The slanted seat check valve also offers enhanced resistance to water hammer. The valve has a double eccentric shaft position as well as an increased seating angle. This yields a shorter valve stroke, thus reducing the time taken for the door to close.
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Hydraulic dampers are recommended, especially when the valves are installed on a pumping station where high frequency opening and closing of the valve is required. The valve disc closes quickly over the first 85% of its angular travel before meeting the hydraulic damper. The damper then dissipates the kinetic energy of the disc and forces it to open slightly. The disc closes until it contacts the damper again and this cushions the disc until it returns to its fully closed position, sealing the valve. This function greatly reduces the onset of water hammer due to the damped and controlled method of valve closure.Hydraulic dampers are recommended, especially when the valves are installed on a pumping station where high frequency opening and closing of the valve is required. The valve disc closes quickly over the first 85% of its angular travel before meeting the hydraulic damper. The damper then dissipates the kinetic energy of the disc and forces it to open slightly. The disc closes until it contacts the damper again and this cushions the disc until it returns to its fully closed position, sealing the valve. This function greatly reduces the onset of water hammer due to the damped and controlled method of valve closure.
For more details, please see our slanted seat check valve product information.
Nozzle check valves are designed with the valve disc connected to the stem which is guided on the central horizontal axis. A spring is positioned between the disc and the diffuser sleeve. When flow enters the valve, the hydraulic force exerted onto the front face reacts against the spring, causing the spring to compress and allow the valve to open. When the flow stops, the spring forces the disc to return to the closed position.
Due to the spring-assisted closure and the short linear valve stroke, the nozzle check valve is one of the quickest acting check valves available and is commonly used in pumped systems where water hammer is a potential concern. Because the disc is constantly in the direct line of flow, the head loss characteristics of this valve are higher compared to that of conventional swing check valves.
For more details, please see our nozzle check valve product information.
In order to choose the right check valve for your application, several selection criteria should be considered. First, however, there is not one type of check valves being the best choice for all applications, and the selection criteria may not be equally important for all cases. Some of the things you may need to consider are fluid compatibility, flow characteristics, head loss, non-slam characteristics and total cost of ownership.
All check valves referred to in this article are designed for water and treated wastewater applications, but using the valves for raw wastewater/sewage applications may cause some issues. When selecting a valve for these fluids, you should consider how the presence of solids may potentially affect operation of the valve.
If a check valve closes very fast, it may prevent slamming against upstream equipment such as pumps. However, the rapid closure will not protect against the surges caused by pumps being started and shut down. If the valve opens (and closes) quickly, the flow will change rapidly and thus increase likeliness of surge occurrence.
Head loss is, among other things, a function of fluid velocity. The head loss through a valve is determined by the internal design of the valve and the opening degree. When a valve is designed with a restricted (narrowed) opening compared to the pipeline, the velocity will increase through the valve, increasing the head loss as a result. Vice versa, if a valve is designed with less restriction and bore is equal size to the pipeline, the head loss will be smaller, and the valve will in practice not affect the overall head loss of the system. There are a number of values for head loss, amongst others zeta values, Kv and Kvs values.
The costs for your check valve consist of more than just the purchase price. For some installations, the most important costs may be purchasing and installation, but in other cases, maintenance or energy costs may be equally or even more important. Also protecting more valuable equipment such as e.g. pumps has to be considered, and looking at the valve performance will be crucial. When considering costs as a selection criterion for your check valve, the total costs over the life of the valve should be considered. In general, the simpler the valve construction is, the lower are the maintenance requirements. The higher the Kv value, the lower the energy consumption. The higher the performance, the better the protection ability.
Check valve slam can affect pressure surges in a negative way. First step of the process is when the pump stops, starting the pressure surge. Second step is, when the flow is reversed, slamming against the fully closed check valve. If the check valve closes too fast, the kinetic energy is turned into high pressure, stressing the pipes, and causing high noise.
A slam sounds like if the disc or the ball from the check valve is hitting the seat and can make quite some noise. However, the sound is not caused by the physical closing but by a sound wave arising from a pressure spike stretching the pipe wall.
To prevent the occurrence of check valve slam, the valve should close in a controlled way and slower when near closed position. For a check valve to close slowly, it requires additional ancillary equipment, such as hydraulic dampers, which act as a cushion to the valve door, as it comes into its seated position. This slower closure allows the fluid to pass through the check valve until it closes, causing less kinetic energy turning into high pressure, and thus less energy to feed and maintain the surge. Consideration must be given to the upstream pump to ensure that it is suitable for reverse spin and flow.
As swing check valves have the disc in the flow stream, helping with rapid closure, they have better non-slam characteristics. However, today many pumps are frequency converted, enabling them to adjust the start-up and closure time to avoid water hammer.
To maintain the efficient operation and safety of your piping system, it is very important to select the appropriate check valve types. For stopping backflows and protecting water hammer, check valves play a central role in this aspect. Different types of check valves exist, each designed for different flow conditions and performance requirements, which make it difficult for one to choose the best check valve for their particular project. To find the right type for you, we have put together a comparison of various check valve types with application examples in this article that will surely guide you through the entire process.
To select the appropriate valve for your system, understanding various check valve types and their specific applications is paramount. Differentiates in features and advantages among them have made each type appropriate in particular circumstances. The following sections will discuss five common types of check valves and their typical uses. By doing so, you will be able to decide which valve types are most suitable for your project&#;s requirements.
The purpose of Lift check valves is to allow fluid flow in one direction by raising a disk from the valve seat. When the flow stops or is reversed, the disc drops back onto the seat which prevents backflowing. These valves are usually found in systems that have high fluid pressures and relatively clean fluids. Being available in sizes that range from 1/2 inch to 8 inches, lift check valves can be used for different pipeline dimensions. They can effectively handle moderate to high flow rates, thereby guaranteeing their operation will remain uninterruptible under significant flow pressures.
Lift check valves are known for their excellent performance in high-pressure applications. Their gravity-assisted closure mechanism ensures reliable sealing thus making system integrity impeccable. They also require little maintenance thus reducing operational costs over time. However, they may not work with suspended particle fluids as debris may hinder proper seating of the disk. Furthermore, high cracking pressure required to operate them makes them unsuitable for low-pressure differential systems.
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The oil and gas industry widely utilizes lift check valves due to presence of pressurized atmosphere in these sectors. Chemical processing plants also use them as well as those having high pressure steam and water networks since they help achieve safe and efficient flow of fluids in such demanding environments.
Swing check valves make use of a valve disc that swings on a hinge or trunnion to either permit or obstruct the flow of fluid. These are suitable for systems with low flow rates and low pressure drops. Swing check valves are available in sizes ranging from 2 inches to 30 inches and can accommodate a wide range of pipeline diameters, making them suitable for various applications. They are especially effective in situations where the flow rate is low to moderate and the cracking pressure is typically low permitting operation under minimal pressure differentials.
Among the most important benefits of swing check valves is their simple design. Their uncomplicated design ensures that they are easily operated and maintained thus contributing to long-term reliability of system operations. The swing check valve is also recommended for larger diameter pipelines and has a low-pressure drop across the valve that improves overall system efficiency. Nonetheless, it suffers from water hammers in high velocity systems. Also, slower response to reverse flow compared to other types.
In water and wastewater treatment plants, swing check valves are widely utilized because they help maintain flow direction. Furthermore, these instruments are used extensively in pumping stations and boiler systems which form critical components in an infrastructure that functions reliably.
Dual plate check valves are also referred to as wafer check valves because they have two discs that open and close according to the direction of flow. These valves are small in size and lightweight, which makes them perfect for restricted spaces. Dual plate check valves can be found in different sizes ranging from 2 inches up to 24 inches, with a capacity to operate at varying flow rates balancing between lift and swing check valves as far as cracking pressure is concerned.
The compactness and light weight of dual plate check valves help save space in systems with limited installation area. They have low pressure drop, reducing energy consumption and enhancing flow efficiency. Moreover, these kinds of check valves accommodate various ones including gases; liquids; steam etc. Nevertheless, their maintenance requirements may be more than those for other designs or not ideal for high particle content fluids.
Dual-plate check valves are commonly found in HVAC systems, chemical processing and maritime applications where efficiency of space utilization and reliability are important.
Non-slam check valves are designed in such a way that they close smoothly and quietly. For such valves, there is normally the use of a spring mechanism to assist in closure whereby this facilitates prompt response to reverse flow. They have sizes from 1/2 inch all the way up to 24 inches and can effectively handle both low and high flow rates. Most non-slam check valves have relatively low to moderate cracking pressure that allows them to respond quickly to changes in direction of flow.
Among other things, these types of valves minimize or eliminate water hammer which usually causes massive damage to pipelines as well as associated equipment. Moreover, their suitability for delicate operations is further improved by their quietness and quick response to change in flow direction. However, because of more complicated design involved in non-slam check valves compared with simpler counterparts, more maintenance is required while initial cost might be higher.
Non-slam check valves are ideal for pumping stations, high-rise building water systems, and other applications where hydraulic shock could disrupt operations or damage equipment.
The disc of tilting disk check valves can tilt such that it allows flow in one direction and returns to its original position when the pressure is removed. It has a design that gives low pressure drops as well as being able to handle flow rates and pressures that vary. These types of valves are available in sizes ranging from 2 to 30 inches, making them suitable for a wide range of applications. They have very low cracking pressure which makes them ideal for low-pressure systems, ensuring smooth and efficient operation.
One of the main advantages of tilting-disc check valves is their versatility. In addition, they can be used to handle different flow conditions and have been engineered with durability in mind requiring minimal upkeep. For this reason, their users are guaranteed reduced costs because &#; as a result &#; system efficiency is better enhanced by the low pressure drop across these devices. Nevertheless, compared to swing check, tilting disc checks cost more and may need to be installed correctly so as to operate effectively.
Water distribution systems, industrial processes and power production use tilting disc check valve extensively due to their reliability in these disparate applications.
Make an informed decision regarding the check valve types that best suit your project by understanding these different types of check valves and their specific applications.
When choosing the right check valve for your system, there are several factors that need to be considered to get the best results. Here are the primary factors to keep in mind:
Thus, taking into consideration these factors, you will be able to choose the right check valve for your system and achieve the desired performance.
Among the types of check valves mentioned in this article were lift, swing, dual plate, non-slam and tilting-disc types that were described by focussing on their key features and applications. Some important factors to consider when selecting a check valve such as flow conditions, material compatibility, cracking pressure, size and maintenance requirements are discussed in the above context. We believe that with the help of this guide you will be able get the right check valve for your business.
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