The WORST hydraulic equipment owner in the world?|
As the year draws to a close, if you're feeling over-worked and under-appreciated, I can relate.
But spare a thought for Rick Sosnowski. Rick is a long-time member and battle-weary spanner man from Boston Bar in Canada. He's also a "yes we can" kind of operator. Which means you shouldn't be surprised if you find him overhauling the boom cylinder off a 25-ton excavator in the middle of forest somewhere in the interior of Canada. He'll find a (safe) way to do it.
Rick is no slouch when it comes to hydraulics, but he could use a little help choosing his customers, as this story shows:
"A few months ago I got a call to fix a big old Link-Belt excavator with travel problems. When I got there it had just blown a bucket hose and the oil was just pouring out all over the ground and into a couple of dirty buckets. I ran to the machine and released the pressure in the hydraulic tank. The owner didn't know that the pressure in the tank would push his oil out.
I had a used hose that fit, so on it went. The machine needed about five or six pails of oil just to get close to the safe level. And this is when the fun started.
First thing the owner wanted to do was put back in the oil he caught in the dirty buckets. I explained that it was a not a good idea and gave him two pails I had in the truck. In a big tank like that it didn't make much difference so I told him he needed to get more oil before I would even consider starting the machine.
Now get this. He didn't want to spend the money on oil and wanted to put in diesel fuel instead. I told him that if the machine was on a beach and the tide was coming in I would do it, but not in this case. I spent a good twenty minutes arguing with the man about why he should not do it. He knew someone who had done it, so he wanted to do the same. In the end, he did buy new oil but he wasn't convinced that I was right."
I've heard several stories of diesel being put into the hydraulic tank - but NEVER intentionally. And besides, I wonder why this machine owner was willing to waste money on diesel fuel anyway. When he could have just topped off the hydraulic tank with water. Sheez!
But there is a point to all this. A light-hearted one. Rick reckons this story of being cheap (and stupid) will take some beating. Maybe it will. Then again, maybe it won't. To find out one way or the other, I thought I'd run a little competition - to find the WORST hydraulic equipment owner or operator in the world.
So if you have a story to rival the one above, send it to me at firstname.lastname@example.org
The only criteria is it must be related to hydraulic equipment maintenance, repair or troubleshooting AND it should illustrate the LAST thing you should do in the situation described - like putting diesel in the hydraulic tank, in Rick's story.
I will edit and compile all the stories submitted into a single document and make it available to all members who'd like a copy. It'll be good for a laugh and likely instructive as well.
The entry I judge to be best (worst in the world) will win 12 month's membership to Hydraulics Pro Club.
So cast your mind back and send in your story. Like I said, it's a bit of fun. Because all work and no play makes Jonnie a dull boy.
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A common problem with solenoid valves|
From one of our members:
"Could you explain heat generation in hydraulic valve solenoid coils? If the temperature of the coil increases what shall happen to the valve's function?"
The short answer to this is: the solenoid coil will fail and therefore the valve itself will cease to function.
In AC electric coils the resistance or impedance of the coil is lowest when the solenoid is open, i.e. when the plunger is out. Impedance increases as the plunger is pulled into the closed position.
As a result, the current draw of an AC solenoid is highest when the solenoid is open (plunger out) and lowest when the solenoid is closed (plunger in).
The high current draw of an open AC solenoid is known as inrush current. And the current draw when the solenoid is closed is called holding current. AC solenoids can only dissipate the heat generated by their holding current. This means it's very important for the plunger to close completely when an AC solenoid is energized.
In other words, the high inrush current generates more heat than can be continuously dissipated by the solenoid. So if the plunger is not able to be completely pulled into its coil - due to a mechanical problem with the valve for example, then the insulation around the coil windings will burn and the coil will short out.
But what could go wrong with a hydraulic valve that would stop the solenoid plunger from being pulled in completely? Well, contamination is a common cause. When hard or soft particles invade the clearance between the spool and its bore, the solenoid may not have enough power to fully shift the spool. This is often referred to as "silt-lock".
If silt-lock is the problem, then replacing the solenoid is a waste of time. Replacing the entire valve will buy some time - until it too becomes 'silt-locked'. The solution of course, is to get the contamination problem under control.
Another problem presented by the inrush current characteristics of AC solenoids, is the possibility of overheating to due to rapid cycling. Each time the solenoid is closed it is subject to the heating affect of the high inrush current. If the solenoid is switched on and off too rapidly, the successive inrush currents can generate more heat than can be dissipated, leading to failure of the solenoid.
Still, an AC solenoid can be cycled quite rapidly. To give you some idea, a class H solenoid, which has insulation rated to 180°C, can be safely switched twice per second. But a DC solenoid with class F insulation rated to 150°C can be cycled four times per second without any fear of overheating. And the nice thing about DC solenoids is they don't burn out if the plunger doesn't completely close - due to silt lock or any other reason.
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Plant Maintenance Resource Center
Hydraulic hoses and tubes are not interchangeable. They are different “tools” for different jobs.
In the July 2010 Issue of Machinery Lubrication
I explain why hose should ONLY be used where tubing cannot.
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