Proper air venting is essential when designing and installing a wet pipe fire sprinkler system to reduce corrosion risks and ensure system performance. While NFPA 13 allows for different methods of venting air from a sprinkler system, including a manual valve, an automatic air vent, or a remote inspector’s test valve, it is crucial to understand why a remote inspector’s test valve is not an effective air venting solution.
What is an Inspector’s Test Valve and What Does It Do?
An Inspector’s Test Valve is an important part of a fire sprinkler system. It simulates sprinkler activation and checks if the system works. The purpose of the Inspector’s Test Valve includes:
- Testing the sprinkler system’s alarm/waterflow device – Ensuring the alarm system activates when water begins flowing.
- Testing the opening of a dry-pipe or pre-action valve – Required for dry-pipe and pre-action systems to confirm proper function.
- Measuring trip time – In some systems, it helps find out how long it takes for water to reach the test valve after activation.
Inspector’s Test Valve Requirements: When & Where Required
Inspector’s test valves are required for each wet, dry, or pre-action sprinkler system but are not required for deluge systems since they have open orifices.
Wet Systems
- Must be located downstream of the waterflow alarm.
- Placement can be at the sprinkler riser or remote from the riser.
- Some jurisdictions prefer or require remote placement (NFPA 13: 2022: 16.14.1.4).
- FM Global systems mandate remote location of inspector’s test valves for wet systems (FM Global 2-0 2.6.5).
Dry & Pre-Action Systems
- Must be placed at the end of the most distant sprinkler pipe on the upper story of the system.
- Must include an accessible shutoff valve.
- Requires a plug (at least 1-inch), with at least one being brass, or a nipple and cap.
- Referenced NFPA 13 sections:
- Dry Systems: 2022: 16.4.2.2.
- Pre-Action Systems: 2022: 16.14.3.4
Deluge Systems
- No inspector’s test is required (NFPA 13 does not mandate it).
- FM Global confirms no requirement (FM Global 2-0 2.6.5).
Understanding NFPA 13 Air Venting Requirements
NFPA 13 mandates that all wet pipe systems utilizing metallic pipe must include a single air vent (Section 8.1.5). The purpose of this vent is to remove trapped air from the system. Trapped air can cause corrosion and system degradation. Section 16.7 further specifies acceptable methods of air venting, which include:
- A manual valve (minimum 1/2 inch in size)
- An automatic air vent
- A remote inspector’s test valve
- Other approved means
Although a remote inspector’s test valve is listed as a potential venting method, using an inspector’s test drain for this purpose is problematic for several reasons.
Why An Inspector’s Test Valve Fails as an Air Vent
- Location Matters: The effectiveness of an air vent depends on its placement. NFPA 13 states that the vent should be located near a high point in the system to allow air to escape. However, an inspector’s test drain is typically installed at a remote location for testing system functionality, not at the highest point where air naturally accumulates.
- Vertical Pipes Full of Water Don’t Vent: Air can indeed be vented through the remote inspector’s test when a system is filling. Once water fills the vertical pipe to the drain, the system cannot vent anymore air. This leaves air trapped in the horizontal pipes and higher points in the system.
- Designed for Testing, Not Venting The primary function of an inspector’s test valve is to simulate the activation of a sprinkler head and to verify water flow. It is not designed for continuous or effective air removal because it remains closed except during testing. Unlike a dedicated air vent, an inspector’s test drain does not provide a controlled means of releasing trapped air without water discharge.
- Limited Accessibility for Testing For efficient testing, FM Global (FM Global 2-0 2.6.5) requires the installation of the Inspector’s Test Connection in an easily accessible location. An air vent needs to be near a high point in the system, making it not easily accessible. This location reduces the likelihood of consistent air removal, allowing air pockets to persist in the system.
The Right Approach: Dedicated Air Vents
To ensure effective air venting, it is best to install a dedicated air venting device, such as:
- Automatic Air Vents: These vents continuously release trapped air without manual intervention, reducing maintenance needs and improving system longevity. AGF’s automatic air vents include a purge valve to assist with filling and draining of the system and integrated barrel strainer to prevent dirt or debris from entering the vent and are designed to be installed near a high point and require minimal maintenance.
- Manual Air Vents: These provide a controlled way to purge air from the system but require operation by maintenance personnel to release trapped air. They also have a potential for leaks if left open while a system is filling. AGF’s 7910 manual air vent features a mesh strainer and ball float to allow air to vent from the system while it is filling with water. The ball check prevents water from spilling out when it reaches the valve.
- Properly Located Remote Inspector’s Test Valves: If an inspector’s test valve is to be used for venting, it must be strategically placed near a high point in the system rather than solely in a location for flow testing. This approach makes maintenance more time-consuming since the valve is no longer accessible.
While NFPA 13 acknowledges the use of a remote inspector’s test valve as a potential air venting method, relying on an inspector’s test drain for this purpose is not advisable. Its location, design, function, and operational limitations make it ineffective for proper air removal.
To maintain system integrity, reduce corrosion risks, and ensure compliance with NFPA 13, dedicated air venting solutions such as automatic or manual air vents should be prioritized over inspector’s test drains. By implementing the right venting strategy, fire protection professionals can enhance system reliability and longevity while minimizing maintenance issues.