Types of Valves: Everything You Need to Know As Marine Engineer
Valves are among the most important components in any fluid-handling system. They are used to control, regulate, isolate, direct, and, in certain applications, protect systems from excessive pressure. Onboard ships, valves are found throughout essential systems such as seawater cooling, freshwater, fuel oil, lubricating oil, steam, compressed air, fire-fighting, bilge, ballast, and hydraulic systems.
For a marine engineer, understanding the construction, working principle, advantages, limitations, and applications of different valves is essential for safe and efficient operation of machinery.
What Is a Valve?
A valve is a mechanical device used to control the flow of a fluid through a pipe or passage. Depending on its design and application, a valve can start or stop flow, regulate the flow rate, change the direction of flow, or protect a system against excessive pressure.
The component inside a valve that moves to open, close, or regulate the flow is generally referred to as the disc. The shape and movement of this component are often responsible for the valve's name.
For example:
A ball valve uses a ball-shaped disc.
A butterfly valve has a disc resembling a butterfly wing.
A gate valve uses a gate-like disc.
A needle valve has a needle-shaped regulating element.
The globe valve is an exception, as its name is associated with the shape of its valve body or cover rather than its disc.
Functions of Valves
Valves perform several important functions in a piping system.
1. Starting and Stopping Flow
A valve can completely open or close a pipeline, allowing engineers to isolate equipment or sections of a system.
2. Regulating Flow
Some valves can be partially opened to control the rate of fluid flow.
3. Changing the Direction of Flow
Certain valve arrangements allow fluid to be directed from one part of a system to another.
4. Pressure Protection
Pressure-relieving valves can discharge excess pressure and protect equipment and piping from potentially dangerous overpressure conditions.
Classification of Valves
Valves can be classified in several ways depending on their construction, movement, function, and method of operation.
One basic classification is according to the movement of the valve's closing element.
1. Rotary Motion Valves
In rotary-motion valves, the disc or closing element rotates, commonly through approximately 90° between the fully open and fully closed positions.
Because of their quick operation, they are often referred to as fast-acting valves.
Examples include:
Ball valve
Butterfly valve
2. Linear Motion Valves
In linear-motion valves, the closing element moves along a straight path, generally up and down, to open, close, or regulate the flow.
Examples include:
Gate valve
Globe valve
Valve Actuation
A valve actuator is the mechanism or method used to operate a valve.
Depending on the application, valves can be operated in several ways:
Manual Operation: The valve is operated by a handwheel, lever, or similar mechanism.
Electric Operation: An electric motor or solenoid is used to operate the valve.
Hydraulic Operation: Hydraulic pressure provides the force required to operate the valve.
Pneumatic Operation: Compressed air is used to open, close, or position the valve.
These four basic methods—mechanical, electrical, hydraulic, and pneumatic—are commonly used depending on the valve design and system requirements.
Major Types of Valves
1. Ball Valve
A ball valve uses a spherical disc with a passage through its centre. Rotating the ball changes the alignment of the passage with the pipeline.
Because the ball normally rotates through approximately 90°, the valve can be operated quickly.
Advantages
Fast operation.
Low pressure drop when fully open.
Compact design.
Suitable for isolation applications.
Limitation
Ball valves are generally intended for fully open or fully closed operation and are not normally preferred for continuous flow regulation.
The reference material identifies the 90° operation and low pressure drop as key advantages while noting the limitation for flow regulation.
2. Globe Valve
A globe valve is designed with a movable disc that travels toward or away from a valve seat. Its construction makes it particularly suitable where flow regulation is required.
Advantages
Suitable for regulating flow.
Provides good sealing.
Limitations
Relatively heavy.
Produces a comparatively high pressure drop when fully open.
Requires greater operating effort than some other valve designs.
Because of its regulating capability, the globe valve is commonly associated with applications where controlling flow rather than simply isolating a line is important.
3. Gate Valve
A gate valve uses a gate-like disc that moves linearly to open or close the passage.
When fully open, the gate is withdrawn from the main flow path, resulting in very little obstruction to the fluid.
Advantages
Simple construction.
Relatively inexpensive.
Very low pressure drop when fully open.
Limitation
A gate valve is primarily intended for fully open or fully closed operation rather than throttling.
Marine application: Gate valves may be encountered in various piping systems where reliable isolation and low pressure loss are required.
4. Butterfly Valve
A butterfly valve consists of a disc mounted on a rotating shaft. The disc rotates to control the flow through the pipeline.
It is a rotary-motion valve and can normally be operated quickly.
Advantages
Can be used for opening and closing.
Can also be used for flow regulation in suitable applications.
Fast operation.
Lightweight compared with many other valve designs.
Requires relatively little space.
Economical.
Limitation
The suitability of a particular butterfly valve for high-temperature service depends on its construction, materials, and seat arrangement; therefore, the valve manufacturer's temperature rating must always be considered.
The reference material specifically highlights the valve's low weight, compactness, speed, and cost advantages.
5. Relief Valve
A relief valve is a pressure-protection device designed to release excess pressure when system pressure rises beyond an acceptable level.
Its primary purpose is to prevent damage to equipment and piping caused by excessive pressure.
A familiar example is the pressure-relief arrangement used in a pressure cooker.
In marine engineering, pressure-relief devices are important wherever pressure can rise beyond the safe working limit of equipment or piping.
6. Check Valve
A check valve, also known as a non-return valve (NRV), permits fluid to flow in one direction while preventing reverse flow.
Unlike manually operated isolation valves, a check valve operates automatically in response to the flow and pressure conditions in the system.
Main Function
Its primary purpose is to prevent backflow.
Check valves are commonly used in fluid systems where reverse flow could damage equipment, interfere with system operation, or cause contamination.
The reference material specifically describes swing check valves as one commonly used form.
7. Needle Valve
A needle valve is designed for precise and fine control of fluid flow.
It contains a small, tapered regulating element that allows the flow passage to be adjusted very accurately.
Main Features
Provides fine flow adjustment.
Suitable where small changes in flow are significant.
Useful in instrumentation and pressure-gauge applications.
Needle valves are particularly useful when precise adjustment is more important than providing a large flow capacity.
Directional Control Valves
Directional control valves are particularly important in hydraulic systems.
A directional control valve determines the path of hydraulic fluid and allows the operator or control system to start, stop, reverse, or hold the movement of hydraulic actuators.
Most directional control valves use a sliding spool that moves inside a precisely machined valve body. Movement of the spool opens different internal passages and changes the direction of hydraulic flow.
4/3 Directional Control Valve
A common arrangement is a 4/3 directional control valve.
It has:
Four ports:
P — Pressure
T — Tank/Return
A — Work port
B — Work port
Three positions:
Neutral
Extend
Retract
Moving the spool in one direction sends hydraulic fluid to one side of a cylinder, while moving it in the opposite direction reverses the flow.
Common Centre Configurations
The centre position determines how the hydraulic fluid behaves when the valve is not actuated.
Closed Centre:All ports are blocked, holding the actuator in position.
Open Centre:Pump flow is allowed to return to the tank.
Tandem Centre:Pump flow returns to the tank while the actuator ports remain blocked.
Float Centre:Both actuator ports are connected to the tank, allowing the actuator to move freely.
Directional control valves are widely used in marine hydraulic systems such as steering gear, cargo cranes, hydraulic winches, hatch covers, mooring equipment, deck machinery, stabilizers, bow thrusters, and hydraulic power units.
Colour Coding of Valves Onboard Ships
Ships contain a large number of piping systems, including seawater, freshwater, steam, compressed air, fuel oil, and lubricating oil systems.
Colour coding can help identify the service associated with different valves and piping arrangements.
The reference material provides the following examples:
System | Colour |
Seawater | Green |
Freshwater | Blue |
Lubricating Oil | Yellow |
Steam | Silver |
Air | Grey |
Fuel Oil | Brown |
Fire Line | Red |
However, engineers should always follow the vessel's approved piping diagrams, identification system, and onboard procedures because colour conventions may vary between vessels and standards.
Factors Considered When Selecting a Valve
Selecting the correct valve is an important engineering decision. The valve must be suitable for the operating conditions of the system.
Important factors include:
Type of Valve
The valve must match the required function—such as isolation, regulation, non-return protection, pressure relief, or directional control.
Valve Material
The material must be compatible with the fluid and operating environment.
Maximum Working Pressure
The valve must be rated for the maximum pressure expected in the pipeline.
Maximum Working Temperature
The valve and its sealing materials must be suitable for the maximum temperature of the fluid.
These factors are specifically identified in the reference material as important considerations when ordering valves.
Valve Standards and Identification
Marine spare parts and equipment are generally required to conform to applicable standards and specifications.
The reference material notes that valves and other marine stores may be ordered using the Marine Stores Guide published by IMPA (International Marine Purchasing Association) and refers to standards such as JIS, DIN, and ANSI.
Valve markings can provide important information about pressure rating and nominal size.
For example, the source explains that a 5K50 marking under JIS indicates a valve associated with a 5 bar pressure rating and 50 mm nominal diameter.
Engineers should always interpret valve markings according to the applicable standard and manufacturer's documentation rather than relying on the marking alone.
Valve Selection: Which Valve Should Be Used?
There is no single valve that is suitable for every application.
The selection depends primarily on what the system needs the valve to do.
Requirement | Common Valve Choice |
Quick isolation | Ball Valve |
Low-pressure-drop isolation | Gate Valve |
Flow regulation | Globe Valve |
Compact isolation/regulation | Butterfly Valve |
Prevent reverse flow | Check Valve |
Fine flow adjustment | Needle Valve |
Overpressure protection | Relief Valve |
Hydraulic directional control | Directional Control Valve |
This table is a practical summary of the functions described in the reference materials; actual selection must also consider pressure, temperature, fluid properties, materials, size, standards, and manufacturer specifications.
Frequently Asked Questions (FAQs)
What is the main function of a valve?
The main function of a valve is to control the flow of a fluid through a piping system. Depending on its design, a valve can start or stop flow, regulate the flow rate, change the direction of flow, or provide pressure protection.
What are the main types of valves used onboard ships?
Common valve types used in marine systems include:
Ball valves
Gate valves
Globe valves
Butterfly valves
Check valves or non-return valves
Needle valves
Relief valves
Directional control valves
The appropriate valve depends on the function and operating conditions of the particular system.
What is the difference between a gate valve and a globe valve?
A gate valve is primarily used for isolation and provides very little pressure drop when fully open. It is generally operated in fully open or fully closed positions.
A globe valve, on the other hand, is particularly suitable for regulating fluid flow. However, it generally produces a greater pressure drop when fully open.
What is the difference between a ball valve and a butterfly valve?
Both are rotary-motion valves and can be operated quickly.
A ball valve uses a spherical closing element, while a butterfly valve uses a disc mounted on a rotating shaft. Ball valves are commonly associated with quick isolation, whereas butterfly valves offer a compact and lightweight design and can also be used for flow regulation in suitable applications.
What is a check valve or non-return valve?
A check valve, also known as a non-return valve (NRV), is designed to allow fluid to flow in one direction while preventing reverse flow. It operates automatically according to the flow and pressure conditions in the system.
