What do lifting chains, bladder-type accumulators and hydraulic hoses all have in common? Well, they typically have only one mode of failure - and that's catastrophic. One minute they're working as they should and the next thing you know, they've gone to hell.
Oh sure, hoses can leak from around their ferrules and show obvious signs of abrasion, both of which are early warning signs that a change-out would be prudent. But even under these conditions, estimating their remaining service life is virtually impossible.
The Trouble With Hose
Beyond the fact that their service life is finite and difficult to estimate, other disadvantages of hydraulic hoses when compared to tube include:
- They expand and stretch under pressure. This flexing requires extra volume and adds to machine cycle time.
- They typically have a limited operating temperature range.
- Their requirement for regular replacement makes them a source of contaminant ingression.
- They are expensive.
Despite the above disadvantages, hoses are a necessary feature of most hydraulic systems. This is because the alternative conductor - tube, cannot be used where:
- There is limited space (particularly in mobile hydraulics).
- There is relative movement between machine components and superstructure.
- Noise and vibration need to be suppressed.
However, hose is often substituted for tube when it's not necessary. This is because a hose assembly can usually be fabricated much faster than a tube assembly. And the additional labor cost required to fabricate and install a tube, can make a hose appear to be the cheaper solution.
But this ignores the fact that the same hose may need to be replaced many times, over the life of the machine. This false economy is similar to buying the machine itself on initial capital outlay alone - without considering its total life-of-ownership cost.
Tube Is Cool
And tube has some compelling advantages of its own. One of these is its superior heat transfer - especially if it's painted. One aspect of heat transfer is thermal radiation. The total radiation from an object is the sum of its reflection, emissivity and transmission of heat through the object. When hydraulic tube is painted, it reduces its reflectance and increases its emissivity, enabling better heat rejection.
In summary, hydraulic hose and tube are not interchangeable; they're different 'tools' for different jobs. The benefits of hose, which make it a necessary feature of most hydraulic machines, come at a cost. It has a finite service life and usually gives no warning of failure. This makes it a difficult maintenance item to manage. For these reasons, substituting hose for tube is usually a mistake. And to discover six other costly mistakes you want to be sure to avoid, get "Six Costly Mistakes Most Hydraulics Users Make... And How You Can Avoid Them!" available for FREE download here.