Pfeiffer Vacuum has taken the Atex directive and the manufacturer’s obligations concerning risk analyses and ignition hazard assessments as the starting point for optimising its proven roots pump principle. The result is the Oktaline Atex. This magnetically coupled roots pump combines a magnetic coupling with category 2 or 3 explosion protection.
Authors Meike König Market Segment Industry, Pfeiffer Vacuum Steffen Herrmann Development, Pfeiffer Vacuum
However, potential ignition sources cannot be avoided completely when designing vac-uum pumps. Owing to the heat of compression, for example, which occurs in practically every pump, the pump surfaces cannot be prevented from heating up during operation. Pfeiffer Vacuum has made it its mission to see to it that any potential ignition sources which cannot be excluded completely are designed in such a way that they will not present a hazard. For instance, the surface temperature must not exceed the limits of the respective temperature class. The Oktaline Atex roots pump therefore has a temperature sensor which performs continuous measurements to make sure that these limits are adhered to. In addition, the Atex series pumps are equipped with a housing that can withstand up to 1600 kPa of internal pressure. Each pump is tested for this before it is shipped.
The built-in magnetic coupling ensures that the pumps in the Oktaline Atex series are hermetically sealed. Their low leakage rate of no more than 1 x 10–6 Pa m³/s also provides added safety, as it prevents gas from being exchanged between the process-specific internal and external atmosphere. A gas exchange risk arises, amongst other things, if explosive mixtures escape from the pump. As a result, the internal explosion zone is shifted to the outside, where the system operator does not generally expect any such mixtures. The risk potential is therefore accordingly higher. The magnetic coupling with its low leakage rate reduces the explosion risk to a minimum.
The shaft sealing rings, which are inherently vulnerable in case of pressure surges and require considerable maintenance, have been eliminated, allowing the maintenance intervals for the Oktaline Atex to be extended. The frictionless rotors are another key feature, resulting in a technically dry operation. The air cooling system needs less energy than a water cooling system and is therefore also cheaper.
With the Atex series, all safety-relevant parameters are determined and documented for every single pump throughout the production phase. Provided the pump is used for its intended purpose, sparking can be ruled out. The Oktaline is ideal for evacuating explosive gases. All pumps in this series are suitable for temperature class T3 and speeds from 280 to 5190 m³/h. Compared to the standard version of the Oktaline roots pumps, the Atex version has a few modifications to guarantee compatibility with the Atex directive. For example, the integrated temperature sensor of the Atex pump is redundantly designed to enable the temperature to be measured under all circumstances and regardless of any complications during the process. Instead of a PEEK split case, the Atex pumps have a ceramic case which is coated on both sides. The coating prevents static charge from building up on the split case and averts the risk of ignitable sparks due to discharges. Both the magnetic coupling incorporated in the Atex version and the motor are fully Atex compliant. The overflow valve is blocked to prevent sparking due to the rapid collision of the grey cast iron materials. Other materials can also be used and the valve opened again at the customer’s request. The rotors of the Atex version are slightly shorter than with the standard version. Larger clearances can thus be achieved, leading to enhanced explosion protection, particularly in the event of a power outage. If the pump suddenly shuts off, the housing cools down faster than the piston. The pistons are consequently still expanded when the housing begins to contract again, resulting in small clearances that can cause sparking. Thanks to the larger clearances facilitated by the shorter rotor, the pump can be started up immediately following a power failure without creating a potential ignition source.
The material of the sight glass in the pump has been modified to make sure it passes the impact test stipulated in EN 13463. Furthermore, far more elaborate inspections are carried out during the production process, in order to identify and document the various tolerances for the parts and components.
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