Routing and installing a hydraulic hose is more than simply tightening the metal connections. Hoses don’t last forever, but by observing a few routing rules before final installation you can help maximize their service life.
Metal tubing has a much longer service life than a hose, but it is not flexible. When you need flexibility under pressure, a hose is your best choice. Hydraulic hose is designed to transfer pressurized fluid while the hose itself is in motion.
When installing a hose where the routing is basically a straight line, the length must be longer than the distance from port to port. As the hose is pressurized, the diameter increases to contain the force and the length will decrease. Depending on the pressure, the length may decrease by as much as 4 percent. This means a 3-foot assembly could shorten by 2 inches!
So if there isn’t enough slack, the hose fitting connections will be stressed causing a leak or worse…the hose can pull loose from the fitting causing a catastrophic failure. Allowing enough slack is important, but too much slack could introduce new risks of hose abrasion or snag on nearby components.
Your ParkerStore professional can help with additional information and to answer questions you have about proper hose selection, routing, and installation. Please check our ParkerStore finder to locate the store nearest to you.
While the hydraulic hose is flexible, it does have mechanical properties that limit its flexibility because of the wire reinforcement. One of those limitations is the hose minimum bend radius, or how much you can bend the hose before the wire reinforcement begins to kink, going from a smooth arc to a sharp corner.
Think of it this way: take two ends of a cut hose with one in each hand and form the letter “U.” The distance between is the hose bend diameter and half of that is the radius. Some hoses have better flexibility with a smaller bend radius than others. See the Parker hose catalog 4400 or ask your ParkerStore professional about the bend radius needed for your application.
Another important rule to follow when installing a hydraulic hose assembly has to do with the area where the metal fitting meets the flexible hose material. When you need the hose to immediately bend near the metal fitting, the rule is to keep the hose straight for twice the hose outside diameter. So if the hose OD is ½”, you want the hose to remain “straight” beyond the metal fitting for a minimum of one inch. If this is not possible, then consider using 90 degrees or 45-degree elbow fittings instead of straights.
When fluid under pressure at high speed enters the hose, you don’t want it “crashing” into the inner core tube because over time this will quickly deteriorate the core and dramatically shorten the service of the hose. If you “Keep it straight for 2 ID’s” this should maintain a smooth flow of fluid into the hose and minimize premature core tube failure.
While the hydraulic hose is flexible, it does have mechanical properties that limit its flexibility because of the steel wire reinforcement. One way to reduce mechanical strain is by avoiding hose twist. The continuous label/writing on the side of the hose is called the “lay line.” When you install the hose, look at the lay line. If it appears like a stripe on a candy cane, then the hose was twisted during installation. Loosen the ends and tighten again using two wrenches or “double wrenching”; one to hold the hose from twisting and the other to tighten the connection.
The next routing rule is also focused on preventing hose twist. Simply stated, you want to limit the bending motion of the hose to a single-dimensional “plane”. Think of it this way: a hose that is bending left to right is moving in a single plane or dimension, as would a hose that only moves up and down or only forward and backward. Any combination of left/right, forward/backward, and up/down movement represents 2 planes of motion and all three represent 3 planes of movement. Multiple planes of motion are called a compound bend” and this can cause the hose to twist because the hose ends are fixed and held tight. This routing rule is to limit hose motion to a single plane; however, if your application requires hose movement to cross multiple planes, ask your ParkerStore professional for a recommendation.
One of the primary causes of premature hose failure is from abrasion that removes the outside cover, exposing the steel wire reinforcement. When the steel wire reinforcement is exposed to moisture it begins to rust and deteriorate, reducing the hose service life. This routing rule is to clamp the hose so that it is held in place and supported, preventing abrasion. In the Routing Rules video part 1, we talked about how a pressurized hose can shorten, so you don’t want to clamp the hose too tight! Hoses rubbing against other hoses can also cause abrasion, so each hose should be clamped individually. If the use of clamps is not possible, then there are other abrasion resistance choices from Parker. Just ask your ParkerStore professional.
Have you ever had to loosen a connection, but in order to get a wrench on the nut you had to take apart and remove obstructions or buy a special tool? The routing rule of planning for future maintenance can be a real time saver. Take, for example, a hydraulic manifold where multiple hoses are stacked one atop the other in a small space. To reach the hose connections in back you need to remove those in front. Also, don’t forget which hoses connect to which ports! This could be avoided by using different combinations of hose ends and tube fittings. There are short and long straights as well as short and long elbows that could make the job much easier. This is just one example of how following the routing rule of planning for future maintenance can make hose replacement faster and reduce downtime.
Let’s recap the basic routing rules for hose:
Hose length shortens under pressure as much as 4%, so allow sufficient slack.
Do not bend the hose in an arc tighter than its minimum bend radius.
When exiting the fitting, keep the hose straight for a distance equal to least 2x the width of the hose's inside diameter.
Always "double wrench" during installation while using the lay line to inspect for hose twist.
Limit hose bends to a single plane.
Clamp hoses to prevent abrasion.
Make installations neat and accessible for future maintenance.
By following these simple rules you can help maximize the service life of the hydraulic hose.
Watch our video of routing rules and be sure to view hydraulic hose routing rules Part 2 for a more complete understanding of preventing premature hose failure.
Remember, your ParkerStore is a great resource not only for hose and fitting services but also tube fittings, adapters, quick couplers, and many other fluid power components. Thank you for your business and for taking the time to learn about routing rules. Please use our handy ParkerStore or HoseDoctor Locator tool on our website to find the location nearest to you.
Article contributed by:
Suzanne Favri, Digital Marketing Specialist
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