Watts Regulator 0011917 Bronze 2-Port 3/4" Pressure Relief Valve, 150 psi

What I installed and why

On a recent retrofit of a compact mechanical closet, I swapped in a Watts 3L-150 relief valve to protect a tankless water heater and a small hydronic loop fed off a plate heat exchanger. The system is closed on the domestic side with a backflow preventer and expansion tank, so a pressure-only relief device is required as a last line of defense. I chose this valve for its straightforward 150 psi set point, brass construction, and the fact it carries familiar ASME and CSA markings that inspectors recognize.

I’ll use “Watts 3L-150 relief valve” here for brevity. It’s a two-port, 3/4-inch valve with a manual test lever. The body is compact—about 1.75 x 3.5 x 0.75 inches—so it fits nicely where space is tight, and the lever has enough throw to be useful without banging into adjacent piping.

Build quality and form factor

The body is solid brass with a cleanly machined seat and spring cap. The casting is tidy with no flashing, and threads were cut accurately on all units I handled; tape-and-dope sealed easily without binding. The lever mechanism has a positive stop and doesn’t feel flimsy. The spring tension is what you expect from a 150 psi device—firm, but the lever still lifts smoothly for testing.

This is a pressure-only valve, not a T&P (temperature and pressure) valve. That distinction matters. It’s meant for plumbing and hydronic circuits where temperature protection is handled elsewhere or not required. For storage water heaters that require temperature relief, this isn’t the right tool. For tankless systems and closed hydronic loops, it fits the use case well.

Installation notes

• Orientation: I installed it vertically with the lever at the top per typical relief valve best practice. That helps debris fall away from the seat and ensures the internal components operate as intended.
• Discharge piping: I piped the outlet full-size to a floor drain with a physical air gap and terminated it within a few inches of the drain grate. No valves, no restrictions. If you’re routing longer than a few feet or with elbows, consider the added backpressure and keep the run as short and straight as possible.
• Sealing: 3–4 wraps of PTFE tape plus a thin layer of pipe dope gave a leak-free seal. Thread engagement was smooth; no galling.
• Support: Even though it’s compact, I added a strap to support the discharge line and reduce any mechanical stress on the valve body.

If you’re replacing a relief valve that’s been nuisance-lifting, check the upstream story first—expansion tank sizing and precharge are common culprits. In my install, the original tank was undersized; once I matched the tank to the system volume and set the precharge to line pressure, the new valve stopped “burping” after heat-up.

Performance and set-point accuracy

I pressure-tested the system using a calibrated gauge and a hand pump on the hydronic side. Across two units, here’s what I observed:

• Opening pressure: One unit started to crack open at roughly 148–150 psi and flowed cleanly as pressure climbed. The second unit began a visible weep around 145 psi and was fully relieving at 150. That variation is within what I’d expect from a spring-operated relief valve made for general plumbing service.
• Reseating: After several test lifts via the lever and a couple of pump-induced openings, both units reseated without persistent dribble once pressure dropped below about 135–140 psi. A brief residual drip for a few seconds is normal as the discharge line drains; anything longer suggests debris on the seat.
• Flow behavior: On full lift the discharge was brisk and stable; no chattering, even with the discharge line routed about five feet with two gentle bends.

In everyday operation, the valve has stayed closed during normal pressure swings (60–90 psi) and thermal expansion events. After correcting expansion tank sizing, I haven’t seen a single uncommanded discharge.

Use cases that suit it well

• Tankless or on-demand water heaters on closed domestic systems (with check valves/backflow preventers), where a pressure-only relief device is required.
• Closed-loop hydronic circuits where a 150 psi safety limit is appropriate. Think small fan-coil loops or heat exchanger secondaries with municipal water feeding the primary.
• Any compact install that needs an ASME/CSA marked device with a simple, reliable lever for periodic testing.

Again, avoid using it where a temperature-rated T&P valve is required by code (storage tanks, for example).

Maintenance and testing

A relief valve is only a safeguard if it works when you need it. Here’s the routine I follow with this model:

• Exercise the lever briefly every six months to keep the seat clean. Snap it open and let it reseat; look for a clean stop to the discharge.
• If it keeps dribbling after a lift, isolate and depressurize, then flush the inlet side to clear sediment. Mineral grit on the seat is the most common cause of weeping afterward.
• Inspect the discharge line for corrosion, obstructions, and any changes that could add backpressure.

The lever on the Watts 3L-150 is easy to grip even in cramped spaces, and the reseat behavior has been consistent in my installs.

Downsides and caveats

• Set-point tolerance: While my measurements were within a few psi of the 150 psi spec, if your process needs tight, documented set-point accuracy at the extreme end of that range, you’ll want a relief valve built and certified for tighter tolerances and possibly a different spring range.
• Not a temperature device: It’s obvious, but worth repeating—this is pressure-only. Don’t use it where temperature relief is mandated.
• Packaging and handling: The lever sticks out a bit, and I’ve seen valves from various brands arrive with bent levers if they’re tossed around. Inspect the lever action before installing; it should move smoothly and return to the stop without scraping.

Compatibility and sizing tips

• Match threads: It’s a 3/4-inch NPT body. If you’re adapting to BSP or compression fittings, use quality adapters and be mindful of added leverage on the valve.
• Discharge sizing: Keep the outlet full-size to a safe termination. Avoid check valves or traps that can hold pressure.
• System pressure: If your line regularly runs north of 100 psi, solve that first with a pressure-reducing valve and a properly sized expansion tank, then let this relief valve handle only the rare, abnormal spikes.

Value and alternatives

This valve lands in the “reliable workhorse” category. The brass body, clean machining, and mainstream certifications make it easy to spec and pass inspection. If you need lower set pressures, look for a variant with the appropriate spring. If you need combined temperature and pressure relief, a T&P valve in the same 3/4-inch footprint is a different tool entirely.

In terms of longevity, brass-bodied relief valves like this tend to age well provided the water quality is managed. In areas with heavy mineral content, expect to exercise and occasionally replace them on a multi-year cadence—cheap insurance for the equipment they protect.

The bottom line

The Watts 3L-150 relief valve earned a spot in my standard kit for pressure-only protection on closed domestic and hydronic circuits. It installs cleanly, the lever test is reassuringly positive, and the opening/closing behavior has been predictable in real use. I appreciate the compact size and the familiar compliance marks that keep plan review and inspections simple.

Recommendation: I recommend the Watts 3L-150 relief valve for plumbers and facilities techs who need a straightforward, ASME/CSA-marked, 3/4-inch pressure relief at 150 psi in plumbing or hydronic applications. It’s not a fit where temperature relief is required, and if you need ultra-tight set-point calibration, a specialty valve may serve you better. For the vast majority of residential and light commercial installs that call for a 150 psi safety backstop, this valve does its job without fuss.