Generally speaking, a valve is a device that controls the flow of a gas or liquid.
In the marine industry, the substances commonly controlled by a valve are sea water, fuels, and waste. Before you decide on the type of valve for your project, it is important to establish the substance that will come into contact with the valve, the pressure with which the substance will be passing through, and if it will be consistent for pulsating. Valves are made up of different materials, therefore, knowing the substance before will help you define how resistant to corrosion the material will be. There are some key terms to understand before we dive further into types of valves:
When a valve restricts the flow but does not completely stop it, it is referred to as Throttling.
When a valve allows the substance to flow completely through it, it is considered to be open.
A valve that completely stops the flow is considered closed.
While most valves have similar parts, there are minor differences according to which a valve’s function could vary. Every valve has an inlet, it is the place through which a gas/fluid flows, and an outlet, where the substance flows out of the valve. Having said that, valves also have a part, known as the disc that allows it to decide when to throttle or close the flow of gas/fluid.
Another component that stops a substance from flowing is a ball. There are two ways of incorporating this component in a valve – it can either be attached to the stem, in which case it would need to be operated manually like the disc, or it can be suspended and held in place by a spring/gravity. Generally speaking, a suspended ball lasts longer as it rotates when a substance passes over it which leads to an even wear.
Now that we have understood a bit about how a valve functions, let us look at the different types of marine valves:
Gate valves – one of the most common types of valves on a ship. These control the flow of liquid via pipes by raising or lowering, exactly like a gate. Although gate valves have a simple design and function, there are two variations – rising and non-rising stem gate valves.
Butterfly valves – these are lightweight and used for ships that work with substances such as fuel, freshwater, lube oil, or cold-water systems. The valve gets its name because of the way it functions, like a butterfly! The central disk hinges to open and close the valve as the shaft turns.
Globe valves – in marine can regulate flow through a pipe by means of a movable disk and stationary ring set. An angle valve allows for a reverse flow. There are variations of globe valves – screw lift and screw down non return.
Relief valves – as the name suggests, these valves are meant to relieve the pressure within the pipes. When pressure increases, a spring inside the valves opens up and can be adjusted so that the valve opens fast or slow as required.
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