hydraulic valve spools

How to Replace Hydraulic Hoses

Heavy equipment uses a hydraulic pump, valve spools, and cylinders to perform their tasks. These components are interconnected with a series of steel tubes and steel reinforced rubber hoses, and the hydraulic oil may eventually begin to leak through these hoses, making it necessary to replace them. It can be a dirty job, but doing it yourself can save considerable costs and time.

  • Locate the problem hose. This may be obvious if the hose has burst, since they typically handle oil at over 2000 PSI pressure, and one that bursts will discharge a large amount of oil in a short time. If the situation is a small leak, though, you will need to observe where the oil is dripping, and follow the wet trail it leaves to the source. Never use your hands or body parts to find the leak. Use cardboard, paper or hydraulic leak detection fluid so no oil injection is accrued. A good hydraulic shop stocks leak detection additives that assist on location the leak safely.


  • Assess how many components must be removed to facilitate replacing the damaged hose. Always label the component removed by number and letter so replacement of parts can be re-installed with ease. This may include housings, guards, clamps, other hoses, hydraulic cylinders, and more. Follow the hose from one end to the other, noting the route you will use to uninstall and re-install it. Putting a number and letter on the ports and hose ends.


  • Determine if the hydraulic component the hose serves, or any other hydraulic components which must be removed have a live load, or weight on them. If the oil in the system you are disconnecting is under pressure, it may blow out forcefully when the fittings which hold it are loosened, causing oil to be discharged under pressure. Relieve the pressure from these cylinders or components before proceeding.


  • Make sure any attachments that are supported by the hydraulic cylinder that the hose operates are lowered to the ground or blocked or chained up. The weight of an attachment can crush a mechanic if it suddenly falls when pressure is relieved in the cylinder that is supporting it.


  • Get the tools you will need to perform the job of removing the hose. The fittings on the each end of the hose will be removed with a wrench, which may vary in size from 9/16 to over 1 1/2 inches. Many of these fittings are designed to swivel or turn as they operate, so two wrenches will be required to remove each of them. Hold the stationary side of the coupling with one wrench to prevent it from turning, and possibly damaging an O-ring while turning the other to separate the coupling.


  • Remove all clamps and attachments which will interfere with removing the hose. Often, the hydraulic cylinder itself will need to be removed or supported so that fittings can be accessed. Hydraulic cylinders are either bolted directly to the boss or fixture which it operates, or is anchored with a steel pin, such as the one in the illustration.


  • Loosen the fitting that attaches the hydraulic hose to the hydraulic system, either at a coupling, a cylinder, or the valve spool itself. Make sure the fitting turns at the threaded connection, and does not twist any other part. If needed, you may have to hold the fitting the hose is attached to with a separate wrench.


  • Pull the hose off of the equipment when both ends are unfastened. Be aware that some hydraulic oil may leak from either or both connections, and the oil that is remaining in the hose will also dump out, so having a bucket handy to catch this spillage is a good idea.


  • Plug the fittings that remain on the machine to keep debris from getting into the system during the interval the fitting is open. If you do not have oil dripping from the fitting, and do not have a plug with the correct threads on it, you may tie a clean rag around the fitting to protect it, but be careful if rain is in the forecast, since a rag won’t protect the system from being contaminated with water.


  • Wipe excess oil from the hose, and give us a call to get a new one weather we have it on the shelf or we have to make it for you. We supply replacement hoses and fittings which can be assembled while you wait, and are less expensive than ordering an original equipment manufacturer’s product.


  • Clean all the fittings on the equipment before re-installing the hose. Make sure there is no dirt in the tubing or fitting which will end up in the hydraulic system when you are finished.


  • Plug the ends of your new hoses with a special cap or a clean rag before routing it through the equipment to where it goes. This will keep dirt and debris from being forced into the hose while installing it. Remove these temporary plugs immediately before installing the fittings where they mate up with their counterparts.


  • Make sure the hose is in the correct location, and it has the proper amount of slack where needed when it is installed, then thread the fittings back on the cylinder or other component where they were removed. Tighten these connections snugly. You may have access to a specification book which recommends a torque to apply to each fitting, but failing this, tighten them as much as you can without risking damaging the seals or stripping the threads which hold them.


  • Replace any clamps, guards, or other components which were removed to accomplish the task. Align any cylinder pins which were removed, and re-install them, and return any split or snap rings which hold them in place.


  • Check the fluid level in the machine, crank it up, and check for leaks. If you have had a chance to clean all surfaces that were soiled by the initial leak, any leaks that occur now will be much easier to spot. Keep in mind some hydraulic circuits will require bleeding to remove air from the system prior to using the machine. This usually applied to steering and brake systems, but there are other situations where air can become trapped, such as a single action cylinder where the hydraulic supply is at a low point in the cylinder.


Craig Cook


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