Only a few days ago I had a call to look at a problem on a log handling system in a Saw Mills.
I was shown a fault on a log flipper. Flippers that can turn the log to any position to pass through the saw. Each pair of flipper rams are connected to a 3 position CETOP 5 solenoid valve mounted on a common manifold. An unloading valve is electrically sequenced to prevent the pump being continuously on load and creating heat.
So now for the problem, if a set of flippers were moved to say, half way and stopped and the other set of flippers were switched to move, the first set would continue moving. Now I hear you say, what ghost like things are going on in them there Hydraulics.
I got down close to the manifold and soon identified the valve responsible for the first set of flippers and removed the Electrical Hirschman plugs to see if I could repeat the problem with the electrics removed. Low and behold I could!
I would have bet a weeks pay that this was an electrical problem and be able to pass over to the Electrician. Now was the time to look very closely and find out what was going on as this was becoming a much more interesting fault.
“Ah! Found it,” I said.
The symbol on the valve showed that it was “Detented” making it not a 3 position valve but 2 position.
A detent will allow the solenoid to fire the spool across from one position to the other and hold the spool in that position even when the electrical signal is removed. So with our flipper when the ram is moved half way and the signal is removed and the dump valve diverts the flow to tank the ram will stop moving but only until the dump valve is re energised and allow the ram to complete its movement. So by operating the other flippers the first set will continue to move.
So how did a 2 position detent valve end up on this manifold block doing this job and causing this problem? Seems that no one knows except ghosties and things that go bump in the night.
Advice for you budding Hydraulic fault finders. Sometimes you will come across faults that will remain a mystery and no one will admit to touching.
More Hydraulics at www.hydraulicbrain.com
Cheers
Bob
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