Definition of Check Valve

A check Valve, also known as a check valve, check valve, return valve, or isolation valve, is an automatic valve whose main function is to prevent the backflow of media (such as water, oil, gas, etc.) in the pipeline. The design of the check valve allows the fluid to flow freely in only one direction, while it is automatically closed in the opposite direction, thus ensuring the stability and safety of the system.

The working principle of check valves usually relies on the automatic action of the valve disc (also known as the opening and closing member). When the medium flows along, the valve disc will open and allow the medium to pass through; When the medium tries to reverse the flow, the valve disc closes under the action of fluid pressure or its own gravity, cutting off the flow path. In this way, the check valve plays a role in preventing the backflow of the medium.

Check valves are critical in a variety of industrial and commercial applications, including but not limited to water treatment and HVAC systems, industrial production, gas systems, and drainage systems in construction projects. In these systems, check valves protect equipment from backflow media, ensure proper system operation, and prevent possible contamination or safety incidents.

According to the different structure and function, check valves can be divided into many types, such as lift check valves, swing check valves and butterfly check valves. Each type of check valve has its specific application scenarios and advantages and disadvantages, so the selection of check valves needs to be considered according to the specific needs and working conditions.

Classification of check valves

lift check valve:
Structure features: The disc slides along the vertical center line of the valve body. The lift check valve can only be installed on the horizontal pipe, and the direction of the medium flow must be consistent with the direction of the body arrow.
Working principle: When the medium flow, the valve disc is pushed open by the fluid pressure, the medium can pass; When the medium counterflows, the valve disc is closed under the combined force of fluid pressure and self-weight, cutting off the flow.
swing check valve:
Structure features: The disc rotates around the pin in the seat of the check valve. The disc of the swing check valve is disk-shaped and rotates around the shaft of the valve seat channel. Because the channel in the valve is streamlined, the flow resistance is smaller than that of the lift type. It is suitable for large diameter occasions where the flow rate is low and the flow does not change often, but it is not suitable for pulsating flow.
Working principle: When the medium flows along, the valve disc is pushed open by the fluid pressure, and the medium can pass through; When the medium counterflows, the valve disc is closed under the combined force of fluid pressure and self-weight, cutting off the flow. Swing check valves can be installed in horizontal or vertical pipes.

Butterfly check valve:

Structure features: The disc is a disc, revolving around the shaft in the seat of the check valve. The butterfly check valve is relatively simple in structure, but can only be installed on horizontal pipes.
The working principle is similar to swing check valve, through the rotation of the valve disc to achieve the flow through the medium and counterflow blocking.
Pipeline check valve:
This type of check valve usually refers to the check valve installed directly in the pipeline, and its structure and type may vary according to specific needs, but the basic principle is to prevent the backflow of the medium.
Silent check valve:
The silent check valve is based on the traditional check valve, and the noise generated by the valve in the closing process is reduced by improving the structure or adding the noise reduction device. This type of check valve is especially suitable for occasions where there are strict requirements for noise.

Check valve application scenarios

Water supply and drainage system:

In the water supply system, the check valve is used to prevent water from going against the flow in the pipeline to ensure the unidirectional flow of water, especially at the pump outlet, to prevent the water from flowing back to impact the pump when the pump is stopped.
In the drainage system, especially in the sewage discharge pipe of the building, the check valve can prevent the sewage back into the room and keep the indoor environment sanitary.
Hvac System:
In the hot water supply system, the check valve ensures that the hot water flows from the boiler or water heater to the user, preventing the return of cooling water or cold water and affecting the heating effect.
In air conditioning systems, check valves are used to prevent refrigerant from backflow in the pipes and protect compressors and other equipment from damage.

Industrial production:
In chemical, petroleum, metallurgy and other industries, check valves are widely used in pipelines conveying corrosive or high-viscosity media to prevent media backflow and protect the safety of equipment and pipelines.
Check valves also play an important role in processes that require precise control of the flow of media.
Gas system:
In natural gas or gas pipelines, check valves are used to prevent gas backflow and prevent safety accidents such as fire or explosion.
Fire protection system:
A check valve is usually installed at the outlet of the pump in the fire fighting system to prevent water from flowing back from the fire fighting pipe to the pump when the fire fighting pump stops running, affecting the normal use of the fire fighting system.

Advantages and disadvantages of check valves

Advantage

Prevent media backflow: The check valve can effectively prevent the media from countercurrent in the pipeline, protect equipment and pipelines from damage, and ensure the normal flow of the media.
High safety: By preventing media backflow, the check valve reduces pipe bursts, equipment damage and other safety hazards, improving the overall safety of the system.
Simple structure: Check valves usually have a relatively simple structure that is easy to manufacture and maintain, reducing the cost of use.
Economical and practical: Because the cost of the check valve is relatively low, and it can be used for a long time, it has a high economy.
Wide range of application: Check valves are suitable for a variety of media and working conditions, including liquid, gas and steam, etc., to meet the needs of different fields.
Energy saving: The check valve relies on the pressure difference of the medium itself to achieve opening and closing, and does not require additional power equipment, which helps to save energy.
Flexible and reliable opening and closing: the opening and closing action of the check valve is flexible and rapid, and the sealing performance is good, which can ensure the smooth flow of the medium and effective truncation.

Shortcoming
Increased resistance: After the check valve is installed in the pipeline, it will increase a certain amount of resistance, thus affecting the flow rate of the medium. This can reduce the efficiency of the system and increase energy consumption.
Pressure loss: In a piping system, the presence of a check valve may result in a certain loss of pressure. This may affect the stability and safety of the system, especially in situations with high pressure requirements.
Difficult cleaning and maintenance: Due to the relatively complex internal structure of the check valve, dirt and sediment may accumulate after a period of use. This increases the difficulty and cost of cleaning and maintenance.
Noise problems: Some types of check valves (such as lift check valves) may produce noise during opening and closing. This can have a bad impact on the working environment and people.
High installation requirements: The position and direction of the check valve must be strictly in accordance with requirements to ensure normal operation and reliability. Improper installation may result in media backflow or system failure.
Sensitive to media: The performance and life of the check valve may be affected by the nature of the medium. For example, corrosive media may accelerate the damage and failure of check valves.