The Watts 174A-35 is a 3/4" pressure relief valve for hot water boiler service, factory set at 35 psi. It features a bronze body. Rated to 150 psi and up to 250°F.
This 3/4 inch boiler pressure relief valve is used in hot water heating and domestic supply boiler applications to protect against excessive pressures on all types of hot water heating supply boiler equipment. It consists of a bronze body construction with NPT threaded female inlet and NPT threaded female outlet (drain) connections, non-metallic disc-to-metal seating, stainless steel spring, and test lever. It resists corrosive water conditions, sticking and freezing, and prevents water and sediment from being trapped in the seat. It is designed for emergency safety relief, not as an operating control. The pressure relief is set at 35 psi (241.3 kPa) with corresponding high pressure ratings up to 725,000 BTU/HR
Features
- Spring loaded
- Non mechanical seat-to-disc alignment will not stick or freeze
- Water can't be trapped and sediment can't foul seat
- Automatic reseating
Common Questions
- What pressure is this valve set to?
- It is factory set to relieve at 35 psi. The setting is fixed and is not field-adjustable. Note the 150 psi figure in the specifications is the maximum of the series' pressure range — the ceiling the body is built for, not this valve's relief point. This valve opens at 35 psi. Match it to the appliance nameplate: the relief setting must not exceed the working pressure stamped on the vessel you are protecting.
- Will it fit my water heater — what BTU input does it cover?
- This valve is rated for 725,000 BTU/hr on the ASME pressure-steam basis. Code requires the relief valve's discharge capacity to equal or exceed the input of the appliance it protects, so the number on your heater or boiler nameplate must be at or below that figure. This is the ASME pressure-steam rating quoted at this valve's set pressure; do not compare it against a CSA temperature-steam figure, which is a different measurement entirely.
- Is this ASME rated?
- Yes. It is ASME rated and carries the "HV" code symbol under ASME BPVC Section XIII (the section that replaced Section IV for overpressure protection), and it is National Board (NBBI) certified. Inspectors look for that stamp on the valve body, and it is there.
- Can I use this on potable water?
- No. This is a boiler valve and is not approved for potable water, and that is true regardless of what the lead-free column says — hydronic boiler water is a closed, treated loop and is not drinking water. For a potable hot water heater or storage tank, use a T&P relief valve listed to ANSI Z21.22 / CSA 4.4 instead.
- Does the discharge have to be piped?
- Yes. Codes require the outlet to be piped full-size to a safe point of discharge, terminating with an air gap and no valve, cap, or reducer anywhere in the line — a relief valve that cannot discharge freely is not protecting anything. The manual test lever should be operated at least annually to confirm the valve is not seized.
Specifications
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Type: Relief
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Size: 3/4"
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Inlet Size: 3/4"
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Outlet Size: 3/4"
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Connection: NPT
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Body Material: Bronze
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Max Pressure (psi): 150
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Pack Quantity: 25
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Country of Origin: United States
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Warranty: 1 Year Limited
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MPN: 174A-35
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Temperature: up to 250°F
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Certifications: ASME Section XIII (HV), NBBI
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Lead-Free: No
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Relief Type: Pressure Only
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Factory Set Pressure (psi): 35
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Discharge Capacity (BTU/hr): 725000
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BTU Rating Basis: ASME Pressure Steam
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ASME Code Rating: ASME Section XIII (HV)
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Application: Hot Water Boiler
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Connection Configuration: FNPT inlet x FNPT outlet
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Automatic Reseating: Yes
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Manual Test Lever: Yes
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Approved for Potable Water: No
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SentryPlus Alert Flood Sensor: No
