BS ISO 7425-1:2021 pdf free download – Hydraulic fluid power cylinders一Dimensions and tolerances of housings for elastomer- energized, plastic-faced seals Part 1: Piston seal housings.
In hydraulic fluid power systems, power is transmitted and controlled through a liquid under pressure within an enclosed circuit. Sealing devices are used to contain the pressurized fluid with components with elements with linear motion, i.e. hydraulic cylinders. In general, these sealing devices are used with both cylinder rod and piston seal housings. This document covers piston seal housings.
This document is one part of the ISO 7425 series of standards covering dimensions and tolerances of reciprocating seal housings.
2 Normative references
The following documents are referred to in the text in such a way that some or all of’ their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3320, Fluid power systems and components — Cylinder bores and piston rod diameters and area ratios
— Metric series
ISO 4287:1997, Geometrical Product Specifications (GPS) — Surface texture: Profile method — Terms, definitions and surface texture parameters
ISO 5598. Fluid power systems and components — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5598 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
5.2 Axial length
For axial lengths for the nominal piston diameters, see Table 3.
If the extrusion gap exceeds the capabilities of the plastic-faced material to bridge such a gap, length L2
should be selected and back-up rings (anti-extrusion rings) used (see Clause 7).
5.3 Radial depth
5.3.1 For radial depths, see Table 3.
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. D-d3 — 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.