Pressure-activated check valves prevent contamination and flooding from water sources used in fire protection systems
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 one works, 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.
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How does a check valve for fire protection work?
Each fire sprinkler system needs a dependable source of water for immediate use in a fire emergency. Most fire sprinkler systems use some combination of gravity tanks, municipal water supplies, and fire department connections to provide water to sprinkler heads. But while multiple 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.
Check valves for fire protection prevent this 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 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.
When firefighters pump water into a fire department connection, it passes through a check valve before reaching fire sprinklers or hose connections.
The hinged clapper inside this 6-inch grooved check valve is held in place by a spring until water flows push it open.
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.
How does a check valve for fire protection prevent contamination of potable water?
When multiple water supplies serve the same fire sprinkler system, each must have a check valve.
From the 2016 Edition of NFPA 13
8.16.1.1.3.1 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.
What are the types of check valve for fire protection and their benefits?
There are four main types of check valve for fire protection:
- Alarm check valve
- Swing check valve
- Grooved check valve
- Grooved shotgun riser check valve
An alarm check valve consists of a spring, valve clapper, and 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 2016 edition of NFPA 13
6.8.2 Waterflow Detection Devices.
6.8.2.1 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 glow 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.
This riser check valve combines a grooved riser check valve trim kit, which features valves and gauges, to a grooved check valve.
Do check valves require periodic maintenance?
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.
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.
NFPA 25 also requires inspection of alarm and check valves’ internal components every five years.
Maintenance should be performed by following the guidelines set by the manufacturer. Following an inspection, the manufacturer’s guidelines should then be used to return the system to service.
What’s the best brand of check valve? What should I look for in a check valve for fire protection?
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 the NFPA for check valves on fire sprinkler FDCs and the alarm check valves used with wet-pipe fire sprinkler systems.
In addition, when you’re purchasing a check valve for fire protection, you should also consider:
- The size and pressure ratings of your fire protection system
- How easy and fast the check valve is to install
- The quality and construction of the valve’s components
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.
