Metering Pumps and Pump Systems

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Metering Pumps and Pump Systems
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METERING PUMP DEFINITION

• Convey (like any pump)
• Measure (repeated displacement of defined volume)
• Adjust
• Volume per displacement
• Frequency of displacements

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METERING PHILOSOPHY

• Think of the pump as a continuous fluid
  measurement device
• Converts batch processes (fluid measured, then
  mixed), to in-line processes (fluids continuously
  measured and mixed)

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What is a Metering Pump?
Hydraulic Institute Definition A controlled
volume pump (also called a metering,
proportioning or chemical injection pump) is
a reciprocating power pump used to accurately
displace a predetermined volume of liquid in a
specified time period and is driven by power from
an outside source applied to the pump mechanism.
It includes a mechanism for varying the effective
plunger, piston or diaphragm displacement.
Some Pump Manufacturers Add It includes a
mechanism for varying the effective frequency of
displacements.
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What claims to be a Metering Pump, but isnt?
Gear Pump
Displacement per revolution not adjustable. Not
linear from high to low RPMs due to slip at low
speed.
Air Operated Diaphragm Pump
Displacement per stroke not adjustable. Not
repeatable due to variable air pressure, flexible
diaphragm.
Progressing Cavity Pump
Displacement per revolution not adjustable.
Chemical incompatibility common w/ rotor.
Displacement per revolution not adjustable. Tube
stretch prevents repeatability.
Peristaltic Pump
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Whats all This?
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Metering Pump System Hydraulics and Application
of Accessories
The metering pump system design, the fluid
pumped, and the accessories installed all play a
vital role in system safety, repeatability and
reliability. Key Concept Metering Pump System
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Suction Head
Negative Suction Head (suction lift)
Positive Suction Head (flooded suction)
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Suction Lift
Atmospheric pressure always pushes down on any
fluid surface. When the pump diaphragm creates a
negative pressure in the pump head, atmospheric
pressure forces fluid up the suction tube to fill
the cavity. Atmospheric pressure at 500 feet
above sea level 14.5 psia 1 bar 34 feet of
water If the pump pulled a perfect vacuum, the
maximum suction lift possible on earth, pumping
water, is 34 feet.
14.5 psia
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Suction Lift
What happens if the tank is not vented (open to
atmosphere)?
14.5 psia
14.5 psia
14.5 psia
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Specific Gravity
Specific Gravity is the fluids density in
relation to the density of water (S.G. 1.0). For
example Sulfuric acid density 15.34
lbs/gal Therefore
Water density 8.34 lbs/gal S.G.
1.84 Ammonia density 5.25
lbs/gal Therefore
Water density 8.34 lbs/gal S.G.
0.63 Because atmospheric pressure forces fluid
into the pump head during the suction stroke, if
the fluid has a specific gravity greater than
1.0, the suction lift ability will be
reduced. Specific gravity is independent of
viscosity, and does not impact pump capacity,
only suction lift capability.
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Specific Gravity Impact on Suction Lift
Actual Suction Lift Rated Suction Lift (water)
/ S.G.
Rated Suction Lift for VAMb04120 6.6
feet Application Chromic Acid (1.4 SG) Actual
Suction Lift 6.6 / 1.4 4.7
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Viscosity
Viscosity is a measure of a fluids resistance to
flow. Viscosities greater than that of water
increase friction loss and result in reduced pump
capacity. When selecting a pump for viscous
fluids Oversize the pump Put springs in the
valves to help seat the balls Use high viscosity
solenoid pumps Reduce stroking rate to minimum
possible Keep stroke length as great as
possible Provide flooded suction with oversized
suction line
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Specific Gravity and Viscosity of Common Fluids
Fluid S.G. Viscosity (SSU)

• Ammonia 0.63 29.5
• SAE 30 oil 0.9 200 _at_ 130 deg F
• Brine 1.2 33
• Gasoline 0.73 30
• Glycerine 1.26 2950
• Nitric Acid 1.42 31.5
• Sulfuric Acid 1.84 66
• Water 1.00 31.5

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Vapor Pressure
Matter exist as solids, liquids or gasses. The
state of matter depends on the compound itself,
the pressure around it, and the temperature. The
Vapor Pressure of any fluid relates to the
pressure and temperature at which it flashes from
a liquid phase to a gas phase. It is defined as
the pressure exerted when a liquid is in
equilibrium with its own vapor. The higher the
vapor pressure, the more likely the fluid will
vaporize on the suction side of a pump during the
suction stroke, causing cavitation.
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Pressure Relief Valve
Prevents over-pressurizing pump and piping
system.
Pressure Adjusting Nut
Spring
Diaphragm
Diaphragm Hub
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Pressure Relief Options - Flooded Suction
Pressure Relief may discharge back to tank, but
where tank is distant from pump, relief back to
suction line is common.
3-port PRV
2-Port BPV on Tee
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Pressure Relief Options - Suction Lift
Two port back-pressure valve off of a tee on the
discharge line
Three port in-line pressure relief valve
discharges to tank through relief port
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Backpressure Valve
Provides backpressure to improve repeatability.
Prevents siphoning when suction head exceeds
discharge head.
Pressure Adjusting Nut
Spring
Diaphragm
Diaphragm Hub
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Backpressure Valve
The injection quill can create a venturi effect
in a flowing pipe, developing a vacuum. This can
draw chemical through the system even if the pump
is stopped. The anti-siphon (backpressure) valve
prevents the vacuum from causing chemical to be
drawn into water line.
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Backpressure Valve
The backpressure valve also prevents fluid from
simply free-flowing through the system when the
suction port is higher than the point of
discharge.
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Backpressure Valve
When discharging into a vacuum line, use two
backpressure valves to ensure maximum protection
against siphoning. Regulatory agencies may
require use of two anti-siphon valves in certain
applications such as adding fluoride to drinking
water. The backpressure created by the two valves
(and the injection valve) is not additive.
Whichever valve is set at the highest pressure
will determine the system pressure at the pump.
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Pulsation Dampener
In a reciprocating pump system, the entire fluid
column between the pump and injection point stops
flowing at each suction stroke and is forced to
flow at each discharge stroke. Overcoming
inertia creates large momentary pressure spikes
on the pump system.
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Pulsation Dampener
AIR
FLUID
A pulsation dampener minimizes the pressure
spikes by using compressed air to absorb the
forces due to momentum of the fluid inertia. The
flow losses are called acceleration/deceleration
forces.
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Pulsation Dampener
Principle of Operation Air is compressible,
fluid is not.
Size dampener volume to 26 times fluid
displacement per stroke, or consult piping
program. Charge dampener air pressure to 90 of
fluid pressure. You must have backpressure for
dampener to be effective. Locate dampener as
close to pump as possible, preferably as shown.
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Suction Lift vs. Flooded Suction
Suction Lift Actual lift Rated lift (water)/
Specific Gravity Requires foot valve/strainer Shor
t suction line best. Line should always be
sloping upwards. Required for self-degassing
pumps and degassing bleed valves.
Flooded Suction Minimizes cavitation and
off-gassing problems. Best for viscous
fluids. Requires isolating valve. Short suction
line best. Line should always be sloping
upwards. Diaphragm failure can drain tank.
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Suction Side Pulsation Dampening
Where losses in suction line cause cavitation, a
suction side pulsation dampener may be required.
The air side of the dampener should be at
atmospheric pressure (not charged).
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Foot Valve
The foot valve is used in a suction lift
application to prevent loss of prime when the
pump is stopped, and to improve repeatability by
preventing cavitation.
Suction Tube
Tube Fitting
Check Ball
Ball Check Seat
30 mesh screen keeps solids out
Ceramic weight keeps suction line straight, ports
let fluid in.
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Injection Valve
Injection quill puts chemical into flow for good
mixing
NPT thread to mount into pipe
Valve Spring (not used in PTFE valves) provides
backpressure, ensures ball seating.
Check Ball
Ball Check Seat
Tube Fitting
Discharge Tubing from Pump
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Calibration Column
noelt Real pic of cal column

• Provide a verification of the flow rate of the
  chemical feed pump
• Available in borosilicate glass or PVC
• Sizes from 100 mL to 10000 mL
• Marked in gallons or milliliters

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Multifunction Valve

• Operated by smooth-action rotary knobs which
  automatically return to their initial position
  when released
• Mounted directly on the liquid end of the pump
  for
• Backpressure
• Antisiphon
• Pressure relief
• Priming
• Draining the discharge line

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Float Switch

• Monitors the fluid level in the chemical tank
• Single stage function
• Minimum level indication with simultaneous shut
  down of the pump
• Two stage function
• First stage early warning annunciation
• Second stage will shut down the pump after an
  additional drop in the fluid level

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Flow Monitor
The metering monitor is used to monitor the
volume per pump stroke by using a plastic
encapsulated metal float that is detected by the
adjustable proximity sensor. Adjustable from
1-125 strokes. Plugs into front of pump.
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Typical Accessory InstallationSuction Lift
noelt Ken to find different graphic
Injection Valve prevents backflow from pipe
Backpressure/Antisiphon valve provides
backpressure for repeatability, prevents siphoning
Pressure gauge allows setting valve pressures
Pulsation dampener reduces head loss, pulsation
Pressure relief valve protects system components
Foot valve/strainer prevents loss of prime,
plugging by solids
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Piping Simulation

• Used for motor driven pumps only
• Shows if you need accessories
• Solves problems BEFORE they happen
• Application will run well

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Information Necessary

• Pump type
• Information from the technical data in the
  catalog
• Chemical being metered
• Suction lift
• Chemical tank pressure
• Size and length of suction and discharge lines
• Number of valves and fittings in the lines
• Back-pressure
• Discharge head

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Any Questions?