This article outlines some important points to follow which will help in selecting the optimum hose assembly for hydraulic equipment or system
Often you purchase a hose assembly for your hydraulic equipment or system just to experience a premature failure. In this article we will discuss some very important points to follow which will help you select the optimum hose assembly for your application, thus obtaining the maximum life for your application.
Optimum life of a hose in a particular application is achieved by:l Safe hose selectionl Safe coupling selectionl Safe hose assemblyl Safe installation of that assembly.
All of the abovementioned points are critical for getting maximum hose life. We will discuss these points here in detail.
Safe hose selection Proper hose selection is critical to a safe hydraulic system. A simple rule of thumb for proper hose selection is the word “STAMPED” where:S = SizeT = TemperatureA = ApplicationM = MaterialP = PressureE = EndsD = Delivery.
The first step in achieving a safe hydraulic system is selecting correct components that meet your needs. Compromises in components selection, either hose or couplings, may put you in danger, as well as affect the performance and life of your system.
S (Size):  The inside diameter of the hose must be adequate to keep pressure loss to minimum and avoid damage to the hose due to heat generation created by excessive turbulence.
T (Temperature):  The hose selected must be capable of withstanding the minimum and maximum temperature of the system. Do not expose hose to internal or external temperatures exceeding the recommended limits.  An increase of 10 C above the maximum recommended temperature may reduce the hose life by half.  Also, hose will crack if flexed at temperatures below the minimum recommended.A (Application):  Select the proper hose for the application. Determine where, or how, the assembly is to be used.
M (Material):  Hose selection must assure compatibility of the hose tube, cover, reinforcement, couplings, o-rings, etc., with the fluid used. Many hoses are compatible with one type of fluid or another, but often times not all fluids.
P (Pressure):  It is essential in the hose selection process to know the system pressure, including pressure spikes. Published working pressure must be equal to or, greater than the system pressure. Pressure spikes greater than the published working pressure will shorten hose life or lead to hose ruptures
E (Ends): Connecting ends of coupling must be correctly identified.
D (Delivery):  How much fluid must go through the hose?  This will determine the size of hose that must be used.  Under sizing a hose leads to increased pressure loss, while over sizing the hose adds unnecessary cost, weight and bulk.
Safe coupling selectionIt is critical that the hose and coupling manufacturer are the same. Don’t mix and match hose and couplings from various manufacturers. Always use couplings that are recommended by the hose manufacturer for that particular hose.  Thread ends must also be compatible in order to prevent leaking or assembly blow off from equipment.
Safe hose assemblyOnce the hose and couplings are selected, it is important that the assembly is made properly. If not, the ends could blow off or, the hose may fail at coupling.
It is important that the hose and couplings are from the same manufacturer and they are assembled using the manufacturers recommended equipment and procedures.  It is critical to follow the hose manufacturer’s recommendations on hose, couplings and assembly technique. Following these recommendations will assure maximum assembly life. If recommended practices are not followed, or hose and couplings from different manufactures are used, there is a significant risk of catastrophic or premature assembly failure.
Safe installationThe art of making leak proof connections with hydraulic couplings is to tighten the couplings properly at the time of installation. An over tightened (over torque) coupling may be just as apt to leak as an under-tightened coupling. Over tightening can create a coupling that is overstressed which in turn can lead to cracking and leaks or possibly complete coupling failures.  In addition, it is important to pay particular attention to the hose routing. A properly installed hose ensures hazard prevention as well as ensures long life.
Avoid twisted hose installation. A twisted hose installation misaligns the reinforcement (which is the strength imparting component of hose) and reduces its ability to withstand pressure.
Twisting a high pressure hose as little as 7 degree may reduce service life by as much as 90 per cent.
Avoid positioning hose next to heat sources. Excessive heat may cause hose cover or tube to develop cracks. As explained above, an increase of 10 C above the recommended maximum temperature range may decrease hose life by half.  Also excessive low temperatures beyond recommended limits will create cracks in the cover and/or tube when flexed.
Avoid positioning hose next to metal edges or too close to other hose where any of them or both has movement. The hose cover and reinforcement may be damaged by abrasion leading to hose failure. This may also lead to safety problem.
The selection process for proper hose and couplings can sometimes seem overwhelming and complicated.  When in doubt it is best to contact your local hose manufacturing representative who can assist in the selection of the best hose and couplings for your application.  But please keep in mind the best value is the hose assembly that gives you the maximum life, not the hose assembly that costs the least.
Authored by__
U. K. Prasad, GM-Technical, Gates India Pvt. Ltd.