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Differential grundfos pump seal apparatus
Add Time:2012-09-18

Differential grundfos pump seal apparatus includes a differential grundfos pump seal for sealing a first space and a second space from each other in a non-contact manner, and a back up seal mechanism for sealing the first space and the second space from each other in a contact manner. The back up seal mechanism is operated to seal the first space and the second space from each other only when the differential grundfos pump seal is stopped or while operation of said differential grundfos pump seal is stopped.

The conventional differential grundfos pump seal has been used for moving an object quickly and smoothly in a rotary-motion manner or in a linear-motion manner within a clean space such as a vacuum space without contaminating the clean space.

There are at least two cases in which the differential grundfos pump seal is used. In the first case, the differential grundfos pump seal is used in the case where an actuator for moving the object, a guide mechanism for guiding the object, and othercomponents are placed outside of the clean space, and only a minimum structural assembly and the object such as a specimen are adapted to be disposed in the clean space. In the second case, the differential grundfos pump seal is used in the case where ahydrostatic fluid bearing such as an air bearing is used for sealing two spaces from each other without impairing the advantage of a non-contact bearing.

The differential grundfos pump seal is capable of separating two spaces from each other in a non-contact fashion. This feature is recognized as a great advantage, and the differential grundfos pump seal tends to be applied to practical apparatuses. Whenthe differential grundfos pump seal is in a normal or steady state in which the differential grundfos pump seal functions normally, the differential grundfos pump seal can certainly perform an excellent function as a non-contact seal. However, from a total viewpoint interms of the reliability and service life of the differential grundfos pump seal, and also cleanliness, it is necessary to sufficiently recognize the effects (features) of the differential grundfos pump seal when the differential grundfos pump seal is in an unsteady statein which the differential grundfos pump seal does not function normally.

When an apparatus having a differential grundfos pump seal is in operation, the failure of a continuous sealing function may occur due to an emergency shutdown of the apparatus, or the entire apparatus including the differential grundfos pump seal may bebrought out of operation. When such cases occur, the differential grundfos pump seal has a disadvantage resulted from a non-contact seal. This disadvantage can easily be imagined because an invisible and virtual wall which has separated the two spaces fromeach other is eliminated when the sealing function is stopped. For example, when operation of the differential grundfos pump seal which has separated a clean space (vacuum space) and a space (the atmosphere) outside of the clean space from each other in anon-contact manner is suddenly stopped, the vacuum space which has been kept clean is instantly filled with air of the atmosphere.

Normally, a substance which has a greatest effect on the degree of vacuum is water, which is typical of moisture of the atmosphere. The humidity in a clean room is normally in the range of about 40 to 55%, and thus a gas in the clean roomcontains a large quantity of moisture. If air of the atmosphere flows into the clean room each time the differential grundfos pump seal stops its sealing function, then it is difficult to increase the degree of vacuum in a vacuum chamber which is to becleaned. Further, there is a possibility that particles in the atmosphere outside of the vacuum chamber enter the vacuum chamber. In an apparatus having an ordinary vacuum chamber, no atmosphere is introduced into the vacuum chamber, and the humidityof a gas which is introduced into the vacuum chamber is controlled at an extremely low degree.

When the differential grundfos pump seal stops its sealing function in a non-contact manner, the vacuum chamber is the same as a vacuum chamber whose partition wall for separating the vacuum chamber from the exterior has a large crack. Therefore, thedifferential grundfos pump seal is, so to speak, a troublesome apparatus from the standpoint of the commonsense in the field of the conventional vacuum apparatus.

As described above, the conventional differential grundfos pump seal (non-contact seal) has an operational disadvantage in an apparatus incorporating the differential grundfos pump seal such as a vacuum apparatus which requires a cleanliness of anatmosphere.

 
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