This invention relates to a device for sealing a rotary shaft extending into a container, in which overpressure is maintained.

The device can be used, for example, in a pressurized screen for the screening of pulp suspensions, in which case the container is the air-tight housing of the press¬ urized screen.

A pressurized screen for screening, ^' pulp suspensions com¬ prises an air-tight housing, in which a screening member is located. The housing has an inlet for the pulp suspens¬ ion and outlets for accept and reject, respectively. In order to promote the screening process,, the pulp suspens¬ ion is caused to flow along the screening member, and the accept passes through the screening member, which can be rotary or stationary. In the latter case, a rotor is loc¬ ated in the housing for generating the flow along the screening member .

The rotor or the rotary screening member is mounted on a shaft, which is driven by a motor located outside the hous¬ ing. The shaft is supported in bearings and extends into the housing. The housing is pressurized and, therefore, a sealing is provided where the shaft enters the housing. In order to provide stability for the shaft, an intern¬ al axial bearing is located in an air-tight casing, which extends into the housing. The seal is mounted in a seal holder between the casing and the interior of the hous¬ ing inside of the internal bearing.

This structural design has the disadvantage that the external (atmospheric) side of the shaft seal is access¬ ible only after the entire shaft with its bearings has been dismounted. This implies, that conventional shaft seals of the type mechanical seal, for example a so-called

cartridge seal, cannot be applied. In many cases this is a considerable disadvantage, because it requires complic¬ ated structures and lengthy dismanteling work at seal ex¬ change.

The present invention has the object to eliminate the aforesaid problems. The device according to the invention, thus, renders it possible that the shaft seal side loc¬ ated outside the container, i.e. in the casing, can be made accessible at seal exchange in a simple way. The characterizing features of the invention are appar¬ ent from the attached claims.

The invention is described in greater detail in the foll¬ owing, with reference to the accompanying Figure illustrat¬ ing an embodiment of the device.

A pressurized screen for screeening pulp suspensions com¬ prises an air-tight housing 10, in which a stationary screening member 11 is located. The housing has an inlet 12 for the suspension and outlets 13 and 14 for accept and reject, respectively. A rotor 15 located inside of the screening member 11 is provided with pulsation means 16, which move along the screening member 11 for promoting the screening process. The rotor 15 is supported on a shaft 17, which is mounted in an upper (inner) bearing 18 and a lower (outer) bearing 19. The shaft 17 extends into the housing 10 and is enclosed by an air-tight cas¬ ing 20. in which the bearings 18,19 are located .Above (inside of) the upper (inner) bearing 18, the passage of the shaft 17 into the housing 10 is sealed by a mchanical seal 21, preferably a mechanical cartridge seal, which is mounted in a seal holder 22 attached in the casing20. The seal 21 has the object to resist the overpressure in the housing 10 and prevent the pulp suspension from pene¬ trating into the bearing space in the casing 20.

In order to render it possible to gain access to the side of the seal 21 located in the casing 20, the casing is provided with openings 23. The casing portion comprising the openings 23 preferably is detachably attached to the unbroken portion of the casing. At operating shaft the said openings 23 are closed by a detachable air-tight cover 24, preferably in the form of a cylindric sleeve. The cover 24 is attached sealingly to the seal holder 22 and extends past the openings 23 so as to seal-against the unbroken portion of the casing 20. The seals of the cover 24 pref¬ erably are O-rings.

The gland 25 of the mechanical seal 21 is attached to the seal holder 22, and the seal portion rotating with the shaft is attached to the shaft. The seal is attached and, respectively, dismounted via the openings 23 after the detachable cover 24 has been removed.

For exchanging the mechanical seal 21, the housing 10 is opened and the rotor 15 is dismounted. Thereafter the air- -tight cover 24 is removed, whereby the mechanical seal 21 is accessible through the openings 23 and can be re¬ moved from the shaft. The transport protection for the seal can also be dismounted through the openings 23.

The invention, of course, is not restricted to the em¬ bodiment shown, but can be varied within the scope of the invention idea.