BS ISO 7425-1:2021 pdf free
BS ISO 7425-1:2021 pdf free.Hydraulic fluid power cylinders – Dimensions and tolerances of housings for elastomer – energized, plastic-faced seals Part 1: Piston seal housings.
5.3.1 For radial depths, see Tab1.
NOTE This document includes an alternative seal housing radial depth for bore diameters where D 25 mm.
5.3.2 The larger radial depths shall be selected where higher stresses or wider tolerances are involved. Consultation with the manufacturer, however, is recommended when making the appropriate selection.
6 Dimensions and tolerances
Seal housing dimensions and tolerances shall be selected from Table 3.
7 Extrusion gap
7.1 The extrusion gap (g, see Figure 1) is determined by the bore diameter and adjacent metal components on either side of the seal.
NOTE 1 The extrusion gap varies considerably depending upon use or non-use of non-metallic bearings on the piston.
NOTE 2 Maximum value for the extrusion gap is achieved when the piston is in contact with one side of the cylinder or bearing (i.e. Dd3 — see Figure 1).
NOTE 3 The extrusion gap is widened by the expansion of the cylinder due to internal pressure.
7.2 It is recommended that details concerning the extrusion gap and need for non-extrusion rings be
the subject of consultation between the housing designer and seal manufacturer.
8 Surface finish
8.1 General statement
The surface roughness of the seal housing and any mating part has a signiticant impact on the tile ana sealing performance of the seal.
Where surface roughness measurements are taken, it is recommended that instruments complying with lSQ274, including an electric wave filter, be used.
8.2 Sliding and static sealing surfaces
8.2.1 Unless otherwise agreed, the roughness values shall be in accordance with Table 1.
8.2.2 Unless otherwise agreed the material ratio, Rrnr, of housing surfaces that are in mating contact with the seal should be between 50 % and 80 % at a profile section level (RSc) of 25 % of Rz, from a reference level, C0, of 5 % Rmr (in accordance with ISO 4287:1997. 4.5.4).BS ISO 7425-1 pdf download.
