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Original article → Sprinklers Made Simple
By Author(s): Ron Kanterman
Published January 29, 2015 | From Volume 168, Issue 1 of Fire Engineering

Whether you’ve been on the line for one year or 25 years and have not had the time to understand sprinkler systems basics, this article is for you.

Frederick Grinnell, a graduate of Rensselaer Polytechnic Institute, worked in railroad engineering until he retired as chief mechanical engineer and general manager of the Jersey City Locomotive Works. Soon after his retirement, he purchased a controlling interest in the Providence Steam and Gas Pipe Company. Grinnell already knew Henry S. Parmalee, who patented the first automatic fire sprinkler head in 1874. Providence Steam & Gas partnered with Parmalee and manufactured the Parmalee sprinkler. Grinnell also designed and erected the piping installations into which the Parmalee sprinkler heads were fitted. Grinnell improved Parmalee’s first practical automatic sprinkler and patented his own Grinnell sprinkler in 1882.

Continual improvements resulted in the glass disc sprinkler in 1890. With slight modifications, this sprinkler head is still used in modern fire sprinkler systems; sprinklers are even called le Grinnells in France. In 1892, Grinnell organized the General Fire Extinguisher Company, which was renamed the Grinnell Fire Protection Company after his death in 1919.

So, sprinklers have been around and effective in fire control for about 140 years. Yes, those little brass and chrome-plated beauties have been the front line of defense against fire in commercial buildings for quite some time and, more recently, in people’s homes. For many years, it was the insurance industry that advocated for sprinklers in commercial buildings. Sprinklers minimized the loss, minimizing insurance payouts and enhancing their profits at the same time. Although the insurance industry still avidly supports sprinkler system installations, the National Fallen Firefighters Foundation (NFFF) is the current advocate for residential sprinklers, according to Initiative 15 of the NFFF’s 16 Life Safety Initiatives: “Advocacy must be strengthened for the enforcement of codes and the installation of home fire sprinklers.”


There are two common types of systems, wet and dry pipe systems. In addition, there are two other less common systems, preaction and deluge, used for special hazards and applications. Foam may be used in some systems, particularly when dealing with flammable liquid hazards. All of these systems simply send water or foam (foam is just water with its specific gravity rearranged so it floats on top of hydrocarbons instead of sinking in them) to the fire’s location to control; confine; and, in some cases, extinguish it. Very effective! You still need people to rescue victims and pull them out of harm’s way, so sprinklers only support staffing – they do not replace it. They are a tool to protect property and, in some cases, life (residential) and to assist the fire service with effective, efficient, and safe operations. Sprinklers save firefighters lives, too!

Wet Systems

As implied, they are wet, and the system pipes are full of water up to the sprinkler heads. Because of this, wet systems are the quickest, most reliable sprinklers around. The fire actuates the individual sprinkler heads-this is the only way that water gets on the fire. Sprinkler heads use either a fusible link with a predetermined melting point or a glass bulb filled with a liquid designed to boil, expand, and shatter the bulb. Others use a chemical pellet to retain the water cap, which is released after the pellet melts or bursts, and the water is there immediately. The main riser and related equipment (known as “trim” in the sprinkler business) is where it all starts. The riser is connected to a water supply with a main control valve, a main drain, an alarm check, a retard chamber, a couple of gauges, a fire department connection (FDC), and a water motor gong (photo 1).

Sprinklers Made Simple Wet Trim.jpg

When one or several sprinkler heads open, water flows though the alarm check, which sends an alarm (that’s why they called it that) possibly to a central station and to the local water motor gong on the outside of the building. That’s the bell that’s ringing when you pull up at 0300 hours and there’s water pouring out from under the door. The exterior gong is there to notify people walking or driving by to call the fire department. The retard chamber is there to take surges in the main. The surge enters the retard chamber so it won’t lift the alarm check clapper, it won’t send a water flow alarm, and you can stay in bed on a 10°F night. It retards the alarm and then automatically drains.

You will find wet systems in areas that are heated at all times and not subject to freezing conditions, such as malls, hotels, schools, office buildings, warehouses, factories, hospitals, and industrial processing sites. Wet systems are also found in private homes. Unless there is a reason you shouldn’t have a wet system (e.g., no heat, water-reactive chemical storage) then most codes and standards (and insurance companies) require wet systems.

Dry Systems

A dry pipe sprinkler system has no water in the pipes. A compressor or other source of air or nitrogen holds back the dry pipe valve (a clapper) until the heat of the fire melts the link or bursts the bulb on the sprinkler heads. The air then rushes out of the heads, releasing the pressure on the dry pipe valve, and the water starts to flow. These systems are used in buildings and areas of buildings where there is no heat (e.g., refrigerated warehouses, outdoor sheds, loading docks, multilevel parking structures, and structure attic areas). To reduce response time, some systems use “accelerators” or “exhausters,” also known as quick opening devices (QODs), which help release the air out of the system and more quickly open the dry pipe valve (photo 2).

Sprinklers Made Simple Dry Trim.jpg

As with the wet system, the riser is connected to a water supply, but there is a dry pipe valve in place of the alarm check. It will also send a water flow signal after it trips. It has a main control valve, a main drain, a couple of gauges, an FDC, and a water motor gong. This system also has a compressor or a nitrogen supply, and an air gauge is on the upstream side of the dry pipe. If it starts to bleed down, a signal will go to the fire alarm panel, reporting a “low air alarm.”


A pre-action system is also dry, but two distinct actions must occur for water to enter the occupancy. Pre-action sprinkler systems are used in places (e.g., computer rooms, hospital operating rooms, and museums) in which any accidental water discharge is to be avoided. Because two distinct actions must take place to put water in the room, merely snapping off a sprinkler head by accident will not activate the system. Unlike the dry pipe, an opening caused by an accidental break in the piping or a head will not trip the valve. Pre-action valves are electronically tripped through heat or smoke detection (photo 3).

Sprinklers Made Simple Pre-action Controls.jpg

Note the following sequence of actuation of a typical pre-action system in a computer room:

  1. A smoke condition occurs in the room.
  2. A smoke detector picks up the smoke and signals a small pre-action panel (similar to a fire alarm panel) or the main fire alarm panel for the entire building. In either event, the signal goes to a panel. The smoke detector indicates, “Smoke has been detected in the room. Open the pre-action valve.”
  3. The panel signals the pre-action valve at the riser, “A smoke condition has been detected in the computer room. Trip and open to flood the piping system and stand by for fire.”
  4. An electronic solenoid switch on the pre-action valve at the riser activates and electronically “pulls a pin,” which trips the valve. Water flows into the system. At this point, we now have a wet system.
  5. When the fire grows and reaches the set temperatures of the sprinkler heads (usually 165-175°F in a computer room), the heads will start to open over the fire.


The main difference between the deluge system and a dry system is that all sprinkler heads are open with no fusible elements or glass bulbs. It discharges lots of water everywhere and all at once. These systems are usually actuated by heat detection and are mainly found in heavy industrial applications (e.g., around transformers, processing tanks, processing pads with large vessels, small flammable liquid storage tanks). Since the heads are always open, using compressed air to hold a dry pipe valve back won’t work. Activation is similar to that of a pre-action system.

  1. A heat detector detects fire around a transformer and signals the panel.
  2. The panel signals the deluge valve at the riser, “A fire condition has been detected. Trip and open to deliver water to all heads and all sides of the transformer.”
  3. An electronic solenoid switch on the deluge valve at the riser activates and electronically “pulls a pin,” which allows the valve to trip. Water flows into the system and all heads. At this point, we now have a deluge of water surrounding the subject equipment on fire.
  4. Deluge systems sometimes require an immediate activation pull station at the hazard (in this case, the transformer) and in the riser room, so a person can intervene and manually activate the system even before the detection kicks in.

Sprinklers Made Simple Deluge Trim.jpg

Sprinklers Made Simple Deluge Manual Control.jpg


All fire service control valves must be indicating valves – i.e., just by looking at them you can see whether they are open or closed.

Outside stem and yoke (OS&Y). The amount of stem showing should be the same as the depth of the valve body – i.e., six inches of valve, six inches of stem. When the stem is out, it’s open. The red box is a tamper switch that will send a signal to the panel if someone tries to maliciously shut the valve. The lock and chain shown here are an insurance requirement, not code.

Sprinklers Made Simple OSY.jpg

Post indicator valve (PIV). This valve is found outside buildings and has a window that will indicate OPEN or SHUT. A wrench sits on the operating nut as it does on a hydrant and can be locked on the side. Both PIVs shown are also electronically supervised with tamper switches.

Sprinklers Made Simple PIV.jpg

Wall PIV. Found on the outside wall of a commercial building, similar to the PIV, it has a window indicating OPEN or SHUT. On the inside of the wall attached to this valve is a large fork that spears the operating valve on the riser so you can operate the riser valve from the outside of the building. The valve shown has a tamper switch on it as well.

Sprinklers Made Simple Wall PIV.jpg

Indicating butterfly valve (IBV). This valve is found on the riser usually for smaller piped systems. Larger risers require larger valves and operating handles. The indicator is the yellow bar in the center of the valve. As it opens and closes, the bar rotates. Since sprinkler valves must be indicator valves, an open valve will show the bar in line with the pipe. This one is open.

Sprinklers Made Simple IBV.jpg

Sprinkler Heads

Sprinkler heads come in various sizes, configurations, and temperatures. All have a specific purpose and use. One size does not fit all!

Upright. This sits on top of the pipe and is usually found in dry systems so that when the system drains down after tripping, the water doesn’t remain in the heads and pipe nipples. In an unheated area, if the temperature were to drop below freezing, water remaining in the system could damage it. This head has a chemical pellet fusible element that melts and allows the water to flow.

Sprinklers Made Simple Upright Sprinkler.jpg

Pendant. This sprinkler head hangs from under the piping. In some cases, it’s placed on a long “drop” and pokes through a dropped ceiling. The oblong device is a lead link holding the two levers together under tension. It’s designed to melt at a given temperature, releasing the arms and allowing water to flow.

Sprinklers Made Simple Pendant Sprinkler.jpg

Sidewall. These were designed primarily for retrofitting hotels and motels. A pipe is placed along the upper corner of the corridor and a sprinkler head is inserted into each room and into the corridor itself. It operates like other standard sprinklers and will have a link, a glass bulb, or a chemical pellet.

Sprinklers Made Simple Sidewall Sprinkler.jpg

Early suppression fast response (ESFR). The insurance industry designed this head for high-piled storage warehouses (e.g., big-box stores and other places with high racks of combustible storage). Because of the large water demand, you need larger pipes than usual and, in most cases, a fire pump. If ever you’ve noticed sprinklers inside the racks in your favorite home supply store, they can be eliminated if an ESFR system in installed at the ceiling. It puts out lots of water really fast. Compare the difference in size between an ESFR and a standard head. The “fast response” comes from a pencil-thin glass bulb that will burst a lot more quickly than a standard-size sprinkler bulb.

Sprinklers Made Simple ESFR vs Standard Head Sprinkler.jpg

Sprinklers Made Simple ESFR Sprinkler.jpg

High-pressure water mist sprinkler head. Developed by and for the cruise ship industry, these sprinkler heads can provide extinguishment into a compartment without necessarily flooding it. The water is discharged as a high mist fog and cools the atmosphere and the burning materials. Other applications include computer rooms instead of gas systems using halon and laboratory fume hoods where the scientists do their experiments. The water output from these heads is negligible, and they are also the only heads that have a filter screen on the nipple where it connects to the piping to eliminate any pipe scale, sludge, or other foreign matter that would be detrimental to the operation of this type of head. Note the quartzite bulb for activation.

Sprinklers Made Simple HPWM Sprinkler.jpg

Tactical Tips

  1. Always send personnel with a radio to the riser room on arrival to check the status of the sprinkler system.
  2. Place a dry line from the first-due engine to the FDC, and prepare to augment pressure in the system. Know the local pressure demands for the systems in your district; also know that the rule of thumb for FDCs for sprinklers is 150 psi.
  3. Shut sprinkler control valves only on the express order of the incident commander (IC). Let the system do what it was designed for, which is to confine, contain, and possibly extinguish the fire. ESFRs are designed to extinguish. Sprinklers will buy you some time to set up and get going.
  4. Carry sprinkler head clamps to help minimize water damage. Sometimes two wood chocks work, but they would have to be cut to the right size.
  5. Be ready to deploy salvage tarps for water traveling down to the floors below.
  6. It’s extremely difficult and dangerous to fight a fire when sprinklers are operating. It is recommended that you don’t. The water from the heads is pushing the heat and steam down on top of you, and visibility is worse than usual. Coordinate your actions. Vent, shut the valve (by the IC’s order), and move in with a line as simultaneously as you can.
  7. For stubborn deep-seated Class A or Class B fires, consider pumping finished foam solution into the FDC. Also consider pumping foam solution into FDCs feeding standpipe systems so you can have a foam handline if you need one on the upper floors of a building. We tried this in industry, and it worked! (New Uses for Foam in Industry, Fire Engineering, November 2001). Standard sprinkler heads, although not necessarily listed for “foam service,” will effectively discharge foam.
  8. Depending on your department’s policies, you may be expected to restore the system before you leave. There should be six spare heads and a wrench at the riser for this purpose. It is ultimately the owner’s responsibility to ensure that the system gets restored in a timely manner. Codes will not allow some occupancies to be occupied unless the sprinklers are in service (e.g., child care center), so immediate restoration of the system may be warranted vs. a “vacate” order.
  9. If the swivels on the FDC are frozen, won’t spin, and won’t allow you to hook up, pull three feet of the line between your knees, and lock it there. Backtwist the line about seven turns and then place it on the frozen swivel and let it thread itself. Try this during a drill. Different thread types will bring different numbers of backtwists.

Sprinkler Training Tips for the Company Officer

One of the many responsibilities of the company officer is to ensure the members of his crew are familiar with active and passive fire protection. This segment on sprinklers (active fire protection) is key to understanding the basics of water-based fire protection systems. Knowledge of these systems lends itself to safe and efficient operations. Try these training tips to get your crew familiar with sprinklers:

  1. Review the basic wet and dry systems as outlined. Explain the importance of knowing these systems and how they will help you fight the fire more effectively and how they assist with firefighter safety.
  2. Review the tactical tips as outlined.
  3. After review, go to the field and find these systems.
  4. At a building in your response district, have the building engineer or other responsible party walk you through the systems.
  5. Go to another building and have the members identify the components on the systems there. They need to know and understand the basics so when you send them to the “main control valve,” they’ll know what you mean.
  6. Take advantage of your fire prevention bureau, fire marshal’s office, or fire academy. They have expertise in this area. Drop your pride, and improve your safety and fireground efficiency.
  7. When you think your members know the basics, do it one more time. Just like standard tactics, knowledge of these systems needs to be second nature.
  8. Make this part of your regular training, and take the time to examine these systems. Do it on or after runs or during downtime. If you’re driving by a building and you spot a water motor gong, an FDC, or a fire pump manifold, stop and take a look.


RON KANTERMAN is the chief of the Wilton (CT) Fire Department and a 40-year fire service veteran with experience in municipal and industrial fire protection, volunteer and career services, emergency management, and emergency response. He has a bachelor’s degree in fire administration and master degrees in fire protection management and in environmental sciences. Kanterman is a contributing author to Fire Engineering,, Fire Engineering’s Handbook for Firefighter I and II, and the new edition of The Fire Chief’s Handbook. He co-hosts an FE Blog Talk Radio show “The Back Step Boys” and lectures around the country on various fire service topics. He is an adjunct professor of fire science and emergency management at the University of New Haven in Connecticut. Kanterman is also an advocate for the National Fallen Firefighters Foundation and its programs and is the chief of operations for the annual National Memorial Weekend.