Fluid Power World Contributing Editor Josh Cosford gave a webinar presentation on Proper Hose Assembly Guidelines. The transcript has been divided into an 8-part blog post series. The following excerpt from that webinar transcript is the fourth part of the series.
Application discusses the nuts and bolts, the details of how your hose assembly is going to be used. Where is the hose used? What kind of machinery is used? What’s the ambient temperature? It kind of goes within temperature as well, but What is the required bend radius? And some other factors.
If you have a tight bend radius in some applications or specific hose, that’s called HighFlex hose, that will typically have half the radius of bending or more. This is an advantage in a couple of ways. Not only does it allow you to fit a hose bend into a tighter space, but it has a high bend rate. By bend rate, I’m talking about the general flexibility and the fatigue, how many times the hose can bend through an arc without failing early. As you know, any kind of steel braided wire, even rubber, the more you flex it back and forth, the quicker it’ll fatigue. HighFlex hose is more resistant to that.
There are also external conditions you need to consider for an application. Is there risk of abrasion? Most hose has a neoprene outside, but if you have hoses that will inevitably rub against materials, against machinery, against the jib or boom, any application where it can rub back and forth, a high abrasion carcass is a good way to go. Hoses tend to fail by rubbing on the outside until they wear through the outer wall into the braiding and start wearing that away, and eventually, enough so that the hose can no longer contain pressure. You get a hose burst. Probably the number one cause of hose failure would be external abrasion.
Most of the hose assemblies that I’ve done repairs on, a customer would come in with a blasted hose that’s been sitting there rubbing against something for months or years and finally just gave way. There are some cases where even on an abrasion resistant outer carcass you may still require a hose wrap. That will be either a braided or nylon wound wrap that goes on the OD of your hose that protects it from direct abrasion from machinery, engines or wherever you can name that would be vibrating and rubbing against the hose.
Also of consideration is corrosion. Is there something in the environment that’s caustic that would cause fluid to permeate through the outer carcass of the hose and perhaps rust, corrode or breakdown the layers of spiral or winding that are around reinforcement? You need a hose that maybe perhaps says synthetic material that won’t rust, that is non-reactive against whatever the ambient conditions that cause corrosion.
On top of that, another application consideration is electrical conductivity. In the image here you have an electrical boom truck. You can imagine that any opportunity to conduct electricity back through the machine or to an individual want to be reduced. If there is some sort of electrical break or that electricity is not transmitted through the hose itself. A hose would be constructed of a synthetic material that is non-conductive and so you can get non-conductive hydraulic hose, sometimes with reduced pressure, but nowadays they’re all really well made and have the same high performance as a regular hydraulic hose, albeit with often extra cost.
Now on to the material. By material, not necessarily meaning the construction of the hose itself, but that can play a part in it, but what type of fluid or material is being used. Considering this is critical to hose selection. If you have something exotic and requires a specific rubber compound you need to consider at this stage. Most mineral based hydraulic fluid is compatible with most types of hose. Majority of hydraulic hose has a nitrile interior with a neoprene outside, but if you were running exotic fluids sometimes you need to change that up.
For example, if you have a phosphate ester, which is a kind of fluid that is used in Skydrol, it’s non-flammable but it’s kind of nasty stuff, so you might have to have synthetic core like EPDM. Most hydraulic hose is synthetic, nitrile and neoprene, both synthetic rubbers, but you can get the more exotic and obviously, these kind of things are extra cost as well. The material could also be outside. Like I discussed earlier, if you’re exposed to any kind of caustic or nasty environmental conditions that could cause breakdown or corrosion on the outside you may have to choose that as well.
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