Check Valve Leaks Inspect, Avoid, and How to Fix

Check valves are often labeled as "zero leakage" valves, but this may not always be the case. Some common and simple problems can cause a check valve to leak, causing system inefficiency, performance issues, and damage. Prompt identification and resolution of check valve leaks is therefore critical to maintaining system efficiency and integrity.

 

Check valves are often labeled as "zero leakage" valves, but this may not always be the case. Some common and simple problems can cause a check valve to leak, causing system inefficiency, performance issues, and damage. Prompt identification and resolution of check valve leaks is therefore critical to maintaining system efficiency and integrity.

 

Table of contents

• What is a check valve
• Inspect a check valve
• How to avoid check valve leakage
• How to fix a leaking check valve
• Key Takeaway

What is a check valve

A check valve, also known as a non-return valve or one-way valve, is a device that allows fluid or gas to flow through it in only one direction. This valve operates automatically without the need for an operator. The concept that explains this is cracking pressure. Every check valve has a minimum upstream pressure requirement for the valve to open and allow media to flow past it. The check valve closes when the upstream pressure drops below the cracking pressure, preventing downstream media from flowing backward. Check valves can be specified for a specific cracking pressure. Read our check valve overview article to learn more about how these valves work.

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Check Valve

Inspect a check valve

Things to Check Beforehand

Preventing check valve leaks can be achieved by checking certain items beforehand. Here are some key points that buyers must check before purchasing industrial check valves to avoid leaks.

Check valves are classified as non-return valves or one-way valves, primarily used to prevent the reverse flow of fluid in a system. Not all systems require the same type of check valve - there are several valves classified based on their type, function, leak tolerance, and working pressure limits. Check these points before selecting the right type of check valve for your system.

Types of Check Valves:

Check Valves come in various types, including swing check valves, lift check valves, tilting check valve, ball check valve and non-slam check valves, each suitable for different applications based on their design and mechanism.

Here are some of the common types of check valves and their functions.

Swing Check Valve: This type of valve has a hinged disc that swings open when the flow of fluid is in the correct direction, allowing the fluid to pass through. It closes automatically to prevent backflow when the flow direction reverses.

Ball Check Valve: In a ball check valve, a ball sits inside the valve body and moves up and down to control the flow of fluid. When the flow is in the correct direction, the ball is pushed up, allowing the fluid to pass. When the flow reverses, the ball falls back into place, blocking the flow.

Tilting Check Valve: A tilting check valve is designed to allow fluid to flow in only one direction while preventing backflow. It accomplishes this by using a hinged disc that swings or tilts to block the flow when it reverses. This type of valve helps maintain pressure, reduces the effects of water hammer, minimizes noise, and is easy to maintain, making it an essential component in fluid systems where backflow prevention is critical.

Lift Check Valve: Lift check valves have a disc or piston-like element that lifts up from the seat to allow flow in one direction. When the flow reverses, the disc or piston is forced back onto the seat, preventing backflow.

Non-slam check valves: Their primary function is to allow flow in one direction while preventing backflow, thereby ensuring the unidirectional flow of fluids. These valves are designed to open and close swiftly, minimizing the risk of water hammer or pressure surges in the pipeline. They are widely used in various industries to protect pumps, pipelines, and other equipment from damage caused by reverse flow.

Leakage Tolerance

According to ANSI standards, there are six different levels of leakage for check valves, each representing a specific range of allowable leakage. These levels, marked as Grade I to Grade VI, have their own valve manufacturing standards and settings. Here is a basic overview of these check valve leakage levels:

Class II - The maximum allowable leakage is 0.5% of the rated capacity. This capacity is determined by pressurizing the valve inlet while leaving the outlet open.

Class III - The maximum allowable leakage is 0.1% of the rated capacity. This capacity is determined by pressurizing the valve inlet while leaving the outlet open.

Class IV - The maximum allowable leakage is 0.01% of the rated capacity. This capacity is determined by pressurizing the valve inlet while leaving the outlet open.

Class V - The maximum allowable leakage is 0.005 ml per minute of water per inch. This capacity is determined by pressurizing the valve inlet after filling the entire body of the valve, connecting the pipe with water, and keeping the valve plug closed.

Operating Pressure Limit

Industrial check valves are characterized by their lack of need for levers or external control functions such as automation. These valves operate based on the pressure differential across their length and the velocity of the fluid. There are many different standards that regulate the working pressure limits of valves.

The opening pressure in a valve is the pressure at which static failure and flow begin. For check valves, the opening pressure can range from 1 to 5 psi. Manufacturers produce check valves with different opening pressure levels based on specific requirements.

 

After obvious symptoms of leakage

If a check valve shows obvious signs of leakage, inspecting the valve is the fastest way to determine the source of the leak. Therefore, if a check valve is suspected of leaking, checking the valve should be the first priority. Before checking a check valve, refer to the manufacturer's product guide to determine if specific steps need to be taken. The following procedure is a general method and may not apply to all check valve models.

Safety: Perform a visual inspection (see below) and then depressurize the system before further inspection. Wear personal protective equipment (PPE) such as gloves, safety glasses, and a hard hat if necessary. Visual inspection: Look for signs of leakage around the valve body and pipe connections, such as dampness, corrosion, and rust. For areas that are difficult to see, be sure to have a flashlight and inspection mirror ready. Touch inspection: Touch around the valve body and pipe connections with a clean, dry cloth. If the cloth becomes wet, the valve may be leaking. Sound inspection: If possible, listen to the operation of the check valve in a quiet place. A properly functioning check valve should not make any sound. Gurgling or hissing noises may indicate a leak. Soap solution test: If gas passes through the check valve, for example, if an air compressor check valve may be leaking, use a soap solution test. Apply a soap solution to the valve body and pipe connections. If bubbles form in the solution, it indicates a gas leak.

 

How to avoid check valve leakage

There are several methods to avoid check valve leakage or minimize the risk.

1. Correct selection: Choose the right check valve for the application. This means considering factors like valve material compatibility with the media, pressure and temperature ratings, and flow requirements of the application. Refer to our chemical compatibility guide for help in selecting the valve material.
2. Regular maintenance and inspection: Identifying issues through regular maintenance and inspection can prevent them from escalating into leaks.
3. Proper installation: Improper installation of check valves can lead to leaks. Correct installation includes ensuring the valve is aligned correctly with the pipeline and in the right orientation (horizontal or vertical), and that the system flow direction matches the arrow on the valve body. Refer to our check valve installation guide for more information on the installation process.
4. Replacement of worn parts: The valve seat and disc of check valves may wear out over time. Replace them as needed.
5. Avoiding excessive pressure: Check valves may leak if subjected to pressures higher than their rating.
6. Cleaning and debris removal: Debris trapped in the valve can damage its sealing surfaces, leading to leaks. Clean the valve and ensure there are no fragments passing through the valve.

 

How to fix a leaking check valve

Deciding whether to attempt repairing a leaking check valve depends on the severity of the issue and the convenience versus cost. If the valve body is damaged, such as severe rusting or corrosion, then replacing the valve is necessary. However, if only internal components are found to be damaged or worn, then replacing those parts instead of the entire valve is possible. However, for relatively inexpensive valves (e.g., those primarily made of PVC), replacing individual parts might be more trouble than it's worth. More expensive check valves, such as stainless steel check valves or very large check valves, might incur high replacement costs, making it more necessary to replace individual parts.

After reviewing the specific instructions in the check valve product guide, follow these steps to replace the check valve components of a leaking check valve.

1. Equip yourself with appropriate personal protective equipment to avoid injury or contact with hazardous substances.
2. Disassemble the valve to access its internal components.
3. Inspect the check valve's disc, seat, spring, and any other internal components. Look for signs of wear, damage, or fragments that could be causing the leak.
4. Determine the cause of the check valve leak. Is the issue with internal components, such as worn seals or a damaged disc? Or is the problem more severe, such as damage or deformation to the valve body?
5. Replace any worn or damaged internal components. Take the opportunity to replace O-rings even if they appear to be in good condition.
6. Thoroughly clean all non-replaced internal components. Also, clean the inside of the valve body.
7. Reassemble and reinstall the valve.
8. Test the valve by gradually introducing pressure into the system. If the repair is successful, there should be no more leaks. If leaks persist, it may be necessary to replace the entire valve.

 

Key Takeaway

Check valves are among the most commonly used valves in many industries. These one-way valves only allow fluid to flow in one direction and prevent backflow. They do not require any external control to regulate their movement—they are self-actuating valves.

Check valve leaks often occur for various reasons. These can be avoided with proper valve maintenance. Select the right check valve, install it correctly, and perform regular maintenance and inspections to ensure industrial check valves operate without issues.