Hoses vs. Tubes

I would think the initial investment in learning tubes as well as the equipment to do so would be the only reason to NOT use a combination.

any plumber will tell you.

Nice!

and easy..

Thanks for the reply, but just as I got here I was charged with bringing in the tube bending equipment they had purchased. So, now it have the equipment and the know how to bend tubes, I need to find a compelling reason for the engineers that have been doing this for years to switch to tubes.

So far, out of about 1,500 hose applications, I've gotten them to convert 1.

Put the toilet drains on flexible hoses (with extra fittings) and run them through the work/break area until they convert?

good luck with you endeavor.

Well the first thing that jumps out at me is that hoses don't get dented, they just spring right back, not so for tubes...so I think it's the flexibility that is the advantage...also would be more forgiving at absorbing pressure shock, better to bend than break...

Thanks SE, you make a good argument for not using tubes, but why does the rest of the industry use them as the primary method of delivering power?

I really don't have a good answer, I was hoping someone here did..

Well that's easy, it's cheaper...

+ more efficient, cleaner, profitable, professional, expected, right, UV and abrasion resistant.

---Question? If you had two same size apartment buildings to chose from.

One was piped copper plumbing, emt for electrical, black pipe for gas versus

one wired with flexible lines romex/pex/flexible gas lines?

which one would you rather invest in and why?

Rhetorical question.

The first one. But, I have no evidence that the first methid is the superior method. That is just how I have always seen it done. But more and more homes are utilizing the second case. The hoses get rid of fittings (which can be leak points). Hoses bring flexibility, reduction in cost, less leaks, they allow for the house to settle without stressing joints, and so forth.

I do not think most everyone in the industry is stupid. There must be compelling reasons to choose hoses. So, I thank you for this comment. It made me want to investigate this further.

I suspect the lower reliability of some connectors might persuade designers to choose one long flexible hose over multiple tubes and hoses.

Tubes don't rot in the sun? Yeah, yeah, I know, U.V. inhibitor etc, but the sun destroys just about everything eventually.

Plus tubes just look 'cooler'.

Think about it. What looks more professional? A collection of artfully bent tubes or a bundle of hoses?

This might be more about marketing than an engineering trade study.

I don't think it's an all or none question, it's more what works best in what position...so it seems to me a mix would turn out to be best....You need flexibility in moving extensions, and where there is a long protected run then the tube would probably be best, but of course you have to eliminate as many connections as you can and still be easily serviceable...The movement, vibration and expansion and exposure of mounting locations and materials comes into play....So there are many determining factors that need to be evaluated to arrive at the best material and mounting method for each section of hydraulic line that is necessary...and that knowledge is best gained by forensic analysis of failures in the field and costs associated which would include parts inventory burden and associated costs...

this is what our competitors are doing, and I'm pushing for us to do it as well.

use tube where it makes sense, and hoses where it makes sense, not hoses 100% everywhere.

Then some research on the history of hydraulic failures in the field will be necessary to make your case...

http://info.texasfinaldrive.com/shop-talk-blog/causes-of-hydraulic-hose-failure-on-heavy-equipment

https://www.google.com/search?safe=off&sxsrf=ALeKk00fZbQgBSiTETVlj8IQo_FcpHItDA%3A1593121392334&source=hp&ei=cBr1Xq2wEOGh_QaDh4XQCw&q=history+of+hydraulic+line+failures+on+heavy+equipment&oq=history+of+hydraulic+line+failures+on+heavy+equipment&gs_lcp=CgZwc3ktYWIQARgAMgUIIRCrAjoECCMQJzoICAAQsQMQkQI6BQgAEIMBOgUIABCxAzoCCAA6BQgAEJECOgQIABBDOgYIABAKEEM6BwgAELEDEEM6BggAEBYQHjoICCEQFhAdEB46BQghEKABOgcIIRAKEKABUKwMWLl6YN-QAWgAcAB4AYAB_gWIAaI3kgEIOC40NC42LTGYAQCgAQGqAQdnd3Mtd2l6&sclient=psy-ab

Yes, customer and customer's customer satisfaction can be an angle you can pursue. We get daily deliveries of liquid N2, and several times a year the truck blows a pump hose and there's a bunch of hydraulic fluid to be cleaned up. Frustrating for everyone, and potentially an environmental problem for sites that need to avoid petroleum products in the soil and stormwater.

To me it looks like too many offsets in those short tube runs, but maybe there is a reason.

Imagine a case of a 2-ft hose run connected to a 2-ft tube run connected to a 2-ft hose run. A single 6-ft hose run would be simpler and cheaper.

OTOH, if the tube run is quite long, then the hose-tube-hose idea makes more sense.

A lot depends on each particular run, with a complex balance of simplicity, aesthetics, cost, reliability, etc. No single answer is likely to fit all situations.

Marketing and Robotics(Mechanical Engineering) Academic Analysis

These tubes in your picture are complicated enough to bring the customer back to make an exact fit part number purchase rather than getting a third party replacement. Marketing 101 says make it that way to keep the customer buying something from you more frequently. Hoses are often made by third party suppliers and using hoses will keep your customer visiting someone else. The fact that hoses generally need replacement more frequently means that your customer views your machine as a maintenance expense at the same time that you are sending him to a potential competitor for a wear part on your machine. You are creating a leveraged marketing blunder using hoses where tubes are break-even or even have an actual operational advantage. Unfortunately, your business has been successful selling mostly hoses and inertia applies to apparent business success as well as to mass.

Also, there is an ostensibly satisfying Robotics 101 answer. Naturally heavier hoses are also pressure accumulators. Both of these characteristics mean that your travel movement has a bigger energy storage than with tubes. Energy storage is the arch-enemy of precise end effector positioning for great repeatability, accuracy, and precision at high speed. In computer tape drives, for example, air columns were used to eliminate the mass of the spinning reels in the motion control of the tape across the head. Expert human heavy equipment operators often mask the advantage of reducing energy storage in precise movement so the highly experienced human controllers who are now company executives maladaptively prefer to retain energy storage so that their experience advantage remains essential to a better result. This remains true even when the execs no longer depend for their personal job security on their higher experience level since they identify with their best employees and continue nostalgically defending that higher skill level as essential to an excellent result(see Kondratiev)

So, you see that Psychology 101 phenomena have locked your company into a competitive dead end in direct conflict with the facts from Marketing and Robotics 101.

_____________

thewildotter

For any question that asks "Why do they? --or Why don't they...? the answer is usually: Money.

This is probably the case here:

Reduced material and installation costs.

Easy to customize lengths and complex turns are no problem.

Hoses will last long enough to get past the warranty period.

After that..not their problem.

Funny, I just came in from my shop where I was making some mounting brackets for hydraulic lines for my airplane. The original tubes, 72 years old mind you, are just fine, but they are not 'pretty'. The lines were not really bent in a craftsman-like manner. The new ones will be. Also, I'm converting from the original automotive-style fittings to standard aircraft fittings.

The 1/4" OD tubes tie-in to 1/2" OD hoses that weigh probably 4 times what the aluminum tubes weigh.

One other advantage of tubes over hoses is that it is relatively difficult to hook up pre-bent tubes incorrectly. Hoses can be hooked up incorrectly--with interesting results!

Have your engineers look at some pictures of tubing systems, then do the same with hose systems, and finally ask them one simple question.

"Which system do they think is more exposed to damages during the rough trade uses they will be exposed to?"

I would hazard a guess most of your engineers have spent little, if any, time in their careers on the working end of a job site, so from the been there-done that department here's some insight. Metal tubing mounted flush to the body of the machine, actuator or implement is far less likely to come into the incidental/ accidental damage contact that is endemic to construction equipment. Hoses by their very nature need open space to operate and when replaced the mechanics/ field service technicians rarely, if ever, do so according to factory spec. More often they either make them up onsite or go to their local supply house where they are made on bench. This means that while the product comes out of your factory with the hoses in the optimal lengths and positions, once repaired the hoses tend to be floppy over length wear and accident traps.

Hi Labyguy,

I have had quite a bit of experience with hose and tube failure over the years starting from farm machinery a few years as a wheel and a track mechanic in artillery and Core units, then in commercial construction for the past 40 years. What I usually see is tubes almost never fail. Usually when they do it is because they are struck by something, big rocks, other equipment, trees, etc. If they are not isolated sometimes the clamps will rub a hole in them -- this is in a 10 or 20 year old machine. The next thing I see is if you have an offset at the hose connection it might break there. Hoses can start to fail after 2 or 3 years unless hit or cut by foreign matter- they are more expensive to buy if you are fabbing the tube your self.

It depends entirely on how OCD the design engineer is.

Mining equipment seems to use tubes on the prefabricated sections with hoses only used to connect across moving joints. If you compare a tube for 30,000PSI and a hose for 30,000PSI you will see a great difference in outside diameter and complexity of the hose construction.

Tubes can be extruded with greater wall thickness during manufacturing process and are easier to create than a hose of comparable pressure. The tubes can have the connections welded on in situ for flexible connections. Tubes are used in power stations to transfer high pressure and temperature where preformed bends and connections can all be welded in place and x rayed to ensure integrity.

If a flexible connection is needed than use a hose else run tubes. Tubes can be clamped close to the frame and just be stepped up for the flexible connection.

Tubes can take abuse and I have seen them partly flattened where hoses can have the outer sheath damaged and allow moisture and contaminants into the braid and cause corrosion and failure.

Horses for courses I would say....use a combination to best effect.

As an aside, but on topic, the choice could be related to servicing manuals and worldwide translation....and compliance with standards (if any).

To cut a long story short, having worked on BSI/CEN/ISO committees dealing with breathing apparatus, where English was the prime language for discussion, but formally published in English, French and German (for the rest of the World to translate to their native language for internal use).

An early indication of the problem, was when one delegate said it would translate better in his country if the standard specified 'rigid hoses' .... or could the draft be rephrased to use a better combination of words - hoses, pipes, ducts, conduits, tubes etc - so that their equivalent meant the same to all of us.

..... worth a mention..!

You will probably have to dig into your part numbering and control system for part of the answer and the nature of your business.

Typically fabricated tubing for hydraulic systems are typically routed, designed and drawn as specific part numbers for installations. These typically have a part drawing and typically are aimed at installations that are either godawful expensive or are produced frequently, as in a piece of equipment that rolls a few thousand off a production line. Metal tubing doesn't work well for installations where a tech goes in with a stick of tube, a bender and tube cutter and just makes something that will fit.

Hoses tend to be used where the effort to design individual tube fabrications with drawings and part numbers can't be justified.

Mechanically, hydraulic systems using hose are squishier than systems using rigid tubing unless you pay for more highly reinforced hoses. Hoses are more prone to fatigue failure due to the constant motion and the mass of the hoses in use and the material properties of the hoses themselves.

In 25 years working on earthmoving and mining equipment I have never seen a hydraulic pipe burst except during destructive testing intended to validate its specifications.

i have repaired half a dozen tubes that developed pinhole leaks which were found to have tiny weld defects , usually porosity or cold lap at stop starts of the robot orbital welds where the tube is joined to its fitting.

i have seen many dozens of burst hoses , some within a couple of years of manufacture but typically from 10 - 15 years of age they have elevated failures.

where rock breaker hydraulic hammers are used I have also seen delamination of the inner layer of rubber on hoses , probably partly due to the oscillating hydraulic pressure pulses.

There are hose burst protection sleeves available these days that dissipate pressure and prevent the risk of hydraulic embolism into human flesh however hose bursts are rated high on the safety radar of anyone in this industry.

On equipment I manufacture I use steel or stainless tube everywhere possible and hose only where movement , vibration or temperature variations occur.

I rest my case

(i wish it were mine!)

I have worked with heavy equipment and in the maintenance side of manufacturing for over thirty years, and i nave seen advantages for both hoses and tubes, heavy machinery like forklifts combine both for the already mentioned reasons, ease of application and durability, both, and the same goes for bulldozers, backhoes and farm equipment, like tractors, i have also worked on high pressure presses. i agree the tubes are usually oem replacement items and hoses are aftermarket. With all said and done converting to both tubes and hoses will insure aftermarket sales for your company, and extended life of the oem parts.