Hydraulic hose provides a basic means for transferring hydraulic fluid from one component to another in hydraulic system, and at the same time it provides an inherent versatility to hydraulic systems designers.
To consider hydraulic system hose is an important part of a hydraulic system is a huge understatement. The flexibility of hose enables hydraulic systems components to be positioned/located in the most efficient or convenient places, due to the fact that hydraulic hose has the ability to bend around corners, through tight spaces, or across long distances.
The hydraulic hose typically consists of at least three parts: an inner tube that carries the hydraulic fluid, a layer for reinforcement, and outer layer the protective.
The inner tube should have some flexibility and needs to be compatible with the type of hydraulic fluid it will carry. Normally used compounds include synthetic rubber, PTFE, called as Teflon and thermoplastics. The reinforcement layer comprises of one or more sheaths of braided wire, spiral-wound wire, or textile yarn. The outside layer is often weather-, oil-, or abrasion-resistant, depending upon the type of environment the hose is designed and to be used for:
Below are seven recommended steps the system designer should follow during the hose and coupling selection process. To help determine the proper hose for an application, use the acronym STAMPED - from Size, Temperature, Application, Materials, Pressure, Ends, and Delivery. Here is what to consider in each area:
Size - In order to select the proper hose size for replacement, it is important to measure the inside and outside hose diameters exactly using a precision-engineered caliper, as well as the length of the hose. Hose OD is particularly important when hose-support clamps are used or when hoses are routed through bulkheads. Check individual hose specification tables for ODs in suppliers' catalogs. When replacing a hose assembly, always cut the new hose the same length as the one being removed. Moving components of the equipment may pinch or even sever too long a hose. If the replacement hose is too short, pressure may cause the hose to contract and be stretched, leading to reduced service life.
Changes in hose length when pressurized range between +2% to 4% while hydraulic mechanisms are in operation. Allow for possible shortening of the hose during operation by making the hose lengths slightly longer than the actual distance between the two connections.
Temperature - All hoses are rated with a maximum working temperature ranging from 200° to 300° F based on the fluid temperature. Exposure to continuous high temperatures can lead to hoses losing their flexibility. Failure to use hydraulic oil with the proper viscosity to hold up under high temperatures can accelerate this problem. Always follow the hose manufacturer's recommendations.
Exceeding these temperature recommendations can reduce hose life by as much as 80%. Depending on materials used, acceptable temperatures may range from -65° F (Hytrel and winterized rubber compounds) to 400° F (PTFE). External temperatures become a factor when hoses are exposed to a turbo manifold or some other heat source.
When hoses are exposed to high external and internal temperatures concurrently, there will be a considerable reduction in hose service life. Insulating sleeves can help protect hose from hot equipment parts and other high temperature sources that are potentially hazardous. In these situations, an additional barrier is usually required to shield hydraulic fluid from a potential source of ignition.
Application - Will the selected hose meet bend radius requirements? This refers to the minimum bend radius (usually in inches) that a hydraulic hose must meet. Exceeding this bend radius (using a radius smaller than recommended) is likely to injure the hose reinforcement and reduce hose life.
Materials - It is mandatory to consult a compatibility chart to check that the tube compound is compatible with the fluid used in the system. Elevated temperature, fluid contamination, and concentration will affect the chemical compatibility of the tube and fluid. Most hydraulic hoses are compatible with petroleum-based oils. Note that new readily biodegradable or green fluids may present a problem for some hoses.
Pressure capabilities - Hose working pressure must always be chosen so that it is greater than or equal to the maximum system pressure, including pressure spikes. Pressure spikes greater than the published working pressure will significantly shorten hose life.
Hose ends - The coupling-to-hose mechanical interface must be compatible with the hose selected. The proper mating thread end must be chosen so that connection of the mating components will result in leak-free sealing.