Fire sprinkler test and drain valves are designed to do double-duty—and more!
A test and drain valve combines the inspector’s test connection and draining functionalities into a single valve on a fire sprinkler system. This simple device meets installation requirements and enables the completion of two significant tests mandated by National Fire Protection Association (NFPA) standards. However, there’s more to this part than its well-known double versatility. Test and drain valves also have a 1/2” plugged port—and some QRFS customers wonder why it’s there.
Many people assume that the port is a good place to install a pressure gauge for the readings required during a main drain test. However, that’s actually a bad idea (and NFPA says don’t do it). So, here’s your guide to what this port can do, along with other test-and-drain information, including:
- The main functions and features of a test and drain valve
- Why the 1/2” port can’t be used for a gauge that reads residual pressure
- How the test and drain can be combined with a pressure relief valve (PRV) and be used for acceptance hydrostatic tests
QRFS has AGF Manufacturing, Landsdale, and FPPI test and drain valves in stock and ready to ship! Check out our online selection today or contact our customer service team if you need help finding the right part.
Fire Sprinkler test and drain features and functions
A test and drain valve is a specialized part that combines a drain valve with an inspector’s test connection into a single piece of hardware.
Serving as a drain
Drain connections are located on the main sprinkler riser and at any riser section of the system that can be isolated by a valve (e.g., an upper floor’s floor control assembly).
Drain valves are obviously used to drain sprinkler pipes for maintenance purposes, such as when replacing broken sprinkler heads. NFPA 13: Standard for the Installation of Sprinkler Systems (2025 edition), specifies that drain valves must be sized to efficiently drain different sizes of system risers or branch lines (16.10.4.2). Besides draining the system during maintenance tasks, drains are also used to execute the annual main drain test outlined in NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems (2023 edition, 13.2.2).
To conduct a main drain test, testers first evaluate the system’s static pressure (pressure with no water flowing) by reading a gauge attached to the system. Then, the drain valve is opened wide to flow water. Once the flow and system pressure stabilize, the residential pressure—the pressure of the system under flow—is recorded. These static and residual values are then compared with numbers taken during previous tests, including at system acceptance. The purpose of this test is to check for any degradation of the water supply’s pressure year-to-year, and a 10% drop triggers an investigation of the cause.
Serving as the inspector’s test connection
The inspector’s test connection, aka “alarm test connection” in NFPA-speak, is designed to mimic the flow of water through a single sprinkler of a particular K-factor, simulating a sprinkler activation and testing the subsequent alarm.
A small orifice that mimics a sprinkler is not useful for draining a system. Instead, the inspector’s test connection is opened to check whether different flow-monitoring devices will truly function in the event of a single sprinkler operation. This equipment includes supervisory flow or pressure switches, whose inspection, testing, and maintenance we’ve discussed in detail in a previous blog.
NFPA 13 requires systems to have an alarm test connection (16.14.1), and NFPA 25 requires a test of the alarm either quarterly (for Mechanical Waterflow Alarm Devices, 13.2.3.1.2) or semiannually (for Vane-Type, Paddle-Type, and Pressure-Switch-Type Waterflow Devices, 13.2.3.3).
Fire sprinkler test and drain valve components
A test and drain valve typically includes some key parts and features:
- Two female NPT threads on the inlet and outlet
- A sight glass to verify that water is flowing without going outside to check the water flow
- A three-position valve:
- Closed
- Test—simulates the flow from one sprinkler
- Drain—wide open for maximum flow during drainage
- Plugged 1/2-inch NPT port
Many wonder why the test and drain valve has a plugged access port. Here’s what it is (and isn’t) for:
A test and drain port is NOT for a pressure gauge taking residual pressure readings
As mentioned, the annual main drain test requires measuring the residual water pressure (the pressure under flow) while the main drain is open. This assessment requires reading a pressure gauge, and some people think the 1/2″ port on a test and drain valve is a great place to attach that gauge. But that’s NOT the case!
Measuring residual water pressure accurately requires smooth, non-turbulent flow. Unfortunately, pipe tees and elbows create turbulence in flowing water when they force it to change direction. So, inserting a pressure gauge into the port of a test and drain valve effectively puts the gauge into an elbow, reducing the accuracy of pressure readings. NFPA 13 addresses this issue in section A.16.10.4 and provides an example of an incorrect arrangement:
Note that you can install a gauge at the 1/2″ port on a test and drain to take accurate static pressure readings, assessing the PSI under normal system conditions when there is no flow. However, again, it’s not the best place for obtaining the residual readings needed for the annual main drain test.
Test and drain ports ARE for pressure relief valves and an acceptance hydrostatic test
One actual purpose of these 1/2” access ports on test and drain valves is to accept an optional pressure relief valve (PRV). For example, unless a wet sprinkler system has “auxiliary air reservoirs […] to absorb pressure increases,” NFPA 13 requires the system to have a PRV of at least 1/2” that is set to operate at whichever is greater: 175 PSI or 10 PSI greater than the maximum system pressure (8.1.2.1).
PRVs are necessary because sprinkler pipes are closed systems, and temperature fluctuations and other factors can increase pressure, sometimes causing dramatic spikes. The PRV discharges water from the system to relieve pressure and prevent damage to pipes and fittings from pressures exceeding the system’s tolerances. And since the PRV discharges water, it also makes sense to locate it at the system’s drain.
PRV kits are fairly simple for fire protection pros to install themselves, even in wet, pressurized systems (see the video below). But these parts are also available preinstalled on some test and drain valve models.
For new systems, it’s common to install a test and drain valve without the PRV attached, perform an acceptance hydrostatic test, and then install the PRV. If the PRV were installed before the hydrostatic test, it would need to be removed or disabled before conducting the test, since the required test pressure often exceeds the factory-set pressure for these PRVs. The PRV relieving pressure may defeat the purpose of a hydrostatic test, which would read as a “fail.”
This video from AFG explains the installation of a PRV:
The order of operations for installing a PRV brings up a second use for the system access port on a test and drain valve: conducting a hydrostatic test as part of a new system’s acceptance tests. Since new systems require hydrostatic tests to ensure the integrity of piping, hydro tests must be done before installing a PRV, and subsequently installing a PRV requires draining the system anyway, the port is a convenient spot to hook up a hydrostatic test pump to conduct the acceptance test!
Test and drain valves offer extra utility
Test and drain valves make fire sprinkler system upkeep more efficient by combining multiple features and uses into a single piece of hardware. You can drain the system (or a section of it) through this part, conduct the annual main drain test with it, or use it to test flow and pressure monitoring devices. It’s also possible to mount a PRV to a test and drain and use it as an access port for a hydrostatic test!
Check out QRFS’s selection of test and drain valves with a range of sizes to match various risers and sprinkler K-factors, and with and without pressure relief valves (PRVs). If you have questions or need help finding a part, contact the QRFS customer service team.
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