what is a check valve ？
Table of Contents
01 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 (liquid or gas) to flow in only one direction. It typically consists of a movable disc or a ball that is held against a seat by a spring or gravity. When the fluid flows in the intended direction, the disc or ball is pushed open, allowing the fluid to pass through. However, when the fluid tries to flow in the opposite direction, the disc or ball is forced against the seat, preventing the backflow. Check valves are commonly used in various industries and applications to prevent reverse flow, protect pumps and equipment, and maintain system efficiency.
02 Types of check valves
This is the most common type of check valve. It has a hinged disc that swings open and closed to allow fluid to flow in one direction. Swing check valves are simple and inexpensive, but they can be noisy and may not be suitable for high-pressure applications.
Similar to swing check valves, but with a disc that tilts instead of swings. This makes them less likely to slam shut and cause water hammer.
These have a nozzle that creates a jet of fluid that helps to keep the valve open. This makes them ideal for high-flow applications.
Quick-closing silent non-return valve
These close quickly to prevent backflow. They are often used in water systems to prevent contamination.
These have two discs that work together to prevent backflow. They are ideal for high-pressure applications.
These have a flanged connection that makes them easy to install and remove. They are often used in industrial applications.
A type of swing check valve that is designed to be installed between two flanges. They are often used in piping systems.
These have a ball that seals the valve opening. They are ideal for low-pressure applications.
The right check valve for your application will depend on a number of factors, including the type of fluid, the flow rate, the pressure, and the temperature. It is important to consult with a qualified engineer to select the right check valve for your needs.
03 Application of check valves
Flow Media Type |
Velocity Range FPS (m/s) |
Recommended Check Valve |
Remarks |
|---|---|---|---|
|
Water Or Oil |
1 to 6 (0.3 to 2) |
Swing check valve |
For low velocity liquids |
|
Steam, Water, Gas |
7 to 100 (2 to 30) |
Tilting disc check valve |
For higher velocity fluids |
|
Uniform Water Or Oil |
5 to 10 Max (1.5 to 3) |
Axial nozzle check valve |
For uniform liquids with low max velocity |
|
Pulsating Air Or Gas |
5 to 10 Max (1.5 to 3) |
Quick-closing silent non-return valve |
For pulsating gases |
|
Uniform With Normal Reversal Water Or Oil |
7 to 10 (2 to 3) |
Dual plate check valve |
For liquids with normal reversal |
|
Uniform With Severe Reversal Water Or Oil |
7 to 10 (2 to 3) |
Flanged lift check valve |
For liquids with severe reversal |
|
Uniform Or Pulsating Steam, Water, Or Gas |
8 to 160 (2.5 to 50) |
Wafer swing check valve |
For uniform or pulsating steam, water or gas |
|
Uniform Or Pulsating (Severe Revesal) Steam, Water, Or Gas |
10 to 160 (3 to 50) |
Ball check valve |
For fluids with severe reversal |
|
Uniform Steam, Water, Or Gas |
12 to 250 (4 to 75) |
Ball check valve |
For high velocity uniform fluids |
|
Uniform Or Pulsating Steam, Water, Or Gas Or Oil |
20 to 250 (6 to 75) |
Tilting disc check valve |
For high velocity uniform or pulsating fluids |
04 What are check valves used for?
1. Protecting Equipment:
- Pumps: Installed on the outlet side of pumps, check valves prevent backflow when the pump stops, protecting it from damage and ensuring proper operation upon restart.
- Heat Exchangers: Placed in circuits, check valves direct the flow through the exchanger in the intended direction, maximizing heat transfer efficiency and preventing cold and hot fluids from mixing.
2. Preventing Backflow Contamination:
- Plumbing Systems: Check valves in water supply lines prevent contaminated water from entering clean water sources, ensuring safe drinking water and preventing cross-contamination.
- Sewage Systems: Installed in drainage systems, check valves stop sewage from backing up into buildings or flowing in the wrong direction, preventing health hazards and property damage.
3. Maintaining Pressure:
- Air Conditioning Systems: Check valves in condensate drainage lines prevent the backflow of condensate, ensuring proper drainage and maintaining efficient operation of the AC unit.
- Hydraulic Systems: Used in pressurized lines, check valves maintain pressure by preventing fluid from flowing back to the reservoir, ensuring proper functioning of hydraulic machinery.
4. Other Applications:
- Fuel Systems: Check valves in fuel lines prevent fuel from siphoning back from the engine, ensuring proper fuel delivery and preventing engine problems.
- Chemical Processing Plants: Used in various pipelines, check valves ensure the proper flow of chemicals, preventing mixing of incompatible substances and maintaining process integrity.
The specific uses of check valves are diverse, but their core function of directing flow in one direction and preventing backflow remains constant across various applications.
05 How do check valves work?
To understand how a check valve works, it helps to first look at their anatomy. Check valves have four main parts: the body, seat, disc, and cover, as shown in the diagram.
Understanding How Check Valves Work
Swing
Swing check valves utilize a disc that swings open when fluid flows through the valve. The disc is unconstrained and moves freely based on the pressure and flow rate. When the forward pressure decreases, the disc swings back to the closed position and prevents backflow. Swing check valves come in a variety of sizes and configurations to accommodate different pipe diameters, pressure ratings, and flow parameters.
Lift
Lift check valves employ a guided disc that lifts when forward flow enters the valve. This spring-loaded disc allows fluid to pass in one direction, and automatically closes to prevent backflow when the pressure reverses. The threaded seat ensures a secure and leak-proof connection to the valve body. Notably, the inlet, outlet, and flow path of a lift check valve maintain the same diameter, minimizing pressure drops within the system.
Tilting
Tilting disc check valves were developed to address some of the drawbacks of conventional swing check valves. They utilize a disc that pivots on a hinge rather than swinging freely. This allows the valve to remain fully open even at low fluid velocities, reducing flow restriction. The disc’s controlled motion also enables faster closure when flow stops, preventing backflow sooner. Tilting disc designs excel in high velocity flow conditions where uncontrolled swing checks can slam closed violently. The tilting mechanism allows smooth opening and closing even with rapid changes in flow. Tilting disc check valves are well-suited to applications like pumps that involve high flow velocities or frequent start-stop operation. Their controlled disc action provides reliable backflow prevention without excessive water hammer. Overall, tilting disc check valves offer performance advantages over swing checks in many demanding applications with dynamic flow.
Ball
Ball check valves rely on a freely-moving ball that rises and falls within the valve body to control flow. The ball rests on a specially designed seat with a conical chamber that guides the ball into a sealing position when there’s no flow. The weight of the ball can be adjusted based on the system’s pump capacity and the potential for water hammer.
When forward flow applies pressure, the ball lifts off the seat, allowing the fluid to pass. However, when the pressure drops or backflow occurs, the ball settles back down onto the seat, blocking the flow in the reverse direction.
06 What is the function of a check valve
The primary advantage of check valves is their autonomous operation, eliminating the need for constant monitoring or control. Their simple construction enables them to be easily installed in a pipe’s flow to regulate the flow without requiring active management.
Despite their numerous advantages, check valves, like any other mechanical device, also possess limitations.
Advantages of Check Valves
- Prevents backflow: Their primary function is to prevent fluids from flowing backward in a piping system. This is crucial in protecting equipment, preventing contamination, and maintaining system integrity.
- Maintains pressure: Check valves help maintain desired pressure in a system by preventing the flow from reversing direction. This is essential in applications like pumping systems where pressure needs to be maintained for efficient operation.
- Simple and reliable: Check valves are known for their simple design and reliable operation. They have no complex moving parts and require minimal maintenance, making them cost-effective and long-lasting.
- Automatic operation: Check valves function automatically based on the pressure differential across the valve. They don’t require any external power or manual intervention, making them suitable for various applications.
- Wide range of applications: Check valves come in various types and materials, allowing them to be used in diverse applications involving liquids, gases, and even slurries. They are commonly found in plumbing systems, HVAC systems, chemical processing plants, and more.
Disadvantages of Check Valves
- Pressure drop: The opening mechanism of a check valve creates a slight pressure drop in the forward flow direction. While minimal in most cases, this pressure drop can be a concern in applications requiring high flow efficiency.
- Flow limitations: Check valves are not designed for precise flow control. They simply allow flow in one direction and prevent it in the other. For applications requiring flow regulation, other types of valves are more suitable.
- Potential for water hammer: Abrupt closing of the check valve can cause water hammer, a pressure surge that can damage pipes and equipment. Careful selection and installation of check valves can help mitigate this risk.
- Limited cleaning: Some check valve designs make it difficult to clean them thoroughly. This can be an issue in applications involving sterile fluids or those prone to buildup of debris.
- Not suitable for pulsating flow: Check valves are not ideal for systems with pulsating or fluctuating flow, as this can lead to rapid opening and closing, causing wear and tear on the valve components.
In conclusion, check valves offer several advantages, making them valuable components in various piping systems. However, it’s crucial to understand their limitations and choose the right type for the specific application to ensure optimal performance and avoid potential issues.
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