• TABLE OF CONTENTS
HIDE
 Copyright
 Front Cover
 Table of Contents
 Introduction
 Chemical injection methods for...
 Centrifugal pumps
 Positive displacement pumps
 Pressure differential methods
 Venturi injector
 Combination methods
 Backflow prevention law
 Summary
 Reference
 Back Cover






Group Title: Florida Cooperative Extension Service circular 864
Title: Chemical injection methods for irrigation
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00049222/00001
 Material Information
Title: Chemical injection methods for irrigation
Series Title: Circular
Physical Description: 21 p. : ill. ; 23 cm.
Language: English
Creator: Haman, D. Z ( Dorota Z )
Smajstrla, A. G ( Allen George )
Zazueta, F. S ( Fedro S )
Publisher: Florida Cooperative Extension Service, University of Florida
Place of Publication: Gainesville
Publication Date: 1990
 Subjects
Subject: Irrigation engineering   ( lcsh )
Irrigation -- Equipment and supplies   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 21).
Statement of Responsibility: Dorota Z. Haman, Allen G. Smajstrla, Fedro S. Zazueta.
General Note: Cover title.
General Note: "May 1990."
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00049222
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: oclc - 22942307

Table of Contents
    Copyright
        Copyright
    Front Cover
        Page i
    Table of Contents
        Page ii
    Introduction
        Page 1
    Chemical injection methods for irrigation
        Page 1
    Centrifugal pumps
        Page 1
        Page 2
        Page 3
    Positive displacement pumps
        Page 4
        Reciprocating pumps- piston and diaphragm
            Page 5
            Page 6
            Page 7
            Page 8
        Rotary pumps – gear and lobe
            Page 9
        Peristaltic pumps
            Page 9
            Page 10
    Pressure differential methods
        Page 11
        Suction pipe injection
            Page 11
        Discharge line injection
            Page 12
            Pressurized mixing tanks
                Page 13
            Proportional mixers
                Page 13
    Venturi injector
        Page 14
        Page 15
        Page 16
    Combination methods
        Page 17
    Backflow prevention law
        Page 18
    Summary
        Page 18
        Page 19
        Page 20
    Reference
        Page 21
    Back Cover
        Page 22
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida











.ntrar Science
library


EP 26 1990

S' r",ty,, of Florida




Chemical Injection

Methods for Irrigation








Dorota Z. Haman
Allen G. Smajstrla
Fedro S. Zazueta





Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida
John T. Woeste, Dean


1 .
11 ^_


May 1990


Circular 864


L







Table of Contents



Chemical Injection Methods for Irrigation ....... 1

Centrifugal Pumps ......................... 1


Positive Displacement Pumps ..........
Reciprocating Pumps Piston and Diaphragm .
Rotary Pumps Gear and Lobe ............
Peristaltic Pumps ......................

Pressure Differential Methods ..........
Suction Pipe Injection ...................
Discharge Line Injection .................
Pressurized mixing tanks ..............
Proportional mixers ..................


. . 4
.... 5
....... 9
....... 9


Venturi Injector ................


............ 14


Combination Methods ..................... 17

Backflow Prevention Law ..................... 18

Summary ....... ............................ 18


Dorota Z. Haman Associate Professor, Irrigation Specialist,
Agricultural Engineering Department, University of Florida,
Gainesville.

Allen G. Smajstrla Professor, Water Management Specialist,
Agricultural Engineering Department, University of Florida,
Gainesville.

Fedro S. Zazueta Associate Professor, Water Management
Specialist, Agricultural Engineering Department, University of
Florida, Gainesville.







Chemical Injection Methods for Irrigation
Dorota Z. Haman, Allen G. Smajstrla, and Fedro S. Zazueta


Introduction
Chemical application through irrigation systems is called
chemigation. Chemigation has been practiced for many years es-
pecially for fertilizer application (fertigation). In recent years, other
chemicals are also being applied through irrigation systems with
increasing frequency. The primary reason for chemigation is ec-
onomy. It is normally less expensive to apply chemicals with irri-
gation water than by other methods. The other major advantage
is the ability of applying chemical only when needed and in
required amounts. This "prescription" application not only follows
plant needs much closer than traditional methods, but also min-
imizes the possibility of environmental pollution. Through chem-
igation, chemicals can be applied only in amounts needed and thus
large quantities are not subject to leaching losses if heavy rainfalls
follow applications. Additional advantages of chemigation include
less operator hazard and possibly reduced amounts of chemicals.
There are several methods of chemical injection into an
irrigation system. These methods can be classified into four major
groups: centrifugal pumps, positive displacement pumps, pressure
differential methods, and methods based on the venturi principle.
These four groups can be further subdivided into specific methods
(see Figure 1). In addition, some injectors use a combination of
these methods. This publication will discuss each group of chemical
injectors, their applications, and advantages and disadvantages. A
summary of advantages and disadvantages of injectors discussed in
this publication is presented in Table 1 on page 19.

Centrifugal Pumps
Small radial flow centrifugal pumps (booster pumps) can be
used to inject chemicals into irrigation systems. The principle of
operation of a centrifugal pump is described in detail in IFAS
Extension Circular 832. Basically, fluid enters the centrifugal pump
near the axis of the high-speed impeller, and by centrifugal force
is thrown radially outward into the pump casing. The velocity head
imparted to the fluid by the impeller is converted into a pressure
head by means of volute or by a set of stationary diffusion vanes
surrounding the impeller (Figure 2).







Chemical Injection Methods for Irrigation
Dorota Z. Haman, Allen G. Smajstrla, and Fedro S. Zazueta


Introduction
Chemical application through irrigation systems is called
chemigation. Chemigation has been practiced for many years es-
pecially for fertilizer application (fertigation). In recent years, other
chemicals are also being applied through irrigation systems with
increasing frequency. The primary reason for chemigation is ec-
onomy. It is normally less expensive to apply chemicals with irri-
gation water than by other methods. The other major advantage
is the ability of applying chemical only when needed and in
required amounts. This "prescription" application not only follows
plant needs much closer than traditional methods, but also min-
imizes the possibility of environmental pollution. Through chem-
igation, chemicals can be applied only in amounts needed and thus
large quantities are not subject to leaching losses if heavy rainfalls
follow applications. Additional advantages of chemigation include
less operator hazard and possibly reduced amounts of chemicals.
There are several methods of chemical injection into an
irrigation system. These methods can be classified into four major
groups: centrifugal pumps, positive displacement pumps, pressure
differential methods, and methods based on the venturi principle.
These four groups can be further subdivided into specific methods
(see Figure 1). In addition, some injectors use a combination of
these methods. This publication will discuss each group of chemical
injectors, their applications, and advantages and disadvantages. A
summary of advantages and disadvantages of injectors discussed in
this publication is presented in Table 1 on page 19.

Centrifugal Pumps
Small radial flow centrifugal pumps (booster pumps) can be
used to inject chemicals into irrigation systems. The principle of
operation of a centrifugal pump is described in detail in IFAS
Extension Circular 832. Basically, fluid enters the centrifugal pump
near the axis of the high-speed impeller, and by centrifugal force
is thrown radially outward into the pump casing. The velocity head
imparted to the fluid by the impeller is converted into a pressure
head by means of volute or by a set of stationary diffusion vanes
surrounding the impeller (Figure 2).







Chemical Injection Methods for Irrigation
Dorota Z. Haman, Allen G. Smajstrla, and Fedro S. Zazueta


Introduction
Chemical application through irrigation systems is called
chemigation. Chemigation has been practiced for many years es-
pecially for fertilizer application (fertigation). In recent years, other
chemicals are also being applied through irrigation systems with
increasing frequency. The primary reason for chemigation is ec-
onomy. It is normally less expensive to apply chemicals with irri-
gation water than by other methods. The other major advantage
is the ability of applying chemical only when needed and in
required amounts. This "prescription" application not only follows
plant needs much closer than traditional methods, but also min-
imizes the possibility of environmental pollution. Through chem-
igation, chemicals can be applied only in amounts needed and thus
large quantities are not subject to leaching losses if heavy rainfalls
follow applications. Additional advantages of chemigation include
less operator hazard and possibly reduced amounts of chemicals.
There are several methods of chemical injection into an
irrigation system. These methods can be classified into four major
groups: centrifugal pumps, positive displacement pumps, pressure
differential methods, and methods based on the venturi principle.
These four groups can be further subdivided into specific methods
(see Figure 1). In addition, some injectors use a combination of
these methods. This publication will discuss each group of chemical
injectors, their applications, and advantages and disadvantages. A
summary of advantages and disadvantages of injectors discussed in
this publication is presented in Table 1 on page 19.

Centrifugal Pumps
Small radial flow centrifugal pumps (booster pumps) can be
used to inject chemicals into irrigation systems. The principle of
operation of a centrifugal pump is described in detail in IFAS
Extension Circular 832. Basically, fluid enters the centrifugal pump
near the axis of the high-speed impeller, and by centrifugal force
is thrown radially outward into the pump casing. The velocity head
imparted to the fluid by the impeller is converted into a pressure
head by means of volute or by a set of stationary diffusion vanes
surrounding the impeller (Figure 2).




































Figure 1. Classification of chemical injection methods for irrigation systems.

















CENTRIFUGAL
PUMP


CHEMICAL TANK


Figure 2. Centrifugal pump chemical injector.







For a centrifugal pump to operate as an injector, it is necessary
that the pressure produced by the pump be higher than the
pressure in the irrigation line. However, the flow rate of the
chemical from the pump depends on the pressure in the irrigation
line. The higher the pressure in the irrigation line the smaller the
flow rate from the injection pump. Because of that, centrifugal
pumps require calibration while operating. It is also not recom-
mended that this type of pump be used for the injection of toxic
chemicals where the injection rate must be controlled very
precisely.

Positive Displacement Pumps
Positive displacement pumps are frequently used for injection
of chemicals into a pressurized irrigation system. Positive displace-
ment pumps are classified as reciprocating, rotary and miscel-
laneous types (Figure 1), depending on the mechanism used to
transfer energy to the fluid. Reciprocating pumps include piston,
diaphragm and combination piston/diaphragm pumps, all common-
ly used for chemical injection into irrigation systems. Most rotary
and miscellaneous pumps are not used for chemical injections and
are not discussed in this publication. The exceptions are gear and
lobe rotary pumps which are occasionally used, and peristaltic
pumps which can be used when only small injection rates are
required. Therefore, gear, lobe and peristaltic pumps will be
discussed briefly in this publication. An interested reader is
referred to IAS Extension Circular 826 for a detailed description,
typical applications and discussion of advantages and disadvantages
of the various positive displacement pumps used in agriculture.
By definition, a positive displacement pump moves a certain,
constant volume of fluid from the intake side of the pump to the
discharge side of the pump. Theoretically, the volume displaced by
the pump should be independent of the pressure encountered at
the discharge point. However, this is not necessarily true for all
pumps classified as positive displacement pumps. If the internal
parts of the pump can deform due to the increased pressure (as in
a mechanically driven diaphragm pump) the displacement volume
of the pump will change and the injection rate will not be
constant. Excessive pressure at the discharge may also result in
some back flow through the clearances of the pump parts (for
example, between the gears and the housing in the gear pump).
Piston, fluid-filled diaphragm, and piston/diaphragm pumps come
closest to being ideal positive displacement pumps and to providing








a constant flow rate independent of the discharge pressure.
However, even with these pumps, excessive discharge pressures
should be avoided (for example, due to a closed valve in a
discharge line), because excessively high pressures may result in
pump or line damage.

Reciprocating Pumps
Reciprocating pumps are pumps in which a piston or a
diaphragm displaces a given amount of chemical with each stroke.
The change in internal volume of the pump creates high pressure,
which forces chemical into the discharge pipe. These pumps are
classified as piston pumps, diaphragm pumps or a combination of
piston and diaphragm.
In most diaphragm, piston, and diaphragm/piston combination
pumps the rotary motion of a drive wheel is transformed into the
reciprocating motion of a cylinder or a diaphragm.
The operation of a piston pump is similar to the operation of
the cylinder of an automobile engine. On an intake stroke (Figure
3a), the chemical enters the cylinder through the suction check
valve. On a compression stroke (Figure 3b) the chemical is forced
into the discharge line through the discharge check valve.
The operation of a diaphragm pump is similar to that of a
piston pump. The pulsating motion is transmitted to the dia-
phragm through a fluid or a mechanical drive, and then through
the diaphragm to the chemical being injected (Figure 4a and
Figure 4b).
Combination pumps usually contain a piston that forces oil or
other fluid against a diaphragm which displaces the concentrated
chemical. The advantage of these pumps is that they combine the
high precision of a piston pump with the resistance to chemicals
characteristic of diaphragm pumps.
Reciprocating pumps are often electrically driven. The chemical
injection rate from an electrically driven pump is approximately
constant regardless of the water flow rate. Thus, the injection rate
must be adjusted between zones if the flow rate is not constant to
all zones.
To assure constant concentration of chemical in the irrigation
line an electrically driven injector can be equipped with a water
flow sensor to detect changes in flow rate and automatically adjust
the speed of the injector or injection time. The other possibility is
to measure the conductivity of the irrigation water (if fertilizers
are being injected) and use this information for automatic adjust-


















DISCHARGE


SUCTION


Figure 3a. Piston pump on an intake stroke.


SUCTION


VALVE

Figure 3b. Piston pump on a compression stroke.

6

































Figure 4a. Diaphragm pump suction stroke.


Figure 4b. Diaphragm pump discharge stroke.







ment. Sensors that measure the conductivity must be recalibrated
for different chemicals.
Some piston and diaphragm pumps are driven by a water
motor. As water flows through the injector, it causes a cam to
turn and push a piston back and forth. In a diaphragm pump, the
piston or cam motion is transmitted to the diaphragm. Conse-
quently, since the revolution of the cam depends on the flow rate
of water in the irrigation system, oscillation of the piston and/or
diaphragm also varies with water flow rate. In this case the chem-
ical flow is proportional to the flow rate in the irrigation system.
Another way of driving an injector using irrigation water is
presented in Figure 5. In this case a mechanism contains two
pistons of different sizes and a series of valves. The larger piston
is driven by the pressure in the irrigation system. The smaller
piston injects the chemical into the irrigation line.
Piston and diaphragm pumps inject chemicals in concentrated
pulses separated in time. Some pumps are equipped with double
acting pistons or diaphragms to minimize variations in the
concentration of chemicals in the irrigation system. In these cases
the volume on both sides of the piston or the diaphragm is used
for pumping chemical (Figure 6). However, if the pipe line length
between the injection port and the first point of application is


FRESH (i CHEMICAL
WATER WATER
__ If MIXTURE


CYLINDER B


Figure 5. Water driven piston injector.
























LIQUID~/
CYLINDER
Figure 6. Double acting piston pump.

short, a blending tank should follow the injection point to ensure
adequate mixing of water and fertilizer.

Rotary Pumps
Rotary pumps transfer chemical from suction to discharge
through the action of rotating gears, lobes or other similar
mechanisms. Both gear or lobe types of rotary pumps are some-
times used for chemical injection into irrigation systems. The
operation of a gear or lobe pump is based on the partial vacuum
which is created by the unmeshing of the rotating gears (Figure
7) or lobes (Figure 8). This vacuum causes the chemical to flow
into the pump. Then it is carried between the gears or lobes and
the casing to the discharge side of the pump. Gear and lobe pumps
produce approximately constant flow for a given rotor speed, and
the injection rate does not change with flow rate in the irrigation
system. Flow sensors, described above for reciprocating pumps, can
be used to assure a constant injection rate.

Peristaltic Pumps
Peristaltic pumps are used mostly in chemical laboratories, but
they can be used for injection of chemicals into small irrigation
systems. Their capacity is limited and most of them produce a
























LIQUID~/
CYLINDER
Figure 6. Double acting piston pump.

short, a blending tank should follow the injection point to ensure
adequate mixing of water and fertilizer.

Rotary Pumps
Rotary pumps transfer chemical from suction to discharge
through the action of rotating gears, lobes or other similar
mechanisms. Both gear or lobe types of rotary pumps are some-
times used for chemical injection into irrigation systems. The
operation of a gear or lobe pump is based on the partial vacuum
which is created by the unmeshing of the rotating gears (Figure
7) or lobes (Figure 8). This vacuum causes the chemical to flow
into the pump. Then it is carried between the gears or lobes and
the casing to the discharge side of the pump. Gear and lobe pumps
produce approximately constant flow for a given rotor speed, and
the injection rate does not change with flow rate in the irrigation
system. Flow sensors, described above for reciprocating pumps, can
be used to assure a constant injection rate.

Peristaltic Pumps
Peristaltic pumps are used mostly in chemical laboratories, but
they can be used for injection of chemicals into small irrigation
systems. Their capacity is limited and most of them produce a
























SUCTION








Figure 7. Gear pump.




















SUC











Figure 8. Lobe pump.


ROTOR


DISCHARGE


CASING


LOBE





























Figure 9. Peristaltic pump.


pressure of only 30 to 40 psi. A typical peristaltic pump is
presented in Figure 9. A flexible tube is pressed by a set of rollers
and an even flow is produced by this squeezing action. The pump
is suitable for pumping corrosive chemicals since the pumped
liquid is completely isolated from all moving parts of the pump.

Pressure Differential Methods
The idea of injection using pressure differential is quite simple.
Basically, if the pressure at the point of injection is lower than at
the point of intake of the chemical, the chemical will flow into the
line. There are several injection techniques which use the above
principle. They can be separated into two distinctive groups.
Injection on the suction side of the irrigation pump and injection
on the discharge side of the irrigation pump.

Suction Pipe Injection
The suction pipe injection technique can be used in irrigation
systems using centrifugal pumps which are pumping water from





























Figure 9. Peristaltic pump.


pressure of only 30 to 40 psi. A typical peristaltic pump is
presented in Figure 9. A flexible tube is pressed by a set of rollers
and an even flow is produced by this squeezing action. The pump
is suitable for pumping corrosive chemicals since the pumped
liquid is completely isolated from all moving parts of the pump.

Pressure Differential Methods
The idea of injection using pressure differential is quite simple.
Basically, if the pressure at the point of injection is lower than at
the point of intake of the chemical, the chemical will flow into the
line. There are several injection techniques which use the above
principle. They can be separated into two distinctive groups.
Injection on the suction side of the irrigation pump and injection
on the discharge side of the irrigation pump.

Suction Pipe Injection
The suction pipe injection technique can be used in irrigation
systems using centrifugal pumps which are pumping water from








the surface source such as a pond, lake, canal or river. In Florida,
this method is not permitted for irrigation systems using ground-
water supply, and it is approved for injection of fertilizer only (see
IFAS Extension Bulletin 217).
The method described above requires only a minimum
investment. The equipment necessary for this type of injection is
a pipe or a hose, a few fittings and an open container to hold the
fertilizer solution (Figure 10). The rate of chemical flow depends
on the suction produced by the irrigation pump, the length and
size of the suction line, and the level of chemical in the supply
tank.


Discharge Line Injection
The differential pressure injection technique can also be used
on the discharge side of the pump. This is usually done by
redirecting part of the main flow through the chemical tank and
providing a pressure drop in the irrigation line between the point
where the water is taken and the point where the chemical enters

Pressure Actuated
Chemical -Valve
Solution To Irrigation
System


Check Valves

Power
Pump -^ Unit

Suction
Pipe
OTHER BACKFLOW PREVENTION
DEVICES MAY BE REQUIRED.

TOXIC CHEMICALS PROHIBITED.
SEE STATE LAW.
Foot
Valve

Strainer-


Figure 10. Suction line injection.







the irrigation line. The pressure drop is accomplished by using
some kind of restriction in the line, such as a valve, orifice,
pressure regulator or other device which would create a pressure
drop. The use of valves allows for adjustment of the pressure drop
which also allows for some adjustment of the injection rate.

Pressurized mixing tanks. A mixing tank injector operates at
the discharge line on a pressure differential concept. The water is
diverted from the main flow, mixed with fertilizer and injected or
drawn back into the main stream of the system (Figure 11). A
measured amount of fertilizer required for one injection is placed in
the cylinder. The flow back into the main line is often controlled by
a metering device installed on the inlet side of the injector. The
concentration of the injection changes as the chemical becomes
diluted as the water enters the tank during injection. As described
previously, there must be a pressure differential in the irrigation
line between the inlet and the outlet of the injector.

Proportional mixers. Proportional mixers are modified pres-
surized mixing tanks. They operate on the displacement principle.
The chemical is placed in a collapsible bag which separates the
chemical from the water (Figure 12). The amount of chemical
forced into the proportioning valve is replaced with displacement
water outside the chemical solution bag. As water enters the tank
it displaces chemical and never returns into the system. As long

Partially Closed Valve or Other
Pressure Reducing
Device


Low High
Pressure \ / Pressure


Figure 11. Pressurized mixing tank.







the irrigation line. The pressure drop is accomplished by using
some kind of restriction in the line, such as a valve, orifice,
pressure regulator or other device which would create a pressure
drop. The use of valves allows for adjustment of the pressure drop
which also allows for some adjustment of the injection rate.

Pressurized mixing tanks. A mixing tank injector operates at
the discharge line on a pressure differential concept. The water is
diverted from the main flow, mixed with fertilizer and injected or
drawn back into the main stream of the system (Figure 11). A
measured amount of fertilizer required for one injection is placed in
the cylinder. The flow back into the main line is often controlled by
a metering device installed on the inlet side of the injector. The
concentration of the injection changes as the chemical becomes
diluted as the water enters the tank during injection. As described
previously, there must be a pressure differential in the irrigation
line between the inlet and the outlet of the injector.

Proportional mixers. Proportional mixers are modified pres-
surized mixing tanks. They operate on the displacement principle.
The chemical is placed in a collapsible bag which separates the
chemical from the water (Figure 12). The amount of chemical
forced into the proportioning valve is replaced with displacement
water outside the chemical solution bag. As water enters the tank
it displaces chemical and never returns into the system. As long

Partially Closed Valve or Other
Pressure Reducing
Device


Low High
Pressure \ / Pressure


Figure 11. Pressurized mixing tank.












Low } High
Pressure Pressure



Regulating i _
Valve
Chemical
Solution
Bag


Water


Figure 12. Proportional mixer.
as the pressure and the flow rate in the system do not vary
significantly the injection rate will remain constant.
In irrigation systems where flow fluctuations can be expected,
proportioning control valves must be used. If the injector is a true
proportional mixer the proportioning valve must respond to
changes in flow, not pressure changes in the irrigation system.

Venturi Injector
Chemicals can be injected into a pressurized pipe using the
venturi principle. A venturi injector is a tapered constriction which
operates on the principle that a pressure drop accompanies the
change in velocity of the water as it passes through the constric-
tion. The pressure drop through a venturi must be sufficient to
create a negative pressure (vacuum) as measured relative to
atmospheric pressure. Under these conditions the fluid from the
tank will flow into the injector (Figure 13). Most venturi injectors
require at least a 20% differential pressure to initiate a vacuum.
A full vacuum of 28 inches of mercury is attained with a differen-
tial pressure of 35% or more.
A small venturi can be used to inject small chemical flow rates
into a relatively large main line by shunting a portion of the flow







through the injector. To assure that the water will flow through
the shunt, a pressure drop must occur in the main line. For this
reason the injector is used around a point of restriction such as
valve, orifice, pressure regulator or other device which creates a
differential pressure (Figure 14). A centrifugal pump, used to
provide additional pressure in the shunt (Figure 15), can also be
used.
A venturi injector does not require external power to operate.
It does not have any moving parts, which increases its life and
decreases probability of failure. The injector is usually constructed
of plastic, and it is resistant to most chemicals. It requires minimal
operator attention and maintenance. Since the device is very
simple, its cost is low as compared to other equipment of similar
function and capability. It is easy to adopt to most new or existing
systems providing that there is sufficient pressure in the system
to create the required pressure differential.
Venturi injectors come in various sizes and can be operated
under different pressure conditions. Suction capacity (injection
rate), head loss required, and working pressure range will depend
on the model. It is important to realize that the suction capacity
depends on the liquid level in the supply tank. As the liquid level
drops, the suction head increases, resulting in a decreased injection
rate. To avoid this problem some manufacturers provide an
additional small tank on the side of the supply tank, where a float
valve maintains the fluid level relatively constant. The fluid is
injected from this additional tank.

VENTURI
I 1 FLOW


CHEMICAL
SUCTION LINE -




STRAINER


CHEMICAL
BULK
TANK


Figure 13. Venturi injector in the main line.













CENTRIFUGAL
PUMP -.


VALVE


Figure 14. Small venturi injector with regulator valve for pressure
drop in the main line.


Figure 15. Small venturi injector in conjunction with a centrifugal
booster pump.







Combination Methods
There are some injectors on the market which employ combina-
tions of the different principles of injection at the same time. The
most common combination is a pressure differential combined with
a venturi meter or some measuring device which operates on the
venturi principle.
Use of the pressure differential method in combination with a
venturi can be found in some systems where the pressure drop
required for a venturi may be difficult to provide due to design
restrictions of the existing irrigation system. The combination of
a venturi device with a pressurized chemical tank may be used in
this case (Figure 16). The chemicals are placed in the tank. Since
the water flowing through the tank is under pressure, a sealed
airtight pressure supply tank which is constructed to withstand the
maximum operating pressure is required. In this case the injection
rate will change gradually due to the change of chemical con-
centration in the tank as the water enters the tank during
injection.
Various metering valves which are used with mixing and
proportioning tanks operate on pressure or flow changes in the


Figure 16. Combination of a pressurized tank and venturi injector.







irrigation system. There are many designs of these valves.
Frequently it is some application of the venturi meter or an orifice
with changing diameter. The manufacturer should be contacted for
descriptions and operation instructions for various metering and
proportioning valves.

Backflow Prevention Law
Before injecting any chemicals into an irrigation system it is
necessary to check that the system is provided with the required
backflow prevention system for a given type of chemical. The
general rules for backflow prevention in Florida are presented in
IFAS Extension Bulletins 217 and 248. In addition local ordinances
should be checked since they may be more restrictive.
Chemical injection on the suction side of a centrifugal pump is
generally not permitted in Florida. The exception is a system
which is using a surface water supply and only fertilizers are being
injected into the system. Florida backflow prevention law requires
that double protection of a check valve and a foot valve be used
upstream of the injection port in this case.
According to the Environmental Protection Agency (EPA) only
piston and diaphragm injection pumps can be used for pesticides
and other toxic chemicals. Other methods described in this
publication can be used for injection of fertilizers or cleaning
agents, such as bactericides (for example, chlorine) or acids.

Summary
Different types of injectors are discussed in this publication.
These injectors are classified into five basic groups depending on
their principles of operation. Basic principles of operation, ad-
vantages and disadvantages are presented.







irrigation system. There are many designs of these valves.
Frequently it is some application of the venturi meter or an orifice
with changing diameter. The manufacturer should be contacted for
descriptions and operation instructions for various metering and
proportioning valves.

Backflow Prevention Law
Before injecting any chemicals into an irrigation system it is
necessary to check that the system is provided with the required
backflow prevention system for a given type of chemical. The
general rules for backflow prevention in Florida are presented in
IFAS Extension Bulletins 217 and 248. In addition local ordinances
should be checked since they may be more restrictive.
Chemical injection on the suction side of a centrifugal pump is
generally not permitted in Florida. The exception is a system
which is using a surface water supply and only fertilizers are being
injected into the system. Florida backflow prevention law requires
that double protection of a check valve and a foot valve be used
upstream of the injection port in this case.
According to the Environmental Protection Agency (EPA) only
piston and diaphragm injection pumps can be used for pesticides
and other toxic chemicals. Other methods described in this
publication can be used for injection of fertilizers or cleaning
agents, such as bactericides (for example, chlorine) or acids.

Summary
Different types of injectors are discussed in this publication.
These injectors are classified into five basic groups depending on
their principles of operation. Basic principles of operation, ad-
vantages and disadvantages are presented.








Table 1. Comparison of various chemical Injection methods.
CENTRIFUGAL PUMPS
Injector Advantages Disadvantages

Centrifugal Low cost. Can be Calibration depends on system
Pump In- adjusted while run- pressure. Cannot accurately
jector ning. control low injection rates.



POSITIVE DISPLACEMENT PUMPS

Injector Advantages Disadvantages

RECIPROCATING PUMPS


High precision. Lin-
ear calibration. Very
high pressure. Cali-
bration independent
of pressure.


Adjust calibration
while injecting. High
chemical resistance.


High precision. Lin-
ear calibration. High
chemical resistance.
Very high pressure.
Calibration indepen-
dent of pressure.


High cost. May need to stop to
adjust calibration. Chemical
flow not continuous.



Non-linear calibration. Calibra-
tion depends on system pres-
sure. Medium to high cost.
Chemical flow not continuous.


High cost. May need to stop to
adjust calibration.


Injector Advantages Disadvantages

ROTARY PUMPS


Injection rate can be
adjusted when run-
ning.


Fluid pumped cannot be abra-
sive. Injection rate is depen-
dent on system pressure. Con-
tinuity of chemical flow
depends on number of lobes
in a lobe pump.


Piston
Pumps




Dia-
phragm
Pumps


Piston/-
Dia-
phragm


Gear
Pumps
Lobe
Pumps








Injector Advantages '-~ rntages


MISCELLANEOUS PUMPS


High chemical resis-
tance. Major adjust-
ment can be done by
changing tubing size.
Injection rate can be
adjusted when run-
ning.


Short tubing life expectancy.
Injection rate dependent on
system pressure. Low to
medium injection pressure.


PRESSURE DIFFERENTIAL METHODS

Injector Advantages Disadvantages

Suction Very low cost. Injec- Permitted only for surface
Line Injec- tion rate can be ad- water source and injection of
tion justed while running. fertilizer. Injection rate depends
on main pump operation.

DISCHARGE LINE INJECTION

Pressurized Low to medium cost. Variable chemical concentra-
Mixing Easy operation. Total tion. Cannot be calibrated ac-
Tanks chemical volume curately for constant injection
controlled. rate.


Proportion- Low to medium cost. Pressure differential
al Mixers Calibrate while oper- required. Volume to be in-
ating. Injection rates jected is limited by the size of
accurately controlled. the injector. Frequent refills
required.

VENTURI INJECTORS

Injector Advantages Disadvantages


Low cost. Water
powered. Simple to
use. Calibrate while
operating. No mov-
ing parts.


Pressure drop created in the
system. Calibration depends
on chemical level in the tank.


Peristaltic
Pumps


Venturi
Injector


Injector


Advantages


~" *' vintages




UNIVERSITY OF FLORIDA
!/I/I_________I!t______IIIII/_i_1111111111111111i
3 1262 05586 2873
COMBINATION METHODS
Injector Advantages Disadvantages
Proportion- Greater precision Higher cost than
al Mixers/ than proportional proportional mixer
Venturi mixer or venturi or venturi alone.
alone.



References
Haman D.Z., GA. Clark, A.G. Smajstrla. 1989. Positive Displace-
ment Pumps for Agricultural Applications. Extension Circular
826. Dept. of Agricultural Engineering. IFAS. University of
Florida. Gainesville, FL.

Haman D.Z., F.T. Izuno, A.G. Smajstrla. 1989. Pumps for Flor-
ida Irrigation and Drainage Systems. Extension Circular 832.
Dept. of Agricultural Engineering. IFAS. University of Florida.
Gainesville, FL.

Machmeier R.E. Nitrogen Fertilizer Injection. 1970. Agricultural
Extension Service. University of Minnesota.

Richardson M.R. 1987. Choosing the Right Injector. Fruit Grow-
er 107(4): pp. 54-60.

Yeager T.Y., R.W. Henley. 1986. Techniques of Diluting Solution
Fertilizers in Commercial Nurseries and Greenhouses. Circular
695. Florida Extension Service. University of Florida. Gainesville,
FL.




DOCUMENf






















































This publication was produced at a cost of $929.16, or 33.2 cents
per copy, to provide detailed information of various injection
methods used in irrigation. 6-2.8M-90


COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTI-
TUTE OF FOOD AND AGRICULTURAL SCIENCES, John T. Woeste, director,
in cooperation with the United States Department of Agriculture, publishes this
information to further the purpose of the May 8 and June 30, 1914 Acts of
Congress; and is authorized to provide research, educational information and
other services only to individuals and institutions that function without regard to
race, color, sex, age, handicap or national origin. Single copies of extension publications (excluding
4-H and youth publications) are available free to Florida residents from county extension offices.
Information on bulk rates or copies for out-of-state purchasers is available from C.M. Hinton,
Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611.
Before publicizing this publication, editors should contact this address to determine availability.




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