A fire sprinkler system is constructed of a number of pieces.
Let's start from the water source and work our way as the water would flow.
Most sprinkler systems are fed by a public water supply.
This is often a water tower or series of towers that feed a gridded pipe network. The water towers are fed by pumps that kick water up into the storage tanks to the top of the water tower. Holding that water up high creates pressure everywhere downstream of that water tower. The water tower effectively allows water to maintain a higher pressure and flows on its own down through the pipe network below.
Individual buildings can tap this network with a tap at the street and a feed into an individual building. Where the tap occurs, we usually locate a valve right at the street. That valve is included so the water can be shut off to a building if there's a main break or if for some reason, we're needing to disconnect that building from the city water supply, without having to shut down the entire grid.
The feed into the building is usually called a water service. Where the water service enters the building, well, we call this the service entry. The service entry can be combined with fire and domestic water together, or those could be two separate pipes running into the building.
Once the water service comes into the building, we usually have a backflow preventer. The backflow preventer can be oriented vertically or horizontally, and it's not always located inside the building. The backflow preventer could be outside below grade in a vault, or it could be outside above grade in a heated enclosure. Or in some very warm climates, they even locate backflow preventers outside above grade with no heat protection, just exposed.
A backflow preventer is included so that water only flows in one direction. We don't want our stagnant, dirty water or any contaminated water to flow back into the public water supply and contaminate drinking water for everybody else. Sprinkler systems are usually filled with clean water initially, but that water sits for months or years at a time and collects bacteria that would make it very harmful if it traveled back and got into the public water supply. Backflow preventers are required by plumbing codes in order to protect public health.
After a backflow preventer or downstream of a backflow preventer is the feed to the sprinkler riser.
The sprinkler riser, or sometimes called a riser assembly, can take a few different forms.
Here in this example, we have a horizontal backflow preventer and two sprinkler risers. The water comes in from the underground and goes through the backflow and then runs horizontally to the manifold. Then, water travels vertically up each sprinkler riser to go out to the system.
Each riser here is serving a different zone. Zones are helpful to allow us to isolate different parts of the building, especially when we need to do maintenance work testing or renovate, and we then don't have to shut down the entire building. Isolating different zones for the building also helps limit some risks. We don't want a massive building to be able to lose all of its water supply for the sprinkler system with just one valve.
Let's look at how each of these risers works in a little more detail.
So, here's that same setup, but now we're looking only at an individual riser that controls one zone.
At the bottom is a control valve. This can also be called an isolation valve or a zone valve, but control valve as a generic term that just says the valve gives us the ability to control the water. This specific type of valve is a butterfly valve.
This is also considered an indicating valve. The term indicating means that when you look at the valve, you can tell, again just by looking at it, whether it's open or closed. For butterfly valves like this, the direction of that yellow or orange, call it a plate is the same direction that the paddle is on the inside of the pipe. So, if we're looking at a vertical pipe or water's flowing vertically and that orange or yellow plate is straight up and down also vertical, that would mean that that paddle inside the pipe is also vertical or in the open position. Basically, allowing water to flow on either side of that pedal. When we turn the valve and close it, and that yellow or orange indicator is perpendicular to the pipe or in this case that indicators horizontal left and right, that would mean that the paddle inside the pipe is turned also perpendicular to the pipe and blocking the flow of water. This would be a closed valve. Indicating valves are really helpful. Because again, at one quick glance, an inspection or whether we're doing maintenance on the system, we can tell with quick glance, whether that valve is open or closed. Sprinkler systems only work when those valves are open.
Next, after a control valve, there can be a check valve. The check valve is used to hold pressure in a system. It basically only allows flow in one direction and it locks in that pressure in that system. You can't lose it because as soon as water would try to flow down, the check valve is going to close and it's going to maintain pressure within that zone. Check valves are only required on systems where we have a combined sprinkler standpipe system. And that's so that firefighters who are pulling water off the standpipe system, don't also accidentally pull water out of the sprinkler system that's also fighting the fire. The check valves basically keep the pressure only going, keep it locked in the sprinkler system, but also keep water only flowing in the correct direction.
Downstream of our control valve and potentially check valve, we usually see some way to monitor the sprinkler system. We monitor a sprinkler system so that a fire department can be automatically notified whenever we have a fire. And when we have a fire alarm system in the building, that our building occupants are made aware that there is a fire condition automatically.
So, what is this monitoring device?
The most common way to monitor is a waterflow switch. A waterflow switch has a paddle on the inside of the pipe. It's not rigid. It's more I would say like it's a plastic paddle that's flexible on the inside of the pipe. And when water starts flowing, it's going to move that paddle, and close an electronic contact, and when that contact is closed, it sends a signal to our panel that there's water flowing inside the pipe. These water flow switches are adjusted, so that they're just sensitive enough to activate when one sprinkler flows, but hopefully not so sensitive that a change in a water pressure would create a false alarm.
When we get into dry sprinkler systems, we use pressure switches instead of waterflow switches to monitor pressure on the air side and pressure on the water side of a dry valve. When the air pressure starts to deplete rapidly, because we've got a sprinkler that's activated and it's letting air out of the system, then we pick up on that loss in pressure and send a signal to our panel that a fire condition is occurring.
Once we have a water flow switch, this is back to a wet system. We need some way to test that water flow switch. We always want to make sure that these switches are activating properly. There are a really important part of the sprinkler system. So downstream of waterflow switch, we have an inspectors test. Here, the inspectors test is just pass a water flow switch and on the riser itself. Sometimes, these inspectors test can be located at the most remote location on the far edge of our system. Some inspectors prefer the remote location because they can have confidence that water is actually making it from the control valve all the way to the opposite side of the system. But for a wet pipe sprinkler system, the inspectors test is only required to be located right on the riser downstream of the waterflow switch. When we get back to dry systems, the inspector test has to be located remotely on the far side of the system. That's a requirement out of NFPA 13.
On the riser itself, we also have a main drain. Each system has to be capable of being drained completely with the setup that we have shown here, the inspectors test and the main drain are combined into a single device or a combination inspectors test and drain.
The last thing we have on the riser is a pressure gauge. Inspectors and installers need to be able to tell if there's pressure on our system. We don't want somebody servicing the system that has pressurized water on it. This could be really dangerous situation. Think about loosening a coupling with pressurized water behind it. Well, as soon as you loosen those components, the pipe could disconnect, you could be flowing a lot of water. I mean, there'd be a lot of damage, but it's also for that person that servicing the system, it's a very dangerous condition. Pressure gauges are important so that we know when the system is pressurized just by looking at it. The pressure gauge allows us to do all of that.
So here we have a pressure gauge that is attached to a three-way valve. The three-way valve allows us to close that valve and pull off the pressure gauge, remove, and replace it without having to drain down the entire system.
I mentioned earlier that this is just one possible setup. So, there's a few different ways that we can arrange this whole riser assembly.
When we get into tall multistory buildings, the same setup can be located on each individual floor level. The equipment, devices are mostly the same, but they might be arranged horizontally instead of vertically and located at each floor level instead of altogether in one location.
Here's an example of the same riser assembly set up, except that we're now oriented horizontally in coming off a vertical sprinkler riser that spans multiple floors of a tall building.
So here we have a combination standpipe and sprinkler riser coming from the floor below and going to the floor above. Our floor control assembly starts at the control valve, then the check valve. Just like the riser we looked at before, we then go to a waterflow switch, we have a combination inspectors test and drain. And this is also where we would usually have a pressure relief valve to make sure that the pressure doesn't get too high on the system. And finally, we have a pressure gauge.
So, when we have this multi-floor setup, it's not always easy to just drain right out the wall to the exterior because we could be on level 7 or level 17. So, we have a drain riser that runs down to the floor below, and hopefully it gets us out of the building or to a location that we're allowed to drain.
So, what's downstream of this whole riser assembly setup?
Well, as the water would flow, it would go to a feed main, which is the pipe between the riser and our cross main.
The cross main, which is next, is a portion of pipe that connects or “crosses” our branch lines.
Just like a tree, branch lines, or I guess more properly the branch pipe, carries the water all the way out to the sprinklers themselves.
But wait, the sprinkler, oh, the sprinkler.
The sprinkler is attached to pipe. The sprinkler is automatic. There is a glycerin filled glass bulb, or our other style is a metal fusible link. But in this case, what we're showing is that glycerin filled glass bulb. When a fire occurs, it creates enough heat that warms up the water inside that bulb. So, the point that the glycerin expands and breaks the glass. Once that glass breaks, the plug on the sprinkler is no longer holding back the water.
Water is able to discharge right out of the sprinkler and cool down the fire. An important note here is that sprinklers are automatic. But they also only operate one at a time, not altogether. There has to be enough heat to overcome the sensitivity of that glass bulb in order to break the bulb and release the plug, allowing water to flow.
So, in aggregate, this is the main flow path that water experiences from the source all the way through to a sprinkler. That's the typical flow path.
Sprinkler systems also include some other attachments.
Each system is usually required to have a fire department connection, which is where the fire department hooks up to the sprinkler system and provides additional water and pressure to help fight the fire.
There are also major add-ons and other combinations too. Like we could have water storage tanks or fire pumps or standpipes.
We'll break out each of these in more detail, but for today, that's about it for the main components that go into a typical sprinkler system.
I'm Joe Meyer, this is MeyerFire University.
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