A primary source of hydraulic hose failure is cover abrasion resulting from cuts, friction caused by other moving parts, or from mechanical impacts. For example, changes in fluid pressure can cause hoses to either elongate or contract, repeatedly impacting adjacent machine elements or other hoses, eventually wearing away the hose cover to expose the underlying reinforcement. Erosion of the cover material can also be caused by non-compatible fluids such as toxic chemicals, acids, detergents, and non-compatible hydraulic fluids.

Major manufacturers have developed upgraded cover stocks to resist abrasion, environmental degradation, and excessive heat. Made of special rubber/plastic compounds, these new hybrid cover materials have a slick surface with a low coefficient of friction. They have been tested to last up to 300 times longer than traditional hose cover materials, such as Neoprene and Nitrile. This feature increases service life, lowers maintenance, and eliminates the need for hose protectors such as guards, sleeves, and bundling.

Protect with guards and sleeves
To further protect hydraulic hoses from external damage and wear, design engineers and operations managers can use several different types of hose guards or sleeves:

Metal Spring Guard — This form of hose protection is often used when an exposed hose may encounter flexing, twisting, kinking, tensile or side loads, a tight-bend radius, and/or vibrations. The metal spring guard needs to be fitted before the hose is assembled.

Plastic Spring Guard — This flat, plastic guard is also used on exposed hoses, but has the added advantage of being able to be fitted after the hose has been assembled and sometimes after it has been attached to the equipment.

Textile/Nylon Sleeving — This type of sleeving is often used on hoses inside the equipment or in places where abrasion may occur. The textile sleeving offers excellent wear resistance and can help reduce the amount of oil spillage.

Although these sleeve covers may protect a hydraulic hose from abrasion and cuts, they typically offer little or no protection from hose bursts and pinhole leaks that can compromise operator safety.

A pinhole leak in a hydraulic hose that is under pressure can release toxic fluid at more than 600 ft/sec — close to the muzzle velocity of a gun. The very fine jet of hydraulic fluid at high pressure will act like a hypodermic needle that may penetrate both protective clothing and skin.

To protect operators of hydraulic equipment from catastrophic hydraulic hose bursts or pinhole leaks, several hose manufacturers have developed their own versions of a safe “line-of-sight” nylon sleeving.

Dennis Kemper is Team Leader, Worldwide Product Application for Gates Corp. Contact him at (303) 744-4391, dkemper@gates.com, or visit www.gates.com/hydraulics.

LifeGuard sleeve
Gates’ LifeGuard sleeve is comprised of two nylon layers to help absorb the energy of a burst or pinhole leak and contain pressurized fluid.
Protect the operator, not just the hose
When choosing a sleeve product, design engineers need to understand that current standards and specifications relating to hydraulic hose protection are vague.

ISO 3457 and EN474-1 state, “Hydraulic hoses containing fluid with a pressure of more than 5MPa (50 bar) and/or having a temperature over 50°C, and which are located within 1.0 m of the operator, shall be guarded.”

Mining industry equipment must conform to Mine Safety and Health Administration (MSHA) standards and be certified. MSHA’s Accident Prevention Program simply says, “Install abrasion protection such as spiral wrapping, sleeves and guards.”

ISO and European standards don’t specify a test method for sleeving products.

Although no current industry regulations exist, Gates Corp. has developed its LifeGuard sleeve following a rigorous testing program that could likely be used to establish future standards for end-user applications. The LifeGuard sleeve has been tested both in the lab and in the field to verify its performance and capabilities at typical fluid pressure and temperature levels.

Gates’ LifeGuard sleeve is comprised of two nylon layers. During manufacture, the two sleeve layers are continuously woven at the same time, one inside the other, but they are not attached to one another.

The inside sleeve layer is made of nylon fiber that elongates or stretches up to 20%. By stretching, it can absorb the energy of a burst or pinhole leak. The outer sleeve contains the fluid and redirects it to the clamped ends. The outer sleeve is resistant to abrasion, but is not specifically designed for abrasive environments. Worker safety within a three-foot line-of-sight of a burst or pinhole leak is the primary benefit.

The sleeve is secured at either end of the hose with special “channel” clamps. The clamps allow leaking fluid to escape, so the fluid won’t collect behind the sleeve and cause it to rupture. Fluid leaking past the clamps lets the operator know that there’s a leak in the hose.

LifeGuard sleeving protects hoses from 3000 psi pinhole leaks and 6000 psi bursts on –4 (1/4 in.), –6 (3/8 in.) and –8 (1/2 in.) hose sizes. The sleeving is compatible with a wide range of fluids, including environmentally friendly liquids and biodiesel fuel. It protects up to 212° F, the SAE standard for most industrial hydraulic applications. The line-of-sight sleeving is a safe, effective, economical alternative to other costly metal, plastic, and nylon shielding.

For more information on LifeGuard line-of-sight sleeving and other Gates hydraulic products, visit www.gates.com/lifeguard.