The float is made by gluing caps on the end of a PVC pipe that has been partially filled with sand, or some other type of clean dry fill. A hook is then screwed into the center of the top of the float to serve as an anchor. Rope or some other type of tough string then ties the float to the end of the lever arm.
Calibration
Once the CD is built it is important to zero the lever arm properly. Do this by draining the entrance tank until it is barely at zero plant flow. This is when the water level in the tank is halfway up the bottom row of holes in the linear flow orifice meter. When the tank is at zero plant flow, just barely lower than the lowest flow rate, adjust the length of the lever arm-to-float rope so that the lever arm is exactly horizontal. After it is leveled, adjust the height of the FC as needed to make sure that there is just barely no alum flowing. Alum should begin to flow with one extra millimeter of driving head from this zero. Now tighten the hose clamps to ensure that the FC will remain at its calibrated height.
Next fill the plant entrance tank to its height for maximum flow rate, halfway up the top row of holes in the linear flow orifice meter. The lever arm should be at the top end of its height range (20 cm down at the tip).
| Wiki Markup |
|---|
!CD Calibration^CDLeverArmWNotches.png! To assemble the CD stand for Tamara it is important to keep the FC water level below the stock tank outflow. Cut the 1 ½" PVC pipe for the stand so that it will be 13 cm tall when attached to the saddle and flange. The wall saddle will be constructed locally, so simply subtract the thickness of the saddle and flange from 13 cm and then make the stand that tall. h3. Dosing tube system A flow controller (FC) is already in place in AguaClara plants, and that existing FC can be clamped onto the CD. Use two hose clamps with a strip of metal connecting them so that the FC is firmly in place. The exact height of the FC on the CD is very important with respect to two parameters. The alum level in the FC cannot be above the height of the stock tank outflow, but this constraint should be met automatically by keeping the height of the CD frame as tall as the outflow while ensuring that the FC is not sticking up above the pivot. The second parameter is that there should be no alum flow when the lever arm is exactly horizontal. This means that the FC must be placed at a height where the pressure break tee is even with the alum level in the FC. Temporarily attach the FC and continue to assemble the tubing before moving onto the [section on calibration] for more detail on FC height. The length and inner diameter of the FC outflow tubing are calculated parameters based on the CD MathCAD sheet. This is designed to give the plant the correct dosing response for the desired dosing increments. The ½" outer diameter tubing from the pressure break tee is designed to be long enough to allow some alum to always remain in the tube, while not overflowing when the highest dosage and flow rate are used. It is 25 cm long to hold 2 cm of alum in it at a plant flow rate of zero, while containing 22 cm of alum when the lever arm moves down by 20 cm at full plant flow. The ¼" outer diameter tubing leaving the ½" tube needs to plug into the rapid mix 2 cm above the bottom of the ½" tube at the zero plant flow rate. This is what keeps 2 cm of alum in the ½" tube at all times. The length of the ¼" tubing depends on the distance between the rapid mix and the CD. Make sure the tubing is long enough to reach at the full lever arm range of motion (20 cm). A series of connectors are required to switch between ¼" and ½" tubing and fittings. A ½" pressure break tee is used, with two reducer stems (1/2" to 3/8" and 3/8" to ¼"). At the bottom of the ½" tube a ½" to 3/8" reducing union and a 3/8" to ¼" reducer stem are used to connect tubing. The ½" pressure break tee is also used to attach the dosing tube system to the lever arm. A dosing ring (loop that can be made from any type of rigid wire) is threaded through small holes drilled through the open top of the tee. The ring should be designed so that it fits into the lever arm notches well without slipping out because it will be the only thing used to set the dosing tube position. h4. Dosing tube specifics for Tamara Make sure for Tamara that 3.25 m long 3/16" inner diameter tubing is used to connect the FC to the pressure break tee. The rest of the general tubing specifications above are correct for the system but the FC outflow tubing is a plant-specific parameter. !CD Calibration^TubingSizingInstallation.PNG! h3. Float assembly The main factors governing float assembly are diameter of the float and its center of mass. The minimum outer diameter for a float being used with this chemical dosing tube system is 6.3 inches, based on the weight of the dosing tube system. This is designed to give no greater than 5 mm of variation in float height as the dosing tube system is moved toward and away from the pivot across the entire range of plant flow rates. The height of the float is not designed for quantitatively, but the following conditions must be met: * When filled with sand the float's center of mass is below the water line ** This ensures float stability * The float is not so short that it is light enough to be pushed around the entrance tank by turbulence The float is made by gluing caps on the end of a PVC pipe that has been partially filled with sand, or some other type of clean dry fill. A hook is then screwed into the center of the top of the float to serve as an anchor. Rope or some other type of tough string then ties the float to the end of the lever arm. h2. Calibration Once the CD is built it is important to zero the lever arm properly. Do this by draining the entrance tank until it is barely at zero plant flow. This is when the water level in the tank is halfway up the bottom row of holes in the [linear flow orifice meter|LFOM Preset Designs]. When the tank is at zero plant flow, just barely lower than the lowest flow rate, adjust the length of the lever arm-to-float rope so that the lever arm is exactly horizontal. After it is leveled, adjust the height of the FC as needed to make sure that there is just barely no alum flowing. Alum should begin to flow with one extra millimeter of driving head from this zero. Now tighten the hose clamps to ensure that the FC will remain at its calibrated height. Next fill the plant entrance tank to its height for maximum flow rate, halfway up the top row of holes in the linear flow orifice meter. The lever arm should be at the top end of its height range (20 cm down at the tip). {float:right|border=2px solid black|width=500px400px} [!CD Calibration^NotchesWDosingRing.png|width=500px400px!|CD Calibration] {float} |
Double
...
check
...
that
...
the
...
dosing
...
tube
...
system
...
stays
...
in
...
place
...
by
...
moving
...
the
...
dosing
...
ring
...
up
...
and
...
down
...
the
...
lever
...
arm.
...
Make
...
sure
...
the
...
ring
...
does
...
not
...
slip
...
out
...
of
...
any
...
notch
...
as
...
this
...
would
...
cause
...
improper
...
dosing.
...
If
...
it
...
does
...
not
...
appear
...
secure
...
then
...
cut
...
the
...
notches
...
deeper.
...
Take
...
an
...
alum
...
flow
...
rate
...
measurement
...
at
...
different
...
locations
...
along
...
the
...
lever
...
arm.
...
Check to
...
make
...
sure
...
the
...
CD
...
is
...
delivering
...
the
...
correct
...
mass
...
of
...
alum
...
per
...
plant
...
flow
...
rate
...
at
...
respective
...
notches.
...
It
...
is
...
important
...
to
...
check
...
several
...
notches
...
because
...
the
...
CD
...
could
...
correctly
...
dose
...
one
...
notch
...
while
...
not
...
performing
...
correctly
...
at
...
other
...
notches.
...
Calibration specifics for Tamara
Check to make sure the CD is delivering the correct multiple of 2 mg alum per liter plant flow at the respective notch. Expected alum flow rates at each notch are listed in the table below.
Notch from pivot | Alum Dosing (mg alum/L plant flow) | Expected alum flow rate (mL/min) at full plant flow |
|---|---|---|
1 | 2 | (2 mg/L * 700L/min)/120 |
...
g/L |
...
= |
...
11.67 |
...
mL/min |
...
2 | 4 | 23 |
3 | 6 | 35 |
4 | 8 | 47 |
5 | 10 | 58 |
6 | 12 | 70 |
7 | 14 | 82 |
8 | 16 | 93 |
9 | 18 | 105 |
10 | 20 | 117 |
11 | 22 | 128 |
12 | 24 | 140 |
13 | 26 | 152 |
14 | 28 | 163 |
15 | 30 | 175 |
16 | 32 | 187 |
17 | 34 | 198 |
18 | 36 | 210 |
19 | 38 | 222 |
20 | 40 | 233 |
21 | 42 | 245 |
22 | 44 | 256 |
23 | 46 | 268 |
24 | 48 | 280 |
25 | 50 | 292 |
If the CD is not dosing as much alum as expected, the FC outflow tubing may need to be shortened. Cut off small pieces of the tubing and re-check flow rate. Conversely, a high flow rate would mean that longer tubing is needed. Also make sure to double-check that the tubing is in fact 3/16" inner diameter. The table above is designed for 3/16"ID tubing that is 3.25 m long.