Fig. 46 gives a view of a patent flat vacuum strainer made by the same firm, which may also be used for cleaning straw or esparto previous to its passage over a _presse-pâte_. The pulp flows on to the strainer at _a_, and passes away by {149} the cast-iron pipes _f_. The valve _g_ is for running off waste pulp. The plates are placed at a slope of about 1 in. in their length; those nearest the supply of pulp are provided with coarser slits, as the impetus carries the knots forward. The vacuum pumps are worked by the rods _d_ from the shaft _e_. By means of the tubes _c_ water can be directed on to the plates, whereby the coarser particles of fibre are carried forward, and the slits are kept clean. The plates can be removed in a few minutes. Figs. 47 and 48 show in side and end elevation, Messrs. Masson, Scott, & Bertram’s patent self-cleaning strainer. The novelty consists in an arrangement by means of which the upper surface of the plates are continually freed from those portions of the pulp which cannot pass through the slits. The scrapers _d_ are made of vulcanised indiarubber, and are continually carried forward by an endless chain; the knots, &c., collect in a heap at the end of a strainer. The {150} pulp flows on at _a_, and passes away through the pipe _b_. The pumps are driven from the shaft _e_. [Illustration: FIG. 47.] [Illustration: FIG. 48.] Messrs. C. H. & F. L. Roeckner’s patent strainer (No. 7932, 1885) consists of a series of cylindrical tubes, open at one end and perforated with slits. They are placed in a vat into which the pulp flows. Inside the cylinders are placed two, three, or more plates, fixed to the shafts on which the cylinders are supported, and extending to the circumference. These plates form a kind of fan, which, together with the cylinders, are caused to oscillate by means of a rod and cranks. This oscillating motion serves to draw the fibres through the slits, and at the same time to keep the outsides of the cylinders clean. The cylinders are easily removable. After a time, the slits in the plates get too large, owing to the plate having been worn away by the constant friction of the fibres, and as they are very expensive, various attempts have been made to invent plans for partially closing them again. Hammering will effect this, but is liable to break the plates. Annandale of Beltonford has introduced a method of closing the plates, by means of heavy pressure acting on small steel rollers moving on each side of the slit, in which is placed a small sheet of metal the exact thickness of the width desired. {151} Another method of closing the plates consists in filling them up by means of electrically deposited copper or other metal. They can then be recut in the usual way.