<p>A slide valve comprises a valve housing having a transverse opening defining a flow passage and a slide valve in the housing which is movable upwardly and downwardly to open and close said flow passage. A compressible packing bears against at least one face of the slide preferably at the location of the parting plane between two parts making up the housing. The housing includes an adjustable screw member which extends inwardly from the exterior for the purpose of adjusting the compression on the packing and the force upon which it acts against the slide.</p>
