Why mag drive pumps are chosen for corrosive chemical transfer

Use of centrifugal mag drive pumps for corrosive chemical transfer applications is a popular choice for many engineers. What makes these pumps a better option for corrosive chemical transfer? Let’s look at the technology and advantages of using a mag drive pump for these applications.

A mag drive pump includes features that make it right for transferring corrosive chemicals. Here are some of the features that make these pumps a compelling option:

Seal-less technology: Other pump styles use a direct-drive mechanism, with the drive shaft connected to the impeller. This requires the use of a seal on the shaft.

Mag drive pumps eliminate the seal using a magnetic connection. Neodymium magnets attached to the motor shaft spin in synchronization with the impeller. This magnetic attraction passes the motor’s torque to the impeller and eliminates the need for a shaft seal.

Highly efficient seal-less technology is a game-changer for many pump applications. No mechanical seal means no leaks. A mag drive pump maintains two separate contained areas for the motor and impeller. The pumped fluid remains in a hermetically sealed housing. As a result, even the most corrosive chemicals are pumped without leakage.

Figure 1: A mechanically sealed pump. Courtesy: Finish Thompson

Run-Dry Capability: Running dry can quickly damage or even destroy a pump. Many pump designs can’t withstand a run-dry situation. This may happen because of operator error or an issue in another part of the system.

Some centrifugal mag drive pumps use a carbon bushing with a unique carbon formulation that provides outstanding chemical resistance and a low coefficient of friction. Mag drive pump models with this design can run dry for hours without issue. This is a significant advantage in locations where pumps are not under constant supervision.

Chemical resistance: Not all pumps can handle harsh substances. Centrifugal, mag-drive chemical pumps are typically made with corrosion-resistant materials. It allows them to withstand harsh chemicals and conditions inside and out.

Durability: The design and materials of construction of a mag drive pump make it long-lasting and reliable. Applications that involve the transfer of harsh chemicals, the potential of running dry, and other challenges don’t overwhelm these pumps.

Low maintenance: These pumps require little to no maintenance to deliver long-term top performance, potentially for years at a time. The lack of mechanical seal again comes into play here: there is no seal to replace periodically due to wear or corrosion due to chemical attack.

Types of centrifugal mag drive pumps

Pump selection can be complex. To choose the correct pump for the desired application, a variety of factors are considered. Adding seal options to the mix (seal type, seal faces and elastomer options, for example) makes pump selection more complex.

Mag drive pumps simplify the selection process. There are three types of mag drive pumps for different types of applications:

Flooded suction: For use when the fluid supply level is above the pump’s centerline or impeller eye. A storage tank feeding the pump from an outlet near the bottom is an example. Gravity enables the fluid to flow into the pump. Heavy-duty ANSI dimensional pumps, that conform to the flange and foot dimensional specifications in ANSI/ASME B73.1 and B73.3, also fall into this category.

Multi-stage: A unique flooded suction configuration where multiple pump stages, with multiple impellers, enable the pump to produce much higher heads at lower flow rates. Generally, this enables the specification of a smaller, less expensive pump for low-flow applications such as spray systems, tight-media filtration, wet scrubbers, small-diameter piping systems or long-distance transfer.

Figure 2: A seal-less mag drive pump. Courtesy: Finish Thompson

Self-priming: A self-priming pump creates a vacuum in the suction piping allowing atmospheric pressure to push the fluid up the suction piping to the pump inlet. A sump located below the pump would be a typical example. Another common example is pulling liquid out of the top of a tank. To reduce the chance for leakage, it is becoming common for storage tanks or railcars to no longer feature an outlet below the liquid level.

Benefits of a mag drive pump

The numerous benefits of using a mag drive pump when handling corrosive chemicals include the following:

Increases worker safety: Pumps with mechanical seals inevitably leak, creating safety hazards, particularly corrosive or toxic chemicals. This exposure could happen suddenly with a drastic leak, or over time, as liquid or fumes slowly escape through a failing seal.

Improves productivity: Every time a mechanical seal requires replacement, it affects operations. First, there’s the cost of the new seal. Then there’s labor to uninstall the pump, replace the seal and reinstall the unit. This maintenance cycle may well incur downtime – potentially causing a line or system shutdown – risking delayed or lost production.

If maintenance is done, it can significantly disrupt operations. This adds the associated costs of delayed or unfilled orders, customer dissatisfaction, safety hazards and potentially overtime labor costs for repair technicians and the operations team.

Prevents fugitive emissions: Volatile organic compounds (VOCs) and volatile hazardous air pollutants (VHAPs) are a top concern for facilities that use pumps for chemical transfers. Not only could these emissions prove dangerous to employees and public, but pump owners are also liable and at risk of failing compliance checks.

Figure 3: An example of a caustic chemical transfer application from bulk storage tank to a smaller day tank. Courtesy: Finish Thompson

Mag drive pumps prevent fugitive emissions. Companies remain compliant with local, state, and federal health and safety standards. This increases overall plant safety and reduces the likelihood of non-compliance fines or shutdown orders.

Resists corrosion: Mag drive pump technology is proven to withstand even the most corrosive and hazardous fluids. This durability makes mag drive pumps ideal for highly corrosive applications that would be too challenging for many pump designs.

Because of this resilience, fluids that would be far too harsh for other pumps are not a problem for mag drive designs. They offer a versatile option for tough jobs.

Figure 4: Anodizing system batch: an application where multiple chemicals (used for pickling, agitation, filtering, rinsing and waste treatment systems) require transfer to and from multiple tanks to facilitate the process. Courtesy: Finish Thompson

Final words on chemical transfer

Mag drive pumps are becoming the standard for corrosive chemical transfer because of their reliability and durability. With these pumps in place, it is also possible to reduce the cost and complexity of your next project.

Common chemical transfer applications

• Transfer chemicals from bulk storage to blending tanks

• Circulate chemicals in blending tanks

• Load/unload chemicals from trucks & rail cars

• Load chemicals on filling machines

• Transfer chemicals through piping within the plant

• Rapidly empty batch treatment tanks

• Transfer chemicals and rinse waters from sumps.

How to spec a centrifugal chemical pump

To spec the ideal pump, the pump supplier needs several key pieces of information. Details about the chemicals involved, your processes and the environment, the pump manufacturer can spec the right pump for each aspect of your operations. To provide the required information, consider the following questions about the fluid and your application.

About the fluid

1. What is the name of the fluid(s) the pump will transfer? This may include more than one name if you will be mixing products, or the fluid is a mixture of chemicals.

2. What is the concentration of the fluid? This helps determine the chemical’s level of corrosivity.

3. What is the fluid temperature? Chemical resistance can vary by temperature, so this quality is important to note.

4. What is the specific gravity of the fluid? This is used to select the correct motor power and lift capacity.

5. What is the viscosity of the fluid at pumping temperature? This affects the flow, head, and motor power of the centrifugal chemical pump.

6. Will the pump be used for solids? If so, you must identify the hardness, particle size, and concentration of the solids. These details affect the material specs of the pump.

7. Is the fluid flammable or combustible? This affects what components and materials are used for the construction of the pump.

About the application for chemical transfer

1. What is the total head? This is based on the piping system and is used for reviewing a manufacturer’s pump head-capacity curves.

2. What is the flow rate? This is the volume of liquid that needs to be pumped per unit of time.

3. What is the Net Positive Suction Head (NPSHa) available? This is the suction head made available to the pump and provided by the piping system, which must be taken into consideration to avoid damage to pump components.

4. What is the application? A detailed description of how the pump will be used allows the manufacturer to spec the appropriate pump.

5. What other materials are involved? Some materials may be suitable for some chemicals but can be negatively affected by certain combinations of products.

6. What is the ambient temperature range? In settings where the temperature is not controlled, this must be taken into account when selecting the motor and construction materials.

7. What is the atmosphere environment? This helps determine the motor enclosure type.

8. What is the altitude? Atmospheric pressure affects maximum lift, NPSHa, and motor cooling ability.

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