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Metering Pumps and Pump Systems

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1 Metering Pumps and Pump Systems

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

3 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)

4 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.” ProMinent Fluid Controls

5 What claims to be a Metering Pump, but isn’t?
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 ProMinent Fluid Controls

6 What’s all This?

7 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 ProMinent Fluid Controls

8 Suction Head Negative Suction Head (suction lift)
Positive Suction Head (flooded suction) ProMinent Fluid Controls

9 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 ProMinent Fluid Controls

10 What happens if the tank is not vented (open to atmosphere)?
Suction Lift What happens if the tank is not vented (open to atmosphere)? 14.5 psia 14.5 psia 14.5 psia ProMinent Fluid Controls

11 Specific Gravity Specific Gravity is the fluid’s density in relation to the density of water (S.G. 1.0). For example: Sulfuric acid density = lbs/gal Therefore: Water density = lbs/gal S.G. = 1.84 Ammonia density = lbs/gal Therefore Water density = 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. ProMinent Fluid Controls

12 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’ ProMinent Fluid Controls

13 Viscosity Viscosity is a measure of a fluid’s 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 ProMinent Fluid Controls

14 Specific Gravity and Viscosity of Common Fluids
Fluid S.G. Viscosity (SSU) Ammonia SAE 30 oil deg F Brine Gasoline Glycerine Nitric Acid Sulfuric Acid Water ProMinent Fluid Controls

15 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.

16 Pressure Relief Valve Prevents over-pressurizing pump and piping system. Pressure Adjusting Nut Diaphragm Spring Diaphragm Hub

17 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

18 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

19 Backpressure Valve Provides backpressure to improve repeatability.
Prevents siphoning when suction head exceeds discharge head. Pressure Adjusting Nut Spring Diaphragm Diaphragm Hub

20 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.

21 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.

22 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.

23 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.

24 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.

25 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.

26 Suction Lift vs. Flooded Suction
Actual lift = Rated lift (water)/ Specific Gravity Requires foot valve/strainer Short 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.

27 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).

28 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.

29 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

30 noelt: Real pic of cal column Calibration Column Provide a verification of the flow rate of the chemical feed pump Available in borosilicate glass or PVC Sizes from 100 mL to mL Marked in gallons or milliliters

31 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

32 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

33 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 strokes. Plugs into front of pump.

34 Typical Accessory Installation Suction Lift
noelt: Ken to find different graphic Typical Accessory Installation Suction Lift 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

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

36 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

37 Any Questions?

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