Germany’s CM Technologies (CMT) has introduced a compact Pressure Drop Test Instrument (PDTI) designed to identify cylinder pressure leaks before the result in increased fuel consumption, costly repairs and ship downtime.
During a diesel engine’s compression process, a pressure loss can provide an early indication of deteriorating piston rings (“blow by”), cylinder liner wear or damage or leakage at air inlet and exhaust valves.
Although the initial symptoms may appear relatively minor, pressure loss can actually point to developing wear within the combustion chamber, said CMT managing director David Fuhlbrügge.
“Any loss of cylinder pressure also represents a loss of energy that would otherwise act on the piston during combustion. As a result, an engine will require more fuel to compensate for the reduced pressure and maintain the required power output,” he said.
The company said pressure drop testing should form part of routine engine condition monitoring, but the availability of a simple, purpose-specific test is limited.
“Checking whether a cylinder is losing pressure should be a standard test, but there are relatively few dedicated instruments available,” said Fuhlbrügge. “Some crews have developed their own rudimentary tests, which may work, but do not provide a uniform solution across a fleet. Customers approached us because they wanted a simple, standardised instrument capable of more consistent results.”
The PDTI works by introducing pressurised air into the combustion chamber through the engine indicator valve. Once the required pressure has been established, the system is locked and allowed to stand for a defined period. The pressure loss over a fixed time is measured.
By repeating the procedure across the engine and comparing the rate of pressure decay between individual cylinders, engineers can identify cylinders that lose pressure more rapidly than others.
These outliers may indicate leakage associated with worn or damaged piston rings, cylinder liner condition, or leaking valves.
“Acceptable pressure loss depends on the engine and its specified operating limits. However, comparing results across cylinders provides engineers with a practical means of identifying deviations and determining where further inspection may be required,” Fuhlbrügge said.
“If pressure is escaping from the combustion chamber, energy is being lost. That can contribute to higher fuel consumption because additional fuel may be required to compensate for the loss. Pressure drop testing can also indicate common problems such as piston-ring deterioration or problems with the exhaust-valve.”
The PDTI itself is manufactured using additive manufacturing, with stainless-steel powder formed layer by layer using a specialised 3D-printing process. This method allows complex internal pathways to be incorporated while maintaining the integrity of the instrument’s external structure.
“Pressure leakage is easy to overlook, but it can be an early indication that the engine is beginning to deteriorate. A simple comparison of pressure decay between cylinders will help saving fuel and give engineers useful information before it becomes a costly problem,” he said.
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