Watts 40L & 40XL T&P Relief Valves

Watts 40L and 40XL T&P Relief Valves protect domestic hot water storage tanks and water heaters from excessive temperature and pressure buildup in commercial applications. Both series are ASME rated and CSA listed, relieving at 210 degrees Fahrenheit and at a pressure range of 75 to 150 psi, with standard settings available at 75, 100, 125, or 150 psi depending on the model. A bronze body with NPTF male inlet and female outlet threads makes up the core construction, along with a coated thermostat, tamper-resistant bonnet screws, and a test lever for manual verification. The main difference between the two series comes down to thermostat length: the 40L uses a short thermostat for installation directly in an available tank tapping, while the 40XL uses an extension thermostat for tanks where the hot water outlet sits farther from the top. Matching thermostat length and pressure setting to the specific tank determines which of the two series is correct for a given installation.

Subcategories

• 40L Short Thermostat Valves: The 40L series uses a short thermostat designed to install directly into a tank tapping without an extension. This makes it the straightforward choice when the tank's tapping location sits close enough to the hot water zone for the short probe to read an accurate temperature. Standard pressure settings of 75, 100, 125, or 150 psi are available across the series, all relieving at 210 degrees Fahrenheit. The bronze body, tamper-resistant bonnet screws, and test lever carry through from the shared 40-series design.
• 40XL Extension Thermostat Valves: The 40XL series adds an extension thermostat so the temperature-sensing probe can reach farther into the tank than the tapping location alone allows. This is the series to specify when the hot water outlet sits beyond the reach of a short-thermostat valve, since an extension keeps the probe positioned within the manufacturer's allowable distance from the top of the tank. Pressure settings and the 210 degree Fahrenheit temperature relief match the 40L series. Confirming the correct extension length for the specific tank model is the key step when specifying a 40XL.

Buying Guide

Choosing between the Watts 40L and 40XL comes down to thermostat length before anything else. The 40L's short thermostat works when the tank tapping is close enough to the hot water zone to give an accurate reading, while the 40XL's extension thermostat is required when the tapping is farther away and a short probe would sit in a cooler part of the tank. Installing the wrong length risks a valve that reads inaccurately and either relieves too early or fails to relieve when it should, so confirming the tank manufacturer's specification for thermostat reach matters more than defaulting to whichever valve is on the shelf. Pressure setting is the second variable, with both series offered at 75, 100, 125, or 150 psi; the setting has to match the tank's rated working pressure rather than being chosen independently of it. Both series share the same 210 degree Fahrenheit temperature relief point, bronze body construction, NPTF male inlet with female outlet threads, and a tamper-resistant bonnet that discourages field adjustment of the factory setting. The included test lever allows a technician to manually check that the valve operates before it is needed in an actual overpressure or overtemperature event, and periodic testing is part of standard maintenance on any commercial hot water tank. Because both series are ASME rated and CSA listed, they are built for the commercial applications where code compliance on relief protection is typically required, though confirming local code requirements for tank relief valve sizing remains part of any installation.

Frequently Asked Questions

What is the difference between the Watts 40L and 40XL relief valves?

The 40L uses a short thermostat for installation directly in a tank tapping, while the 40XL uses an extension thermostat for tanks where the hot water outlet sits farther from the top.

What temperature and pressure do these valves relieve at?

Both series relieve at 210 degrees Fahrenheit and are available in pressure settings of 75, 100, 125, or 150 psi depending on the model.

What are the 40L and 40XL valves made of?

Both use a bronze body with NPTF male inlet and female outlet threads, a coated thermostat, tamper-resistant bonnet screws, and a test lever.

How is the correct thermostat length determined?

Thermostat length is matched to how far the tank's hot water outlet sits from the tapping location, following the tank manufacturer's allowable distance for the thermostat to read accurately.

Are these valves rated for commercial applications?

Yes. Both the 40L and 40XL series are ASME rated and CSA listed, built for higher capacity temperature and pressure protection on commercial hot water supply tanks and water heaters.