Hydraulic Hose KnowHow

Robert Deierlein

Hydraulic hose assemblies must be checked regularly for signs of damage. When replacing the hose, make sure that the replacement will produce the same temperature, service and pressure capability while meeting the industry, Department of Transportation and Society of Automotive Engineers standards.

The following guidelines can help maximize design life, according to Ron Wacker of Gates Rubber Co., Denver:

* To guarantee compatibility, don't use couplings and hoses from different manufacturers. Some hose tube materials and hydraulic fluids are incompatible, which can cause blistering and fluid bleed through. Phosphate ester and petroleum-based hydraulic fluids have different chemical characteristics. Also remember to determine the correct coupling threads for proper port attachment.

* The hydraulic system pressure should not exceed the hose's rated working pressure; consider surges or peaks when specifying a hose. All hoses are rated with a maximum working temperature between 200 and 300 degrees, based on the fluid temperature. Continuous exposure to high temperatures can make hoses lose their flexibility.

* Performance testing has proven that a hose's routing will impact its service life. Mechanics must be aware of the manufacturer's recommended minimum-bend radius and avoid using routes that twist the hose or cause it to bend immediately behind the coupling. Use clamps and/or hose sleeves to avoid excessive flexing, whipping or contact with other moving parts.

* When routing the hose, allow some slack since it may lengthen or shorten when pressurized. Replacement hoses must be cut the same length as the ones they replace. If the hose is too long, it can get severed or pinched in moving components; if it's too short, pressure may cause it to contract and pull away from the fitting.