Why spinners or valve rotator and rotocap are fitted on valve stem?

Spinner or valve rotator is fitted to exhaust valve stern to rotate the valve during operation particularly in diesels engines burning residual fuel oils containing elements like vanadium and sodium.

In case any hard materials logged at a particular point between the valve and the seat, it will get repeatedly hammered forming a deep dent and allowing combustion gases to leak, there will be intense local temp rise and further damage due to erosion by high speed gas. A valve rotator may be of advantages in braking up the deposit. Rotation of the valve results in even temperature distribution around sealing surface and reduces carbon build-up. Rotation of the valve has a polishing effect removing combustion deposit between the valve and seat.

In 2-stroke engine, the hydraulically operated exhaust valve is provided with winged part on the stem in way of the gas stream. the valve is rotated by the high speed exhaust gas flowing past it.

In 4-stroke engines rotocap is fitted to the exhaust valve operating mechanism for the same purpose.

Comments

Difference Between A, B & C-Class Divisions?

IMO Symbol A Class Division IMO Symbol B Class Division SOLAS has tables for structural fire protection requirement of bulkheads and decks. The requirements depend on the spaces in question and are different for passenger ships and cargo ships. The Administration has required a test of a prototype bulkhead or deck in accordance with the Fire Test Procedures Code to ensure that it meets the above requirements for integrity and temperature rise. Types of Divisions: "A" Class "B" Class "C" Class "A" Class: "A" class divisions are those divisions formed by bulkheads and decks which comply with the following criteria: They are constructed of steel or equivalent material They are suitably stiffened They are constructed as to be capable of preventing the passage of smoke and flame to the end of the one-hour standard fire test. they are insulated with approved non-combustible materials such that the average tempera

Why do we blow through engine before starting ?

The engine is blown through on air before starting it : a) To Blow out through indicator cock any residual exhaust gas or other products of combustion trapped inside the cylinder after shutting the engine. b) To check if any jacket cooling water from cylinder head or turbocharger or any other source, has leaked while the engine was shut and collected on top of piston. If while blowing through, water comes out of indicator cock or relief valve, we need to investigate and rectify the fault before starting the engine. It is imperative that the engine is blown through before starting. There have been cases where the generator engine has been started from control room without bothering to blow through first, and water collected on top of piston has resulted in a bent connecting rod and broken piston.( Reason – water can not be compressed )

Load Line & Why it is Important

Merchant ships have a marking on their hull know as the Plimsoll line or the Plimsoll mark, which indicates the limit until which ships can be loaded with enough cargo, internationally, the Plimsoll line on a ship is officially referred to as the international load line. Every type of ship has a different level of floating and the Plimsoll line on a ship generally varies from one vessel to another. All vessels of 24 meters and more are required to have this Load line marking at the centre position of the length of summer load water line. There are two types of Load line markings:- Standard Load Line marking – This is applicable to all types of vessels. Timber Load Line Markings – This is applicable to vessels carrying timber cargo. These marks shall be punched on the surface of the hull making it visible even if the ship side paint fades out. The marks shall again be painted with white or yellow colour on a dark background/black on a light background. The comp

Marine Engineering

Search This Blog