How It Works: Check Valves

Types

Swing (tilting-disc) check valves consist of a clapper with a disc that is convex on the upstream inlet side and flat on the downstream outlet side. For API Spec 600 valves, this disc swings on a hinge that is mounted to the bottom of the valve bonnet. For API Spec 6D valves, the typical construction is a cast pocket in the valve body with a drop-in shaft or pin-and-bushing arrangement that the clapper will turn on. This type of construction requires some sort of restraint to keep the clapper in the pocket. The new design features improved modularity and facilitates easier assembly, enabling different configurations to be assembled with a base design.

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Nozzle (axial flow) check valves have a spring-loaded disc that translates horizontally. The spring allows for a nonslam design in that the effects of water hammer are eliminated. These are designed to be in the full open position, even at minimum flow rate, to ensure performance. Nozzle check valves can be installed in both buried and above-grade applications and are ideal for gas applications.

Ball check valves include a spherical ball clapper that is sometimes spring loaded to seal at pressures below the cracking pressure. Because of the spherical design, these valves can easily wear from prolonged use and require frequent maintenance; therefore, they should be installed in places that are easy for repair teams to access.

Diaphragm check valves consist of a rubber diaphragm clapper that flexes open when the pressure on the upstream side is greater than the pressure on the downstream side and closes when this pressure is equalized or lowered below a set pressure differential.

Stop check valves are usually constructed similar to a swing check valve but have an additional external control mechanism&#;such as an actuator, lever, or handwheel&#;that enables the valve to be deliberately closed regardless of flow pressure.

Duckbill valves enable flow to proceed through a soft tube that feeds into the downstream side of the valve wherein backpressure collapses the tube and cuts off the flow.

Features

The main advantage of a check valve is its simple design. Generally, check valves also are smaller and easier to install compared with other valve types, making maintenance easier and more efficient. Check valves can be designed with specific nonslam features to reduce noise and seal wear. ENTECH nozzle check valves are commonly selected for this feature in LNG pump stations and gas compressor stations. Additionally, because of their simple, streamlined design, TOM WHEATLEY check valves and ENTECH check valves have lower pressure drops (less than 1 psi) than comparable piston check valves.

Many industries are dependent on types of check valves within their process systems. There are various types available depending on the application requirements. These valves are specifically designed to be reliable and efficient, maximise an operation, and make sure things run safely and smoothly.

The inventor Frank P Cotter, known for his industrial innovation, created a check valve that was simple and self-sealing that could be adapted to be utilised in pipe connections. The advantage of Cotter&#;s development was that it could be used without needing special fittings to connect to other pipes. These valves were also developed to be easily repaired and inspected.

Famed inventor Nikola Tesla also contributed to check valve development with his deceptively simple one-way valve patented in . Here, we see that the utility of these valves is numerous and contained inside a vast history.

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Different Types of Check Valves Used in Industries

1. Bronze Swing Check Valves

One of the most widely used valves is the Bronze Swing Check Valve which is commonly used in both the industrial and commercial sectors. These valves function by opening in response to forward-moving flow and close due to flow stoppage, preventing or reducing reverse flow occurrences. They protect pumps and pipe systems from the damage resulting from reverse flow. Swing Check valves produce lower pressure loss and are used with hot and cold water, low-pressure steam, HVAC, compressed air and many general utility services.

2. Cast and Ductile Iron Swing Check Valves

Cast and Ductile Iron Swing Check Valves operate under high and low pressures and have a relatively long life expectancy. These valves feature an unrestricted flow path and consequently have an improved flow capacity and lower pressure loss. Their longevity is a result of a solid structure and simple design.

3. Tilting Disc Check Valves

Tilting Disc check valves were developed for use in pumping stations conveying drinking water and other neutral liquids. The Tilting Disc check valve has a reduced closing angle which enables them to provide improved closing performance, subsequently reducing slam and pressure surges developed in the piping system on pump shutdown. These valves are typically installed in water pumping stations where multiple pumps are used and water is discharged from each pump into a common header pipe. Although they have a reduced operating angle, they offer relatively low-pressure loss through the valve.

4. Dual Plate Check Valves

Manufacturer&#;s offer a variety of Dual Plate Check valve designs and configurations including retainer and retainer-less designs, wafer style, lug style along with double flanged style configurations. They are available in a wide variety of different body and trim materials that include both resilient and metal seats. These valves are high-performance, and the original Mission wafer check valves were made available on the market during the late s. These valves are available in sizes ranging up to 88&#; with pressure ratings running up to Class .

5. Ball Check Valves

These are simple and reliable valves. They feature only one moving part in the shape of a spherical ball that blocks any reverse flow. They feature either a reduced or full-ported valve seat that is uniquely designed to allow the ball to seat and create a leak-tight seal without it becoming wedged into the valve seat.

Application of Check Valves

Check valves are &#;self-actuating&#; devices designed to allow media to be transported in a single direction while preventing backflow or flow in the opposite direction. These valves are primarily utilized in potable (drinking) water, wastewater, and irrigation applications. However, they also feature in other applications, including processing, mining, food & beverage, oil & gas, pharmaceutical, power, transporting hot and cold water, HVAC systems, steam, chemical, petroleum refining and production.

How to Choose the Right Check Valve

To ensure your operations run efficiently and safely, the correct check valve must be chosen under the right set of considerations. Some of the things that you need to consider when selecting a check valve include flow characteristics, fluid compatibility, non-slam characteristics, pressure-loss, and the total cost of ownership. You must ask yourself what the system&#;s requirements are and the installation cost. It is essential to look at each type of check valve and discern the specific installation and its particular characteristics before purchasing and installing.

The Best Valve for You

There are many kinds of check valves, and each is made for specific purposes. Some valves are compact, sturdy, and designed with high pressure-temperature services in mind. Other check valves are manufactured to reduce the magnitude of slam and pressure surges that can be generated when the check valve closes following pump stoppage. Commonly known as check valve slam. The innovations of these valves are born from particular purposes and have made the world safer and more productive. 

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