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Control Valves and Drains

Sprinkler Systems Quick Courses


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Typical fire sprinkler system in a commercial building


Automatic sprinklers are the most reliable and effective fire-protection devices available today—provided they operate effectively. To determine if a sprinkler system can adequately protect a property, underwriters should be familiar with the components, operation, and testing of the systems, as well as potential causes for failure.

A sprinkler system consists of the following components:

  • Overhead piping specifically designed or hydraulically designed overhead piping consisting of a riser, cross mains, and branch lines.
  • A water supply and fire department connection
  • Underground and aboveground pipes
  • Valves and drains
  • Alarms and test connections
  • Automatic sprinklers

Role of control valves and drains

Although primarily used to control or isolate portions of a building‘s sprinkler system, control valves and drains play another important role. They allow the building owner or a designated individual to perform testing and maintenance on the system.

In a recent National Fire Protection Association (NFPA) study, in almost two-thirds of cases where a sprinkler failed to operate, someone had shut off the water supply to the system before the fire. A system shutoff typically occurs when the building owner or designated individual doesn’t return a valve to its normally open position once repairs and/or maintenance are completed. Testing the system and verifying the status of water supply control valves help to identify and correct conditions that lead to the failure of the sprinkler system.

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Yellow tags on sprinkler valves usually indicate something substantially wrong with the sprinkler system

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A system riser contains a control valve

Types of control valves

Because the sprinkler system is connected to a water supply, the system needs some way to control flow when replacing a sprinkler, making alterations, or conducting internal inspections of the piping. In many instances, occupancy changes require those types of modifications.

There are two categories of control valves:

  • Indicating valves
  • Nonindicating valves
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Indicating control valve in closed position

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A common type of indicating control valve is an outside stem and yoke valve, shown here in an underground valve pit

Indicating control valves

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Indicating control valve sealed, open position

Indicating control valves

All sprinkler systems are required to have indicating control valves. Indicating valves physically show whether a valve is open or closed. A closed valve indicates that no water will flow beyond the valve and serves to alert the observer to the situation. In the event of a fire, no water would reach the individual sprinklers.

You may sometimes find a control valve sealed in its open position. You can seal a valve by passing a wire and lead seal (or a similar device) through the hand wheel and a stationary object on the valve. A broken seal indicates that the valve has operated after placement of the seal.

Examples of indicating control valves

Outside stem and yoke valve

The outside stem and yoke valve is the most common type of indicating valve. The valve operates by raising and lowering a gate that cuts off the water flowing through the valve casing. The gate connects to a large brass threaded stem with a circular threaded handle that connects to the yoke. As the operator rotates the handle counterclockwise, the stem extends further and further out of the handle, indicating the relative degree of the gate opening. As the operator rotates the handle clockwise, the threaded stem moves back into the valve and presents a lower profile. When the stem is no longer protruding beyond the handle or is flush to the handle, the gate valve is closed.

Outside Stem And Yoke Valve In Open Position

Outside stem and yoke valve in open position

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Outside stem and yoke valve in closed position

Post indicator valve

Located on the outside of a building, the post indicator valve (PIV) extends up from the ground over a water supply main. As a detachable hand crank operates the valve, the target visible through the window connected to the stem reveals the word “open” or “shut” in a window on the side of the valve housing. Note that this does not guarantee the actual condition of the valve, as the target may be misadjusted, or the gate may have separated and dropped from the stem.  For supervision purposes, the hand crank can be physically locked in position using a padlock or chain, or they can be electronically supervised using a weather-resistant tamper switch. 

Post Indicator Valve In Open Position

Post indicator valve in open position

Wall post indicator valve

The wall post indicator valve operates the same way as the post indicator valve, but it is mounted horizontally on a wall, extending through the exterior wall of the building. A wheel operates the valve, and you can see its status by the word “open” or “shut” as read through a window in the valve stem housing.

Wall Post Indicator Valve In Open Position

Wall post indicator valve in open position

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Wall post indicator valve not maintained

Butterfly valve

The butterfly valve is hand-operated open or shut by rotating a disc that remains immersed in the water stream within the piping, perpendicular or parallel to the water flow. On the exterior of the valve housing is an indicator “flag” that moves with the disc to indicate the position of the disc relative to the water flow. When the indicator flag lines up parallel to the pipe, the valve is fully open; when it's perpendicular to the pipe, the valve closes fully.

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Butterfly valve in open position

Butterfly Valve In Closed Position

Butterfly valve in closed position

Nonindicating control valves

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Nonindicating control valves

Underground curb valves

A curb valve is a valve installed in underground water supply piping and is typically used as an isolation valve for a fire hydrant when maintenance is required. It operates similarly to a gate valve. A shaft runs from ground level (or street level) down to the top of the valve. A “curb key,” a long shaft with a tee handle and a fitting designed to fit over the valve stem, reaches the valve stem from ground level. There's no indicator on the valve assembly. This is why periodic fire hydrant flow testing is very important.

Main drain

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Main drain located on the system riser

Main drain

The main drain, or test valve, on an automatic sprinkler system primarily drains water from the system for maintenance. The main drain is also used to conduct a main drain test to comply with NFPA 25 ITM requirements. The purpose of the main drain test MDT) is to test the fire sprinkler system water supply piping lead-in to the building. It is not meant to determine the adequacy of the water supply of the sprinkler system, but to detect partially closed, or closed, water supply valves or obstructions in the water supply piping by historic comparison of both static and residual pressures recorded when the main drain valve is fully open. Therefore, the MDT helps to confirm that all valves controlling the system are open and that water is available.

Documented drain test results on the Automatic Sprinkler Grading Report (ASGR) can help evaluate the reliability of the water supply. Current testing of the main drain is a mandatory part of the ASGR. Without MDT testing and recorded results, the sprinkler system cannot receive insurance rating credit.

Valve identification signs

According to NFPA 13, all control valves, drain valves, and test connections should have permanently marked weatherproof metal or rigid plastic identification signs. Building staff should secure the identification signs with corrosion-resistant wire or chain. The control valve sign needs to indicate the portion of the building served. Knowing which valve controls what part of the building helps mitigate the extent of water damage if the system develops a breach through a broken sprinkler head, failed mechanical fitting or following successful extinguishment of a fire.

Identification Sign For Main Control Valve

Identification sign for main control valve

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Identification sign for main drain valve

Control valves and drains summary

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Control valves and drains summary

A well-designed sprinkler system is a highly effective method of minimizing property damage from a fire. But simply installing a sprinkler system does not guarantee adequate fire protection. Proper inspection, maintenance, and testing ensure that the system will function as intended and control or suppress the fire with minimal water damage.

A few key points:

  • Valves allow qualified contractors to perform testing and maintenance on sprinkler systems.
  • It's extremely important that all valves and drains have proper identification.
  • Indicating valves visibly show when a valve is open or closed.
  • A leading cause of sprinkler failure is not returning a valve to its open position once repairs and/or maintenance are complete.

Verisk has trained field staff to evaluate the design, installation, and condition of sprinkler systems anywhere in the country.

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