The normally open valve is often preferred where:
Continuous flow is critical.
Minimal pressure loss is required, as the valve offers little resistance to flow.
Backflow prevention is needed only in occasional or emergency situations, such as in a power failure or sudden system shutdown.
Normally open check valves are beneficial in applications where the system pressure is consistent and there is little risk of backflow during regular operation. When reverse flow occurs, the valve will close automatically, preventing damage or contamination in downstream components. In contrast, a normally closed (NC) check valve remains closed under standard conditions and only opens when there is a sufficient forward pressure to overcome the valve’s resistance. This type of valve is suitable for applications where flow is required only under specific conditions or where the system needs tight shutoff when there is no active forward flow.
Normally closed check valves are commonly used in:
Safety-sensitive applications, such as pipelines where hazardous materials are present.
Systems with intermittent flow requirements, such as pumps or pressure vessels, where controlled flow is essential.
Backup systems to prevent contamination or fluid loss if the primary system experiences a failure or is turned off.
Normally closed check valves are ideal for systems requiring strict control over flow initiation and shutoff, ensuring no fluid passes through unless the forward pressure exceeds a certain threshold. This makes them a reliable choice for safety-critical and controlled-flow environments. To better understand which type is more suitable for various applications, let’s compare normally open and normally closed check valves across several factors:
Normally Open: These valves are optimal for applications where continuous, unrestricted flow is necessary, offering minimal resistance to fluid movement.
Normally Closed: Designed for systems where flow should be controlled or limited to specific conditions, ideal for preventing unintentional fluid movement.
Normally Open: Closes only when backflow occurs, making it suitable for situations where reverse flow prevention is occasional or secondary.
Normally Closed: Always prevents backflow until the forward pressure is strong enough to open the valve, ensuring controlled flow.
Normally Open: Suitable for systems with stable pressure and low risk of reverse pressure, as the valve stays open by default.
Normally Closed: Requires sufficient forward pressure to open, offering added safety in systems where backflow or pressure variations are a concern.
Normally Open: Offers minimal pressure loss, enhancing energy efficiency in systems where continuous flow is critical.
Normally Closed: Can introduce some pressure resistance, potentially requiring additional energy to maintain the desired flow rate.
Normally Closed: Offers more reliable prevention of contamination or fluid loss, as it blocks reverse flow by default.
Selecting the appropriate check valve type involves understanding the demands of your specific application. Here are some key considerations to guide you:
For safety-critical systems where controlled flow initiation and prevention of backflow are essential, the normally closed check valve is preferable.
For clean, non-hazardous fluids, a normally open valve may suffice, especially if continuous flow is desired.
For systems with variable pressures or applications that only require intermittent flow, a normally closed check valve provides added control.
Normally Closed Check Valves: Common in applications like pipeline safety systems, compressed air or gas systems, and fluid containment, where the valve needs to stay shut unless conditions require flow.
