I was seven when an elderly uncle on my father's side taught me how to play chess. Uncle Ted was a patient man and a good teacher. And you need to be both of these things to teach a seven year old anything - especially chess. I know that from teaching my own son how to play the game.
Although I don't play a lot these days, looking back, it taught me a valuable life skill at a young age: how to think strategically. As a chess novice you learn pretty quickly that things aren't always as they appear at first glance. If you make a rash move without considering all the possible consequences, your folly is quickly revealed to you. So you learn to do your research before you make your move, so that hopefully, there are no nasty surprises afterwards.
Last month we talked about how the majority is not always right and I used the installation of suction strainers as an example. The response to this issue is fairly predictable and usually falls into three groups:
The conscientious objectors - those who are firmly with the majority and like to rattle off the (mostly flawed) reasons why suction strainers are essential; the 'damned if you do, damned if you don't' camp; and the 'band aid' brigade - those who would have us install bypass valves, audible warnings and flashing lights, for the peace of mind that comes from maintaining the status quo, while covering all bases at the same time.
This issue is a bit like an important move in chess game. You have to move something - by that I mean take a position one way or the other. And the more knowledge you have of the game, the better able you are to foresee, understand and be comfortable with the outcome.
If a chess grand master is looking over your shoulder and advises you to make a move that makes no apparent sense to you, you can either ignore the advice or follow it blindly. But only by seeking to really understand the reasoning behind the suggestion, will you become a better player.
Which is why I don't mind if you disagree with me on this or any other hydraulics issue. We each play the game based on our own level of knowledge and experience. And if any of my suggestions encourage you dig deeper; to acquire more knowledge and a better understanding, so you can make better moves and be confident in the outcome, then that can only be a good thing.
The other day I was reading about Eric Ripert the chef at a four-star restaurant in New York who gives his employees a set of very specific rules, 129 of them in fact. Ripert calls them: '129 Cardinal Sins' with the subtitle: 'A bit of advice to restaurant staff from an expert: Pay attention to details.' Then he lists 129 things his staff must not do, for example: 'Having a visible reaction to the amount of the tip'.
I liked this idea so much, I've decided to compile a similar list of 'Cardinal Sins' when it comes to hydraulics. And to make it a bit of fun, I thought I'd run a little competition. Do you have a pet-hate; must-not-do or 'Cardinal Sin' related to hydraulics? If so, please send it to me. The only guideline is it must be expressed as a short, one-liner, For example: 'Installing a suction strainer without an exceptional reason for doing so.'
If yours is one of the best ten submissions, you'll receive a copy of my new, children's book: Farmer Mick Harvest Time Havoc, when it's published later this year - which you can gift to a special child in your life. Or keep for yourself. I won't tell anyone. Like I said, it's a bit of fun - but I'm serious about the list of 'Cardinal Sins'. So put your thinking cap on, and send yours to: firstname.lastname@example.org
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Equipment Maintenance Supervisor
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Hydraulic temperature extremes and how to handle them|
One of our members sent me this recently:
"We have designed an all terrain mobile crane. The machine is designed to operate in hot and cold environments (typical in deserts and mountains - sub zero). We are recommending ISO VG grade 68 mineral oil for hot weather and ISO VG grade 22 for cold environments. I have the following queries:"
1. "If the user shifts the equipment from a hot climate to cold or vice versa will oil replacement be sufficient, or will other changes be necessary?"
2. "How will any remnants of the different grade of oil affect or degrade the replacement oil when mixed?"
In answer to first question, a critical input for the oil viscosity selection process is the minimum and maximum ambient temperatures the machine will operate in. And these numbers need to be considered at the design stage. Here's why:
At the minimum ambient temperature (cold start), the viscosity of the selected grade of oil must be lower than the maximum allowable viscosity for the machine's pumps.
At maximum ambient temperature, the viscosity of the selected grade of oil must not fall below the optimum viscosity (ideally) or the minimum allowable viscosity (certainly) for the hydraulic components in the system. And if high ambient temperatures are involved, then ideally, maximum oil temperature should not exceed 85°C. Temperatures above this figure reduce oil, seal and hose life exponentially.
When this analysis is carried out, if the cold start condition can not be met through oil choice: low viscosity grade; use of a synthetic perhaps, then a means of pre-heating the oil may be necessary. Similarly, if the machine is expected to operate in high ambient temperatures, installed cooling capacity must be sufficient to maintain appropriate viscosity levels and, for reasons mentioned above, limit 'red line' operating temperature to 85°C - even if a VG68 grade oil is being used.
So the short answer to first question is: if the designer has does his homework properly and the machine is being operated within the ambient temperature range for which it was designed, then changing the viscosity grade of the oil to match seasonal conditions is all that should be required.
The second question reminds me of an instructive and somewhat amusing story told to me by another of our members:
"We have adverse weather conditions at our mine site from -40C to about +30C range. The +30C is a much shorter period than is the -40C. We use VG68 hydraulic oil during the warmer months and then switch to VG32 for the cold months."
"The hydraulic oil storage tank has a capacity of 55,000 litres. Last September when the VG32 was ordered for the winter, 15,000 litres of the stuff was just added to an unknown amount of VG68 remaining in the tank."
"I had just recently started working for the company and it took me some time to figure out why viscosity on the oil analysis reports was so far out of whack."
As this story dramatically demonstrates, if two different oils of differing viscosity grades (but hopefully with the same additive chemistry) are mixed, the viscosity of the mixture will fall somewhere between the two grades - depending on the amount of dilution.
The practical difficulties involved in thoroughly draining the oil from a large and complex hydraulic machine during seasonal oil changes, certainly presents a compelling case for considering the use of a multi-grade in these types of applications.
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A look over my shoulder|
In this month's Hydraulics Pro Club simulation video I analyze and explain the
reasons why the design of a press circuit is causing the cylinder to lunge when
it's switched from fast approach to slow-speed for pressing.
On next month's video CD, I'll explain the not so
subtle difference between a counterbalance and an overcenter valve, and demonstrate
one application in which a counterbalance valve should not be used.
Not a member yet? You can fix that here
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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
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