Operating principle of check valves

Products

Check valves, also known as non-return valves, are automatic devices designed to allow fluid to flow in one direction only, preventing backflow. They are used in hydraulic, industrial, fluid-power and process systems to protect pumps, compressors and pipelines from potentially damaging flow reversals.
Their operation is based on a simple but essential principle: opening and closing occur automatically according to the pressure differential between the upstream and downstream sides of the system. They require neither manual operation nor external actuators, responding solely to fluid dynamics.
There are several types of check valves — swing, dual-plate, disc and spring-loaded — each designed for specific operating conditions, pressure drops, installation orientations and fluid types.

A check valve operates according to the pressure differential between its inlet (upstream) and outlet (downstream).

1. Opening phase
When upstream pressure exceeds downstream pressure, a force acts on the internal moving element (flap, disc, poppet or ball). If this force is sufficient to overcome:
- the weight of the closure element
- any spring force
- seal friction
the valve opens, allowing the fluid to pass through.
The minimum pressure differential needed to initiate opening is called the cracking pressure.

2. What is cracking pressure?
Cracking pressure is the minimum differential pressure required to start opening the valve.
This parameter is essential when designing a system because it affects:
- pump start-up
- overall pressure losses
- flow stability
- water hammer prevention

An excessively high cracking pressure can:
- increase energy consumption
- delay valve opening
- cause upstream overloads

Conversely, an excessively low cracking pressure can cause:
- unstable closing
- vibrations
- noise
- premature wear of the valve seats

3. Closing phase
When downstream pressure becomes higher than upstream pressure (for example, when a pump stops), the flow tends to reverse.
The valve responds automatically:
- the disc or flap returns to its closed position
- the spring (if present) speeds up closing
- the seal against backflow is restored
Closing speed is a key factor in reducing the risk of water hammer, especially in systems with rapid changes in flow rate.

4. Operating differences between spring-loaded and non-spring-loaded valves
- Gravity-operated valves (e.g. conventional swing check valves): these rely mainly on the weight of the closure element and on backpressure. They are suitable for low flow velocities but may close more slowly.
- Spring-loaded valves: these provide a faster, more controlled response, reducing vibrations and water hammer. They are particularly suitable for dynamic systems or systems with centrifugal pumps.
 

As explained above, check valves play an essential role in the systems in which they are installed. They stop backflow in pipelines and prevent unpleasant or damaging consequences that can also lead to significant damage.
However, the term check valve encompasses numerous types, as shown in the Intertubi catalogue. The main differences concern their operating mechanisms, although each category also includes variants according to material, size, pressure rating and specific geometrical features.
In general, the main types are:
- dual-plate wafer check valve: made of CF8M stainless steel, it can be installed with vertical, horizontal or inclined flow. Its closing mechanism consists of two hinged plates that rotate within the seat and shut off the flow fully or partially, although partial closing is not always desirable because it can cause substantial pressure losses;
- wafer swing check valve: made of AISI 316 stainless steel, it can be installed with vertical or horizontal flow. Closing is achieved by a pivoting element that moves in response to flow in one direction only;
- wafer disc check valve: made of AISI 316 stainless steel, it has features similar to those of the dual-plate version but uses a disc to block reverse flow and prevent associated problems;
- spring-loaded check valves: made of AISI 316 stainless steel, these have a closing mechanism driven by a spring that forces the valve shut and prevents reverse flow. Variations include the gasket material, which may be PTFE or FKM, with different elasticity, mechanical and thermal resistance, and sealing properties.

The choice of one valve type over another depends on the application and on decisions made during the design phase. Consulting the supplier, Intertubi, helps identify the most suitable characteristics for each situation, avoiding choices based solely on a designer's habits.
Stainless steel is essential both to provide the mechanical strength needed to withstand pressure and stress and to ensure corrosion resistance, a fundamental property for components used in water systems.
A certified supply chain and compliance with applicable standards make Intertubi products structurally excellent. Nevertheless, correct installation and preventive maintenance remain essential to prevent wear or deterioration over time that could result in failures or malfunctions.
 

The preceding sections have outlined the main types of check or non-return valves, explaining their general operating principle and briefly examining the materials, variants and benefits of each.
Non-return valves are commonly used in hydraulic systems to prevent reverse-flow problems in the event of pump malfunctions, shutdowns or failures. During operation, various issues can compromise the system, while pumps may also be turned off for different reasons. In these situations, valves must stop backflow, preventing drainage and possible harm to people and nearby buildings.

What are some examples of non-return valve applications?
These components are widely used, and listing every practical application would be difficult. The following are just a few examples:
- Swimming pool or tank filling systems: they prevent the pool or tank from emptying when the pump is switched off, ensuring proper system operation;
- Pipelines: they prevent water backflow, minimising the risk of contamination, backpressure, backfilling and system blockages, thereby improving efficiency and safety;
- Hydraulic cylinders: they help prevent pressure losses during operation. This can be crucial when a minimum hydraulic pressure is needed for the cylinder to perform its function fully, particularly in industrial environments;
- Supply systems: by preventing reverse flow, they reduce the risk of contact with other liquids and/or gases that could cause damage, explosions and other problems.

As noted above, these examples do not cover every possible application, but illustrate the broad range of fields in which these components can be used.
 

The main benefits of using suitable non-return valves include:
- Efficiency: reduced waste and losses;
- Reduced system downtime: savings in both costs and time;
- Improved safety: lower risks to people, premises and facilities located near the systems in which these valves are installed.
However, these benefits require a certified product supply chain together with scheduled inspections and maintenance. Neglecting any stage can cause failure and loss of functionality. Material selection, design, manufacturing, installation and inspection, combined with decades of industry experience, are all crucial aspects of Intertubi's working approach.

As discussed above, check valves are components of fundamental importance. Their effectiveness and reliability are also ensured by using high-performance materials that allow them to operate in different systems and under varying conditions. These include:
- AISI 316 austenitic stainless steel: an austenitic stainless steel with low carbon content and significant amounts of chromium, nickel and molybdenum. These three elements improve corrosion resistance: nickel and chromium are central to stainless steels, while molybdenum is a distinctive addition that further enhances their properties. Like other steels, it has good mechanical properties and reasonable workability, allowing the required shapes to be produced. Furthermore, austenitic grades are well suited to hydraulic components such as check valves because they do not exhibit a ductile-to-brittle transition temperature and retain excellent properties even at low temperatures.
- PTFE: polytetrafluoroethylene is a polymer commonly known as “Teflon”. Its temperature resistance, chemical and water resistance, and non-stick properties make it ideal for manufacturing seals.

Check valves: quality and reliability start with choosing the right supplier

In an industrial system, even a seemingly simple component such as a check valve performs an essential function in ensuring safety and proper operation. For this reason, in addition to selecting the most suitable valve type for the operating conditions, it is essential to rely on dependable products that are correctly identified and supplied with the necessary technical documentation.

Choosing Intertubi means relying on a partner with years of experience in industrial piping components, with particular attention to product quality and traceability.

 

Product inspection and traceability

The quality of a valve depends on more than its rated characteristics. Materials, dimensions, mechanical properties and compliance with relevant standards must be verifiable through appropriate inspections and documentation.

Intertubi pays particular attention to the selection and inspection of the products it supplies, ensuring the availability of the technical documentation needed to trace their characteristics and origin.

Traceability is particularly important in industrial plants, where each component may form part of a complex system subject to specific design, regulatory and safety requirements.

 

A well-stocked warehouse for a rapid response to plant requirements

Alongside quality, product availability is another decisive factor. During plant construction or maintenance, being able to source a valve, fitting, flange or other component quickly can help reduce waiting times and operational downtime.

Intertubi has a particularly extensive warehouse, with many items available for immediate delivery, designed to meet the varied needs of the industrial sector.

Its comprehensive catalogue also allows customers to turn to a single supplier for multiple piping needs, from valves and fittings to flanges, pipes and other components needed to build a system.

 

Intertubi: expertise and service for industrial piping

Choosing a check valve therefore involves assessing not only its diameter, material, pressure rating and closing mechanism, but also supply reliability, product availability and the quality of its accompanying documentation.

Intertubi supports its customers with technical expertise, a well-stocked warehouse, prompt handling of requests and particular attention to product quality and traceability.

To find the check valve best suited to your system, browse the Intertubi catalogue or contact the team directly for further technical and commercial information.