Dual plate check valves vs swing check valves are two main types of check valves that are usually compared side by side, but what are the similarities and differences between the two, and how do you decide which is best for you?
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Either of these valves help to prevent a fluid reversal in a pumping system used in the oil and gas industry.
As such, they ensure that the mechanical equipment within these pipes is safe.
But what do these check valves for water do?
Let&#;s take a closer look.
Check valves are automatic valves that open when fluid flows forward but closes when fluid flow reverses backwardly.
These valves do not rely on operators since they perform automatically based on the forward or reverse movement of the fluid.
Similarly, check valves produce a slamming effect as they restrict reverse fluid flow.
Check valves are important for a number of reasons and some of these include:
Generally, slamming effect in valves is caused by a sudden pump stoppage which results in a forward-moving fluid flowing backward rapidly.
As the fluid reverses and comes in contact with the check valve that is trying to close fully, it is blocked by the valve.
The effect is given off as noise in the form of a slam and water hammering.
Researchers have attributed this check valve slam to two processes and these are:
Thus, check valves are either closed rapidly or slowly which has given rise to two basic types of check valves.
These are the dual plate check valves and swing check valves.
Dual plate check valves are more popularly used in certain regions since they have a low slamming effect.
Swing check valves, on the other hand, are an economic type of check valve.
Their closure or disk is mounted on the seat and it usually moves around the hinge.
Also, the closure is opened as a result of water forcing it to swing.
That is to say, the force of water flowing forward will see the swing open of its own accord while backward flow tends to shut it which gives off a high slamming effect.
Slamming effect is evident in check valves and in some more than others.
An instance is the case of the dual plate check valves which has a lower slamming rate in comparison to the swing check valves which is an advantage over the latter.
Dual plate check valves are closed rapidly even before a fluid reversal occurs. The rapid closure is made possible by closing the check valve disk with the help of a spring&#;s force. As a result, the motion of closing the plates is supported by the spring.
Swing check valves, on the other hand, are closed slowly when reverse flow begins using the disk&#;s weight force which is slammed on the seat thereby giving off a high slamming effect. As a consequence, dual plate check valves are more popular than swing check valves.
When a dual plate check valve&#;s total cost is considered, it is considerably lower than that of a swing check valve.
The total cost includes the installation cost, energy cost, and maintenance cost.
An instance of an estimated cost that can be incurred through the use of either the dual plate or swing check valve is given below:
The above shows that a swing valve&#;s total cost can be twice as high as that of a dual check valve.
In the same vein, more energy consumption and pressure drop in a pumping system that uses a swing check valve mean a higher energy cost.
The high maintenance costs can be attributed to the weak connection of the disk of the swing check valve to the body which increases the potential for the disk to break down while it is in use.
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When it comes to a wafer type check valve design, dual check valves can be made to be more compact in comparison to swing valves.
A dual valve also has its disk weight distributed among two parts instead of one which could help in saving space.
A dual check valve comes with several advantages over a swing check valve, but that does not mean it cannot pose its own issues.
That is to say, minimum or lower flow operational risks can occur which could lead to an increase in energy consumption and wear of the valve.
The latter can be attributed to the minimum flow capacity being unable to produce the required pressure as the dual plate check valves are in use.
Here, the minimum flow is regarded as lower than the minimum critical flow that is sufficient to open the valve fully.
Thus, to prevent these problems from occurring, the following considerations should be given:
Operate the dual plate valve at a sufficient flow velocity which will ensure that the disk of the valve is always pushed to be fully opened.
This is because if the valves are not fully opened, more pressure is lost and the energy consumption is increased unlike when the valves were in an opened state.
On the contrary, operating at a minimum flow that is below the critical flow will cause the disk to vibrate which leads to repeated slams that could wear and tear the valve and shaft bearing.
It is better to install the check valve on a horizontal line instead of a vertical line.
For instance, installing the valve vertically with the fluid moving downward will always keep the valve open.
Trying it the other way round by using the same vertical installation but the upward flow will pose a difficulty when the valve is to be opened.
Thus, horizontal installation is the best way to go.
One more way operational risks can be avoided is by reducing the size of the valve which can help the disk to open efficiently.
The same can be said about reducing the spring torque behind the disk.
After taking a closer look at the dual plate check valves vs swing check valves, their pros and cons can easily be pointed out.
While swing valves are known to be economic valves, their high slamming makes them an unpopular choice compared to dual plate check valves.
The latter comes with the benefits of reducing total cost while also allowing fluid flow in the piping system without damaging its mechanical equipment.
Backed with this information, you too can make a choice on which can serve you with the least noise produced while you save on cost that would&#;ve been tied to the check valve&#;s installation, maintenance, and high energy consumption.
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.
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.
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