A non-return valve is commonly referred to by its short name, NRV. It is also known by several other names like check valve, one-way valve, unidirectional valve, reflux valve, retention valve, clerk valve, and foot valve. Frank P Cotter invented a check valve or non-return valve. His patent on check valve was published on 10 September 1907.
Non return valve allows fluid to flow only in one direction. That’s why it is also called as unidirectional valve.
Many industries, including oil and gas, water treatment, chemical processing, food and beverage, and medical equipment manufacture, rely primarily on non-return valves.
Non-return valve symbol on Piping & Instrumentation Diagram
In above non-return valve symbol arrow shows the flow direction of the fluid. Which is only in one direction.
Functionality Non-Return Valve
Before discussing the functionality of non-return valves, we need to understand some basic terminology of non-return valves.
Cracking Pressure:- This is the minimum pressure required from the inlet side to open the valve. It is also known as unseating pressure or opening pressure.
Reseal Pressure:- It is the pressure difference between the inlet and outlet of the valve during the closing process of the check valve. So, whenever the inlet pressure drops, outlet pressure increases due to backflow pressure. To prevent the backflow valve starts closing at this pressure. It is also known as sealing pressure, seating pressure, and closing pressure.
Back Pressure:- It is the pressure higher at the outlet of the check valve than the inlet of the check valve.
Non-return valves allow fluid to flow only in one direction while blocking the reverse flow. When the inlet pressure is greater than the cracking pressure of the valve. The valve opens to allow fluid to flow. When the flow is reversed or the pressure drops below the cracking pressure, the valve automatically closes. The non-return valve works automatically without the need for any external control element.
Types of Non-Return Valve
Non-return valve comes in a variety of types. Each NRV (non-return valve) is designed to satisfy particular requirements and be appropriate for a specific use.
Some of the most widely used non-return valve types are as follows:
Swing Check Valves:
The swing check valve is a trendy type of NRV (non-return valve). A swinging disc is used in the construction of swing check valves. This disk swings open to the flow of fluid in the forward direction and closes to stop the reverse flow.
The swinging disc in a swing check valve is placed on a hinge or pin. With the flow of fluid, this disk can move freely. The disc opens as the fluid pressure builds up on the disk. It allows the fluid to flow in a forward direction. As the flow reverses or the pressure decreases, the disc swings back into its closed position and stops the reverse flow.
These valves are usually used where little pressure drop and low flow resistance are important.
This type of non-return valve is widely used in pumping applications where a sudden stoppage of flow could cause overpressure.
A swing check valve is commonly used in borewell pumps. Also called a foot valve. It helps maintain water flow in one direction from the earth to the surface. It doesn’t allow fluid to flow back into the borewell when the pump is turned off.
Lift-Check Valves
Lift check valves are operated by a piston or disc. This disk raises off the seat to permit one direction of fluid flow and closes to stop the reverse flow.
This type of check valve is widely used in gas systems, mostly steam or air, where backflow prevention is crucial.
The advantages of Lift Check Valves are quick responses for flow control and on-off operation. Compared to other types of valves, it offers less pressure drop.
Lift check valves, on the other hand, have some limitations, especially when used with steam or air systems. When the disc is partially open, severe seat tapping can occur at low flow rates. It can result in operational inefficiencies and possible valve component damage.
In addition to the limitations of lift check valves, there is the possibility of backflow in certain applications due to their design, which allows for a slight leakage in reverse direction flow.
This limitation of lift check valves can be eliminated through proper valve sizing and selection based on operating conditions and system requirements. Other types of check valves, such as swing check valves or tilting disc check valves, may be preferred to overcome this limitation in applications where absolute return flow prevention is essential.
Ball Check Valves:
A ball check valve is a type of NRV (non-return valve) that uses a ball or sphere to control fluid flow. This type of NRV is commonly used in low-pressure and low-flow applications. Ball check valves are well-known for their simplicity and reliable service. They are made up of a hollow sphere or ball inside the valve body that serves as the flow controller. When the fluid flows in the desired direction, the pressure raises the ball, allowing the fluid to flow. When there is a reverse flow, however, the ball is pushed back into its seat, preventing any reverse flow.
Ball-check valves have the benefit of being able to function well in low-pressure and low-flow conditions. Their simple construction minimizes the possibility of pressure loss while maintaining a constant, smooth flow. In addition, compared to other check valve types, ball check valves are less likely to seat tap. They are an excellent choice for applications involving fluids that are high in particulate matter because they are also much less susceptible to jamming or clogging.
Stop Check Valves:
A stop check valve combines the features of a globe valve and a lift check valve.
When it’s required for a valve to have both a shut-off valve and check valve functionality, a stop-check valve is typically used.
Because a stop check valve only permits one direction of flow and blocks backflow, it functions similarly to a lift check valve. But it also has the additional capacity to function as a shut-off valve by fully closing and sealing off the flow when necessary. Because of this, stop-check valves are adaptable and appropriate for uses requiring exact control.
Stop-check valves are widely used in industries such as oil and gas, power generation, and chemical processing, where halting fluid flow frequently is crucial for both safety and operational efficiency.
Diaphragm Check Valve
A flexible rubber sheet is used as a diaphragm in this type of check valve. Suppose the inlet pressure is higher than the outlet pressure of the valve. Fluid starts to flow in a forward direction by pushing the rubber sheet diaphragm. If the inlet pressure drops diaphragm returns to its original position and closes the valve.
Importance of Non-Return Valves
Non-return valves play an important role in ensuring both the efficacy and safety of many industrial operations.
They ensure the proper and unidirectional flow of fluids by preventing any unwanted backflow. This unwanted backflow can damage the equipment, cause contamination of the fluid, or even pose a risk to human health.
Non-return valves are used in the oil and gas industry to prevent the backflow of dangerous and flammable substances, ensuring the integrity and safety of the entire system.
In the medical field, non-return valves are used in intravenous infusions to prevent backflow and contamination of fluids.
Furthermore, non-return valves are important in irrigation systems to prevent water from returning to the main water supply, protect against contamination, and ensure efficient water distribution to crops.
Additionally, non-return valves are commonly used in plumbing systems to prevent the backflow of sewage or wastewater, which can lead to contamination of the freshwater supply and potential health hazards.
When it comes to choosing the right non-return valve for a specific application, various factors need to be taken into consideration. These factors include the kind of gas or fluid being transferred, the necessary temperatures and pressures, the valve’s size, and its compatibility with different materials.
Applications of Non-Return Valves
Non-return valves have a wide range of applications across various industries.
1. Oil and Gas Industry: Non-return valves are used to prevent the backflow of dangerous and flammable substances in oil and gas pipelines, ensuring the safety and integrity of the entire system.
2. Water and Irrigation Systems: Non-return valves are used in irrigation systems to prevent water from returning to the main water supply, protecting against contamination.
3. Industrial Processes: Non-return valves are used in various industrial processes to prevent the backflow of chemicals, gases, and other fluids that could potentially damage equipment or contaminate the surrounding environment.
4. Pharmaceutical and Medical Industry: Non-return valves are crucial in medical devices to prevent the backflow of fluids, ensuring the accuracy and safety of intravenous infusions.
5. Swimming Pools and Spas: Non-return valves are used in swimming pool and spa systems to prevent water from flowing back into the filtration system, helping to maintain water quality and prevent damage to equipment.
6. HVAC Systems: Non-return valves are also used in HVAC systems (heating, ventilation, and air conditioning). They are used to stop air or fluid from returning into the system. Non-return valves, or check valves, are essential components in various industries and applications.
Advantages of Non-Return Valves
Non-return valves offer several advantages that make them essential components in piping systems. These advantages include:
1. Prevention of backflow: The primary purpose of non-return valves is to prevent the backflow of fluids, ensuring that the flow remains in one direction and preventing any contamination of equipment and pipelines.
2. Maintenance of system pressure: Non-return valves help maintain system pressure by preventing flow reversal and maintaining a constant forward flow.
3. Protection of equipment: Non-return valves protect equipment such as pumps, compressors, and other downstream components from damage caused by backflow.
4. Safety: Non-return valves help maintain the safety of a system by preventing any unexpected or unwanted flow reversal that can lead to accidents or damage.
Disadvantages of Non-Return Valves
Despite their numerous advantages, non-return valves also have certain disadvantages that need to be considered:
1. Complex design: Non-return valves can have a complex design with multiple components and mechanisms, which can make them more prone to failure or malfunction.
2. Flow restrictions: Non-return valves can introduce a certain level of flow restriction, which can cause pressure drops and reduce overall system efficiency.
