Watts LFLL100XL 150-210 3/4 3/4 In Lead Free Self Closing Temperature And Pressure Relief Valve, 150 psi, 210 F, Extended Shank Up To 2 1/2 In Insulation

That's the whole point of the extended shank version. The LFLL100XL has a 2-1/16 inch shank, which lets it pass through tank insulation up to about 2-1/2 inches thick and still put the 2 inch copper thermostat probe into the water. On a heater with thick foam jacketing, a standard short-shank T&P sits too shallow and the probe never reads tank temperature properly. If your tank has a thin jacket or a threaded tapping right at the shell, the extended shank is more length than you need but it will still seat.

Sizing goes by discharge capacity, not by pipe size. The LFLL100XL is rated 200,000 BTU per hour on pressure steam discharge and 105,000 BTU per hour on temperature steam discharge. The temperature figure is the one that governs on a domestic or commercial water heater, so the heater's input rating must not exceed 105,000 BTU per hour. A 199,000 BTU heater needs a larger relief valve than this one.

Yes. The body is a lead free copper silicon alloy, so it's suitable for potable water service where lead free construction is required. It's also Buy American Act compliant, made in the USA, which matters on government, school, and healthcare work where domestic sourcing is a bid condition.

No. Maximum working pressure on this valve is 113 psi even though the relief setting is 150 psi. Those two numbers do different jobs: 113 psi is the continuous system pressure it is built to sit at, and 150 psi is the point at which it dumps. On a building with high incoming street pressure, get a gauge on the line first. If static pressure is running near or over 113 psi, you need a pressure reducing valve upstream, not a different T&P.

A self closing T&P like the LFLL100XL reseats itself once the tank drops back below its 150 psi / 210 F trip points, rather than staying open until someone resets it. In practice that means a heater that briefly overshoots relieves and then goes back to normal service. It does not mean the valve is a substitute for fixing the cause. Repeated discharge points at a failed thermostat, a thermal expansion problem, or a heater running past its limits, and a T&P that has relieved repeatedly should be replaced.

Order Watts model LFLL100XL 150-210 3/4, Watts part number 556002. The number reads straight through: LL is the extended (long) shank, 100XL is the series, 150 is the pressure setting in psi, 210 is the temperature setting in F, and 3/4 is the connection size. If you need a different pressure setting or a standard short shank, that is a different model in the same family, so check the numbers after the series before ordering.

The probe geometry decides it. With a 2 inch copper thermostat probe on a 2-1/16 inch shank, the valve has to be installed so that probe sits in the top 6 inches of the tank, in the hot water, in a tapping that puts it in direct contact. A side tapping low on the tank or a run of nipple between the valve and the shell moves the probe out of the hot zone and the temperature element stops doing its job. Thread it straight into the tank tapping, no extension nipple.

One valve covers both here. The LFLL100XL is a combination temperature and pressure device, so it protects against overpressure at 150 psi and against overheat at 210 F in a single tapping. Straight pressure-only relief valves exist and are used on boilers and expansion applications, but on a storage water heater code wants the combination unit, because a heater can run away on temperature without the pressure ever climbing.