How To Size & Select the Ideal Metering Pump for Your ...

1 32. SPECIAL SECTION. Metering & DOSING pumps . How To Size & Select the Ideal Metering Pump for Your Application Chemical injection will only be successful if all variables are taken into consideration and installation adheres to suggested protocols. BY TOM O'DONNELL. NEPTUNE CHEMICAL PUMP COMPANY. A. typical Metering pump application in water Materials of construction. Metering pumps are treatment, chemical process or agriculture can available in a variety of materials, most commonly deliver large amounts of chemicals during daily 316 stainless steel, C-20 stainless steel, PVC and operations. While the volumes may be large, Kynar polyvinylidene fluoride (PVDF). Users must the Metering also must be precise, with exact amounts consider the corrosion, erosion and solvent action of delivered according to strict injection schedules.

2 The wide the chemical. For example, solvent-based chemicals range of injection pressures, from high to low, must also may dissolve plastic-headed pumps , while acids be governed precisely. These demanding applications and caustics may require stainless-steel models. require the use of a unique pumping technology, one that The effects of erosion must also be considered with can ensure successful, reliable adherence to the injection abrasive slurries. schedule and fluid volumes. Chemical makeup. Chemicals come in many Metering pumps have become a top choice for the formulations, from thin to highly viscous, and they injection of chemicals in water treatment, processing can also be classified as a slurry or off-gas when and agricultural applications.

3 Many styles and modes of transferred. Standard Metering pumps are typically operation are available, so users must understand the able to handle clear liquids with viscosities ranging different Metering pump technologies in order to Select from water-like to 1,500 centipoise (cPs). Chemicals the Ideal equipment for their injection applications. with viscosities that approach 5,000 cPs or have light suspensions will require special liquid ends. Those Know The Parameters with viscosities up to 20,000 cPs or that contain up When determining which Metering pump is the best to 10 percent solids will require special diaphragms, option for a chemical injection application, users must while ones that automatically vent accumulated gas consider several variables: will need their own type of liquid ends.

4 Flow rate. Metering pumps should never be oversized, Driver. Drivers which can be powered by electricity, so determining the exact flow rate required for the water, gas, air or the sun must be selected according application is paramount. A Metering pump should be to the utilities that are available. Users must also sized so that the maximum expected flow rate is 85 to consider any environmental hazards that may be 90 percent of the pump's capacity. found in the operating area, with the operator Se p t e mber 2 0 1 5 | pumps & S y st e m s 33. Image 1. Metering pump users must consider many factors when designing a system (Images courtesy of Neptune Chemical Pump Company). realizing that pumps used in remote locations may flexibility or turndown capabilities, over the range of not be able to be inspected as often as those in the drive, depending on the pump's stroking speed.

5 Controlled environments. Flow rate set-point can be maintained automatically Environment. Determine if the pump will be by using electric or pneumatic positioners to adjust the operating indoors or outdoors. If used outdoors, stroke length, which will deliver a full 10-to-1 turndown the pump must be sheltered from direct sunlight. ratio. In this method, the number of doses remains Any pumps that will be used in freezing constant with the size of each dose reduced, resulting temperatures can only pump fluids that will not in doses that are uniformly distributed in a constantly freeze at that temperature. flowing line. Method of control. The operator must know if the Metering pumps that use a variable speed drive will pump will be used in manual continuous operation, deliver a turndown ratio that is determined by dividing on/off operation or operation that is governed by a the pump's stroke speed by its minimum operating speed.

6 Process signal. A variable speed drive will enable the pump to inject a dose of the same size on each stroke, but because the Method of control is arguably the most important stroke speeds will change, the doses themselves will variable when choosing a Metering pump. Many be less frequent. Additionally, using a variable speed styles of Metering pumps allow their flow rates to be drive with an induction motor - driven pump, which adjusted manually through the use of a micrometer dial. normally operate at speeds less than 100 to 150 strokes Adjusting this dial changes the pump's stroke length per minute (spm), is not practical because slowing the and allows the pump to be operated anywhere between motor causes each stroke to take longer to complete.

7 10 and 100 percent of its rated flow capacity. Metering However, electronic Metering pumps , which are pulsed by pumps with micrometer dials may also feature a variable a solenoid, can operate at less than one spm because the speed drive that allows adjustment of the pump's stroke timing of each stroke, from start to finish, is uniform at speed. Using the two in unison can allow additional every stroking speed. p u m p s a n d s y s te ms . co m | S e p te m ber 2015. 34 SPECIAL SECTION Metering & DOSING pumps . Image 2. Method of control is arguable the most important variable when choosing a Metering pump. Metering Pump Installation must be suitable for the discharge pressure. Typically, When designing a pumping system, users must consider matching the pipe size to the discharge connection any existing location or environmental concerns.

8 Keep in should be sufficient. mind that Metering pumps are able to push against high Suction strainer. A suction strainer should always be pressures but will struggle to pull over longer distances. used, because it prevents foreign matter from entering This means that suction lift should be limited to no the pump's ball checks. more than 4 feet and that a foot valve should be used Flanges/unions/compression fittings. At least one in top-mount installations. Flooded suction is always of these fittings must be installed at the suction and preferred in a Metering pump installation to ensure discharge ports to facilitate maintenance procedures. the pump is easier to prime, but the length of the Isolation valves.

9 Large-port, quick-opening isolation flooded suction should be limited to 6 or 7 feet. Other valves should be placed at both the suction and components of the installation to consider include: discharge ends of the installation as a way to ease Suction piping. The traditional rule of thumb is maintenance operations. Needle valves should not be to use pipe that is one size larger than the pump's used because their design will create flow restriction. suction connection, though using pipe that is the Calibration column. Because Metering pumps same size as the suction connection is acceptable, if often feature pulsed flow at low volumes, a draw- the Metering pump will be operating at a slow speed down calibration column is the most accurate and when transferring low-viscosity chemicals.

10 Generally, convenient method to measure pump performance. do not use hard piping that is smaller than inch in A tall, thin column should be used to ensure ease of diameter or that is smaller than 3/8 inch in diameter reading and reporting accuracy. Calibration columns for low-flow applications that use plastic tubing. can also be helpful in determining if any wear has Discharge piping. The size of discharge pipe is not occurred or dirt has accumulated in the pump's check as critical as that of the suction pipe, but the piping valves. If the liquid in the column bounces, that may Se p t e mber 2 0 1 5 | pumps & S y st e m s 36 SPECIAL SECTION Metering & DOSING pumps . indicate that the valves are worn or dirty.