dosatron D128R Operating instructions

Page 1
800-523-8499 lwww.dosatronusa.com
Proper protection, such as gloves, eye wear, and aprons, are recommended when disassembling a Dosatron.
Step 3: Unscrew and remove the black stem.
Step 2: Grab the metal wishbone and pull the piston
straight out. Set the piston aside.
This D128R Troubleshooting will cover: The medicator is clicking, but
not drawing the solution or liquid is going down into the stock tank.
D128R Troubleshooting - Part 1
NOTE: Before you start, make sure the unit is clicking.
It would be helpful to have a strap wrench, #1 Phillips
screw driver, and a large paper clip or awl.
Step 1: Unscrew and remove the lid. You may what to
use a strap wrench (Part #: TOOL01).
Scan the QR
code to watch
our D128R
Troubleshooting
video.

Page 2
800-523-8499 lwww.dosatronusa.com
Proper protection, such as gloves, eye wear, and aprons, are recommended when disassembling a Dosatron.
Step 4: Remove the top seal (Part #: J002) that is
located between the blue body and the black stem.
NOTE: Sometimes the top seal remains in the body.
If this happens, just remove it.
Step 5: Unscrew the gray hose nut if it isn’t
already removed.
Step 6: Unscrew the black cap and remove the bottom
seal (Part #: J003) between the black stem and the cap.
D128R Troubleshooting - Part 1

Page 3
800-523-8499 lwww.dosatronusa.com
Proper protection, such as gloves, eye wear, and aprons, are recommended when disassembling a Dosatron.
D128R Troubleshooting - Part 1
Step 9: To change the plunger rod use a # 1 Phillips
screw driver and remove the two wishbone screws and
washers.
Step 8: Next, pick up the piston and inspect the plunger
rod (Part #: P009) and slide valve (Part #: P010). The
plunger rides inside the top seal to create suction. If
there is a build up of scale or has deep scratches, it may
not draw the correct amount of solution. If your plunger
rod does have scale build up, just soak the piston
assembly in a solution of Medicator Rx
(Part #: CLEANSER-LS) for 24 to 48 hours. If the
plunger rod has scratches it will need to be replaced.
Step 7: Inspect both seals for nicks, grooves, and wear.
Make sure they aren’t gummy, sticky, or missing. If the
seals are dirty, you may be able to just clean them and
reinstall. But if they are damaged or missing, it is
denitely time to replace.

Page 4
800-523-8499 lwww.dosatronusa.com
Proper protection, such as gloves, eye wear, and aprons, are recommended when disassembling a Dosatron.
D128R Troubleshooting - Part 1
Step 12: Slide the actuator assembly out.
Step 11: Remove the four screws in the center of
the piston.
Step 10: Spread the wishbone and remove from the
inlet valve.

Page 5
800-523-8499 lwww.dosatronusa.com
Proper protection, such as gloves, eye wear, and aprons, are recommended when disassembling a Dosatron.
D128R Troubleshooting - Part 1
Step 15: Remove the plunger rod (Part #: P009) by
lifting it up slightly and out. Set aside the actuator
(Part #: MP001).
Step 14: Remove the push rod (Part #: P008) by
sliding it out.
Step 13: Unhook and remove the actuator springs
(Part #: M009).

Page 6
800-523-8499 lwww.dosatronusa.com
Proper protection, such as gloves, eye wear, and aprons, are recommended when disassembling a Dosatron.
Step 18: To reinstall the slide valve onto the new plunger
rod slide the spring over the slide valve. Push to the
bottom and grasp rmly.
Step 17: Now push the metal pin (Part #: M005) out
using the paper clip. This allows you to remove the
spring from the slide valve.
D128R Troubleshooting - Part 1
Step 16: To remove the slide valve from the plunger rod
you will need a large paper clip or awl. Push the spring
down and hold rmly.

Page 7
800-523-8499 lwww.dosatronusa.com
Proper protection, such as gloves, eye wear, and aprons, are recommended when disassembling a Dosatron.
Step 20: Pick up the actuator and install the new plunger
rod by sliding it into the actuator and pulling it down to
lock. Make sure the head of the plunger rod is ush.
Step 19: Insert the plunger and reinstall the pin. The
center hole is the 1:128 setting. If you need 1:200, install
the pin in the top hole, if you need 1:100, install the pin in
the bottom hole. Make sure the pin is ush so the spring
doesn’t get stuck.
D128R Troubleshooting - Part 1
Step 21: Install the push rod with the long portion up
making sure to insert it with the groove side inward.

Page 8
800-523-8499 lwww.dosatronusa.com
Proper protection, such as gloves, eye wear, and aprons, are recommended when disassembling a Dosatron.
Step 24: To hold the assembly in place use your index
and middle ngers to apply pressure on the base.
Step 23: Align the push rod and inlet valve inside
the piston shell and slide the actuator assembly
in completely.
Step 22: Install the actuator springs.
D128R Troubleshooting - Part 1

Page 9
800-523-8499 lwww.dosatronusa.com
Proper protection, such as gloves, eye wear, and aprons, are recommended when disassembling a Dosatron.
D128R Troubleshooting - Part 1
Step 27: Test the piston by pressing on the top and
bottom of the push rod. It should click both times.
Step 26: Reinstall the wishbone spring, then reinstall the
washers and screws, hand tight.
Step 25: Now reinstall the four screws and tighten in a
star pattern.

Page 10
800-523-8499 lwww.dosatronusa.com
Proper protection, such as gloves, eye wear, and aprons, are recommended when disassembling a Dosatron.
Step 2: Push the spring down and hold rmly.
NOTE: To replace the slide valve and spring you will
need a large paper clip or awl.
Step 1: Inspect the bottom seal (Part #: J003), slide
valve (Part #: P010), and spring (Part #: M003).
If worn, damaged, deformed, or broken, replace
the parts.
D128R Troubleshooting - Part 2
This D128R Troubleshooting will cover: Water going down into the
stock tank.
Step 3: Using the paper clip, push the metal pin
(Part #: M005) out.