![\"Wiper](\"https:\/\/www.bosssealing.com\/wp-content\/uploads\/2026\/11\/a2_hero-3.jpg\")
It Is Not a Pressure Seal<\/h2>\n
The most common specification error we see is a wiper ordered as if it were a rod seal. It is not. A wiper has no pressure-energized geometry, no anti-extrusion feature and no ability to hold fluid pressure. Fit one in a rod seal housing and it will leak from the first stroke; fit a rod seal in a wiper housing and it will run dry against the rod, harden and score the chrome.<\/p>\n
The two parts also fail differently. A \ub85c\ub4dc \uc530<\/a> failure shows up as oil on the rod. A wiper failure shows up as a rod that looks polished in patches, or as a rod seal that keeps failing with no obvious cause. By the time oil appears at the gland, the wiper has usually been gone for a while and the chrome underneath is already damaged. Our breakdown of the common causes of hydraulic seal failure<\/a> covers that sequence in more detail.<\/p>\n There is one exception worth knowing: some heavy-duty designs use a combined wiper and rod seal in a single housing, with a scraping lip outboard and a sealing lip inboard. These are legitimate parts with pressure ratings, and they are specified against the rod seal housing dimensions, not the wiper ones.<\/p>\n ISO 6195:2021 covers wiper-ring housings for rod diameters from 4 mm to 450 mm and defines five housing types. The type determines whether the wiper is retained by a cover plate, pressed into an open groove, or snapped into an undercut. Getting the type wrong is the second most common reason a replacement wiper will not seat.<\/p>\nHousing Types: A to E<\/h2>\n
| Housing type<\/th>\n | Retention<\/th>\n | Wiper it takes<\/th>\n | Typical use<\/th>\n<\/tr>\n<\/thead>\n |
|---|---|---|---|
| A<\/td>\n | Groove with a separate cover plate or retaining ring<\/td>\n | Single-lip elastomer wiper<\/td>\n | ISO 6020-1 \/ 6022 cylinders, repairable glands<\/td>\n<\/tr>\n |
| B<\/td>\n | Open groove, press fit<\/td>\n | Wiper with an integral rigid reinforcement<\/td>\n | ISO 6020-1 \/ 6022, high contamination<\/td>\n<\/tr>\n |
| C<\/td>\n | Closed groove, snap-in<\/td>\n | Double-lip wiper without rigid reinforcement<\/td>\n | ISO 6020-2 \/ 6020-3 compact cylinders<\/td>\n<\/tr>\n |
| D<\/td>\n | Undercut groove<\/td>\n | Elastomer wiper with a plastic-faced scraping edge<\/td>\n | Rods 28 mm and below in split design<\/td>\n<\/tr>\n |
| E<\/td>\n | Closed groove, tight axial tolerance<\/td>\n | Single-lip elastomer wiper with no reinforcement<\/td>\n | ISO 6020-1 \/ 6022, low radial space<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Housing descriptions follow ISO 6195:2021. Axial length tolerances differ between types, and type E is the tightest at 0 \/ +0.15 mm, so a generic wiper height will not always fit a type E groove.<\/p>\n Two dimensions in the standard cause most of the field problems. The radial depth sets how much the wiper is compressed against the rod; too shallow and the lip cannot follow rod runout, too deep and the lip barely touches. The lead-in chamfer matters as much: the standard calls for a chamfer finish of Ra \u2264 4 \u00b5m, because a burr on the chamfer cuts the wiper lip on installation and the cut becomes a leak path for dirt. Dynamic faces in the housing are specified at Ra \u2264 0.4 \u00b5m and Rz \u2264 1.6 \u00b5m, with a material ratio between 50 and 80 percent.<\/p>\n Single Lip, Double Lip, and What the Second Lip Does<\/h2>\nA single-lip wiper scrapes in one direction and relies on the rod seal behind it to handle whatever film remains. It is cheap, it has low friction, and it is adequate in clean indoor service \u2014 machine tools, presses, indoor automation.<\/p>\n A double-lip wiper adds a second, usually shorter lip inboard of the scraping edge. The second lip does not seal pressure. It acts as a secondary scraper and, on some designs, as a return lip that pushes residual oil back toward the gland instead of letting it migrate out. On mobile equipment working in mud, the second lip is the difference between a rod seal that lasts a season and one that lasts a month.<\/p>\n The trade is friction and the risk of running dry. A double-lip wiper with a tight second lip can starve the rod of the thin oil film it needs, which raises rod wear. That is why double-lip wipers are usually specified with a defined interference and a groove that allows a small reservoir of oil between the lips.<\/p>\n Materials: Polyurethane Wins Most of the Time<\/h2>\nThe wiper works in the least friendly place in the cylinder. It sees UV, ozone, water, grit, and on mobile machines, hydraulic oil only as a trace film. Material choice follows from that, not from the fluid inside the barrel.<\/p>\n |
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