News/Blog
News/Blog
01, 1970
A check valve, also known as a non-return or one-way valve, are one-way valves installed in pipeline systems to prevent backflow. The check valve allows fluid to flow freely in one direction, but if the flow reverses, the valve will automatically close to protect pipes, pumps and other equipment. The direction in which the fluid or gas can flow freely is called the "free flow direction," while the direction where flow is blocked is referred to as the "checked" or "non-return" direction. Check valves are commonly found in everyday household items. For instance, when inflating a raft or air mattress, a check valve allows air to enter while preventing it from escaping until the release mechanism is activated. They are also used in irrigation systems, where they enable water to flow out of sprinkler heads and stop mud and rainwater from flowing back into the pipes connected to the water supply.
The function of a check valve in a given application plays a crucial role in determining its design parameters. Generally, check valve functions can be classified into three categories: non-return, vent, and fill and drain. Choosing the appropriate check valve ensures proper system operation and efficiency.
Non-return check valves allow fluid to flow in one direction with minimal pressure loss while preventing reverse flow. A common application for these valves is in pump inlet and outlet ports. A check valve at the pump inlet allows fluid to flow from the desired source, while another at the outlet ensures the pump can dispense the fluid effectively.
Vent check valves are designed to open and relieve pressure buildup in a system, while preventing flow in the reverse (non-return) direction. A prime example is their use in vehicle fuel tanks, where gasoline volume fluctuates as the temperature changes. When the gasoline expands, air needs to vent from the tank to prevent pressure buildup. The check valve allows this release of air while blocking debris and moisture from entering the tank, thus protecting the system from damage.
Fill and drain check valves enable fluid to flow into a system while preventing fluid from escaping once the system is filled. These valves are typically found near the tanks of hydraulic or pneumatic systems. In cases where maintenance is needed or when the system is decommissioned, safety protocols may require the system to be depressurized. In such situations, check valves can be manually, mechanically, or pilot-operated to safely drain the system fluid.
A check valve is a direct-acting device, meaning that pressure directly influences its internal components. Typically, check valves are designed to be normally closed. They are often held shut by a force-producing mechanism inside the valve, which is minimal but sufficient to return the valve to its closed position when there is no longer a pressure differential in the flow direction. In some configurations, check valves lack a force-producing mechanism and instead rely on a pressure differential in both directions to move their internal components. When a pressure differential occurs in the flow direction, the valve opens, allowing fluid to flow freely from one location to another within the system. Once the pressure is removed, the valve returns to its normally closed position.
Check valves come in a variety of configurations, each suited for different applications. Standard configurations typically feature a ball bearing, poppet, disc, or another type of seal that is pressed against a seat when pressure is applied in the checked direction. Often, a lightly compressed spring biases the seal into position, creating an internal seal that prevents flow in the reverse direction.
There are various internal flow path designs in spring-loaded check valves. For instance, fluid may flow axially between the ball or poppet and the valve housing, or it may pass through internal passages within the poppet and down through the center of the valve. Some configurations allow flow to exit at a 90-degree angle relative to the valve inlet.
In low-pressure applications, check valves may use flexible materials, such as diaphragms or duckbill configurations, to regulate flow based on pressure conditions. In high-flow hydraulic applications, butterfly and swing check valves are commonly used. These valves feature large, flat metal doors attached to the housing, which open with flow in one direction and close when the flow reverses.
Like a backflow preventer, a check valve stops media from flowing through it in the reverse direction. Check valves, however, do not offer the degree of protection that backflow preventers do and therefore are not suitable for protecting drinking water sources.
