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Chemical Pumps: Plastic vs Metal
A Chemical Pump is not an official pump industry term or a specific type of pump. Rather, the term refers to a pump that meets two criteria:
First, the pump must be resistant to various chemicals at various temperatures and concentrations.
Second, the pump should be emission free if operating properly, ensuring that no chemical is leaked into the environment.
As many chemicals are hazardous and potentially deadly to a person’s health, it is essential that a chemical pump has chemical resistance and will not leak for the safety of those operating near it. Not only is it safer for the operators, but it protects the surrounding physical area from requiring decontamination if the chemical was to escape confinement.
The two most common chemical pumps used for transferring chemicals are Magnetic Drive Pumps and Air Operated Diaphragm Pumps (AOD pumps). Both pumps are sealless, which means the pump does not have a shaft seal. The shaft seal is the most likely part to fail over time during the operation of a pump, and without a shaft seal, the pump is assured to be leak free if operated properly.
Magnetic Drive Pumps are centrifugal pumps while Air Operated Diaphragm Pumps are positive displacement pumps. Both pumps have their advantages and disadvantages, but with both being seal-less, they should not leak any liquid into the environment if properly selected and maintained. As such, they fulfil the 2nd criterion needed to be a chemical pump.
Jumping back to the first criterion, a chemical pump must use materials that are compatible or resistant to a wide range of chemicals. For example, when pumping water, cast iron or brass is compatible. However, if pumping Sodium Hypochlorite, cast iron or brass will quickly become compromised and begin leaking Sodium Hypochlorite into the environment.
In general, plastics have a wider range and are more resistant then metal to chemicals. For a chemical like Sodium Hypochlorite, for example, it is recommended to use Kynar in a chemical pump. Certain plastics are better than others-Kynar is better than Polyurethane or Polycarbonate, for example.
It is important to know what plastic is best for the application at hand. Just because one plastic pump is more expensive than another does not mean the more expensive plastic pump is more compatible than the cheaper one. A good example is with the chemical Sodium Hydroxide: Sodium Hydroxide is not compatible with Kynar but it is compatible with Polypropylene, which is much less expensive than Kynar.
While being resistant and not leaking are the only two unofficial criteria needed for a chemical pump, consider that not all chemical pumps are created equal. Differences between chemical pumps include the following considerations:
Manufacturers may use more or less expensive types of plastics, O-rings, or bushings.
The design of the pump may be more or less resistant to poor pumping conditions, affecting the life of the wet end.
The manufacturer may not use UL listed motors, which may result in the motor have shorter life or being safe.
And finally, not all manufacturers may have the experience to properly design a pump for long life, or the capacity or desire to help select the correct pump for an end user using one pump to an OEM using thousands.
March uses quality American suppliers of plastics and materials, designs that have decades of experience, all AC motors have UL File Numbers, and engineers with decades of experience with a sincere desire to help anyone select a pump. Now that you know what a chemical pump is, please consider March Pump for your next chemical pump application.