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Metered Liquid Applicator:
| Problem: |
One Solution: |
| Manual application of liquids (such as growth
regulators) with a spray-wand can cause
worker injury, as well as waste of chemicals
and plant loss. |
Use a semi-automated, metered liquid applicator
to provide a precise dose to each
plant and to eliminate repetitive hand
closure. |
 |
 |
| Worker must squeeze and hold spray-wand
trigger up to 25 times per minute. |
Eliminates virtually all of the repetitive
hand-squeezing motion. |
Highly repetitive hand closure can cause
inflammation of the tendons in the carpal
tunnel. |
Can reduce waste of chemicals and plant
loss. |
| Mental counts to “time” the discharge can
result in inconsistent or improper amounts. |
Curved wand design improves wrist posture
for long reaches. |
| Many spray-wands currently in use are not
appropriate for long reaches, resulting in
prolonged poor wrist posture. |
Can improve productivity. |
| |
Can document production, if fitted with a
counter. |
Metered Liquid Applicator
How Does the Applicator Work?
The system has three parts: a) the electric controls
box, b) the metering cylinder assembly, and
c) the check valve-fitted spray-wand. It uses a
tractor's 12-volt battery to power the timer module
and to create 120-volt electricity that powers the
solenoid valve. Liquid is alternately supplied to
each side of the double-acting cylinder, which
meters a precise dose through the discharge
hose. An adjustable momentary delay provides
time between discharges to move the wand to the
next plant. A spring-loaded check valve at the
end of the spray wand ensures that excess liquid
does not flow out of the spray gun between discharges.
How Can I Make a
Metered Liquid Applicator?
The applicator is composed of off-the-shelf components
with the exception of a steel frame. It
requires a qualified electrician for wiring and
assembly of the electrical components. Material
costs should be about $500.
Caution! Proper assembly of the liquid applicator
requires specific expertise. Consult a
trained electrician or engineer for advice and
assistance. The assembled liquid applicator
should be tested initially using potable water,
not chemicals.
The electric controls box houses the power converter,
ground fault interrupter, system toggle
switch, terminal strip, fuses, and timer module.
The cylinder metering assembly consists of a
steel frame with a double-acting double-rod cylinder,
an adjustable stop for the cylinder, an air
purging valve, and a solenoid valve with inlet/outlet
hose adapters.
The spray gun can be any pistol-style wand, or
one modified to pistol style, to allow for a neutral
wrist position with an outstretched arm.
For a free parts list and detailed instructions on
how to make the metered applicator, write to:
UC Ag Ergonomics Research Center
Bio & Ag Engineering, UC Davis
One Shields Avenue
Davis, CA 95616-5294
Or visit http://ag-ergo.ucdavis.edu.
Operational Tips:
Trapped air in the solenoid valve, tubing, cylinder,
or hose will affect the accuracy of the system. To
help avoid this problem, the cylinder ports face
upward, and the 4-way valve is located directly
above the cylinder. A bypass valve for purging air
from the hose is provided. Rough handling of the
discharge hose can cause unwanted discharge.
Handle the hose relatively gently unless the
spray-wand valve is closed. For more information
about this system, please visit the UC-AERC web
site at http://ag-ergo.ucdavis.edu.
Contact Information:
This Tip Sheet was produced by the University of
California Agricultural Ergonomics Research
Center under a grant from the National Institute
for Occupational Safety and Health.
UC Ag Ergonomics Research Center, Bio & Ag
Engineering, UC Davis, One Shields Avenue,
Davis, CA 95616-5294.
Or visit http://ag-ergo.ucdavis.edu.
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Metered Liquid Applicator 
(53 pages, 1.49MB)