Do You Know All These Valves?

Valves reduce energy in fluid flow, but their uses are essential in operations requiring limited flow. Therefore, it is very important to have a full understanding of the construction and operation of the various types of valves used on ships.
 
Each type of valves has a specific function, including reducing or increasing flow, regulating pressure, starting or stopping flow, relieving pressure in the piping system and controlling flow direction.
 
Valves are made up of many different parts. The first part is the body that holds all parts of the valve together, followed by the valve deck that covers the opening. The internal parts of the valve composed of the stem, seat material, components, disc, plug, and support ring components are collectively referred to as the internal parts of the valve. The disc is designed to throttle or stop flow and the disc seat is provided by the seal ring. Stems are helpful in valve closing.
 
Here's a look at some of the most important valves you'll find on a ship.

Ball Valves
 
This is a kind of globe valves controlling the flow of fluid through a rotating ball with a hole. Media can be blocked or flow through the valve by rotating the ball a quarter turn around its axis. Ball valves are characterized by long service life and it provides a reliable seal throughout service life, even when the valve has not been used for a long time. In some special versions, ball valves are used for control valves. An operation that is less common because the relatively limited accuracy of flow control are compared to other types of control valves.
 
Gate Valves
 
This is one of the most common types of valves used on ships. They raise or lower to help control the flow of fluid through a pipe. Gate valves are similar to gates. It should be noted that gate valves can only be operated in no-flow or full-flow conditions and thus it can only have one position. It provides full flow without changing direction. It is not intended for operations requiring valves to be partially open. Gate valves have a simple design and function, but there are many variations, namely the open stem type and the off stem portion.
 
In open-stem gate valves, the stem threads match the yoke or the integral thread inside the bonnet. During operation, steam rises above the actuator and the valve connected to the stem opens. In dummy stem gate valves, the disc or disc itself has internal threads and is connected to the stem. Stem thread fits disc and valve opens or closes without lifting stems.
 
Gland packing is used to avoid any form of leakage through the space around the spindle in the gate valve. Gland packing can damage in the long run and must be replaced regularly. Gate valves are used where minimum pressure loss is required and where two-way flow is required. The usual material used to make these valves is cast iron.
 
Globe Valves
 
This is a linear motion valve designed to start, stop or regulate flow. The globe disc can be completely removed from the enabled flow channel or completely closed the flow channel. The valve is available in three main body designs, tee type (Z type), angle type and Y type. These valves usually have a rising stem. Larger sizes have an external thread and yoke design. Globe valves have components similar to gate valves. Globe valves seats are parallel or inclined to the streamline in a plane.
 
Globe valves are designed for use in systems requiring flow adjustment. They are used in fuel systems requiring flow adjustment and sealing. They are also used for the feedwater, condenser extraction, chemical feed and extraction drainage systems. Globe valves have good shutoff capacity, medium to good throttling capacity, and a shorter stroke than gate valves. Because the disc is attached to the stem, globe valves can be used as globe check valves.

Butterfly Valves
 
This is a lightweight valve on containers for fuel, fresh water, lubricating oil or chilled water systems. In order to better understand this valve, we can imagine a butterfly moving its wings. It is a quarter turn rotary valve for stopping or starting and regulating flow. These valves are manufactured on the principle of pipe dampers. The element controlling the flow is a disk whose diameter is approximately equal to the inner diameter of the adjacent pipe rotating along the vertical or horizontal axis. When the disc is parallel to the pipeline, the valve is fully open. Valve closes when the disc is vertical.
 
Butterfly valves are ideal for handling large volumes of fluid at relatively low pressures, as well as mud containing large amounts of suspended solids. There are many advantages over globe valves, plug valves, gate valves and ball valves. The most obvious advantage is the savings in weight, space and cost. These valves also have very low maintenance costs because they have very few moving parts.
 
Safety Valves
 
These valves are specially designed to relieve pressure in pipes. When the internal pressure increases, a spring inside the valve opens and releases the pressure. The spring can be adjusted as required to make the valve open faster or slower. To prevent major damage to equipment, mechanical safety valves release elevated pressure before the pressure reaches its limit. When the internal pressure exceeds the predetermined setting, it can be adjusted to make it pop up. Once the internal pressure reaches normal levels, the safety valve closes.
 
Diaphragm Valves
 
This is a two-way on or off throttle valve that controls the flow of fluid by regulating the area of media entering and leaving the valve, effectively changing its speed. A flexible film controls the opening and closing of the valve. Therefore, it is called a diaphragm valve. These are similar to pinch valves, but they use a linear compressor to push the diaphragm into contact with the body. Diaphragm valves provide discrete and variable pressure control for manual and automatic operation. They are also clean, leak-proof, easy to maintain, safe and effective valves best suited for medium pressure and high temperature operations that require start or stop fluid control.
 
Pinch Valves
 
It is a 2/2-way valve for shutting off or regulating the flow of corrosive, abrasive or granular media. Pinch valves use compressed air to open or close the valve. The valve is unrestricted. When in the open position, it allows a range of media to pass through the hole. The valve consists of a flexible internal rubber jacket that insulates the medium to prevent contamination risks. These valves are best suited for granular products and are cost-effective, reliable and easy to use.