The primary purpose of check valves is to permit flow in one direction while prohibiting or stopping the flow in the opposite direction. The key point is that the normal resting state of a check valve is the closed position.
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When flow is reversed in a pipe, this can cause hydraulic shock waves to pass through (also known as water hammer). This can cause severe damage to equipment in the pipeline if measurements are not taken to prevent this. The introduction of the correct check valve, in a fully closed position during reverse flow can prevent this from occurring and causing severe issues at the site.
Valves that prevent water hammer and close rapidly without slamming are called non-slam check valves.
Axial check valves are specifically designed for fast-reversing systems where backflow is a constant concern. It is categorized as a non-slam check valve as the valve closes without slamming meaning no excess pressure spikes are created. Most axial flow check valves are spring-loaded, with a single low-mass disc, which facilitates a fast, dynamic response to reduction in flow. Due to having a single disc and spring when the disc is opening, the force is balanced resulting in an even flow.
When pressure differential between the upstream and downstream side of the valve exceeds cracking pressure of the spring, the obturator will move and allow flow. The flow area of the valve decreases steadily down to the seat diameter; this is the venturi design.
As a result of the venturi design, the reduced flow area increases the kinetic pressure and reduces the static pressure allowing the valve to fully open quickly. The spring is selected so that the disc is fully opened and stable against its backstop under normal flow conditions.
When a noticeable reduction in flow occurs, the spring reacts early against the force of the reducing flow.
Simple conventional swing check valves tend to have a very poor response. Under dynamic conditions, relatively long response times are experienced. This yields high reverse velocities resulting in slam and unwanted pressure surges.
Dual plate spring-assisted valves versus conventional swing checks are designed with small plates, which have less inertia than a single thicker disc. Pre-loading with a spring provides a closing force at all angles, thus helping to reduce response time.
As mentioned, axial flow check valves have an excellent response and are recommended where a high-level performance is essential. As flow decelerates in the pipeline, the forces acting on the disc are reduced, and the spring is able to overcome these smaller forces causing the valve to close. Short displacement of the disc combined with axial spring assistance greatly reduces the response time giving a fast slam-free response with minimal reverse.
Axial flow valves:
The base valve design is available in various body configurations to suit the customers&#; needs for industry standards, specification, weight and connection requirements. The majority of axial flow check valves will be sold as flanged.
The list below summarizes the most important standards for axial flow check valves:
Although axial flow check valves can be utilized in a multitude of applications, a growing number of niche sectors the valves have primarily been utilized in the following:
Oil and gas production, including midstream:
Chemical and pharma:
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Petroleum refining and petrochemicals:
Power:
The most important thing to remember is that axial flow check valves are specifically designed for fast-reversing systems where backflow is a constant concern.
Ian Noble is the Global Business Line manager for the Crane range of Engineered Check valves, working within the Crane Process Flow Technologies (CPFT) business segment. Crane Process Flow Technologies segment is a global provider of highly engineered products and systems, serving chemical, petrochemical, pharmaceutical, water and wastewater and general industrial market among others.
John McIlroy has worked in manufacturing for more than 30 years, including 15 in the valve industry. He has had roles in check valve technical sales, applications engineering and manufacturing. McIlroy&#;s current role of application specialist for Crane Engineered Check Valves has a wide scope from direct customer support, resolving immediate system issues where the correct check valve can be a solution, to technical presentations around the application of check valves within industries like oil and gas, petrochemical, hydrogen production, LNG and renewable energy.
While presenting in a recent VMA Valve Basics 101 Course in Houston, I found myself in a familiar role: explaining solenoid valves (SOVs) to attendees. (I work with solenoids so much that one VMA member at that conference joked that I needed to be wearing an I Heart Solenoids t-shirt). During the hands-on &#;petting zoo&#; portion of the program, which involves smaller groups of attendees, one of the most frequently asked questions I get from people came up: What&#;s the difference between direct-acting and pilot-operated SOVs, and how do we make a choice?
When the pressure inside equipment such as boilers or pressure vessels increases beyond a specified value, the excess pressure may result in a catastrophic failure.
Facilities use many different types of valves to keep themselves operating, and each valve within a plant serves a different function.
Check valves play a critical role in preventing backflow and protecting sensitive equipment, pipes, pumps, and compressors. However, check valves can&#;t function at their best if they aren&#;t installed properly. Mistakes in installation can manifest in valve leakage or failure, compromising the integrity of the entire piping system.
Swing check valves, double-door check valve, or silent spring-assisted axial flow check valves, all control flow through a slightly different mechanism. Swing valves use a disc that swings in and out of the fluid stream while double-door valves use springs to close two &#;doors&#; to stop the flow. Spring-assisted axial flow valves use a disc and stem design and incorporate compression springs to close the valve before the fluid flow has reversed its flow direction. This is important because the quick closing nature of the axial flow design drastically reduces the possibility for water hammer&#;a dangerous malfunction where sudden pump shut down or an abruptly closing valve produces a hydraulic shock wave in the piping. In this guide, we&#;ll discuss ways to prevent water hammer and other common check valve problems.
Industry insiders call check valves the &#;misunderstood valves.&#; Many professionals simply don&#;t know when or how to use check valves appropriately, so they think that the entire category is unnecessary or ineffective.
So when is a check valve necessary? Typically, we recommend a check valve when there is the potential for the media being transported in the pipe to backflow, which can damage the system. Condensate pooling can also lead to water hammer. Installing check valves in condensate recovery lines prevents serious malfunction by automatically preventing backflow. In this way, the right check valve not only prevents serious problems like water hammer but also safeguards the entire process as well as the equipment installed in the piping.
To experience the full benefits of a check valve, it&#;s critical to adhere to installation best practices. A simple mistake in fitting the valve can reduce efficiency at best or cause substantial damage at worst. Some key points to keep in mind include:
Preventing check valve malfunctions like hammer pipe is critical to avoiding serious, costly damage to your pipes, valves or other expensive equipment. At DFT, we never want our clients to experience preventable system failure, which is why we&#;re sharing our expertise: in addition to this guide, we&#;ve put together a comprehensive webinar that expands on proper check valve installation and maintenance, providing expert guidance on piping design that works and lasts.
For specific questions about check valve selection for your application, contact our team. Whether you&#;re looking for a standard stock valve or a completely custom order, we&#;ll work with you to make sure you receive a functional, effective, and safe solution to your piping challenges.
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