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. If you want to learn more, please visit our website LEFLOW. 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.Nozzle check valves
What to consider when choosing your check valves?
Fluid
Flow characteristics
Head loss
Total cost of ownership
Non-slam characteristics
Let's take a look at various types of check valves and discuss how they work, how they're applied and how to select the right type.
Systems that are designed to allow fluid media in only one direction often feature a check valve. Examples of such systems include a sewer line where the waste should only flow in one direction. Check valves are also used where backflow could cause equipment damage.
Before we look at the different check valve types, applications, and selection criteria, let’s first understand how a check valve works.
A check valve, or a non-return valve, is a device that restricts fluid flow to only one direction. Check valves have two ports, an inlet, and an outlet port, designed to prevent fluid backflow in various industrial systems.
There are different check valve types and they differ by the mechanism that causes them to open and close. However, they all rely on a pressure differential to either allow or restrict fluid flow. Unlike the other valves in the market, check valves do not need a lever, a handle, an actuator, or human intervention to work correctly. They are cheap, effective, and easy to deploy.
That said, the check valve will only operate if there’s a pressure differential between the inlet and outlet ports. The minimum pressure differential that the system must exceed for the valve to open is called the ‘cracking pressure.’ The value of this cracking pressure varies from one checking valve to another based on the design and size.
When there’s a back pressure or the cracking pressure is higher than the inlet pressure, the valve will close. The check valve’s closing mechanism varies based on the design, i.e., a ball check valve pushes a ball against the orifice closing it. This closing action can also be assisted either by gravity or a spring.
As stated earlier, there are multiple types of check valves, each designed for their unique applications. However, one type, called the spring loaded in-line check valve, is used in various industrial settings.
The spring-loaded in-line check valve has a spring, a valve body, a disc and a guide. When the inlet pressure is high enough to overcome the cracking pressure and spring force, it pushes the disc, opening the orifice and allowing fluid to flow through the valve.
If backpressure occurs, it pushes the spring and the disc against the hole/orifice, sealing the valve. The short travel distance and the fast-acting spring allow for a quick reaction time during closing. This type of valve can be installed in a horizontal or vertical orientation, in line with the system, hence must be removed entirely for inspection or servicing.
Here are the other types of check valves:
Other types of check valves include the stop check valve, the butterfly/ wafer check valve, the foot valve, and the duckbill check valve.
Check valves find applications in nearly all the industries where fluids have to flow in one direction. These valves are also used in household appliances such as washing machines and dishwashers.
Based on the design and mode of operation, check valves can be used for any of the following use cases:
Some of the factors you need to consider when choosing a check valve include:
The compatibility of the check valve material with the fluid medium.
Check valves are popular devices in the industrial setting that are not only cheap and reliable but also relatively easy to use. When buying a check valve, make sure you understand your unique needs and the check valves’ selection criteria. Similarly, ensure you know the installation requirements to avoid flow direction issues or damaging your system due to pressure build-up.
Charles Kolstad has been working at Tameson since 2017 and is from the United States of America. He has his Mechanical Engineering degree from the University of St. Thomas in Minnesota, USA. He works remotely while traveling throughout Europe, Asia and the Americas. However, he does visit Tameson’s HQ from time to time to meet the new members of the team and to work in the office.
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