In practice, the oil pressure will increase rapidly when the engine starts to vibrate. The forces are transferred through the top bracing cylinders, which will act as rigid connections and thereby detune the natural frequencies.
An oil pressure gauge and a pressure transmitter are placed in the pipe branch connected to the accumulator to monitor the pressure of the pre-charged hydraulic oil. The measuring range of the transmitter is 0-10 bar and the AMS should give an alarm when the pressure of pre-charged hydraulic oil becomes lower than 6.3 bar.
Top bracing is fitted on the top part of the engine on the exhaust side.
- During engine room rounds, the holding down bolts should be observed for slackness.
- Particulat attention to be paid during manoeuvring, when running at reduced power in bad weather and also while increasing the engine load.
- In case of loose holding down bolts, fretting of landing surface can be observed. Fretting of a surface is often indicated by a rust-red powder being present at the outside of the faces that are fretting.
- While engine is stopped, loose holding down bolts can be found out by tapping with a copper hammer. The sound will be different to that of a tight bolt.
- If bolts are found to be loose, inform second engineer and tighten at the earliest opportunity.
Instruction for checking hydraulic top bracing for main engine.
- The hydraulic top bracing should be observed for correct pressure in the pressure gauge.
- It should be observed that there is no leaks from the seals.
- The damping valve must be set at the correct value to allow for optimum damping effect. If not the engine vibrations will be more.
- The maintenance of hydraulic top bracing should be carried out as per makers instructions.
- When engine is not running, the oil supply to the hydraulic top bracing can be shut and checked if the low oil pressure alarm is activated. This can be carried out every three months.
- If any abnormality is found, inform Second engineer and fix it at earliest opportunity.