NOTE: In this blog, when we discuss mast hose, we are specifically referring to over-the-sheave applications in equipment such as fork lifts (including cold and refrigeration lift), delimbers and other material handling equipment.
Inspecting your mast hose for compromises
Investing a small amount of time in mast hose maintenance increases the life of your equipment and reduces injuries. Follow the 8 simple tips below to maximize your operation output.
- Review the hose periodically
Consult your owner’s manual for appropriate intervals based on equipment and usage. Pay attention to the jacket of a hose. Its main job is to protect the structural member of the system and the braided reinforcement. After the jacket has been compromised, a hose is extremely vulnerable to external damage.
- Inspect the entire length of each hose
If sections of jacket are missing, discard and replace the hoses. Missing jacket portions drastically increase the probability of rupture.
- Check for cracks perpendicular to the hose, specifically on the outside bend radius
This could indicate that the hose being used does not have a low enough cold temperature rating. Consult your hose supplier for a lower temperature product. If the hose cracks, it exposes the braid to the environment, chemicals and abrasives that harm its integrity. If a hose ruptures, it can spray hot hydraulic oil in any direction at a high velocity, exposing the operator to severe injury from burns or from oil injection.
- Look for cuts and gouges on the jacket of the hose
Cuts that are parallel with the hose may indicate the hose is coming into contact with the material being transported. Replace the hose if the reinforcement is exposed or damaged.
- Check the hose tension
Many OEM’s ship the mast hoses under tension. Adjust per the owner’s manual.
- Inspect the sides of the hoses that come in contact with the sheaves
If the outside diameter of the hose is too large, the jacket will show excessive wear. Consult your hose supplier for a lower profile hose.
- Search for broken wires when using rubber hoses
Look for broken wires protruding through the jacket by running a cloth over the hose and feeling as you go. DO NOT use your hand (wires are sharp). If wires are broken, the cloth will snag on the wire and you will need to replace the entire hose because the jacket and strength members have both been compromised.
Maintenance Safety Tip: When looking for leaks or identifying where a leak is coming from, do not run your hand down the length of the hose. Instead, use a piece of cardboard. This will prevent injury by oil injection which can be serious.
- Check end connections for leaks
If fluid leaks from the connection end, check the connection to insure it is tight. If the leak continues, disassemble the hose and adapter fitting and inspect the mating surface area or seal for damage. If either is damaged, discard them and replace them with new components. If fluid leaks from the shell end of the fitting, discard the hoses and replace them.
Need to replace a mast hose? Remember it’s all about the sheave width
If you discovered during inspection that you need to replace a mast hose, one of the most important factors to consider is the sheave width. This is especially critical if the OEM installed a thermoplastic hose, because rubber hoses have much larger outside diameters (O.D.). A larger O.D. (rubber or thermoplastic) causes additional wear on the hose as it passes through the sheave, shortening the hose life.
When mast hose is pressurized, the internal force from the pressure causes it to change in length and diameter. A hose that fits snugly in the sheave at rest becomes very tight during operation and may ride out of the sheave, bow out or possibly come in contact with the machine or environment. Also, a tight sheave fit causes added tension on the system and increases wear directly on the hose and sheave.
Most material handling mast manufacturers install mast hose at a tension measured in "stretch of the hose." The stretch specified can vary greatly depending on whether the OEM installed thermoplastic or rubber.
Replacement hose choices – the advantages of thermoplastic mast hose over rubber hose
When it comes to choosing a hose, you will find both rubber and thermoplastic hoses available. Today, most material handling OEM’s use thermoplastic hose in their masts from the factory with sheaves sized specifically to fit the hose they install. Thermoplastic hose is uniquely able to withstand the tension applied with minimal stretching; it requires only 1/5th the amount of stretch (distance) compared to rubber hoses to reach the desired tension, reducing installation time. Also, a thermoplastic hose will outlive conventional rubber products for several reasons:
- Thermoplastic hoses will not delaminate. Rubber hose layers cannot withstand the rigors of an over-the-sheave applications; they will delaminate, leading to jacket failure and wire fatigue.
- Thermoplastic hoses have better low temperature properties (-70ºF) for use in freezers and cold weather, preventing the hose jacket from cracking.
- Fiber reinforcement does not fatigue during constant flexing motion over the sheave.
Parker’s Parflex Division offers thermoplastic over-the-sheave hoses with braids in high tensile fibers or high tensile brass plated steel wire and a specially formulated hose jacket with a high level of UV protection for optimal weather resistance and low coefficient of friction to improve wear. Parker’s thermoplastic hoses meet SAE 100R1AT, 100R2, 100R7, 100R17 or 100R18 specifications. More information on hose routings, installation and safety, review the Parker Parflex Safety Guide in the 4660 Catalog.
For more information about the Parker Parflex line of mast hoses, call 330.296.2871 or visit www.parker.com/parflex.
Article contributed by Greg Hayes, OEM Sales Manager at Parker Parflex Division
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