A vertical 20-in. bore cylinder press with a logic valve setup started drifting down in the neutral position. Unfortunately, many technicians are not familiar with the schematics of how logic valves work.
I always tell people that if they are piloted with a small directional valve then you should treat them like on-off valves. If there is pressure on the top, (spring side) they are held closed and if the top goes back to drain, they will open.
The maintenance technicians did know to remove the covers and check that all the orifices were open and if so, to pull the poppet out and examine it for problems.
Of course, you must also make sure the cylinder piston is not causing the leak by blocking the cap end of the cylinder. A ball valve would work well to determine this; you then energize the circuit to retract the cylinder. If it slightly retracts and stops, the cylinder is fine. If it extends, then there is a piston leak causing the drift. Unfortunately, in this case, they replaced the cylinder thinking it must be the cause.
Can you identify what was the problem? We welcome responses of all kinds directly to Robert Sheaf at firstname.lastname@example.org or to email@example.com. The solution will be provided next month, in conjunction with our June 2023 issue.
A common problem with logic valves is the failure of one of the seals, usually located on the outer side of the sleeve where it contacts the drilled hole in the manifold. Many times, they are difficult to remove. I use a two-toed wheel type puller and a sliding hammer to remove them.
The seal on the 25MM logic sleeve had failed. I always replace them with 95 durometer Viton O-rings, which are extremely resistant to extrusion failures. The failure cause should always be investigated, such as manifold tolerances and/or excessive pressure spikes.
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