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Beyond failing to replace worn hoses that, in some cases, are just begging to break, one of the more common mistakes you can make with hydraulic systems is not selecting the correct components when doing repair,” says Tim Deans of Gates Corporation.
The hydraulic components industry has created a simple acronym to help you select the proper hose and ends for the application. STAMPED represents size, temperature, application, material, pressure, ends, and delivery. The terms provide a step-by-step way to select the correct replacement components.
Size The first critical step in replacing a hose is selecting a product with an inside diameter that can accommodate the flow of fluid for that application.
“It's crucial you size a replacement hose according to the inside – not exterior – diameter of the old hose,” Deans says. “The interior diameter of that original equipment hose was selected by the manufacturer to accommodate a certain volume and velocity of fluid. If you go with a smaller hose, you will restrict flow. That results in turbulent flow conditions that cause pressure loss and excessive heating.”
The hydraulics industry has adopted a measuring system called Dash Numbers to indicate hose and coupling size. “If the label on a hose is worn off, then cut the hose and measure its interior diameter to determine a replacement,” he says.
Temperature Check to see that the replacement hose you're using is rated to withstand both the minimum and maximum temperatures of the system, Deans says.
“You may not realize that different hose stocks are rated to operate at different temperatures. If you exceed a hose's rated maximum temperature, you can cut that hose's life by as much as 80% to 90%. This can be seen in cracked hoses where the hose has been cooked from the inside out.”
Application Not all implements operate the same way. A folding planter, for example, requires hoses that are designed to articulate.
“In this case, you need a hose that is very flexible, like a braided hose,” Dean says. “Spiral hoses, such as those you see on loaders, are designed to withstand a lot of flow impulse. Because of their stiff design, they won't bend as easily and, thus, shouldn't be used on planters.”
Material Hydraulic hoses are made out of different internal tube stocks depending on the fluid they carry and the conditions they operate in. The enforcement (covering that tube) and exterior cover also differ by hose type and use.
Pressure The original hose should list an operating pressure on its cover label. Otherwise, refer to the implement's service manual to determine its operating pressure when selecting hose.
Ends There are huge differences in types of hydraulic fittings today, Deans says. Fittings seal three different ways, using thread interfaces, seat angles, or O-rings. It's crucial that both the male and female fittings are compatible to ensure an effective seal. “Never mix couplings and hoses from different manufacturers,” he says. “And never reuse old fittings.”
Delivery Hoses are sized to carry a certain volume and velocity of fluid. “Undersizing a hose leads to increased pressure loss, and it boosts temperatures,” Dean says.
A detailed guide to hydraulic systems, Safe Hydraulics, is free from Gates Corporation (gates.com/safehydraulics).