Air Venting According to NFPA 13 & NFPA 20

Air Venting for Wet Pipe Sprinkler Systems & Fire Pumps

Air Venting for Wet Pipe Sprinkler Systems & Fire Pumps

For Wet Pipe Sprinkler Systems

A single air vent shall be provided on each wet pipe system utilizing metallic pipe.

Methods of air venting

1. Manual valve (min. 1∕2" size)
2. Automatic air vent
3. Remote inspector’s test valve
4. Other approved means

Purpose of Air Venting

The purpose of the air venting valve is to exhaust as much trapped air as possible from a single location every time the system is filled. then it will reduce the amount of oxygen trapped in the system that will fuel corrosion and microbial activity.

Location of air vent:

Air vent shall be located at an accessible point near a high point in the system where the greatest volume of trapped air is vented during the first fill and each subsequent drain and fill event. 

The vent connection to the system should be located off the top of horizontal piping at a high point in the system; however, the vent connection can also be effectively located off the side of a riser or riser nipple at a high point in the system.

The manual air venting valve preferably located not over 2.1 m above the floor. 

Automatic air valves are not required to comply with the accessibility requirement of manual air venting valves; however, it is recommended the designer locate automatic air vents over areas without ceilings, above a lay-in ceiling, or above an access panel.

Venting from multiple points on each system shall not be required. It is neither the intent nor practical to exhaust all trapped air from a single location on a wet pipe sprinkler system; however, more than one vent can be used on a system at the designer's discretion. Interconnection of branch line piping for venting purposes is not necessary. An inspector's test valve can serve this purpose.

For Fire Pumps:

Air release valves are installed on the top of the pump casings and arranged for automatic or remote-control operation. 

Purpose of using air release valve with fire pumps

The purpose is to release trapped air in the casing and to minimize pump cavitation. An automatic air release is desirable on any pump with a casing that is normally full of water.

For Centrifugal Pumps:

pumps that are automatically controlled shall be provided with a listed float-operated air release valve having a nominal 1/2 in. minimum diameter discharged to atmosphere.

Above requirement shall not apply to overhung impeller–type pumps with top centerline discharge or that are vertically mounted to naturally vent the air.

For Vertical Turbine Pump:

A nominal 1 1/2 in. pipe size or larger automatic air release valve shall be provided to vent air from the column and the discharge head upon the starting of the pump & to shall also admit air to the column to dissipate the vacuum upon stopping of the pump.

This valve shall be located at the highest point in the discharge line between the fire pump and the discharge check valve.

References:

NFPA 13 - 2022 Edition (Standard for the Installation of Sprinkler Systems)

NFPA 20 - 2022 Edition (Standard for the Installation of Stationary Pumps for Fire Protection)