The Ham-Let H400 series check valve is a fixed cracking pressure check valve for general purpose use. The loaded poppet controls fluid flow when differential pressure between inlet and outlet is higher than the set pressure of the spring. The valve body is made of stainless steel 316 for strength and greater ease in welding than stainless steel 304. The lower carbon content of the material minimizes harmful carbide precipitation due to welding, ensuring corrosion resistance. It has female NPT threads for connecting to male threaded pipes, creating a tighter seal than straight threads. The cracking pressure is 0.33 pounds per square inch (psi), and the maximum pressure rating is 3000 psi.

Check valves have two ports and restrict the flow of fluids and other loose materials through a pipe or passageway to one direction. Flow enters through one port and exits through the other, closing when flow reverses or stops. Two common types of check valves are ball cone valves and swing check valves. A ball cone valve utilizes a spring-loaded ball seated against a cone-shaped interior surface to stop the flow of fluid in a forward direction, and a swing check valve has a movable disc on a hinge to block reverse flow. Check valves are rated by their cracking pressure (the minimum upstream pressure required for the valve to operate), and they are used in various water, gas, air, and steam lines.

Ham-Let manufactures instrumentation valves, pipe, and tube fittings. The company, founded in 1950, meets International Organization for Standardization (ISO) standard 9001.