Liquid purification or separation – Plural distinct separators – Filters
Patent
1993-09-23
1995-05-23
Nessler, Cynthia L.
Liquid purification or separation
Plural distinct separators
Filters
210108, 210411, 210393, 425185, 425199, B01D 3344
Patent
active
054178568
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a filter apparatus for fluids to be cleaned, in particular for thermoplastic synthetic plastics material for extrusion purposes, comprising a housing having a guide for at least one screen carrier member carrying at least one screen nest and being reciprocable in the guide between an operating position, a washing position and a screen exchange position, wherein in the operating position fluid to be cleaned can be supplied to the upstream side of the screen nest via at least one supply channel and at least one discharge channel is provided on the downstream side of the screen nest for the discharge of the cleaned fluid after its passage through the screen nest, whereas in the washing position the supply channel is closed by the screen carrier member, and at least one washing channel is provided for the discharge of fluid streaming through the screen nest in a direction opposite to that of the operating position and of the impurities loosened thereby from the screen nest, and wherein only in the screen exchange position the screen carrier member protrudes so far from the guide that the screen nest is accessible for the screen exchange process.
Such filter apparatus are known (for example EP-B 250 895). Within these known apparatus two screen carrier members are disposed parallel to each other in order to avoid an interruption of the supply of the extruder or the like connected to the filter apparatus during washing the screen nests of the one screen carrier member. Within this, the cleaned melt used for washing purposes is taken from the downstream side of that screen carrier member that is just in the operating position. Within this, the washing effect (cleaning effect) depends substantially from the velocity of flow of the backwashing flow that on its parts depends from the backpressure of the tool (for example the extruder head) connected to the downstream side of the filter apparatus. This backpressure, as a rule, is relatively low and cannot be influenced at will. This results in a bad freewashing of the soiled screens or--in particular at bigger screen areas --in an only partial cleaning of the soiled screens. Further, there results a loss in the mass of the main flow at the backwashing moment, what loss is as greater as longer the duration is that is necessary for a sufficient washing of the screen nest or, respectively, of the screen nests of the sieve carrier member that is just in the washing position.
It has also already proposed to dispose a rotary disc valve between two stationary screen carrier members, which valve serves for switching over between normal operation and washing operation. During the washing operation cleaned fluid is pressed from the downstream side through the screen by means of a piston that enters an enlargement of the discharge channel. Since with this the discharge channel leading to the extruder remains open, the fluid can escape through this discharge channel so that only a comparatively low backpressure is at disposal for the backwashing process. The aforesaid disadvantages, therefore, can hardly be avoided also by this construction.
The invention has at its object to avoid these disadvantages, however to retain the initially described construction and to substantially improve the backwashing effect, but at same time to avoid the loss of the mass in the main flow at the backwashing moment and to avoid an access of invironmental air to the screen nests of all screen carrier members in the washing position as well as in the operating position. The invention solves this task by the features that a storage space or a channel leading to such a space branches off in the screen carrier member from the downstream side of the screen nest, which is formed by a filter layer supported between two perforated plates, which storage space takes up cleaned fluid for the washing process, at least one piston that enters into the storage space is provided for pressing the fluid during the washing process in backwashing direct
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Bacher Helmut
Schulz Helmuth
Wendelin Georg
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