People commonly refer to a non return valve by its short name, NRV. It is also known by several other names. These names include check valve, one-way valve, unidirectional valve, reflux valve, retention valve, and clerk valve, foot valve. Frank P Cotter invented a check valve. His patent on check valve was published on 10 September 1907.
A non return valve allows fluid to flow only in one direction. This is why people also call it a unidirectional valve.
Many industries rely primarily on this one-way valves. This includes oil and gas, water treatment, chemical processing, food and beverage, and medical equipment manufacturing.
Non return valve symbol on Piping & Instrumentation Diagram or P& ID Diagram
In above non return valve symbol arrow shows the flow direction of the fluid. Which is only in one direction.
Basic terminology of Check Valve
Cracking Pressure:- The minimum pressure required from the inlet side to open the valve is called unseating pressure. It is also known as opening pressure.
Reseal Pressure:- The reseal pressure refers to the valve’s inlet and outlet pressure difference. This occurs 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:- The pressure is higher at the outlet of the check valve. he pressure is lower at the inlet of the check valve.
Unidirectional 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 check valve works automatically without the need for any external control element.
Types of Non Return Valve
It comes in a variety of types. Each NRV is designed to meet particular requirements and be suitable for specific applications.
Some of the most widely used NRV’s are as follows:
Swing Check Valves:
The swing check valve is a trendy type of NRV. 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.
These valves are usually used where little pressure drop and low flow resistance are important.
This type of check valve is widely used in pumping applications where a sudden stoppage of flow causes over-pressure.
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.
Engineers widely use this type of check valve in gas systems, mostly steam or air, where preventing backflow 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.
Lift check valves have limitations. There is also the possibility of backflow in certain applications. This is due to their design, which allows for a slight leakage in reverse direction flow.
Proper valve sizing and selection based on operating conditions and system requirements can eliminate this limitation of lift check valves. In applications where absolute return flow prevention is essential, engineers prefer other types of check valves. Examples include swing check valves or tilting disc check valves. These options can overcome this limitation.
Ball Check Valves
A ball check valve is a NRV. It controls fluid flow using a ball or sphere. Engineers commonly use this type of NRV in low-pressure and low-flow applications. Ball check valves are well-known for their simplicity and reliable service. A hollow sphere or ball inside the valve body serves as the flow controller in these valves. When the fluid flows in the desired direction, the pressure raises the ball, allowing the fluid to flow. When reverse flow occurs, the ball moves back into its seat, preventing any further 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 to seat tap. They are an excellent choice for applications involving fluids that are high in particulate matter. They remain 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 a valve needs both shut-off and check valve functionality, engineers typically use a stop-check valve.
A stop check valve only permits one direction of flow. It blocks backflow. This makes it function similarly to a lift check valve. It also functions as a shut-off valve. It fully closes and seals off the flow when necessary. Because of this, stop-check valves are adaptable and appropriate for uses requiring exact control.
Industries such as oil and gas, power generation, and chemical processing widely use stop-check valves. Frequently halting fluid flow is crucial for both safety and operational efficiency in these industries.
Diaphragm Check Valve
This type of check valve uses a flexible rubber sheet as a diaphragm. 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 NRV
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.
The oil and gas industry uses nrv’s to prevent the backflow of dangerous and flammable substances. This ensures the integrity and safety of the entire system.
Check valves are important in irrigation systems. They prevent water from returning to the main water supply. They also protect against contamination and ensure efficient water distribution to crops.
Additionally, they are commonly used in plumbing systems. They prevent the backflow of sewage or wastewater. This backflow can contaminate the freshwater supply and pose potential health hazards.
When selecting the right unidirectional valve for a specific application, you should consider several factors. These factors include the type of gas or fluid being transferred. You should also consider the required temperatures and pressures. Valve size and compatibility with different materials are important considerations too.
Applications of NRV
1. Oil and Gas Industry: It prevents the backflow of dangerous and flammable substances in oil and gas pipelines. This ensures the safety and integrity of the entire system.
2. Water and Irrigation Systems: It prevent water from returning to the main water supply in irrigation systems. They protect against contamination.
3. Industrial Processes: Non-return valves prevent the backflow of chemicals, gases, and other fluids in various industrial processes. They protect equipment from damage. They also prevent contamination of the surrounding environment.
4. Pharmaceutical and Medical Industry:Â They are crucial in medical devices. They prevent the backflow of fluids. This ensures the accuracy and safety of intravenous infusions.
5. Swimming Pools and Spas: Non-return valves prevent water from flowing back into the filtration system. This helps maintain water quality. It also protects equipment from damage.
6. HVAC Systems:Â It used in heating, ventilation, and air conditioning systems. They prevent air or fluid from returning into the system.
Advantages of Non Return Valves
1. Prevention of backflow: The primary purpose of non-return valves is to prevent the backflow of fluids. They ensure that the flow remains in one direction. This prevents any contamination of equipment and pipelines.
2. Maintenance of system pressure: It helps to maintain system pressure. They prevent flow reversal and maintain a constant forward flow.
3. Protection of equipment: Non-return valves protect equipment such as pumps and compressors. They also safeguard other downstream components from damage caused by backflow.
4. Safety: It helps to maintain the safety of a system. They prevent any unexpected or unwanted flow reversal. This prevention can lead to accidents or damage.Â
Disadvantages of Non Return Valves
1. Complex design: It can have a complex design with multiple components and mechanisms. This complexity can make them more prone to failure or malfunction.Â
2. Flow restrictions: NRV can introduce a certain level of flow restriction. This can cause pressure drops and reduce overall system efficiency.
Conclusion
Non return valves play a crucial role in ensuring unidirectional flow. They are used in various industrial applications, including chemical processing, water systems, and oil and gas pipelines. By preventing backflow, these valves protect equipment, preserve system integrity, and improve operational efficiency. Selecting the right type of non return valve is essential. You must consider swing, lift, or wafer types. The choice depends on the specific process requirements, flow conditions, and system design. Proper installation and maintenance are key to ensuring their longevity and reliable performance. Understanding their role and benefits can help industries improve their processes and avoid costly disruptions.
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