Types of Valves in A Ship

The primary function of every valve is to control the flow of fluid in pipes, tubes, or cylinders. Valves can effectively manage the transfer of liquids, steam, gases, and slurries. They are also important for regulating pressure and flow in various pipings and machinery systems on ships. If you are a marine engineer, you need to know about the construction and operation of numerous valves used in ships.

Various valves can be added to this category, but in this article, we will discuss some major types of valves used in ships.

1. Diaphragm valve
2. Pinch Valves
3. Pressure relief valve (PRV)
4. Piston Valve
5. Ball valve
6. Butterfly Valve
7. Globe valve

1. Diaphragm valve

The diaphragm valve is a bi-directional start/shut valve that manages fluid flow by regulating the area from where the fluid enters and exits. It uses a flexible disc, diaphragm, that sits on the seat at the top of the valve body to seal the fluid’s passage. The diaphragm is an elastomeric and pressure-responsive membrane that opens, closes, and regulates the valve. Moreover, the valve body can be made of different materials depending on the intended use. Generally, it is made of plastic, metal, or even wood.

The diaphragm valve is similar to a pinch valve, but it employs a linear compression that pushes the diaphragm towards the valve body. It can be actuated both manually and automatically to get a fine control overflow. Additionally, it is well suited for requiring less maintenance and is ideal for moderate pressure and temperature applications. However, it can not be used in multi-turn operations.

2. Pinch Valves

Pinch Valves, also known as clamp valves, come with a flexible tube that can be pinched mechanically to open and close the fluid path. It offers a straight flow path to fluids without any moving parts. Majorly, it has three parts, a housing, an elastomeric tube, and end connections. Plus, there is a pinch mechanism to pinch the tube and create full closure of flow. The pinch mechanism can be a screw-operated mechanism with a pinch on either one side or both sides. Also, the air or hydraulic pressure mechanism can be used to squeeze the tube.

Depending on the construction, the pinch valve can be categorized into two types; open and enclosed pinch valve. The open type is without metal casing, while enclosed valves have a protective metal covering. Pinch valve is ideal for granular products, slurries, foodstuffs, etc. Moreover, these valves are compact, lightweight, and have fast opening and closing speed. But they are not suited to operate at high temperatures because of the elastomeric tube.

3. Pressure relief valve (PRV)

The pressure relief valve is a safety valve that works to protect a system or equipment failure during an overpressure event. It is designed to open at a predetermined pressure and relieve the pressure by allowing the pressurized fluid to exit from the system. The valve automatically closes once the system pressure reaches a safe level. As it is a safety valve, it should be ready for operation at any time, especially when other system controls fail.

The pressure relief valve’s basic purpose is to protect human life and property by venting the fluid out of over pressurized pipes and vessels. Moreover, these valves are also used to maintain sustained pressures downstream or upstream from the valve. The pressure relief valve is important in applications where pressure levels are crucial for fine operations such as steam, air, or gas power generation.

4. Piston Valve

The Piston valve uses a piston to regulate the flow of fluid along a tube or pipe in a chamber. This valve can completely open and close the flow path; it is not designed for throttling applications. When opened, only the bottom face of the piston contacts with fluid while the rest of its body remains protected by the upper sealing rings. Hence, sealing rings are saved from erosion by fluid. It is mostly operated manually, but other actuation methods like electric and hydraulic can be used.

The construction of the piston valve is similar to the globe valve, with only the seat and cone being replaced by a piston and lantern bush. There are two kinds of piston valves, balanced and unbalanced piston valves. A balanced piston valve is ideal for high-pressure services, while an unbalanced one works in low-pressure systems. Moreover, a piston valve is used for handling the flow of gases and hazardous liquids.

5. Ball valve

Ball valves are suitable to start and stop the fluid flow using a ball-shaped disc located in the valve body. The ball has a port at the center, which comes in line with the direction of flow when the valve is open. While during closed position, the port goes perpendicular to the valve end and blocks the flow path. The valve body is constructed from plastic, ceramic, or metal, while the seat is made of nylon, neoprene, etc.

Ball valves are used for quick on/off operation in ships. Moreover, this valve is associated with low-pressure drop and low leakage. It has a long working life and requires very little maintenance. These valves have services in many industries, including high-temperature and high-pressure applications. However, it must not be used for slurries because suspended particles can accumulate and damage the valve.

6. Butterfly Valve

Butterfly Valves are used to isolate, start, stop and throttle the flow of fluids. Its construction may vary, but a butterfly-type disc and sealings are common in every valve. Moreover, it is easy to maintain due to fewer parts and offers low-pressure drop and high-pressure recovery. When the valve is open, the disc becomes parallel to the direction of flow and allows the fluid to flow. While in the closed state, it is perpendicular to the pipe wall and blocks the flow.

Small-sized butterfly valves are operated by a lever, while a handwheel is used to actuate large butterfly valves. They are small in size but can handle a large flow of fluids at low pressure and low temperature. Unlike a ball valve, a butterfly valve can also manage slurries with a high ratio of suspended solids. As they are small in size, they require less space for installation as compared to gate and globe valves.

7. Globe valve

Globe valve can be used for isolation and throttling purposes. It consists of a spherical body divided into two halves by an internal baffle. The baffle diverts the flow of fluid, which ultimately drops the pressure. Furthermore, there is a stationary ring seat and movable disc which controls the fluid flow. This disc is lowered and raised by turning the handle. The flow rate is maximum when the disc is completely raised. On the other hand, the flow is shut off when the disc is lowered completely.

Globe valve can function in high-pressure and high-temperature environments. Plus, it is not so expensive and offers easy installation and maintenance. It offers more pressure drop than ball valves which means it can only be used in systems where pressure drop is not concerned.