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A check valve is a device that permits the flow of semisolids, liquids, or gases in only one direction. Check valves, featured in systems ranging from residential plumbing to pharmaceutical production, often rely simply on changes in pressure to manage flows. In this article, we’ll focus on check valves for fire protection, discussing how they work, the types of check valves, and their benefits in fire sprinkler systems. Additionally, we’ll help you understand what components you should look for when selecting a check valve and discuss how to maintain them. Already know what you need? Feel free to go straight to our check valve product page and selection of grooved riser check valve trim kits. Each fire sprinkler system needs a dependable source of water for immediate use in a fire emergency. Most systems use some combination of gravity tanks, municipal water supplies, and sometimes fire department connections to provide water to sprinkler heads. But while multiple potential water sources provide an extra layer of reliability to fire protection systems, they can also be problematic: drinkable water might be contaminated by water from a fire hydrant, or dirty water from fire sprinkler pipes might flow through nearby streets and into nearby drains. In many other applications, it’s simply important that water only goes one way for performance reasons. These include protecting equipment such as pumps and filters from backflow damage, stopping drainage in a fire sprinkler system with elevation changes, providing pressure relief in liquid or pneumatic applications, and more. Check valves for fire protection prevent the unwanted reverse flow of water, known as backflow, from occurring. Many check valves feature a hinged clapper with a spring, which keeps the valve closed until the water flowing from some water source opens it. These clappers only open in one direction: when these flows reverse (or very nearly stop), the spring presses the clapper against a rubber seat, forming a water-tight seal. Think of the water on either side of the clapper as the supply side (between the water source and the check valve) and the system side (between the check valve and the rest of the system). When a fire sprinkler head discharges, water is released, decreasing the pressure on the system side. Shortly after, the higher pressures from water stored or pumped from the supply side push open the clapper, and water flows through the system. When multiple water supplies serve the same fire sprinkler system, each must have a check valve. From the 2022 Edition of NFPA 13 16.9.4.1 Where there is more than one source of water supply, a check valve shall be installed in each connection. Check valves decide which source actually provides the system with a supply of water at a given moment. When multiple water sources are used simultaneously, only the check valve connected to the highest-pressure water source remains open. Imagine you have a system with three water sources at the following pressure ratings, expressed in pounds per square inch (PSI): (Note: these pressure levels are provided only as illustrations and are not meant to be taken as typical for these water sources.) When water is supplied from all three sources, only the check valve leading to the fire department connection remains open. Why? Of these three sources, the FDC delivers the highest water pressure. This supply pressurizes the water on the system side. This increased system-side pressure is greater than the 75 or 50 PSI on the supply side of the check valves connected to the other water sources and, as a result, their clappers close. To continue with this example, if only the city water and the gravity tank supply water, the check valve to the 75-PSI gravity tank will open, while the city water’s check valve stays closed. Only when all other sources are exhausted or closed does the municipal water supply open the check valve and flow into the system. There are four main types of check valves for fire protection: An alarm check valve consists of a spring, a valve clapper, and an alarm port. The alarm port can be used to direct water to a water motor alarm or an alarm pressure switch used to alert nearby personnel to the system’s activation or send a signal to a fire alarm control panel. A swing check valve can act as an alarm check valve for a wet-pipe fire sprinkler system, but only when that valve can sound an alarm. From the 2022 edition of NFPA 13 16.11.3 Waterflow Detection Devices. 16.11.3.1 Wet Pipe Systems. The alarm apparatus for a wet pipe system shall consist of a listed alarm check valve or other listed waterflow detection alarm device with the necessary attachments required to give an alarm. Typically, these alarms are sounded by flow switches, which send a signal to local alarms and/or the fire alarm control panel when water flows through system piping. Grooved check valves are a type of swing check valve for use in systems that have grooved-connecting pipe ends. Many grooved check valves can be used in a vertical or horizontal orientation, allowing them to be used in various configurations with a fire department connection, bypass connection, gravity pressure tank, or pump discharge connection. A grooved shotgun riser check valve is similar to a grooved check valve but includes pressure gauges to monitor the supply and system pressure. The shotgun configuration, which uses an electric water flow switch and an alarm bell, is only permitted in situations where a water motor alarm is not required. Shotgun riser check valves offer a more compact and economical alternative to an alarm check valve. Finally, there are backflow preventers that are explicitly designed to prevent the contamination of water supplies. They use check valves and extra fail-safes to make absolutely sure water flows one way and doesn’t contaminate potable water supplies. You can read more about them in our other blog: “Backflow Preventer vs. Check Valve: What’s the Difference?” Yes, check valves require periodic inspections and maintenance. For this reason, NFPA 13 warns against burying check valves or positioning them in areas where they will be inaccessible. From the 2023 Edition of NFPA 25 13.4.2 Check Valves 13.4.2.1 Inspection. Valves shall be inspected internally every 5 years to verify that all of the valve’s components operate correctly. 13.4.2.2 Maintenance. Internal components shall be cleaned, repaired, or replaced as necessary in accordance with the manufacturer’s instructions. Alarm check valves and system riser check valves require more frequent inspections. Regular inspections help to verify that the clapper functions properly, that the valve seat is in good condition, and that there aren’t any visible signs of corrosion or blockages. From the 2023 edition of NFPA 25 13.4.1.1* Alarm valves and system riser check valves shall be externally inspected quarterly and shall verify the following: (1) The gauges indicate normal supply water pressure is being maintained. NFPA 25 also requires an inspection of alarm valves’ internal components every five years. 13.4.1.2* Alarm valves and their associated strainers, filters, and restriction orifices shall be inspected internally every 5 years unless tests indicate a greater frequency is necessary. Maintenance should be performed by following the guidelines set by the manufacturer. Following an inspection, the manufacturer’s guidelines should also be used while returning the system to service. Every check valve installed on a fire protection system should be FM-approved and/or UL-listed. Listings certify that a check valve is designed to withstand the conditions it’ll be exposed to while in use. They’re also specifically required by NFPA for check valves on fire sprinkler FDCs and the alarm check valves used with wet-pipe fire sprinkler systems. From the 2022 edition of NFPA 13 16.11.3 Waterflow Detection Devices. 16.11.3.1 Wet Pipe Systems. The alarm apparatus for a wet pipe system shall consist of a listed alarm check valve or other listed waterflow detection alarm device with the necessary attachments required to give an alarm. 16.12.6 Valves. 16.12.6.1 A listed check valve shall be installed in each fire department connection and shall be located in an accessible location. In addition, when you’re purchasing a check valve for fire protection, you should also consider: QRFS carries UL-listed and FM-approved grooved check valves for pipes ranging from 2 to 6 inches. All of our check valves feature a non-slamming, spring-loaded clapper that forms a water-tight seal against an EPDM synthetic rubber seat. With a durable ductile iron exterior and corrosion-resistant stainless steel clapper, these valves are built to last. Any of these valves can be installed in a vertical or horizontal orientation. What’s more, each can be used as an alarm check valve with a shotgun riser check valve trim kit, available for every check valve we carry. When you make a purchase from QRFS, you receive quality products at our competitive pricing. We begin processing your order the moment we receive it so we can provide you with the fastest standard delivery possible, generally reaching you in 2-3 business days. The company is the world’s best nozzle check valve manufacturers supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need. View our selection of grooved, inline, and swing check valves, plus our inventory of grooved riser check valve trim kits. Questions about this article or our grooved check valves? Call us at +1 (888) 361-6662 or email support@qrfs.com. This blog was originally posted by Jason Hugo and Anna Hartenbach at blog.qrfs.com on October 26, 2017, and updated on January 1, 2019. If this article helped you select the right check valve, check us out at Facebook.com/QuickResponseFireSupply or on Twitter @QuickResponseFS.How does a check valve for fire protection work?
How does a check valve for fire protection prevent contamination of potable water?
75 PSI Gravity Tank
50 PSI City Water
FDC, Gravity Tank, & City
Open
Closed
Closed
Gravity Tank & City Water
Closed
Open
Closed
City Water Only
Closed
Closed
Open
What are the types of check valves for fire protection and their benefits?
Do check valves require periodic maintenance?
(2) The valves and trim are free of physical damage.
(3) All valves are in the appropriate open or closed position.
(4) The retarding chamber or alarm drains are not leaking.
(5) Where applicable, the valve in the connection to the pressure-type contacts or water motor–operated alarm devices are either sealed, locked, or electrically supervised in the open position.What’s the best brand of check valve? What should I look for?
The primary purpose of check valves is to permit flow in one direction while prohibiting or stopping the flow in the opposite direction. The key point is that the normal resting state of a check valve is the closed position.
When flow is reversed in a pipe, this can cause hydraulic shock waves to pass through (also known as water hammer). This can cause severe damage to equipment in the pipeline if measurements are not taken to prevent this. The introduction of the correct check valve, in a fully closed position during reverse flow can prevent this from occurring and causing severe issues at the site.
Valves that prevent water hammer and close rapidly without slamming are called non-slam check valves.
Axial check valves are specifically designed for fast-reversing systems where backflow is a constant concern. It is categorized as a non-slam check valve as the valve closes without slamming meaning no excess pressure spikes are created. Most axial flow check valves are spring-loaded, with a single low-mass disc, which facilitates a fast, dynamic response to reduction in flow. Due to having a single disc and spring when the disc is opening, the force is balanced resulting in an even flow.
When pressure differential between the upstream and downstream side of the valve exceeds cracking pressure of the spring, the obturator will move and allow flow. The flow area of the valve decreases steadily down to the seat diameter; this is the venturi design.
As a result of the venturi design, the reduced flow area increases the kinetic pressure and reduces the static pressure allowing the valve to fully open quickly. The spring is selected so that the disc is fully opened and stable against its backstop under normal flow conditions.
When a noticeable reduction in flow occurs, the spring reacts early against the force of the reducing flow.
Simple conventional swing check valves tend to have a very poor response. Under dynamic conditions, relatively long response times are experienced. This yields high reverse velocities resulting in slam and unwanted pressure surges.
Dual plate spring-assisted valves versus conventional swing checks are designed with small plates, which have less inertia than a single thicker disc. Pre-loading with a spring provides a closing force at all angles, thus helping to reduce response time.
As mentioned, axial flow check valves have an excellent response and are recommended where a high-level performance is essential. As flow decelerates in the pipeline, the forces acting on the disc are reduced, and the spring is able to overcome these smaller forces causing the valve to close. Short displacement of the disc combined with axial spring assistance greatly reduces the response time giving a fast slam-free response with minimal reverse.
Axial flow valves:
The base valve design is available in various body configurations to suit the customers’ needs for industry standards, specification, weight and connection requirements. The majority of axial flow check valves will be sold as flanged.
The list below summarizes the most important standards for axial flow check valves:
Although axial flow check valves can be utilized in a multitude of applications, a growing number of niche sectors the valves have primarily been utilized in the following:
Oil and gas production, including midstream:
Chemical and pharma:
Petroleum refining and petrochemicals:
Power:
The most important thing to remember is that axial flow check valves are specifically designed for fast-reversing systems where backflow is a constant concern.
Ian Noble is the Global Business Line manager for the Crane range of Engineered Check valves, working within the Crane Process Flow Technologies (CPFT) business segment. Crane Process Flow Technologies segment is a global provider of highly engineered products and systems, serving chemical, petrochemical, pharmaceutical, water and wastewater and general industrial market among others.
John McIlroy has worked in manufacturing for more than 30 years, including 15 in the valve industry. He has had roles in check valve technical sales, applications engineering and manufacturing. McIlroy’s current role of application specialist for Crane Engineered Check Valves has a wide scope from direct customer support, resolving immediate system issues where the correct check valve can be a solution, to technical presentations around the application of check valves within industries like oil and gas, petrochemical, hydrogen production, LNG and renewable energy.
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