The Right Pump for Liquefied Gases is Crucial for Safety and Efficiency

Related Vendors

Italvacuum, Srl

Donadon SDD Srl

ProMinent GmbH

Sterling Fluid Systems (UK) Ltd

Double Mechanical Seals

Double back-to-back mechanical seals are arranged in such a way that a clean “barrier” liquid can be injected into the space between the two seals. Unlike a single mechanical seal, this arrangement effectively eliminates all leakage to the atmosphere.

As the name suggests, the seals face in opposite directions. The inboard seal keeps the process liquid inside the pump, while the outboard seal contains the barrier liquid. Should the inboard seal fail, the barrier fluid is forced into the pump, preventing external leakage. In the event of outboard seal failure, only the relatively harmless barrier fluid is ejected.

A different approach known as tandem seals is often used when leak-detection devices are necessary, but no pressurised barrier fluid system is available. Here, two seals face the same direction, with a cylindrical chamber containing barrier fluid at atmospheric pressure in–between. If the inner seal should fail, the outer seal holds most of the liquefied gas safely in place.

Sealless Magnetic Couplings

While mechanical seals are safe and effective, they need regular maintenance and are not always absolutely leak-tight. Growing demands to reduce environmental emissions have therefore persuaded more and more users to install sealless magnetically coupled pumps. This configuration removes the need for rotary mechanical sealing altogether.

The drive end of the pump housing terminates in a stationary “shroud” or “can” of non-magnetic material. Inside the can is a ring of permanent magnets attached to the impeller shaft, with a second ring of magnets attached to the motor shaft on the outside.

The magnets are arranged with opposite poles aligned so that the outer magnet’s rotation drags the inner magnets round at the same speed. The result is a pump with no dynamic seals, eliminating the risk of seal failures. Since their bearings completely rely on product lubrication, magnetically coupled pumps must not run dry.

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