For each use of hydraulics, there is a specific hydraulic hose that is right for the job. Selecting the correct specifications for your hydraulic hose is important because the wrong choice could lead to damaging or injurious failures. While all hoses have finite and expected lifespans, there are many factors that contribute to when that lifespan will come to an end. By understanding the most prominent factors that contribute to hose lifespans and failures, you can make informed decisions regarding the type of hose required for any given situation.
Hydraulic hoses can be constructed out of a variety of different materials. These include composites, elastomers, metals, polymers, silicone, and thermoplastics, just to name a few. The materials used in the construction of a specific hose will determine the situations in which the hose is meant to be used and even the type of hydraulic fluid that flows through it. Each hose is made of three layers: The inner tubing, wire reinforcement, and exterior shell.
The inner tubing of hydraulic hoses is often made of plastic or rubber. This is the layer of the hose that comes into contact with the fluid and so must be made out of the correct material for the fluid type. For example, some fluids may break down rubber, and so a plastic construction would be needed instead. You do not want a hose interior that will react with or break down when it comes into contact with the fluid because that could lead to hose failure and damage throughout the rest of the hydraulic system.
There may be multiple reinforcing layers between the inner and outer layers of a hydraulic hose depending on the durability rating. Wire reinforcement layers can be made of metal, plastic, or textile depending on the flexibility and strength required. And, there are also two styles of wire reinforcement that additionally improve either flexibility or strength. Wire braid offers increased flexibility at the cost of some strength, while wire spiral offers increased strength at the cost of some flexibility.
Reinforcement is used to counteract both internal and external pressure. Internal pressure is the main force the reinforcement acts against, as the highly pressurized hydraulic fluid presses against the walls of the inner tube. External pressure is less of an issue but can come into play in some specific situations.
The exterior shell of the hose protects the inner tube and wire reinforcement from the environment. Environmental dangers could come in the form of abrasion, wear, temperature, and even sunlight. This layer of the hose is made from rubber, plastic, metal, or textile. The exact material chosen will depend on where and how the hose is to be used. If the hose is going to be somewhere with more extreme environmental dangers, then it will need to be made of a more robust material.
Diameter and Length
Hose diameter and length both play a role in how the fluid within the hose behaves. The inner diameter is the diameter within the inner tubing through which the liquid flows. If the diameter is too small, it can lead to pressure drops and increased internal temperatures caused by friction with the tube walls. If it is too large, it can lead to suboptimal system performance due to the flow. Common inner diameter sizes range from 3/16in. To 25.in.
The outer diameter of the hose includes the three-layer structure of the hose as well as the inner diameter. By measuring the difference between the inner and outer diameters, you can get the thickness of the hose wall. This diameter is important to keep in mind when it comes to connection points
Hose length is much more important than you may have realized for a hydraulic system. The longer the hose is, the more potential there is for pressure drops. Just as with inner diameters that are too small, this is because there is more contact between the fluid and interior walls which creates friction. For this reason, it is essential that the hose is the proper length for the location where it is to be used.
Hydraulic hoses must be able to withstand the various conditions within which they are expected to operate. They may be used in environments that require increased abrasion and wear resistance, flexibility, pressure resistance, and/or temperature resistance.
Abrasion and Wear Resistance
The number one cause of hydraulic hose failure is abrasion and wear. This damage is caused when hoses rub against each other or other objects within or around the system. Even when you do not think the hoses will move to rub against other objects, the small amount of vibration from the fluid flowing can cause wear to occur over time. For this reason, it is important to consider how abrasion will come into play when routing hoses and avoid high-abrasion contact.
Hoses will also wear naturally both internally and externally over time. Because you cannot see internal wear, it is important to pay close attention to external wear. External wear can be accelerated by the hose being in direct sunlight, which can cause elastic materials to break down.
The flexibility of any given hose should be enough for their intended use, but not more or less flexible than that. An overly flexible hose will have reduced strength that may be needed. And a hose that is too rigid can suffer from three main issues. First, the hose should not be so rigid as to be difficult to bend around necessary turns; hoses should be bent, not twisted. Second, the hose should be flexible enough to fit into compact spaces if need be. And third, if the hose is required to move, such as if it is on the arm of machinery, it needs to be sufficiently flexible.
Some hoses are referred to as “lay-flat” which simply means that they do not have a rigid structure maintaining their shape. When there is no fluid pressure within them, they lay flay. These hoses are more flexible than standard hoses and take up less space to store.
While external pressure on hoses usually is not an issue outside of specific environments, all hydraulic hoses must be able to withstand their internal pressures. Every hose has a maximum pressure rating printed on it. This rating should never be exceeded, even when there is a pressure spike. You should consider what the maximum pressure that could be caused by a spike is before selecting a hose for the job. Exceeding the pressure rating could lead to hoses bursting which may cause damage, injury, and downtime.
Some hydraulic systems are prone to variable internal pressures. The more variable the pressure is, the more it will negatively affect the hose. Constant pressure is relatively easy for hoses to handle, but the stresses associated with pressure variation can lead to excessive wear. For a variable pressure system, you will need a hose with increased strength and durability.
Just as hoses have pressure ratings, they also have temperature range ratings. If a hose is used in conditions that are too hot for it, it could lead to the materials breaking down or even melting. If the temperatures are too cold, then the hose can become rigid, which leads to cracking. Also, you should be considering both the temperature inside and outside of the hose as they both play major roles in the overall temperature.
The temperature of the fluid within the hose can be in the hundreds of degrees celsius depending on the hydraulic system and specific fluid being used. If the internal structure of the hose cannot withstand this, it will fail. These temperatures are generated by the friction between the fluid and the interior walls of the hose. The higher the flow rate and pressure, the higher the fluid temperature will be.
Ambient temperatures can affect hydraulic hoses just as much as internal fluid temperatures. If the hose is part of a hydraulic system that operates outside, it can be exposed to a wide range of temperatures, including those below freezing. Variable temperatures, much like variable pressures, will cause hoses to wear more over time. Additionally, some hoses will be used in high-temperature environments where they are located within close proximity to heat sources such as generators and even furnaces.
Lastly, some specialty hoses come with specific safety qualities that make them ideal for potentially hazardous situations. Static-resistant hoses are made of conductive or semi-conductive materials that are able to dissipate built-up static electricity. This helps to prevent electrical fires from starting. Flame-resistant hoses are a bit different in that they do not prevent fires, but rather prevent fires from potentially becoming worse. These hoses are able to remain intact even in the presence of flames, which prevents them from bursting and fueling the fire with hot hydraulic fluid.
At MAC Hydraulics, we know the importance of preventative maintenance, especially when it comes to hydraulic hoses. Since these are the most vulnerable parts of any hydraulic system, they need to be checked regularly for signs of damage and wear. Contact us today if your hydraulic system is in need of maintenance or repair. Our expert technicians will keep your hydraulics in peak condition.