Understand Hydraulic Hose Selection

by Kim Berndtson
Created: November 1, 2005

When it comes time to replace a hydraulic hose assembly, how do you know which hoses and thread ends are the right ones?

"Above all, follow the manufacturer's recommendations," he continues. "You can't be too careful with hydraulics. Pressures are so high in today's equipment. Even a pin-sized hole can cause problems. There are a lot of ramifications for not doing it correctly and there are a lot of resources available for learning how to do it right."

Prevent, Detect, Inspect …

Customers ask for more efficient machines with lower owning/operating costs and higher breakout forces. Manufacturers respond by engineering units with increasingly higher pressure hydraulic systems that are achieved through tighter tolerances.

Case in point: Just 10 years ago, Caterpillar designed its hydraulic systems with tolerances of 5,000th of an inch. Today, those tolerances have dropped to 3,000th of an inch, according to Colin Olsen, marketing manager for hydraulics at Caterpillar.

While contractors enjoy the greater efficiencies, they come with a price. "Today's machines just can't tolerate dirty oil," says Olsen. "What used to get through the system without damaging the steel surfaces will now scratch the metal, which prematurely wears the surfaces and shortens their service life."

Olsen likens maintaining the hydraulic system to monitoring your cholesterol level. "The ‘cholesterol' buildup in the machine is basically contamination — dirt that comes from external sources," he states.

While some debris is inevitable, it's critical to start with as clean a system as possible.OEMs follow strict guidelines to supply clean hydraulic assemblies to customers. In the case of Caterpillar, each assembly is cleaned twice with a foam plug and capped before shipping. Caterpillar recommends keeping assemblies capped until just prior to installation. Before installing, the company also stresses the importance of cleaning the area to which the assembly will be bolted with a clean, lint-free cloth.

"Admittedly, the dirt won't harm the hose," says Olsen. "But if it reaches the valves, cylinders and pumps, that's when problems occur."

The key, he says, is prevention, detection and inspection: prevent excessive wear and shortened service life by controlling contamination; conduct regular fluid analysis to evaluate contaminants; and develop and adhere to a PM program that includes regular visual inspection of hoses and assemblies. Change components as needed.

"It takes just a half a teaspoon of dirt to contaminate a 55-gal. drum of oil," Olsen points out. "That isn't much."