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#86 -- Draining a Fire Sprinkler System: Main Drain, Auxiliary Drain, and More!

Posted by Jason Hugo on 12/7/2017 to Valves
Without water, most fire protection systems are empty pipes fastened inside walls and ceilings. In more than one article, we’ve emphasized the importance of supplying adequate water to your building’s fire sprinkler and standpipe systems. While all that guidance and advice is still accurate and useful, today we thought exploring the complete opposite problem may be interesting.

Why would a fire protection system need to be drained?

In this article, we’ll discuss the 4 primary reasons why you may need to drain a fire sprinkler system. Then we’ll dive deep into the different types of drain valves, NFPA’s perspective on the placement and usage of those valves, and conclude with some helpful advice about the signs and decals needed to identify drain valves.

Not what you’re looking for? Need a common drain valve: Check out ball valves and test and drain valves.

Fire Sprinkler System Overview

Before we dive into draining a fire sprinkler system, it is important to understand where these drains fit into the overall system you may have in your building. It is also important to know where the water to be drained is held before and after the system is activated.

As a quick refresher, there are four basic types of fire protection systems. Each has their own way of doing the same job, controlling or extinguishing a fire threat.

Wet Fire Sprinkler System -A wet fire sprinkler system always has water in the piping.
Dry Fire Sprinkler System -A dry fire sprinkler system is filled with compressed air and only filled with water when triggered.
Pre-Action System -A pre-action fire sprinkler system begins as dry, once the first alarm is triggered, water fills the system, then a secondary trigger releases the stored water.
Deluge System -A deluge fire sprinkler system is always open, and the water is held back until an alarm is triggered.

If you'd like a broad overview of fire sprinkler systems, please read QRFS blog #75 -- Fire Sprinkler System Types.

Foam Deluge System
Admittedly, this picture is just cool. Deluge foam system in an airplane hangar.

Now that we have refamiliarized ourselves with the different types of systems and how the system holds an extinguishant, let’s consider why you would need to drain a fire sprinkler system.

Cautionary Note:
We do NOT suggest or condone draining a sprinkler system without proper authorization from your local authority having jurisdiction; Always consult them BEFORE modifying your fire sprinkler system in any way. Failure to do so could cause injury to yourself, damage to your system, or damage to your property. Only a licensed and insured fire sprinkler contractor should drain a fire sprinkler system.

Why would a fire sprinkler system need to be drained?

There are several events that could warrant the need for a fire sprinkler system to be drained.

  1. Repairs –Repairs need to be made when; a fire protection system is not properly maintained, and there are signs of corrosion, if the system was damaged after a natural disaster, or an act of vandalism occurs. You would need to drain the fire sprinkler system before beginning repairs.
  2. Restoring an activated dry-pipe system -A dry pipe system does not have water in the pipes like a wet pipe system. Compressed air fills the pipes until the fire sprinkler system is activated. Once activated, in order to get the system back to normal it would need to be drained.
  3. Extending an existing system -When a building has an addition, or you are extending an existing system to cover more area, then you would need to drain the fire protection system before work begins.
  4. Laws Change -We can never know when new laws are going to be enacted. New regulations for fire protection could come out about; the age of the pipe, type of pipe, or type of valves. Each of these would warrant a drainage of the fire sprinkler system to make the necessary changes to the existing system.
If you’d like more info on when a system should be drained, check out this PDF from insurer AIG: Procedures for Draining Sprinkler Systems.

Each fire protection system at some point will need to be drained. In fact, according to NFPA 13, all systems are required to have the ability to be drained when needed. Moving forward we will discuss the main components that enable system drainage.

From NFPA 13: sprinkler pipe and fittings shall be installed so that the system can be drained

Fire Sprinkler Main Drain

The main drain is designed to flush water from the system through a series of the pipe. The size of the main drain is in proportion to the size of the riser and is specified by the National Fire Protection Association.

From NFPA 13:
A. piping should be arranged where practicable to drain to the main drain valve

Main Drain on a Fire Sprinkler System
See the Main Drain sign? That's it. Kudos for snapping the picture: Image Source

When is the Main Drain used and why?

The main drain is the central point of discharge used to flush water from the system. All piping within the system is required to flow to the main drain. If the fire protection system needs repair, retrofit, or a test of the incoming flow of water, the main drain valve is opened to evacuate the system of the water it contains.

Where is the Main Drain located?

The Main Drain is located at the fire sprinkler system riser. It is to discharge outside and away from the building or to a connection that can handle the flow of the drain. Given that the entire system needs to be drained, the amount of water will vary based on the size of the system. This can range from just a few gallons for a dry system to several hundred gallons on a wet system.

Going to take more than 2 five-gallon buckets
Going to take more than 2 buckets to drain your sprinkler system (Image Source)

Think about filling a five-gallon bucket; one is not going to help you flush a full wet system. If the discharge was allowed inside the building to another connection like a janitorial sink it might not be able to handle the flow, which is usually around 100 gallons per minute. You could have a flooding incident on your hands. Therefore, it is preferable that all connections discharge outside the building.

The discharge drain connections are dependent on the riser size. According to NFPA 13, risers that are 2” should use a ¾ inch or larger drain connection. If the riser is 2 ½” or 3”, then the drain connection must be at least 1 ¼ inches. If it's 4”, then the drain connection should be 2 inches or larger. This connection leads to the main drain valve. From the drain valve, another connection leads away from the riser and out of the system to another connection or out of the building into the atmosphere.

If the main drain connection leads out of the building, it should have protection from the elements to prevent clogging or freezing. A turned down elbow will help prevent intentional and accidental clogging. At least 4 feet of exposed piping is required to be in a heated area before the pipe extends beyond the exterior wall.

All four fire sprinkler types are required to have the main drain. While the method of drainage is different for each, they all serve the same purpose; to flush and reset the system for future use.

What kind of valve and signage is required for a fire sprinkler system's Main Drain?

The valve itself can be of three types. A ball valve, a test and drain valve, or a combination of either of those two plus a pressure release valve. The combination would depend on the pressure rating of the system itself.

Ball Valve

All drains and valves of a fire sprinkler system should be listed as required by NFPA 13-6.6.4. Main drains are required to be permanently marked with weatherproof metal or plastic identification signs. The signs are hung from the pipe below the valve they are listing. They must be secured with non-corrosive wire or chain to prevent them from falling off. There also must be means to indicate that the valve is open or closed.

Main Drain Sign

Fire Sprinkler Auxiliary Drain

An auxiliary drain is designed to allow drainage when the main drain valve is insufficient and results in water trapped within the system. The valve size relative to the pipe used is specified by the National Fire Protection Association. How many drains a system contains will depend on how much water can be trapped.

From NFPA 13: drains shall be provided where a change in piping direction prevents drainage of system piping through the man drain valve

When is the Auxiliary Drain used and why?

Auxiliary drains are used after a system flush when the main drain leaves water in the system. Any time there is a change of direction of pipe in the system, there is a danger of water lingering in that area. The auxiliary drains help finish the job of the main drain.

Where is an Auxiliary Drain located?

Auxiliary drains are located at each point where the pipe changes direction. These drains should be accessible, especially those that are in areas subject to freezing. When the pipe changes direction, there is a “T” connection instead of an elbow. One part of the change in direction flows to the remainder of the system. The other direction flows to the auxiliary drain valve.

All four fire sprinkler system types require auxiliary drains when the danger of trapped water is present.

What size of valve and signage is required for a fire sprinkler system's Auxiliary Drain?

The size of the valve will depend on the amount of trapped piping and if the piping is subject to freezing conditions.

NFPA gets very specific in their valve size prescriptions by sprinkler system type.

Wet Pipe systems and Pre-Action systems with no freezing conditions: If trapped piping is more than 50 gallons, the valve should be no less than a 1”, if between 5 and 50 gallons a ¾” valve should be used in addition to a nipple with a cap or plug. And if less than 5 gallons are trapped, then a nipple with a cap or plug that is not less than ½ inch can be used. If trapped piping is less than 5 gallons, then the auxiliary drain can be omitted if the trapped water can be drained by disconnecting a sprinkler head or where easily separated sections are used.

Dry Pipe systems and Pre-Action systems with freezing conditions: If trapped piping is between 5 and 50 gallons, two 1” valves should be used separated by a 2”x12” condensate nipple. If it is less than 5 gallons, a valve not smaller than ½ inch and a plug, or a nipple and cap should be used.

Auxiliary drains are required to have permanently marked waterproof metal or plastic identification signs. The signs must be secured to the pipe and hanging below the valve with non-corrosive wire or chain to prevent the sign from falling off. There also must be means to indicate that the valve is open or closed.

Auxiliary Drain Sign

Additional signage should be placed near the control valve indicating the number of auxiliary drains and the location of each drain.

Fire Sprinkler Test Drain

So far, we have looked at situations draining the entire system. But what if that is not necessary? If your goal is to simply test the fire protection system pressure, then you can use a Test Drain.

From NFPA 13: drain test connections shall be provided at locations that will permit flow tests of water supplies and connections.

When is a Test Drain used and why?

A test drain is used to monitor changes in water flow through the system. While it is not essential to the function of a fire protection system, it is beneficial to have if you need to run tests on the system. Size and type of connections are regulated by the National Fire Protection Association.
A drain test is required annually, or any time the water supply is cut off. It will also need to be conducted anytime there is any maintenance done on the system. The system drain valve is opened until pressure stabilizes. Numbers are recorded, and the valve is closed again. Then the time it takes to pressurize needs to be within certain parameters.

Where is a Test Drain located?
The main test drain should be placed at a location that will permit the flow test. Usually as part of the main drain riser. They can also be found at the end of the system; this allows the ability to check for clogs in the system. It also needs to be placed where the valve can be opened fully.

Placed where the valve can be opened fully. 

Most test drains are designed with the wet fire protection system in mind. Their drain function allows the system to be emptied quickly. It can also serve as the main drain, replacing the drain valve. While it is primarily designed for wet systems, it can be used on all system types.

What type of valve and signage is required for a fire sprinkler system's Test Drain? 13-6.6.3

A test and drain valve is customary and preferable, but a simple ball valve can be used. The difference is that a test and drain valve is equipped with a sight glass that gives visual confirmation of water flowing through the fire protection system and a testing orifice that simulates a sprinkler head discharge. This enables the test to be done without having to drain the system. If a ball valve is used, then you would need an Inspectors test and sight glass AND drain the system.

Test and Drain Valves

The same requirements that are for other signage are applicable for Test drains in line with NPFA 13-6.6.4. They are required to be permanently marked weather-proof metal or plastic identification signs. The signs must be secured to the pipe above the valve they are listing with non-corrosive wire or chain. There also must be means to indicate that the valve is open or closed.

Test and Drain Sign

If you'd like to learn more, NFPA 13 and 25 are both valuable resources. So is this FEMA video.

Fire Sprinkler Sectional Valve

We have learned about the different valves for draining an entire system, and we have looked at valves that enable the system to be tested. But what if you have a multi-sectioned building and you only need to repair or test one section? What do you do then? This is where the sectional valve comes in. A sectional valve, also known as a floor valve, is a control valve that isolates specific areas of the fire sprinkler system.

Sectional valves, like all control valves, need supervision. This means they are to be held in a controlled environment where they cannot be tampered with.

From NFPA 13: an interior sectional or floor control valve(s) is provided, it shall be provided with a drain connection having a minimum size ... to drain that portion of hte system controlled by the sectional valve

When is a Sectional Valve used and why?
The sectional valve is used when the need for repair or testing exists for only a specific section of pipe. The valve to that section is closed so the test or repair can be performed without having to shut down the entire system. It is also used to test for pressure and leaks within each section independently from the others.

Where is a Sectional Valve located?
Sectional valves are located where each new section begins. If you have multiple floors or sections that are protected, then it would be beneficial to begin each branched off area with a sectional valve. Also, in each sectioned area, a separate drain connection is required to enable each isolated area to be drained.

Wet System sectional valves allow one section to be isolated while the other sections, or floors, can remain operational and filled with water. Once repairs or tests are completed, the sectional valve can be reopened, and the isolated section is brought back to use.
Dry, Pre-action, and Deluge System sectional valves are used to isolate an area for maintenance or testing, while the remainder of the system continues to be fully functional.

What kind of signage is required to identify a Sectional Valve?
All sectional valves on a fire sprinkler system should be listed and indicate in accordance with NPFA 13-6.6.4. Sectional and floor valves are required to be permanently marked with weatherproof metal or plastic identification signs. The signs must be secured to the pipe and hang below the valve it is listing, with non-corrosive wire or chain. There also must be means to indicate that the valve is open or closed.

Fire Sprinkler Trim Valves and Signs

Now that we know all about the draining of the system, let's take a look at the components, called trim, that make up these drains and valves and the signs that accompany them. The trim on valves is the network of pipes, valves, gauges, and switches that make up the valve assembly.

Trim begins with the valve itself. The size and type of valve will be determined by the size and type of pipe and the pressure of the system.

Trim valves vary between ball valves, butterfly valves, angle valves, and globe valves. They often come in kits where the multiple trim items are pre-assembled, such as the three-way valve in the fire sprinkler gauge kit...

Air Water Gauge Kit for Sprinkler Systems
Air/Water Gauge Kit: Example of a pre-assembled trim kit

Once the system is designed the valve is selected and trimmed to fit.

A check valve, common in standpipe and sprinkler systems, can also be part of a fire protection system trim assembly. Check valves allow the flow of water in one direction only. It contains a stopper that prevents backflow in the other direction. This is invaluable when there are more than two water sources. In concordance with NPFA 13, the check valve will prevent each water source from becoming contaminated by the other. Look for UL / FM approved check valves and trim kits pre-aggregated.

Check Valve in Shotgun Configuration - See the Drain Valve?
Check valve in the shotgun configuration with trim. Can you spot the drain valve? 
Each fire sprinkler system will have its own set of trim that is used. Since a dry system is filled with compressed air, instead of water, it would require more gauges. NPFA 13-7.2.1 specifies the different gauges involved.

According to NFPA 13 6.6.4, mandatory fire sprinkler system signs connected directly to the valve identifies the valve and gives specific information. Signs are crucial and shouldn't be overlooked. Not only do they help building owners maintain and service their system, it helps first responders quickly familiarize themselves with the system and help licensed professionals locate the system's valves quickly and easily.

Remember, sprinkler system signs must be permanent, able to withstand the elements, and always in view and legible. Like these signs here.

Compliant and working trim inclusive of helpful signs is crucial to the proper function of a fire protection system. Trim aids in testing the system and making sure it is functioning within NPFA standards. When the system does have issues, you will know and so to have proper maintenance completed, which usually begins with draining of your system.

In conclusion, understanding why and how to drain a fire sprinkler system is useful information for managing a building and maintaining fire sprinkler systems. Every valve we discussed in this article can be found on QRFS.com, we encourage you to check them out. If you have further questions or need a sprinkler system component, please call us at 888-361-6662 or contact us here.
This blog was originally posted by Jason Hugo and Maurice Draine at QRFS.com/blog on December 7, 2017. If you found this article useful, check us out at Facebook or on Twitter.

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