Liquid purification or separation – With means to add treating material – Directly applied to separator
Patent
1994-09-09
1996-08-20
Lithgow, Thomas M.
Liquid purification or separation
With means to add treating material
Directly applied to separator
21033301, 210411, 210331, 210338, 210342, 162251, 68181R, D21C 904, B01D 2954, B01D 2972, B01D 3300
Patent
active
055475701
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a screening device in a standing, preferably cylindrical, container for continuous flow-through of a fibre suspension, wherein the liquid content in the said fibre suspension is altered with the aid of the screening device.
BACKGROUND OF THE INVENTION
Screens of the abovementioned category have been known for a long time. The invention will be illustrated below by referring to a specific field of application for such screening devices, namely the pulp industry and in this regard particularly in connection with the washing of pulp.
Through U.S. Pat. No. 5,027,620 (Kamyr) a screening device of this type is already known which comprises a cylindrical housing with: an inlet and an outlet for pulp, a movable supporting member which supports hollow screening members, means for vertical movement of the said supporting member, a container which is arranged on the said supporting member, which container is open at both ends and has a movable piston member arranged inside it together with means for moving the said piston member. In this known screening device, the drive unit for the vertical movement of said piston member, in the form of an hydraulic piston unit, is arranged inside the housing of the screening device, for moving the piston member. However, this arrangement has been found to entail certain disadvantages, since it has been found difficult completely to avoid leakage of hydraulic fluid, which has a negative effect on the quality of the pulp. Consequently a goal is to attempt to eliminate completely the risk of such leakages.
The solution disclosed in U.S. Pat. No. 4,971,694 (Kamyr) solves the latter problem by placing the hydraulic unit entirely outside the housing of the screening device. However, problems of another type have been found to arise with a device of the latter type. These problems are more related to the design of the apparatus and are due to the fact that the drive unit, which moves the piston member, exerts very large forces. This is because, in such a screening device, relatively large liquid volumes (about 1 m.sup.3) have to be moved within relatively short times (about 2 sec). Consequently, rigid structures are needed for mounting the hydraulic unit. In a device according to U.S. Pat. No. 4,971,694, this structure consists of a stout beam which, simply for this reason, has been arranged straight through the housing at its upper end. Despite its relatively generous dimensions, the beam bends markedly when the hydraulic unit is operating, which can be found to be troublesome. For various reasons, therefore, this latter solution cannot be considered to be ideal.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the problems that were initially mentioned above in such a way that the disadvantages arising in association with a solution according to U.S. Pat. No. 4,971,694 are entirely avoided.
This object is achieved with the aid of a screening device, wherein the said means for moving the piston member comprises a drive unit arranged outside the housing, preferably an hydraulic piston unit, from which the reaction forces counteracting the piston member via transmission members act on the supporting member for the screening members.
By using the supporting member for the screening members to absorb the reaction forces from the hydraulic piston unit, the beam according to U.S. Pat. No. 4,971,694 can be eliminated in an economical manner by utilising this rigid structure, i.e. the supporting member for the screening members, present in the screening device.
A further advantage of a solution according to the invention is that the point of application of the reaction forces can be placed in a plane which is in common with the points of application from the hydraulic piston units which drive the supporting member in its reciprocal vertical movement. This eliminates the risk that a piston rod and other transmission members for the centrally located components might be subject to flexural stresses if the suppor
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Kvaerner Pulping Technologies AB
Lithgow Thomas M.
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