When you absolutely cannot risk a leak

flow reports on a leak-free pumping option for applications where a safe fluids handling solution is essential.

Standard centrifugal pumps are driven by a shaft from the motor, connected via a flexible coupling to the impeller through the pump housing. This design will require some form of seal to stop the pumped medium from leaking out around the pump shaft, especially if the pump is working at high pressure.

By contrast, with a magnetic drive pump the drive shaft from the motor rotates an assembly of magnets on the outside of the housing. Opposing this, on the inside of the housing is a matching ring of magnets on a shaft attached to the impeller. As a result of these coupled magnets, torque is transferred through the housing so the impeller and the pumped fluid are contained within a hermetically-sealed housing.

“It is important to understand that the term ‘magnetic drive’ applies to the coupling mechanism and the nature of construction, so magnetic drive options are not restricted to just centrifugal pumps.”

When the pump is primed the liquid is completely contained and so there is no need for any dynamic seals. As the electric motor rotates, the outer ring and the inner ring rotate at the same speed, thus rotating the impeller and causing liquid to be pumped.

In applications where the complete containment of a process fluid is necessary, magnetic drive pumps are worth consideration. Due to the wide variety of volatile, toxic, valuable and hazardous fluids used within chemical processing operations, this industry sector in particular has a need for solutions which help ensure accurate and leak-free flows of pumped fluids.

Since the development of the first sealless pump in 1947 – to handle a heat transfer fluid at 300°C for a British chemical company – magnetic drive pumps have been finding applications in chemical processes to handle fluids which are hazardous, corrosive or aggressive to handle. They also offer a solution which addresses health and safety concerns relating to the potentially harmful effects of fluid leakage on operators involved in the production process.

More recent generations of sealless pump have addressed several weaknesses of the original magnetic drive design, including reducing power consumption and eliminating the risks associated with dry running, which has been a traditional drawback of magnetic drive technology, due to the fact that it is the pumped liquid itself that provides

bearing lubrication. Some manufacturers have developed bearing materials and coatings that are able to run dry for a limitedtime. Stainless steel is the most widely used material in magnetic drive pumps due to its ability to withstand high temperatures and its good corrosion resistance which allows it to cope with hazardous fluids such as acids, corrosive solvents and brine water.

It is important to understand that the term ‘magnetic drive’ applies to the coupling mechanism and the nature of construction, so magnetic drive options are not restricted to just centrifugal pumps. The technology has been welltested over the years and developments continue apace. So, if you are looking for a safe pumping solution for a hazardous fluid do take a closer look at what magnetic drive solutions now have to offer. chevron-

Magnetic drive pumps: pro’s and cons

ADVANTAGES INCLUDE:

• Very low risk of fluid emissions from the pump.

• Low maintenance requirements due to a simple design, with no seals to be replaced.

• No need for alignment of the pump or motor.

DISADVANTAGES INCLUDE:

• An inability to cope with fluids containing solids.

• High initial cost – however this capital cost will be offset over the life of the pump by its reduced maintenance requirements. Magnetic drive pump requires higher power absorption than conventional pump.

• Risks associated with dry running of the pump.