An Insider’s Tip for Pumps: Why You Should Consider Borosilicate

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Beinlich Pumpen GmbH & Co. KG

Selection of Canister for a Magnetically Coupled Pump

Because the canister functions as a static seal between the rotors, it has to be adapted specifically and accurately to the application. The smaller the gap between the rotors, the greater the transmission power of the magnetic coupling will be. The only factors that determine the transmission power are the thickness of the canister wall and the material, as well as the gap between rotor and canister.

Therefore, the wall thickness needs to be selected as thin as possible but at the same time still thick enough in order to withstand high temperatures and pressures. Metallic canisters can best meet these requirements. This is why Hastelloy or titanium are commonly used. Besides the high resistance to corrosion, titanium has the advantage that its specific electrical resistance is even greater than that of Hastelloy, resulting in even less eddy current losses.

Different Materials, Different Strengths and Weaknesses

Other canisters available on the market are made of ceramics or Peek (polyether ether ketone). These are non-conductors and, different from the metallic canisters, completely free of eddy current losses. This means that no additional heat is generated, making it unnecessary to use costly methods to externally cool the pump.

However, ceramic canisters are rather fragile, and Peek canisters quickly reach their temperature and pressure limits (120 °C, approximately 16 bar but only beneath temperatures of +20 °C). This is why it was essential to find a material that at least partially eliminates these disadvantages. One such material is borosilicate.

The Optimal Choice — a Borosilicate Canister

Since recently, a patented canister made out of the entirely amorphous material borosilicate by Beinlich's subsidiary DST has become available on the market. Borosilicate is not only especially durable but also extremely resistant to chemicals and very shock-proof. The pressure limit in combination with a magnetic coupling is constant at 16 bar even at high temperatures up to +350 °C. Borosilicate functions as non-conductor and has no specific electrical resistance; hence no eddy current losses will occur. Thus, a borosilicate canister unites the advantages of other canisters. By using such a canister, both the magnetic coupling and the electrical motor of the pump can be scaled down significantly as compared to models with metallic canisters. Therefore, magnetic couplings with a borosilicate canister have ideal characteristics for high speed applications as well as for dry-running processes.

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