Check valves, which allow fluid to flow in one direction but prevent it from flowing in the other, are available in a wide range of styles. The variety most appropriate for your project will depend on the application at hand and the specific properties it requires in a valve.
In this article, we’ll discuss two of the most common varieties of check valves, non-slam check valves and swing check valves, while comparing their unique uses and benefits.
Key Differences Between Non-Slam and Swing Check Valves
Some styles of check valves are specifically designed to allow their disc, or flapper, to slam shut in certain conditions, such as the reversal of fluid flow. This sudden shutting, or slamming, creates a wave of pressure in the liquid that reverberates throughout the system and, depending on the precise application, can ultimately lead to reduced process efficiency, valve damage, gasketed joint leaks and other issues. This inevitable — but controllable — phenomenon is commonly referred to as water hammer.
Non-Slam Check Valves vs.Swing Check Valves
Non-slam check valves are designed specifically for use in these situations. As their name implies, these valves close without slamming, meaning no excess pressure spikes are created. The disc of a non-slam check valve has an internal spring opposing the opening fluid flow pressure. When the flow of a media is strong enough, the spring compresses and the valve opens; the disc is smoothly pushed back toward the seating surface in the valve by the spring as the flow decreases and stops, but before flow direction reverses.
Often called flapper style check valves, swing check valves are a more traditional variety. The disc of a swing check valve is secured to the body of the valve by a trunnion and hinge arm, without the aid of a spring. Unlike a non-slam check valve, which opens and closes at rates comparable to the pressure of the fluid flow, a swing check valve opens and closes more suddenly, relying on the installation orientation, gravity, and reversing flow to close the valve.
Application
Both non-slam check valves and swing check valves are suitable for use in a wide range of applications. Generally,though, non-slam check valves are ideal for vertical runs of piping, or complex applications that require constant and controllable pressure levels. Alternatively, swing valves are often used in very large-volume applications,horizontal pipe runs, and those applications in which varying pressures and flow rates are not a concern.
Due to the precise pressures required, non-slam check valves are commonly specified in various oil and gas,refining, and power industry processes.
These valves can be found in the following applications:
• Gas and liquid pipelines • Water and steam systems
• Cooling towers • Water treatment
• Cryogenic applications • Gas export facilities
• Product tank farms • Gas storage caverns
• Mine dewatering
Non-slam check valves are also used in similar applications throughout the chemical processing industry, steam condensate systems, and in the power generation industry.
Swing check Valves,because of their less controlled opening and closing mechanics, are used in less sensitive applications. They are most commonly employed in large-scale pipeline applications, such as liquid, gas, and steam, generally only in horizontal configurations. In particular, they’re often used in natural gas applications, as natural gas processing generally does not require as stringent pressure control as the oil and refining industry or in sewage and water treatment systems.
Pros and Cons of Non-Slam and Swing Check Valves
Depending on the application, both non-slam check valves and swing check valves present unique advantages and disadvantages.
Though both non-slam check valves and swing check valves offer versatility in today’s varied industrial landscape,non-slam check valves are increasingly supplanting standard swing valves in many situations.
This is largely due to the commonality of the water hammer phenomenon, which may arise to some degree in any liquid control system. As these systems become more complex and rely on increased process automation, water hammer becomes a more serious issue. Non-slam check valves are proven to be very effective at mitigating this risk.
