For many industrial and mobile applications, hydraulic hoses need to withstand extreme conditions, including aggressive liquids, scorching to freezing temperatures and ultra-high pressure. Do you have the right hose for the job? Take a closer look at hose design for aggressive environments.
Combating aggressive behavior
From the most remote, hostile parts of the world to right inside your car engine, hydraulic hoses must contend with extreme conditions to ensure success. These hoses transmit industrial fluids that can be aggressive including:
- Motor oils
- Heavy-duty coolants
- Transmission and brake fluids
- Obscure fluids including antifreeze and other glycol-based coolants
The challenge in dealing with such a wide variety of fluids is finding the right hose for a particular fluid. "On top of that, fluid manufacturers and oil companies regularly update their products," says Nathan Groves, a chemical engineer and project manager with Parker.
“If an OEM changes a fluid’s base materials, such as going from a distillate to a synthetic, that can be more of a concern than changing additives because the chemical makeups of the two types of oils differ and the fluid may now be more aggressive,” Groves says.
A fluid’s “aggressiveness” refers to the chemical makeup, which is reflected in the solubility of the polymer in the fluid. This is one of the key variables to consider when designing hoses for particular applications since some components within a fluid may be absorbed into a hose’s rubber compound or extract oils out of the rubber, changing the hose’s physical properties. Such changes in physical property can include swelling or contraction. Swelling restricts fluid flow through the hose and softens the rubber, which can lead to fittings leaking at elevated temperatures. Extracting oils makes the hose much stiffer at low temperatures, which causes cracking when the hose is stressed or flexed.
It’s up to hose designers to determine the best materials for a particular hose based on the fluid it will carry and its intended operating environment. Be aware that hose manufacturers maintain compatibility databases based on material testing, so when in doubt, ask your manufacturer.
Beating the heat
There are three heat variables to consider with a hydraulic hose:
- Liquid temperature inside the hose
- Ambient temperature around the hose
- Nearby operations that could negatively affect the hose
Oil temperatures inside a hose can easily exceed the hose’s threshold temperature (usually between -40°F and 257°F). This extreme heat can bake the inner tube, causing it to harden and crack. This happens when a system runs for too long without giving the oil a chance to cool, which is a common problem with heavy machinery that runs consistently for 8-16 hours at a stretch.
Some companies, including Parker's Hose Products Division, design hoses with inner tubes that handle transfer fluid temperatures of up to 302°F. But customers should still closely monitor the temperature of any transfer fluid during operation. Look for the right inner tube design to safely handle the application requirements.
Ambient heat is also of significant concern. The hoses inside the engine compartment of a work truck, for example, see higher temperatures than those in open areas where the heat has an avenue of escape. No one wants to lose up-time because of a simple hose. But closed off engine compartments can result in very high temperatures, degrading hoses from the outside in and can quickly lose integrity.
Nearby operations can also expose hoses to dangerously high temperatures. Anything from vats of molten metal to stray welding spatter can damage unprotected hoses and increase the possibility of failure.
For these situations, Parker and other companies have developed a variety of sleeves to cover and further protect hoses. Sleeve materials range from fabrics to fire-resistant polymers to steel braid, and some also protect against injuries in the event a hose bursts.
Fighting off the cold
Although temperatures above 257°F are a cause for concern, customers also experience issues with temperatures at the other extreme, -40°F and lower.
Extremely cold temperatures can:
- Cause rubber hoses to stiffen and crack
- Affect the fluid being transferred inside the hose (the fluid can thicken and the flow rate decrease)
Fortunately, hoses can be designed for specific operating temperature ranges and there are versions that operate at temperatures as low as -70°F. Designing hoses to withstand extreme cold is a matter of getting the right combination of fluid compatibility and the chemistry of the hose layers. Hose manufacturers perform a balancing act between the compatibility of the inner tube and the conditions of the specific application. Always consult your representative when choosing a hose for frigid environments.
Eliminating high pressure
Not all challenging applications involve extreme temperatures. Pressure is also an important consideration. A hose’s pressure rating is determined by its reinforcements.
“Hoses are constructed in layers, starting with an inner tube, then alternating layers of rubber and reinforcements, such as steel wire. Each reinforcement layer is placed to work with the layer above or below it, so when the hose is pressurized, it creates a hydraulic balance. This balance restricts the hose from moving too much under pressure. If there is no balance, the hose twists or ‘bounces’ under pressure and could start to come apart due to the forces from the pressurized fluid,” Groves explains. “While hoses under the hood of vehicles are usually fairly stationary and don’t move around very much, hoses used on a piece of equipment that has a flexible joint, like a backhoe must flex reliably in all conditions.”
Parker also engineers its hoses with a number of SAE-tested and approved additives to increase resistance to ozone and ultraviolet (UV) light. Without such additives, constant exposure to direct sunlight (like on a piece of construction equipment) degrades the rubber, causing it to break apart and fall off in chunks, which is made worse by any flexing motion.
Hoses can make or break the job
Don’t forget you need to work closely with your manufacturer to ensure the success of any application. Whether your application is in the arctic circle, near molten iron or just inside the engine bay of your truck, using the right hose can make the difference between success and failure.
“Predicting and accounting for all of the potential operating conditions is what makes engineering a hose such a challenge. Solving these challenges lets our customers push the boundaries of hose applications.”
Gregory Reardon, business development manager
Article contributed by Nathan Groves (top), senior project engineer, new product commercialization, and Gregory Reardon (bottom) business development manager, Hose Product Division, Parker Hannifin.
Other related topics on hose, hose application, and selection criteria: