A check valve is a type of valve that allows fluids to flow in one direction but closes automatically to prevent flow in the opposite direction (backflow). Check valves are used in a wide variety of locations, but the focus of the discussion in this tutorial will be the installation of check valves at the steam trap outlet side.

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Questions are often asked about the need and purpose of check valves, such as:

• Is it always necessary to install a check valve downstream of a steam trap?
• Does installation of a check valve prevent water hammer?

Let’s discuss these two points.

Is it always necessary to install a check valve downstream of a steam trap?

Check valves are necessary if there is a risk of condensate backflow. For example, when a trap discharges into a common condensate collection line, there is the potential risk of backflow from condensate discharged from other traps, so as a rule a check valve should be installed. Preventing this backflow is important because it can not only diminish process heating efficiency, but can also damage steam traps. In contrast, when there is a single downward sloping pipe that is not submerged at any point, there is almost no possibility of backflow, so a check valve is not necessary.

Single Dedicated Line

If the trap is gravity drained through a downward sloping dedicated line that releases to atmosphere without being submerged at any point, there is usually no risk of backflow, so there is no need to install a check valve.

Note: Depending on piping configuration after the steam trap, back flow can also occur in open lines if equipment goes to vacuum or if there is positive pressure from a too small vent or pipe rise which can cause unwanted return line pressure. In such cases, installing a check valve may help prevent back flow.

Common Collection Line

If the trap outlet piping is connected to a common condensate collection line, condensate discharged from equipment in operation may backflow into equipment that is out of service unless there is a check valve installed at the trap's outlet.

Illustration C: No check valves at trap outlets

If a check valve is installed, even if the trap outlet piping is connected to a common collection line, the condensate discharged from equipment in operation will not backflow into equipment that is out of service.

Illustration D: Traps with check valves

Does installation of a check valve prevent water hammer?

There are various mechanisms that generate water hammer. A principal cause of water hammer in condensate recovery lines is condensate flowing back down in vertical rises. The installation of a check valve at each of these locations is very effective in preventing water hammer due to backflow.

Water hammer caused by condensate backflow in vertical rises of condensate recovery lines

Illustration E: No check valve on vertical risers

If the condensate discharge piping on a pump with intermittent operation (e.g. TLV PowerTrap® series or motorized pump with ON-OFF control) has a long horizontal run followed by a vertical rise, any condensate that falls back down the vertical rise becomes backflow that may collide with newly discharged condensate, resulting in water hammer. Similarly, in situations where a PowerTrap® discharges high temperature condensate, the combination of flash steam and backflow could be another possible cause for water hammer.

In such cases, water hammer may be prevented by installing a check valve at critical locations within the system (e.g. the beginning of a vertical rise).

Illustration F: Check valve on vertical riser

Additional Info

Check valves can also help prevent water hammer caused by a pulsating flow of low temperature condensate in condensate transport piping.

For more information on water hammer, please visit the water hammer tutorial.

Check Valve Restrictions

When high pressure hot condensate is discharged through a steam trap to lower pressure, flash steam is generated. If this flash steam then flows into a return line that contains sub-cooled condensate at a much lower temperature, an instant collapse (condensing) of the flash steam will occur as it gives off its latent heat to the condensate, and water hammer may result. Installation of a check valve is generally not effective in this situation.

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Check valves prevent backflow, but not back pressure. It is not possible to discharge low pressure condensate into a higher pressure line. Even if a check valve is installed after a steam trap, condensate will not flow if the pressure upstream of the trap is lower than the downstream (return) side.

Additionally, it should be noted that if a check valve is installed at the outlet of a trap operating under an extremely large operating differential pressure, the check valve itself becomes a point of resistance (i.e., the check valve has a pressure drop as well), which means that it is necessary to calculate pressure drop very carefully.

Check Valve Installation

Figure 1: Check valve

Check valves are installed in critical locations to prevent backflow. They are commonly used in plumbing systems to prevent fluid backflow and to protect sensitive equipment, compressors, pipes, and pumps. However, these check valves cannot function properly if they are installed incorrectly. Installation errors can lead to valve leakage and failure, compromising the integrity of the entire piping system. This article discusses the check valve’s installation position and process in detail.

Table of contents

Check valve purpose

A check valve lets the media pass through in one direction but prevents its flow in the opposite direction. Installing the right check valve can prevent serious issues like water hammers and safeguard the entire process and equipment installed in piping. One of the most common residential examples of check valve installation is for plumbing. A check valve will allow dirty water or sewage to leave the residence through pipes, but prevent it from coming back up from the main discharge back into the house.

Check valve installation guidelines

It is critical to employ the best practices for check valve installation to reap the full benefits of the valve. Mistakes during installation can reduce the efficiency of the valve or even cause substantial damage to the equipment. Some key factors to check are:

• Selection: Choose the check valve according to the pipe’s size, media compliance, and flow rate. Choosing the wrong valve can result in premature wear and tear and component failure.
• Positioning: Keep an eye on where the check valve is installed within the piping. Always ensure that the valve is approximately five pipe diameters away from tees, elbows, or other valves that can cause turbulence. As discussed in the next section, all check valves may not function in a vertical piping run.
• Orientation: Note the arrow on the check valve that points towards media flow. The arrow indicates the proper positioning of the check valve relative to the pipe’s flow, as seen in Figure 2. The arrow is normally printed on a separate tag or permanently marked on the valve body.
• Pipeline level: Tilting disk and swing check valves have their seating surfaces machined on a 5-degree inclined plane relative to the valve centerline. If the pipeline angle exceeds 5 degrees, the disk may not touch the seat, so the check valve may leak. However, axial flow check valves do not have this problem as they function through an internal spring.

Figure 2: Check valve; The highlighted arrow shows the direction of media flow

Check valve installation in vertical pipe runs

A horizontal pipe is always preferred while installing a check valve as it rules out the effect of gravity. Not all check valve styles are suitable for vertical flow directions. There are several applications within buildings and towers, where several applications like sump pumps and mine dewatering require vertical runs to move the fluid vertically up or down.

Swing (flapper) check valve installation

If a swing check valve is installed on a vertical pipe where the flow is upwards against gravity, the disk may slam against the seat when the flow stops, potentially leading to water hammer. If the flow is downwards as in the case of boiler supply lines and mining applications with limited spacing, the swing check valve will always be open and hence does not deliver its function. Therefore, swing check valves are not preferred in vertical pipe runs and these valves are installed horizontally in most cases.

Spring-assisted check valve installation

Spring-assisted axial-flow silent check valves perform well in vertical piping locations. These valves depend on the spring’s potential energy to close the valve. Therefore, the valve closes independently without waiting for the fluid to force its way back into the piping. The strong spring of an axial flow check valve ensures the valve closes before the reverse flow happens, thereby eliminating the water hammer; hence, axial flow check valves are preferred in vertical pipe runs.

How to install a check valve

Valve size and type

Measure the pipe to which the check valve is to be attached and get a check valve that fits the diameter. Also, select a check valve type according to the application. There are threaded valves, socket valves, and various materials like PVC, brass, and stainless steel used to manufacture the valve.

Check valve and pipe evaluation

Look inside the valve and check for foreign particles within the valve as these particles can obstruct the smooth flow of media through the valve. Check uneven edges, scratches, or anything that could prevent the check valve from sealing properly. For example, in the case of swing valves, move the flapper by pushing it away from the seating surface to ensure it moves freely. Also, ensure that the pipes are clean and free of debris before installing the check valve.

Check valve placement

An arrow on the valve indicates the flow direction; hence, position the valve accordingly on the pipeline (horizontal or vertical). Ensure that the main water supply is turned off during the check valve installation process.

Attaching the check valve

Attach the check valve to the pipeline. Depending on the check valve type, it can be either screwed to the pipe or simply secured together using a wrench until the parts are sturdy and secure.

Testing the check valve

Turn on the main water supply and let the fluid pass through the installed check valve to test its functionality. If the water gets blocked during testing, double-check the direction in which the valve is installed. If the check valve leaks or any other issue comes to the surface, the user can troubleshoot using the tips mentioned in the next section.

Check valve maintenance

Check valves do not require much maintenance, but they can be kept working more effectively by checking them consistently for leaks, rust, debris, and optimum flow.

1. Clean the check valve thoroughly when it is ready for maintenance; The cleaner, the better.
2. Lubricating the check valve surface and rotating it slightly can keep it working optimally for an extended period.
3. Try to abide by the valve manufacturer’s valve maintenance instructions. This is particularly helpful if the manufacturer has special requirements.

How to fix check valves

Check valve leaking

Loose bolts or a damaged gasket can cause a check valve to leak from the surface. Tighten the bolts and check if that solves the problem. If not, replace the gasket on the valve.

If the check valve leaks water in a closed position, it indicates damage inside the valve. In this case, clean the internal parts and check for damage. If there is damage to the flap, spring, or ball (depending on the type of check valve used), try replacing the specific part as needed. If there is damage to the valve body, replace the entire check valve.

Check valve doesn’t open

If the check valve doesn’t open, it may be due to some kind of obstruction within the valve. In this case, uninstall the valve and disassemble the valve to evaluate it. Cleaning the valve thoroughly should clean the debris and allow the water to pass through.

FAQs

Is it necessary to install a check valve?

Yes, a check valve is necessary to prevent backflow at various locations within a piping system.

How to install a check valve?

A check valve can be either screwed to the pipe or simply secured together using a wrench until the parts are sturdy and secure.

Can a check valve be installed horizontally?

Yes, a check valve can be installed in both vertical and horizontal pipe runs. However, swing check valves are preferred only in horizontal pipe runs, whereas spring-assisted check valves can be installed in both pipe configurations.

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