MAS B-3 Full Port Brass Ball Valve B-3-3/4 | 3/4 in. FNPT
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MAS B-3 Full Port Brass Ball Valve — Part No. B-3-3/4
- Part Number: B-3-3/4
- Supplier SKU: VAL-B-33/4
- Brand: MAS / M.A. Stewart (B-3 Series)
- Type: Full-Port Brass Ball Valve
- Nominal Size: 3/4 in.
- Connection: 3/4 in. Female NPT × Female NPT (both ends)
- Port: Full port / full bore
- Body & Ball: Brass (chrome-plated ball surface)
- Seats & Packing: PTFE
- Handle: Lever-style, quarter-turn operation
- Stem: Blowout-proof with adjustable packing gland
- Pressure Rating: 600 WOG / 150 WSP
- System: Plumbing / Marine Plumbing — on/off isolation service
What This Valve Does
The MAS B-3-3/4 is a 3/4-inch full-port brass ball valve for reliable on/off isolation in compatible fluid systems. The full-bore design maintains flow capacity close to the nominal pipe diameter, reducing pressure drop versus standard-port valves. A quarter-turn lever gives instant open/closed confirmation.
Size note: The supplier SKU (VAL-B-33/4) can read ambiguously — this is the 3/4-inch size of the MAS B-3 series, not a 3-3/4-inch valve. The B-3 family is available in sizes from 1/4 in. through 4 in.; confirm the correct size before ordering.
Compatible Applications
- Fresh water supply and shutoff lines
- Oil lines (confirm fluid compatibility with brass and PTFE)
- Gas lines (confirm applicable installation standards and approvals for your jurisdiction)
- General marine plumbing isolation service in compatible systems
- Other liquid or gaseous media compatible with brass body and PTFE seats at rated pressure and temperature
Fitment & Selection Checklist
- Pipe size: 3/4 in. nominal
- Thread type: NPT (National Pipe Taper) — confirm mating fittings are NPT, not BSP
- System pressure must be within rated limits (600 WOG / 150 WSP)
- Confirm fluid compatibility with brass body and PTFE seats/packing
- For marine below-waterline or seacock applications, verify the complete installation meets applicable standards — a standard inline ball valve is not automatically rated for that use
When to Replace
- Leakage through the closed ball or around the stem
- Seized, stiff, or erratic quarter-turn operation
- Visible cracking, corrosion damage, or stripped NPT threads
- Excessive handle or stem play indicating internal wear
Installation Notes
- Apply thread sealant compatible with the system fluid and brass NPT fittings
- Support adjacent pipework to avoid placing bending or torsional load on the valve body
- Handle parallel to the pipe = open; handle perpendicular = closed
- Use for full-open or full-closed service — ball valves are not suited for fine flow throttling
Related Products
- MAS Full Port Brass Ball Valve B-3-1/2 | 1/2 in. FNPT
- MAS B-3 Full Port Brass Ball Valve B-3-1/4 | 1/4 in. FNPT
- Valves & Strainers — Full Collection
Parts Desk Insights
The 3/4 in. size is one of the most commonly used ball valve sizes in marine plumbing and general service — it fits a wide range of through-hull lines, raw water circuits, and fuel shutoffs where flow capacity matters. The full-port design is the right choice when you need to minimize restriction through the valve. The most frequent ordering issue with this SKU is a size misread: VAL-B-33/4 gets read as a 3-3/4-inch valve. Always confirm you need the 3/4-inch size. As with any inline ball valve, verify separately whether your installation requires a valve rated to a marine seacock standard before installing below the waterline.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
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If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
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