When you are called to site you don’t know what to expect in terms of the information available and potential data collection. The information and data is the most important information to my mind. The background was that a pilot operated directional valve failed the previous day and the new valve worked sporadically, stopping working completely for large periods of time. There were hydraulic circuit drawings but no bills of materials, making it difficult to fully understand the system operation. There was little data available in terms of pressure, one gauge on the HPU and one by a manifold.
I left site with more information but no direction to take on solving the problem. A list was drawn up of the possible causes and how easy they would be to detect. Top of the list and the most obvious was that the new hydraulic valve was faulty or did not work in the way it should. The valve number was qualified against the datasheet and was supposed to be built with an internal pilot and internal drain. We tackled this first to see if any plugs were left in the valve by mistake, and sure enough the drain plug was left in making it externally drained. We took out the plug and trialled the system, it worked first time. The pilot could not be drained and was locking in pressure at both ends of the main spool.
If you have not seen this type of hydraulic valve failure before, then it would be difficult to troubleshoot this problem. I have seen this three times in my career and know some hydraulic valve suppliers can be careless when supplying valves. Experience helps when troubleshooting this type of issue.
This type of hydraulic valves failure does not only happen with pilot operated directional valves, it can also occur with vented relief valves and pressure reducing valves, manifold and line mounted.
I have also recently seen aluminium gear pumps built incorrectly, with the outlet and inlet ports swapped, even though the product code showed it was correct. Supplier problems have been the cause of the last two based site issues that I have attended.
