Types of Check Valves and Their Applications
The purpose of check valves is to prevent backflow within a piping system. Check valves are unidirectional valves that provide unobstructed flow in one direction as long as flow pressure remains constant and protect the piping system against reverse flow. The three main types of check valves we offer are ball, piston, and stop check valves.
Piston Check Valves
Also part of the lift check valve family, piston check valves incorporate a weighted piston (or disc) to prevent backflow. These function in a manner similar to ball check valves, allowing for flow as long as flow pressure remains steady, but applying gravitational closure when flow pressure decreases to a point where it no longer has the force to lift the valve.
The valve bore maintains and guides piston alignment throughout its travel. Depending on flow conditions, piston check valves sometimes include spring assistance to aid in closure. Common cases employing piston check valves include:
- Feed water control in the nuclear industry
- Dump lines
- Make-up water
- Miscellaneous process systems
- N2 systems
- Monitoring and sampling systems
Ball Check Valves
Ball check valves are lift check valves, and use a weighted ball rather than a disc to allow flow and inhibit backflow. Once the cracking pressure is attained, the ball lifts up from its seat, allowing flow to occur. When there is a reduction of flow pressure, it falls back into place to prevent backflow.
Applications of ball check valves include instances where high-pressure and high-velocity flows are critical and backflow may damage upstream components (Applications similar to piston check valves, but more suited to those for more viscous media).
Stop Check Valves
Stop check valves combine the benefits of lift check valves with the positive closure functionality of globe valves. These features allow for the control of flow regardless of direction. The main purpose of stop check valves is to prevent damage to pump or boiler systems upstream of the valve in the piping system. Common case applications of stop check valves include:
- Heat recovery steam
- High-temperature service
- Geothermal service
- High-pressure safety service
- Safety systems
- Shutdown cooling
- Petroleum production and refining
- Hydrocarbon processing
Check Valve FAQ
What are some advantages/disadvantages of check valves?
The primary advantage of a check valve is they prevent reverse flow while typically requiring no external actuation. They also provide a fast-acting solution to preventing backflow. Some disadvantages include the inability to determine the condition of the valve and its status, limitation(s) on its installation configurations, and the possibility of sticking in the open position (not often a problem associated with ball and piston types).
How do you choose the right check valve?
There are several factors to consider when deciding on a check valve for your needs:
- Material Selection: Material used for valve construction must stand up to piping system and media demands associated with the specific type of gas or liquid flowing through the piping system.
- Performance Requirements: Performance considerations include the capability of the valve to handle various temperature and pressure instances.
- Type and Size: Selection of the right check valve includes control considerations, typically related to increased safety in hazardous applications as well as sizing the valve to properly accommodate the piping system’s flow conditions.
- Maintenance: In addition to considering the frequency of maintenance or replacement, operators must also think about the valve’s resistance to clogging, jamming, or otherwise malfunctioning.
- Special Requirements: Check valve selection also includes several special requirements unique to their function, including response time, cracking pressure, normally closed vs. normally open, vertical vs. horizontal mounting, flow direction (upward or downward) and fluid density.
How do you prevent check valves from failing?
One of the disadvantages of check valves is the difficulty of determining the condition of the enclosed valve. Consequently, there are certain measures necessary for recognizing their failure and preventing it. Several indicators that signal failure or potential failure include valve vibration (chattering), measured reverse flow, excessive component wear, audible indications of leakage (water hammer), and leaking. You can prevent failure by:
- Proper sizing
- Routine inspections for cleanliness
- Proper installation
- Replacing valves as needed
Check valves play an important role in controlling flow within high-performance piping systems. Selecting the right check valve provides greater piping system efficiency and improves operational safety.
Conval is a leading global provider of check valves specifically designed to meet the unique needs of our customers. Contact us to learn more about the solutions we offer or request a quote to get started on your next project.