Control the Flow

Service & Repair Truck Parts & Service Staff September 3, 2011

Part choices, maintenance and installation procedures all play important roles in hydraulic performance

When Nelson Jones says every hydraulic system should be well “STAMPED,” he isn’t talking about a label on the hose. The Gates Corporation fleet and hydraulic specialist simply uses the acronym to describe factors that affect performance.

Blistering occurs when a hose is incompatible with the fluids that flow through it.

No matter what system is involved, installers and technicians need to consider size, temperature, application, material, pressure, ends and delivery.

Forget any one of these factors and there can be consequences.

The choice of one hose over another offers a perfect example of the way size can affect a hydraulic system. Technicians who replace a hose with a version that has a smaller inside diameter could generate unwanted turbulence in the fluid, he notes. This can cause tubes to swell, cracks to form and pressures to drop.

Discussions about size are not limited to diameter, either. A length of hose in a hydraulic assembly can shorten by as much as four percent when it’s under pressure. “If it’s barely long enough to go from port to port, when it’s pressurized it will shrink a little bit and it actually will pull out of the coupling,” Jones explains.

Taut lengths may not matter as much when working with the lower pressures of a transmission cooler or hot oil line, but they will present challenges when working with the higher pressures that come with a power steering pump.

Refer to both internal and external factors when selecting a hose for a particular application.

“You always want to make sure there’s significant slack in the hose. You don’t want it sloppy, but you do want to build in sufficient slack to allow for changes to the pressurization,” he says.

When selecting a hose you will need to consider the demands of rising temperatures as well. The life of a hose can be slashed in half if the temperature reaches as little as 18°F above its maximum rating, Jones says. Every hose that looks shiny, glazed or blackened has likely been exposed to that unwanted heat.

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