Marine valves are important equipment used on ships to control the flow of various fluid media (such as seawater, fresh water, fuel oil, lubricating oil, steam, etc.). Different types of marine valves have different working principles. The following are the working principles of common marine valves:
Gate valve
The gate of the gate valve moves vertically along the centerline of the channel to achieve opening and closing. When opened, the gate rises, the fluid channel opens, and the medium can flow in the pipeline; When closed, the gate descends until it tightly adheres to the valve seat, preventing the medium from passing through. Gate valves have the advantages of low fluid resistance and unrestricted medium flow, but their opening and closing speeds are relatively slow, and the sealing surface is prone to wear.
ball valve
Ball valves open and close by rotating the ball around the centerline. When the channel of the sphere is aligned with the pipeline channel, the valve is in the open state, and the fluid can pass smoothly; When the sphere rotates 90 degrees and its channel is perpendicular to the pipeline channel, the valve closes, preventing fluid flow. Ball valves have fast opening and closing, low fluid resistance, and good sealing performance, but require high machining accuracy and are relatively expensive. The commonly used ball valves are mainly divided into two categories: floating ball structure and fixed ball structure:
Floating ball valve: The ball can float, and under the pressure of the medium, the ball will be tightly pressed onto the sealing ring on the outlet side, forming a single seal. However, the sealing of the valve seat in front of the valve cannot be guaranteed. The characteristic of this type of ball valve structure is its simple structure and good single-sided sealing performance, but its sealing surface is subjected to high pressure, resulting in a large opening and closing torque.
Fixed ball valve: The valve seat is floating, and the floating valve seat presses the ball tightly with the pressure of the spring behind the valve seat and the pressure of the medium, thereby achieving sealing. During operation, the pressure of the fluid in front of the valve is only transmitted to the bearing and valve stem, without causing pressure on the valve seat. Therefore, the fixed ball valve has low torque, small valve seat deformation, stable sealing performance, and long service life.
butterfly valve
Butterfly valves control fluid flow through the rotation of disc-shaped butterfly plates. When the butterfly plate rotates parallel to the direction of fluid flow, the valve opens and fluid can pass through; When the butterfly plate rotates 90 degrees to be perpendicular to the direction of fluid flow, the valve closes and cuts off the fluid channel. Butterfly valves have a simple structure, small size, light weight, small opening and closing torque, and are easy and fast to operate. However, their sealing performance is slightly inferior to ball valves, and they are generally suitable for medium and low pressure systems.
stop valve
The globe valve relies on the pressure of the valve stem to tightly fit the sealing surface of the valve disc with the sealing surface of the valve seat, preventing the flow of the medium. In the relevant regulations of valves in our country, the flow direction of globe valves is always from top to bottom, so there is directionality during installation. When opened, the valve stem lifts, the valve disc leaves the valve seat, and the fluid channel opens; When closed, the valve stem descends and the valve disc presses against the valve seat, cutting off the fluid. The globe valve has good sealing performance and is suitable for small-diameter pipelines with high sealing requirements. It can accurately adjust the flow rate.
check valve
Check valve, also known as one-way valve, automatically opens and closes the valve disc by relying on the flow of the medium itself. When the medium flows in the specified direction, the pressure of the medium pushes the valve disc open, allowing the medium to pass through; When the medium shows a reverse flow trend, the pressure of the medium causes the valve disc to automatically close, preventing the medium from flowing back and thus protecting the safety of equipment and systems.
Pneumatic Valve
Pneumatic valves are actually divided into two parts: valve body (valve) and actuator (actuator), and different valves and actuators can be combined according to needs. The working principle of a pneumatic actuator is that when compressed air enters the actuator from nozzle A, the gas pushes the double piston to move linearly towards both ends (cylinder head end). The rack on the piston drives the gear on the rotating shaft to rotate counterclockwise by 90 degrees, and the valve is opened; When compressed air enters the two ends of the pneumatic actuator from nozzle B, the gas pushes the double pistons to move in a straight line towards the middle. The rack on the piston drives the gear on the rotating shaft to rotate clockwise by 90 degrees, and the valve is closed.
