PAXMAN VALENTA (RP200) Hydraulic Lock
Corrective Maintenance carried out on a Paxman 12Y3J after suffering a preventable catastrophic failure.
On this project a Paxman 12Y3J engine had suffered a hydraulic lock whilst running. This is not a normal occurrence due to the fact that when a cylinder is being contaminated by fluid the engine will lock itself on start up before it gets up to speed. This is because the installation requires the engine to be slow turned prior to a full start attempt.
In this incident the inter-cooler had failed and leaked water into the cylinder over time, until there was a requirement to start the engine. The engineers put the engine through the slow turning operation. This allows the inlet valves to open and the water in the cylinder to be pumped out into the inlet manifold. The water should then have drained out via a drain valve in the inlet manifold, however this valve had failed due to corrosion and the water remained in the manifold. The engine was subsequently started and ran. Once the engine produced enough air consumption to lift the water from the inlet manifold, a large quantity entered one of the cylinders causing the engine to hydraulically lock.
These pictures were taken during the initial inspection of the engine, looking up at the cylinder that suffered the hydraulic lock and the piston once it was removed.
The pressure had caused the connecting rod to bend and contact the cylinder liner. This contact had caused two deformations in the liner and pulled the diameter straight into a D shape. The contact marks between the rod and liner can be seen on the connecting rod.
The connecting rod could not be removed without cutting the horns off the ends of the rod, and the cylinder liner had to be machined out due to deformation and potential damage to the E bore of the crankcase during removal.
Once the rod had been removed from the cylinder, the liner was then machined out. Extensive inspections were carried out on the crankcase as this level of failure could have potentially caused enough damage to render the engine un-serviceable. This would have then led to costly down time whilst the engine was replaced in what is a very sensitive application.
The crankcase was fully crack detected and full dimensional readings were taken. The data recorded was then analysed to asses the feasibility of a repair or potential rebuild. We came to the conclusion that the damage to the E bore of the crankcase was far enough below the sealing diameter of the liner O rings to attempt the refit of a new cylinder liner and carry out a subsequent pressure test. This was carried out and proved a successful procedure.
With the crankcase assessed serviceable, a new liner fitted and tested an investigation was then carried out to find the cause of the problem. It was deemed that the inter-cooler had internally leaked into the air side of the system allowing fluid to build up in the inlet manifold. This in in itself is a problem but should not have caused the catastrophic failure due to built in countermeasures in the form of manifold drain valves. These drain valves are supposed to allow any fluid to leave the manifold but due to corrosion had seized solid and caused the fluid to be retained leading to the ingestion of fluid and subsequent hydraulic lock of a cylinder.
The engine was then rebuilt with a new rod and piston, a replacement inter-cooler and new water drain valves. All systems were then thoroughly tested for correct operation and once the engine was proved to function correctly a full running test was completed successfully.
All causes of this particular failure were preventable and with regular seal servicing and overhaul maintenance this would have never occurred. In this instance the client was convinced that they would need to replace the entire engine but K.W Engineering Services Ltd saved them both time and money by taking the time to fully assess the extent of the damage and make repairs where necessary, returning the engine to its optimum operational effectiveness.