How to Keep Dust and Contaminants Out of the System
Posted on 2017/04/15 | Cliff | News
Dust may seem like a minor issue, but it can cause major damage to cylinder walls, rods, seals and other components. If you’re not careful, so can dirt, mud, debris and water.
These foreign contaminants are real problems for mechanical systems operating over time, causing friction, surface wear and imperfect sealed contact between surfaces.
Just as seals keep pressurized fluids and gases in piston/cylinder systems, there are components that keep contaminants out.
These components — wipers, excluders and scrapers — are fitted on the exterior side of the main seals. The exact type you need depends on what you’re protecting against.
- Wipers: used for light applications to seal out fine material like water, dust and wet mud; made of soft plastic or firm elastomer (rubber)
- Scrapers: used for aggressive applications to seal out hard stuff like ice, dry mud or other solid debris; made of hard plastic or metal, such as brass
- Excluders: somewhere in between wipers and scrapers in terms of protection, excluders seal out medium-level material
Scrapers aren’t ideal for preventing finer material from getting in. They also allow piston/rod lubrication leakage, which attracts dust buildup; a soft wiper is sometimes used in tandem on the inside of the scraper.
Excluders prolong seal life by preventing contamination of the hydraulic fluid that would otherwise damage wear rings, seals and other components.
Typically, a microscopic film of hydraulic fluid leaks through the excluder onto the piston/rod on the out-stroke (which can then attract dust), but on the return stroke, it rubs it off to prevent entry into the system.
Excluders are useful for rugged applications like keeping road dirt out of vehicle shock absorbers or mud out of brake cylinders.
Pneumatic cylinders are usually of lighter construction than hydraulic cylinders, so the excluder can be combined with the inner seal in one piece.
The excluder is typically designed for low friction, with a rounded or chamfered profile to allow return of any leaked lubricant.
The performance of the one-piece seal is not as good as a separate excluder, but to compensate, a small amount of compressed air leakage helps to blast out contaminants. This air leak doesn’t matter the same as leaked fluids from pneumatic cylinders.
Endless Optimized Geometries and Configurations
Wipers, excluders and scrapers are built in all sorts of combinations for unique needs and desired functional parameters.