January 5, 2010 

'Inside Hydraulics' Newsletter
http://www.hydraulicsupermarket.com


IN THIS ISSUE
1. Tiger Woods, social proof and Christmas holidays
2. When valves don't open (or close) as they should
3. Mounting hydraulic pumps... for life
4. Content for your web site or e-zine
5. Help us spread the word
6. Tell us what you think

1.

Tiger Woods, social proof and Christmas holidays

School is out for the summer here in Australia. But part of my seven year old's holiday routine is 20 minutes of 'lessons' first thing each morning - math, spelling or something similar. It's just a token amount of work, and really only designed to exercise his gray matter during the two months he is off school.

The logic is sound, the effort required is not onerous, but getting a seven year old's buy-in is a different matter entirely. Benjamin argues - or did initially, that because he is on school holidays, he shouldn't have to do anything which even resembles school work. And in summing up his case, he closes with social proof: "None of the other kids I know do this, so why should I?"

His mum is chief negotiator in these matters and my involvement is usually limited to providing supporting evidence for the parental line. The obvious deflection for: "None of the other kids I know do this, so why should I?" is to explain that learning is a lifelong process, that mummy and daddy still do 'lessons' every day (reading, etc) and we finished school a long time ago.

But this does nothing to address Benjamin's argument that his peers are not doing what he has to do. So I sit my son down and explain that being successful at anything usually involves doing things most others are NOT prepared to do. That Tiger Woods became the best golfer in the world by belting golf balls while his friends were playing with their Wii's and Xboxes (OK, Tiger may not be the best role model anymore but he's certainly more widely known now than ever before).

Of course, kids Benjamin's age live for the moment and are not overly concerned with their future success. Which, as an aside, makes me marvel at how Tiger Wood's father got his son to hit so many golf balls from a very young age. So I'm not sure if my son truly 'gets' the concept of doing things most others aren't prepared to do as a recipe for success, but he has resigned himself to doing his vacation lessons anyway.

And since it's the start of a New Year and we 'grown-ups' don't have the luxury of living in the present the way our kids do, you're probably thinking about what you want to accomplish in 2010. So my point and suggestion is: make sure there is at least one thing on your 'to-do' list, and preferably several, which are things most of your peers are NOT willing to do. It virtually guarantees you'll be successful in your main purpose, business or profession - whether that is hydraulics or anything else.

Oh, and Happy New Year.


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Heavy Equipment Mechanic
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2.   When valves don't open (or close) as they should

Julian Lee, one of our members from Adelaide in South Australia sent me this story:

"I am in the process of rebuilding a large hydraulic cylinder which has been damaged due to pressure intensification. The cylinder dimensions are 300 mm (OD) x 250 mm (ID) x 25 mm wall thickness and a length of 7.3 meters. The cylinder is used to compact loose scrap steel into high density blocks for ease of transport. The normal maximum compaction pressure is 265 Bar.

After some months of operation a fault occurred where the high-flow poppet valves (logic elements) were remaining open and the high pressures required for correct operation were not being achieved.

This was being caused by pieces of wear band jammed under the poppets. These wear band fragments were eventually traced to the main compaction cylinder. So the piston/rod assembly was removed and the bore of the cylinder was checked for damage. It was then noticed the bore was 2.05 mm oversize through the first 1200 mm of the cylinder tube.

It was apparent that the cylinder tube had ballooned due to a massive pressure spike, so we set out to discover why. The tube has a burst rating of 964 Bar and a maximum safe working pressure of 321 Bar. Due to the area differential ratio of 2.77, if a piston pressure of 265 Bar was induced, a rod pressure of 734 Bar could be induced if oil flow was blocked on the exhaust.

The pumps on the power unit are rated to a maximum of 350 Bar so they were ruled out as the cause of the over-pressurization. It then appeared that the regeneration control block at the rear of the cylinder may be the source of the problem.

After studying the regeneration valve set-up, it occurred to me that if the two high-flow poppets remained closed at the end of the regeneration cycle, oil could not escape from the rod-side of the cylinder during pressing, and the cylinder would be subject to massive pressure intensification.

So it appears there has been a problem with the venting of these logic elements, and it is amazing that the proper functioning of low-flow pilot lines for logic elements is so critical - the repair bill for this cylinder will be around $50,000!"

This story is instructive on a couple of levels. Firstly, logic elements or slip-in cartridge valves offer circuit designers a lot of flexibility. But as this story illustrates, if they close when they should be open, the result is usually spectacularly catastrophic - due to the high flows and pressures involved. So the possibility of this occurring should be carefully considered, and ideally mitigated against, at the design stage.

And secondly, it's a graphic example of the extreme forces (and damage) which can result from pressure intensification. If you are not totally familiar with this phenomenon, and how it occurs in a double-acting cylinder, watch this video.


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Alexander (Sandy) Dunn
Plant Maintenance Resource Center



3.   Mounting hydraulic pumps... for life

For a no-holds-barred discussion on how to mount hydraulic pumps for maximum service life, read my column in the September-October 2009 Issue of Machinery Lubrication available here

To get your complimentary subscription to this informative magazine (US and Canada only) go to: http://www.machinerylubrication.com/hydraulic1.asp


4. Content for your web site or e-zine

Need some fresh content for your web site or e-zine? You now have permission to reprint these 'Inside Hydraulics' articles on your web site or in your e-zine, provided:

1. Each article is printed in its full form with no changes.

2. You send an e-mail to editor@hydraulicsupermarket.com to advise us where you'll be publishing them.

3. You include the following acknowledgement at the end of each article:
About the Author: Brendan Casey has more than 20 years experience in the maintenance, repair and overhaul of mobile and industrial hydraulic equipment. For more information on reducing the operating cost and increasing the uptime of your hydraulic equipment, visit his web site: http://www.InsiderSecretsToHydraulics.com


5. Help us spread the word

If you've found our 'Inside Hydraulics' newsletter interesting and informative, then chances are you have a colleague who would too. Help spread the word about 'Inside Hydraulics' by forwarding this issue to a colleague. If they share your interest in hydraulics, then they will surely appreciate being told about this newsletter.

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6. Tell us what you think

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Just e-mail the editor at: newslettersuggestions@hydraulicsupermarket.com

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