Non-Return Check Valves

A check valve, or a non-return valve or one-way valve, is a pivotal component in fluid control systems. This mechanical device is designed to regulate the directional flow of fluids, be it liquid or gas, within pipelines and piping systems.

The key characteristic of a check valve lies in its ability to permit the passage of fluid in one designated direction while steadfastly impeding any backflow, thereby preventing the reverse movement of the fluid.
The operational principle of a check valve is centred around a movable element within the valve body, which response to the differential pressure across the valve.

Depending on the specific check valve type, this movable element may take various forms, such as a swinging disc, a hinged flap, a tilting disc, a ball, or other mechanisms. When the fluid flow exerts pressure in the intended direction, the check valve opens, allowing unimpeded passage. However, when there is an attempt at reverse flow, the valve promptly closes, creating a barrier that obstructs any backflow and maintains the integrity of the desired fluid direction.

This essential functionality finds application across various industries, ranging from water treatment and distribution to oil and gas pipelines, chemical processing plants, and HVAC systems. The check valve’s role is particularly critical in preventing issues such as water hammer, which can occur when there is a sudden cessation of fluid flow, leading to potentially damaging pressure surges.

The versatility of check valves is underscored by their compatibility with a diverse array of fluids and their ability to function effectively in a wide range of temperatures and pressures. The selection of a specific type of check valve depends on factors such as the flow rate, the nature of the fluid, the system’s pressure conditions, and the intended application.

Check valves embody diverse designs, each employing distinct mechanisms to facilitate unidirectional fluid flow while preventing undesirable backflow. The core principle behind their operation involves utilising specialised components that respond to variations in fluid pressure, ensuring a seamless and controlled directional flow. Check valves employ three common mechanisms: the swinging disc, hinged flap, and spring-loaded configurations.

1. Swinging Disc Mechanism:

• • A disc or plate is affixed to a hinge within the valve body in check valves featuring a swinging disc mechanism. The hinge allows the disc to swing freely, responding to the force exerted by the fluid flow. When the pressure in the intended direction surpasses a certain threshold, the swinging disc pivots, enabling the fluid to flow unimpeded. Conversely, during attempts at backflow, the disc swiftly swings back into a closed position, forming a barrier that prevents reverse fluid movement.

1. Hinged Flap Mechanism:

• • Hinged flap check valves utilise a flat or curved flap attached to a hinge point within the valve assembly. The flap opens as the fluid flows in the desired direction, permitting unrestricted passage. However, when the reverse flow is initiated, the flap promptly pivots and sits against the valve’s opening, effectively obstructing any backflow. This hinge-and-flap arrangement ensures a reliable and efficient means of preventing undesired fluid reversal.

1. Spring-Loaded Mechanism:

• • Check valves with a spring-loaded mechanism incorporate a spring within the valve body, working with a movable component such as a disc or poppet. The spring applies force to keep the valve closed by default. When fluid flow occurs in the intended direction, the pressure overcomes the spring force, allowing the valve to open and permit the flow. Once the flow diminishes or attempts at backflow arise, the spring promptly closes the valve, maintaining the unidirectional flow control.

Each of these mechanisms offers specific advantages depending on the application’s requirements. The choice between them is influenced by factors such as the fluid characteristics, pressure conditions, and the need for quick response or tight sealing. Regardless of the mechanism employed, the overarching purpose remains consistent: to regulate fluid flow precisely, allowing for optimal system performance while preventing the unwanted consequences of reverse flow.

Diverse industrial applications necessitate various check valve designs, each tailored to specific operational requirements. The selection of a check valve type is influenced by factors such as the nature of the fluid, pressure conditions, flow rates, and system constraints. Here, we delve into the characteristics of several common types of check valves:

Swing Check Valves:

• Swing check valves feature a hinged disc inside the valve body. The disc swings freely on a hinge, allowing fluid to flow in one direction. When backflow is attempted, the disc swings back and seals the valve. Ideal for applications where low-pressure drop is acceptable and a reliable check valve is needed for horizontal installations.

Lift Check Valves:

• Lift check valves have a disc or piston-like element that lifts off its seat when fluid flows in the desired direction. The valve closes under the influence of gravity when backflow is detected. Suitable for vertical installations where the flow characteristics may benefit from a design that allows the disc to lift against gravity during forward flow.

Tilting Disc Check Valves:

• Tilting disc check valves employ a disc that pivots on a hinge. As fluid flows forward, the disc tilts to allow passage. When backflow occurs, the disc returns to a closed position, preventing reverse flow. Often used in high-pressure systems where a quick response to changing flow conditions is crucial.

Ball Check Valves:

• Ball check valves feature a spherical ball inside the valve body. The ball moves away from the seat during forward flow, permitting fluid passage. Upon backflow, the ball returns to its seat, preventing reverse flow. Suited for applications with low to moderate flow rates and where a quick response to changing flow conditions is essential.

Dual Plate Check Valves:

• Dual plate check valves consist of two plates hinged in the centre. The plates open during forward flow, providing an unobstructed pathway. When backflow is detected, the plates close, preventing reverse flow.  Often preferred in high-pressure and high-velocity systems due to their compact design and reduced pressure drop.

Each check valve type is engineered to address specific challenges and meet the demands of particular applications. Understanding their distinct features empowers engineers and system designers to make informed choices, ensuring that the selected check valve aligns with the operational requirements of the fluid control system in which it is deployed.