Industrial Check Valves

What Is a Check Valve?

A check valve (non-return valve) controls the direction of flow using the force of the fluid itself. While there is forward flow, the disc or clapper stays open; when flow stops or reverses, it closes and blocks backflow. This prevents pumps and compressors from spinning backwards, tanks from draining and systems at different pressures from mixing.

Check valves are grouped by internal design. In swing designs a hinged clapper opens with the flow. In lift designs the disc rises along a vertical axis. Tilting disc designs are built to prevent disc slam while closing quickly. Piston designs are also preferred for certain applications.

These valves are offered in different families: bolted bonnet designs for general service, cryogenic designs for very low temperatures and forged high-pressure designs for safety-critical systems such as nuclear plants. The right type is chosen by considering installation orientation, flow conditions and closing behavior together. On pump discharges in particular, the reverse flow velocity after pump stop and the disc closing time directly affect water hammer risk.

How Does a Check Valve Work?

The valve works on the pressure difference between inlet and outlet; it needs no external actuator or energy.

1.      Forward flow: When inlet pressure slightly exceeds outlet pressure, the disc or clapper opens and flow starts.

2.      Fully open position: When fully open, the clapper rests against a stop inside the body and the flow path remains open.

3.      Flow stops: As flow decreases or stops, the disc moves toward the seat under its weight, spring force or reverse pressure.

4.      Closing and sealing: Reverse pressure presses the disc onto the seat, and the system seals itself without external actuation.

Swing, lift and tilting disc designs

Swing types can be used on horizontal lines and on vertical lines with upward flow. Lift types can be installed on horizontal lines, or on vertical lines with the help of a spring, and can be supplied in a quick-closing version. Tilting disc types are designed to close quickly while preventing disc slam, which helps limit the risk of water hammer.

Cryogenic and high-pressure designs

Cryogenic designs are made from low-temperature steels for temperatures down to -254 °C and undergo cryogenic tests. In forged high-pressure designs for nuclear plants, no shaft passes through the body to the outside; every moving part is mounted on a retaining ring, so the whole assembly comes out easily during servicing. This design eliminates external leakage from shaft packing.

Key Features

·         Multiple designs: Swing, lift, tilting disc and piston types.

·         Robust body: Carbon, alloy and stainless steel, duplex steel and special alloy body options; NACE compliant materials.

·         Easy maintenance: Threaded seat rings simplify maintenance and replacement; tack-welded or seal-welded versions on request.

·         Flexible connections: Flanged, buttweld or special connections such as clamp type.

·         Trim options: 13% Cr, stainless, cobalt-chromium or nickel-chromium hardfaced trims for erosive, corrosive and high-pressure services.

·         Cryogenic verification: Cryogenic designs are tested to the relevant standard and oil and gas cryogenic test procedures.

·         Nuclear-grade design: Forged body, no shaft penetration, mirror-lapped seats and seismically tested design.

·         Bonnet options: Bolted bonnet as standard; pressure seal bonnet option at high pressure.

Technical Specifications

The table summarizes the main technical range of the check valve families.

Larger sizes and classes are evaluated per project; values vary by family and material.

Key Advantages

·         Protection without energy: Prevents backflow using the fluid's own force, without external actuation.

·         Equipment safety: Protects pumps and compressors against reverse rotation and backflow damage.

·         Wide application range: From cryogenic temperatures up to 650 °C and from ASME 150 to 2500.

·         Long service life: Trim and hardfacing options suited to the service resist wear.

·         Easy maintenance: Threaded seat rings and retaining ring assemblies allow in-line servicing.

Applications

These valves are used in a wide range of services where backflow must be prevented.

Oil and gas

Backflow prevention in onshore and offshore drilling and refining facilities.

Chemicals and petrochemicals

Protection against reverse flow on process lines and pump discharges.

Power and nuclear plants

General service in power plants; forged high-pressure designs in systems feeding the primary circuit of pressurized water reactor nuclear plants.

Cryogenic services

Production, storage and transport of very low temperature fluids such as liquefied natural gas, hydrogen and oxygen.

Check Valve Selection Criteria

When type selection is not made together with flow conditions and installation orientation, problems such as slam, vibration or premature wear can occur.

Type and installation

·         Horizontal or vertical (upward flow) installation

·         Need for quick closing and prevention of disc slam

·         Whether normal flow and velocity are enough to keep the disc fully open

Pressure, temperature and material

·         Design pressure and ASME class

·         Minimum and maximum temperature, cryogenic requirement

·         Trim according to erosive or corrosive character of the fluid

·         NACE compliant material requirement

Connection and maintenance

·         Flanged, buttweld or special connection

·         Threaded or welded seat ring

·         Bonnet type and need for in-line service

·         Test and certificate requirements in safety-critical systems

Standards

The valve families comply with the following design, connection and test standards.

In nuclear applications, additional design and qualification requirements apply according to the project code.

Check Valve Selection with TLY Enerji

A non-return valve may look like simple equipment, but the wrong type or size can cause disc flutter, slam, water hammer and premature wear. TLY Enerji evaluates the selection together with line conditions, installation orientation and pump/compressor behavior.

Type and size are selected from process data, and trim and hardfacing options are defined by the fluid's character; for cryogenic and high-pressure applications, material and test requirements are included in the project documentation. Alternatives are presented with technical justification at quotation stage, and installation and site support are planned according to project scope. For existing plants with slam or vibration problems, proposals for type changes and size revisions are also prepared.

·         Type and size selection

·         Trim and material evaluation

·         Cryogenic and high-pressure test requirements

·         Quotation and documentation

·         Site support coordination

Frequently Asked Questions

What does a check valve do?

This valve lets fluid pass in one direction only and closes automatically when reverse flow begins. It protects pumps and compressors against reverse rotation, prevents tanks from draining back and stops systems at different pressures from mixing. It needs no external energy or actuator to work.

Can a swing check valve be installed on a vertical line?

Swing types can be used on horizontal lines and on vertical lines with upward flow. Lift types can be installed on horizontal lines, or on vertical lines with the help of a spring. The installation orientation must always be stated at selection stage, and a suitable type is evaluated separately for vertical lines with downward flow.

What is the advantage of a tilting disc check valve?

Tilting disc designs are built to prevent the disc from slamming onto the seat while closing quickly. Quick closing limits the build-up of reverse flow velocity, and avoiding slam reduces the impact loads on valve internals and the pipeline.

Which check valves are used in cryogenic service?

For temperatures down to -254 °C, cryogenic designs use CF8M, CF8 or other steels suited to low temperatures. These valves are tested to the relevant cryogenic standards and oil and gas cryogenic test procedures. Typical uses are the production, storage and transport of liquefied natural gas, hydrogen and oxygen.

How do check valves for nuclear plants differ?

Nuclear plant designs are forged and have no shaft penetrating the body, which removes the risk of external leakage. All moving parts are attached to a retaining ring assembly that can be removed easily for service. Seat surfaces are mirror-lapped and the design is verified by seismic shake table testing.

Which trim should be chosen for a check valve?

Trim is selected by the erosive or corrosive nature of the fluid, pressure and temperature. A 13% Cr trim suits general erosive or non-corrosive service, stainless trims corrosive service, and cobalt-chromium hardfaced trims high-pressure, slightly erosive service; a nickel-chromium option exists where cobalt is not allowed.