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January 2013

Under Pressure

Special care is needed when dealing with hydraulic hoses on grooming vehicles.

Written by Tom Gitter | 0 comment

 [Ed. Note: This is a reprint from SAM, September 1993. After 20 years, some information is still golden!]

Ski area managers would be hard pressed to find a piece of equipment that runs harder than a grooming vehicle. Operating 16 hours or more a day, often up to 140 days in a row, these machines are hard on hydraulic hoses. With up to 5,000 psi (pressure per square inch), plus pressure spikes, occasional breakage resulting in broken-down equipment happens. But it can be avoided if proper maintenance procedures are followed.

Snagging hydraulic hoses during grooming operations is the primary cause of component failure, which is why it is important that operators keep their equipment cleaned off and avoid ice buildup on the swing frame.


Replacing Hydraulic Assemblies
Both mechanics and equipment operators should be trained in replacing auxiliary hydraulic hoses (under 3,000 psi). The maintenance shop should carry an inventory of hydraulic components and a crimper for replacement assemblies.

For the hydrostat, most maintenance shops keep a supply of 6,000 psi hose assemblies on hand for emergency hydrostat repairs. Improvements in component design have helped reduce the failure rate of extremely high-pressure 6,000 psi lines. And, one-piece fittings with no braze or weld joints are the best way to solve flange head problems due to weak welds. One-piece flange couplings and one-piece adapters with 6,000 psi ratings hold up well.

When replacing a hose assembly, cut the hose length the same length as the one being removed. Changes in hose length when pressurized range between +2 to -4 percent while hydraulic mechanisms are in operation and may cause abrasion. If a replacement hose is too short, pressure may cause the hose to contract and put added stress on the couplings, leading to premature failure. Too long a hose can lead to the hose being severed or pinched in the moving components of the equipment.

Correct crimping is especially critical on high pressure hydrostatic hoses. Some older groomers are capable of momentary, higher spikes up to 10,000 psi, which can blow a hose. These hoses should be replaced every summer.


Avoid Mix and Match
Assembly problems usually can be avoided by following the assembly and crimp recommendations of the hose and coupling manufacturer. Couplings are usually individually designed and tested to handle each hose manufacturer’s product, but that doesn’t mean that each manufacturer uses the same rubber or plastic compounds. An improperly matched or coupled hose can fail, causing down time and possible personal injury. In addition, the proliferation of thread ends from around the world has increased the possibility of mismatching threads. Thread identification kits from suppliers can make this process easier.


Preventing Hydraulic Failure
A good preventive maintenance program involving grooming equipment inspections every 200 to 600 hours is the best way to avoid failure.

Each scheduled inspection should involve a step-by-step check of the engine, hydrostat, auxiliary hydraulics, chassis, cab, tracks, dozer, compactor bar, tiller and other components. Pay special attention to hydraulic hoses and couplings for signs of wear or leakage, which are major indicators of potential trouble.

Among the warning signs for hydraulic hose wear are cuts, friction caused by moving parts or damage from mechanical impact. Hose covers that are cut, torn or worn through are exposed to deterioration and rust.

If hoses appear excessively wet around their fittings, or grimy, loose fittings may be the cause. Tightening the fitting may solve this problem. If the fittings are tight, this is an indication that the coupling/hose interface has reached its service life and should be replaced.


Avoiding Contamination
Changing oil and filters for both the hydrostat and auxiliary systems should be part of the 600-hour inspection, as well as the summer maintenance program. To avoid contamination of the hydraulic system during hose replacement, it’s important to keep the service area clean.

Contamination can result when metal shavings are left during component machining or from clogged filters or moisture and dirt entering the system. Water and snow can enter the hose if it is dropped or dragged on the ground during installation.

To make sure the hose is clean, blow filtered air through it after the couplings are attached, or pass clean solvent or kerosene back and forth through the hose and blow it out after. When flushing is not practical, pass a clean rag, attached to a cable or rod, through the assembly. Cap plugs should be used and removed immediately prior to installation of the hose onto the designated port.


Follow Proper Installation
Rerouting high pressure hoses to prevent abrasion caused from hoses rubbing against each other has been very helpful in improving the service life of these components.

Where separating hoses is not possible, protective sleeves can be used to guard replacement hoses from external mechanical damage. Flat metal and round wire spring guards, or a sheath made of abrasion-resistant material, can help protect a hose from cuts, friction or mechanical impacts. Special insulating sleeves are also available to help protect hoses from hot equipment parts.

Routing of hydraulic hoses directly impacts their service life, so it is important to follow the manufacturer’s recommended minimum bend radius and avoid routes that twist the hose or cause it to bend immediately behind the coupling. Pay special attention to the corners and use 45-degree bent tube couplings.

Many manufacturers recommend routing hydraulic lines parallel to machine contours whenever possible. This practice can help save money by reducing line lengths and minimizing the number of hard-angle, flow-restricting bends. Such routing also can protect lines from external damage and promote easier servicing.

Other recommendations for proper installation are:

Install the most difficult assemblies first. This usually means the largest diameter and shortest hoses due to maneuvering and bending forces in a tight space.

Use clamps. Often, clamps are required to support long hose lengths or to keep hoses away from moving parts. Use clamps of the correct size. A clamp that is too large allows the hose to move which rubs away the cover.

Avoid twisting hoses. When tightening swivel fittings, use two wrenches.

Flange O-Rings. Special care needs to be taken when installing flange

O-rings so they will not be damaged when they are being positioned. Oil should be applied to the O-ring prior to installation. Flange fittings and clamps with four bolts should be tightened in a crisscross sequence.

Proper torquing. All fittings should be torqued according to manufacturer’s catalog information. Over- or undertorquing can lead to leakage and/or fitting damage.

 
Superior Performance Hoses
Many manufacturers offer hydraulic hoses with tighter minimum bend radii that are ideal for high-pressure applications such as those found on grooming equipment. Because of their added flexibility, these hoses are a good substitute for conventional hoses installed where port connections cannot be moved.

In addition to superior flexing, these hoses can be bent twice as tightly as regular hoses.

With the proper care and maintenance of the hydraulic systems in your fleet of grooming equipment, this expensive machinery can spend more time making your slopes ready for the public than being repaired in your maintenance shop.