Opinion ID: 391190
Heading Depth: 1
Heading Rank: 4

Heading: the relationship of the astern guardian valve to the

Text: ASTERN TURBINE Benjamin Franklin once wrote: 28 For the want of a nail the shoe was lost, 29 For the want of a shoe the horse was lost,For the want of a horse the rider was lost, 30 For the want of a rider the battle was lost, 31 For the want of a battle the kingdom was lost 32 And all for the want of a horseshoe nail. 33 Similarly many of the parties assert that for the want of a proper functioning astern guardian valve the collision was caused. 34 Physically, the astern guardian valve is located on the main steam line just outside the steam inlet to the astern element of a low pressure turbine. It is the last valve the steam passes through before it enters the astern turbine. Its purpose is to protect the astern turbine from an accidental opening of the astern throttle valve when the turbine is turning forward RPM. 9 When the valve is open steam passes into the astern turbine and reverses the engine. If steam were accidentally released into the astern turbine while the turbine operated at full speed ahead, it would be seriously damaged. 35 The valve itself is a disc 5 in diameter and 6 high attached to the end of a stem. As the stem is raised or lowered (by a motor or handwheel), it moves up and down inside the valve body. The disc's bearing surfaces, which touch the valve body, are called guide surfaces. At normal room temperature, the clearances between the guide surfaces and valve body are 10-12 /1,000ths of an inch. In this case, the disc and valve body were manufactured with the same material (ASTM-2176 grade WC6) (cast steel). Neither was treated to obtain differing degrees of hardness. 36 The valve operates when steam enters an inlet on its side and exits through a hole in its bottom. As the disc moves up and down, it is kept in position by the guide surfaces which come into contact with the valve's body. The stem obviously does not prevent contact between the valve's disc and body. It simply moves the disc up and down. 37 The valve's defect was caused by the galling or gouging of its surface due to the rubbing of two metal castings manufactured from the same grade of steel. This rubbing caused the surfaces to weld together, and, consequently, broke off pieces of the metal surfaces. This 'chiseling effect' allowed the steam in the valve to project pieces of metal into the astern turbine where they damaged the turbine's blades. This damage reduced the QUEENY's astern power. Thus, when Captain Kellog ordered full astern, the QUEENY's engines were unable to respond with its former full power. 38 The QUEENY's turbines were designed for normal sea use. They were guaranteed to produce an astern RPM equivalent to 70% of 109. If undamaged, therefore, they should have responded to the full astern command by producing 76.3 RPM. In fact, on the QUEENY's sea trial run, they reached 76 RPM. On the day of the accident, however, they were unable to produce the guaranteed level of astern RPM. Hence, the court below found the QUEENY unseaworthy, and ruled that had the astern turbine functioned properly the collision between the QUEENY and the CORINTHOS would not have occurred. 10 39