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Gate valves for Ship service systems

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

Gate valves

Unlike the globe valve, gate (or sluice) valves (Figure 1) give full bore flow without change of direction. The valve disc known appropriately as a gate, is moved at right angles into the flow by a screwed spindle working in a nut. It rests when closed, between circular openings furnished with seats. Valves and seats may be tapered or parallel on their facing sides. Such a valve is not suitable to partially open operation since wire-drawing of the seat will occur.

Gate (or sluice) valve
Figure 1: Gate (or sluice) valve

The bonnets of these valves are frequently of cast iron and care should be taken when overhauling. To ensure tightness, some parallel gates are fitted with twin discs, dimensioned similarly to the chest seats but pressed against the seats by a spring when closed. Where change of direction is required, a full bore angle valve (Figure 2) may be used.

Full bore angle valve
Figure 2:Full bore angle valve

Valve actuators

A variety of valve actuators to control the opening and closing of globe, gate and butterfly valves are available. In some types an electric motor, fitted with limit switches is used to turn a threaded stem through a yoke, purely substituting the action of a handwheel.

Most remotely operated valves have pneumatic or hydraulic actuators. These give linear motion to a piston which for a globe or gate valve moves the valve stem axially up or down. The globe valve disc may be given a slight turn on landing to clean the seat. The piston actuator for a butterfly valve rotates the valve disc through 90 directly or through a scroll arrangement (Figure below )

Pneumatic butterfly valve actuator showing scroll cam arrangement=
Figure :Pneumatic butterfly valve actuator showing scroll cam arrangement

Summarized below some of the basic procedure of machinery valves & pipeline systems :
  1. Valves & pipeline materials corrosion & erosion

  2. 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.....

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

  4. 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.....

  5. Valves & pipelines-system cleaning & draining

  6. 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. ....

  7. Expansion arrangements

  8. 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.....

  9. Valves & cocks

  10. 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. ...

  11. Butterfly valves

  12. 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.....

  13. Gate valves

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

  15. Globe valves

  16. 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....

  17. Relief valves

  18. 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. ....

  19. Valves traps

  20. 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. ....

  21. Flap valves & valve chest

  22. 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.....

  23. Quick closingvalves

  24. 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,....

  25. Strainers & filters

  26. 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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