Scale pad and valve structure

A scale pad for log bunk, said pad including a horizontal table having a central portion and an outer peripheral portion, an upper top plate centered over said table and including an outer peripheral portion, a diaphragm between said top plate and table and secured across and to the outer peripheral portions of said top plate, the central portion of said table and the overlying portion of said diaphragm having registered central openings formed therein, said top plate and table including coacting means guiding said top plate from said table for vertical movement relative thereto, limited horizontal shifting relative thereto and limited canting relative thereto in all directions about a central zone of said table, an elongated pop-off valve assembly sealingly secured through said central portion of said table and the overlying portion of said diaphragm, said pop-off valve assembly including an elongated upstanding sleeve having air inlet means at its lower end and an open upper end provided with a radially outwardly projecting and downwardly facing peripheral abutment flange, said sleeve being passed through said registered openings and said abutment flange overlying the marginal portions of said diaphragm defining the central opening therein, a tubular piston plunger reciprocally received in said sleeve and including a piston thereon between said inlet means, the upper end of said plunger being sealingly slidable through the upper sleeve end, a vent port in said sleeve between said inlet means and said upper sleeve end below said table, said vent port being spaced above said piston when the latter is in its lower limit position and said piston being upwardly displaceable in said sleeve at least to the level of said vent port upon upwardward movement of said piston in said sleeve, said sleeve including a diametrically enlarged externally threaded portion below said vent port, the lower end of said sleeve being open and defining the air inlet means at the lower end of said sleeve, an internally threaded closure nut threadedly engaged on said externally threaded portion and extending below said sleeve, the lower end of said nut including an end wall underlying the lower end of said sleeve and having a fluid pressure inlet port formed therein, the upper end portion of said nut defining an annular channel extending thereabout externally of the upper end portion of said sleeve below said table in which said vent port is formed and into which said vent port opens, the upper end of said nut being tightened against a downwardly facing abutment surface portion of said table extending about the central opening therein through which said sleeve is received, the upper end of said nut including a generally radial port opening into said channel, the portions of said diaphragm and table disposed about said openings being clampingly engaged between said abutment flange and the upper end of said nut and the threaded engagement of said nut with said sleeve as well as the abutting engagement of the upper end of said nut with the undersurface of said table serving to reinforce said pop-off valve assembly against breakage as a result of lateral forces being directed thereon below said horizontal table.