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Valves & pipelines - System cleaning & draining

Cleaning the system: It is often found, in new ships, that the bilges and bilge systems have not been thoroughly cleaned with the result that wood, nuts, bolts, rags and other debris are found inside valves and pipes after initial bilge pumping. These choke the valve-chests and prevent the valves from being properly closed. They also block strainers.

It is vital to clean before the bilge system is tested to ensure that all suction pipes, joints, valves and glands are free from air leaks. Pipes too must be cleaned and checked as being clear before and after assembly. Blockage has sometimes been found due to failure to cut apertures in metal or joints. Obviously with hydraulic or pneumatic pipe systems, foreign objects or residues from manufacture can cause serious malfunction.

Drains:

Disastrous explosions have been caused by accumulations of oil or oil vapour in diesel engine air lines which were not regularly drained. Severe damage has been caused by 'water hammer' when steam has been admitted to pipes containing water, especially when a slight inclination of the pipe from the horizontal allowed the water to have a large free surface area.

On steam being admitted, condensation occurs on the cool water surface or in a cold section of the pipe, a partial vacuum develops and the water moves along the pipe at great speed. The impact of this water at a bend or valve, can cause fracture of the pipe. Water hammer is indicated by severe and often repeated banging in the pipe. Steam pipes are fitted with drains which should be left open so that water will not accumulate otherwise drains must be opened before admitting steam. Steam master valves are first opened very slightly or 'cracked open' when a line is being brought into use until the pipe is thoroughly wanned. Only then should the valve be opened fully. Expansion arrangements Provision must




Summarized below some of the basic procedure of machinery valves & pipeline systems :

1. Valves & pipeline materials corrosion & erosion

Galvanic corrosion is a major challenge for any pipes which carry sea water. Rust is a particular corrosion problem for steel pipes exposed to contact with sea water or moisture generally and air. Pipe runs along tank tops or on deck, are examples of the latter. Steel pipes in these areas require external as well as internal protection.....




2. valves-&-pipelines-strength-of-materials

The strength of materials used for pipes and fittings must be adequate for the system pressures and possible over-pressures. Pipelines and valves, for example, used to carry and control the flow of high temperature, high pressure steam must obviously be made to very exacting specifications by approved manufacturers.....


3. Valves & pipelines-system cleaning & draining

It is often found, in new ships, that the bilges and bilge systems have not been thoroughly cleaned with the result that wood, nuts, bolts, rags and other debris are found inside valves and pipes after initial bilge pumping. These choke the valve-chests and prevent the valves from being properly closed. They also block strainers. ....


4. Expansion arrangements

Provision must be made in pipe systems to accommodate changes in length due to change of temperature, and so prevent undue stress or distortion as pipes expand or contract.....


5. Valves & cocks

Cocks and valves are designed to control or interrupt flow. This is done in cocks by rotating the plug, and in valves by lowering, raising or rotating a disc in relation to a seating surface or by controlling the movement of a ball. ...


6. Butterfly valves

A butterfly valve consists basically of a disc pivoted across the bore of a ring body having the same radial dimensions as the pipe in which it is fitted.....


7. Gate valves

Unlike the globe valve, gate (or sluice) valves give full bore flow without change of direction. The valve disc known appropriately as a gate,....


8. Globe valves

The globe valve has a bulbous body, housing a valve seat and screw down plug or disc arranged at right angles to the axis of the pipe....


9. Relief valves

Excess pressure is eased by a relief valve . This consists of a disc held closed by a spring loaded stem. The compression on the spring can be adjusted so that the valve opens at the desired pressure. ....


10. Valves traps

A steam trap is a special type of valve which prevents the passage of steam but allows condensate through. It works automatically and is used in steam heating lines to drain condensate without passing any steam. ....


11. Flap valves & valve chest

Scupper pipes from accommodation spaces are fitted with non-return valves. Those scuppers from spaces below the bulkhead deck, are required to be fitted with non-return valves which can be positively closed from above the bulkhead deck or, if this is not practical, with two non-return valves.....


12. Quick closingvalves

Fuel oil service and some other tanks must be fitted with valves that can be closed rapidly and remotely in the event of an emergency such as fire. Wire operated valves are commonly fitted,....


13. Strainers & filters

The term strainer is sometimes used specifically for a simple device made up with a single layer of coarse gauze, a very coarse wire mesh or a drilled or perforated plate. ...

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