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The union features a solder cup and female NPT threads. The fitting is used to allow repair to the line without damage as well as adapt from a solder connection to a threaded connection. Please refer to NIBCO technical data sheets and catalogs for engineering and installation information. In addition to its inherent qualities of beauty, durability and low maintenance, copper's reusability makes it an ideal application in sustainable projects. NIBCO® copper fittings are manufactured in an ISO 9001 certified facility, and backed by a 50-year limited warranty. Because of its longstanding reputation for innovation and precision in design and manufacturing, NIBCO is the preferred brand in the industry.
Copper Fittings Installation Instructions
- Dezincification resistant
- Use in U.S. drinking water applications is prohibited after January 3, 2014
- ASTM B584 Alloy C84400
- Material and workmanship per ASME B16.18
Copper Fittings Installation Instructions
Manufacturer Resources
Product Specs
- All Basic Material:
- Bronze
- Classification:
- Solder Pressure Unions
- End Connection:
- Threaded
- Metal End Connection Type:
- C x F (NPT)
- Product Group:
- Fitting
- Product Type:
- Solder Pressure Unions
- System Use:
- Commercial Plumbing, Fire Protection, Heating, HVAC, Industrial, Irrigation, Residential Plumbing
- Product Subgroup:
- Union
- Department:
- Plumbing
Nibco B258850 – Frequently Asked Questions
1) What does the Nibco 733-3 union connect to on each end?
One end is a solder cup that sweats onto copper tube, the other is female NPT thread. So it takes you from a soldered copper line to a threaded connection in a single fitting, which is how most people tie copper into a threaded valve, pump, or piece of equipment. The end configuration is C x F (NPT).
2) Can I use the Nibco 733-3 union on a potable water line?
No. The 733-3 is cast bronze to ASTM B584 Alloy C84400, and use in U.S. drinking water applications has been prohibited since January 3, 2014. For domestic water you need a lead-free union. The 733-3 belongs on non-potable service: hydronic heating, chilled water and HVAC, fire protection, irrigation, and industrial lines.
3) Why put a union in a copper line instead of just a coupling?
A coupling is permanent. The 733-3 union has a ground seat and a nut, so the joint comes apart with a wrench and the line can be serviced or a pump, valve, or water heater pulled without cutting pipe or reheating a solder joint. That is the whole point of it: repair the line without damaging it. If you never need to break the connection, a coupling or a plain adapter is cheaper and has fewer leak paths.
4) What pipe sizes does the Nibco 733-3 copper union come in?
Nine sizes, 1/4, 3/8, 1/2, 3/4, 1, 1-1/4, 1-1/2, 2, and 2-1/2 inch. Size is called by the nominal copper tube size on the solder end, and the NPT thread matches that same nominal size. The 1/2 inch is B258600, 3/4 inch is B258750, and 1 inch is B258850.
5) Does a bronze union like the Nibco 733-3 hold up in hard or aggressive water?
The casting is dezincification resistant, which is the failure mode that eats ordinary brass fittings in aggressive or high-chloride water and leaves a porous pink deposit behind. On a closed hydronic or chilled water loop, or on irrigation service, that resistance is the reason to spend on bronze rather than a commodity brass union.
6) Will a Nibco 733-3 union meet a spec calling out ASME B16.18 solder fittings?
Yes. Material and workmanship on the 733-3 are per ASME B16.18, which is the cast copper alloy solder joint pressure fitting standard specifiers write into commercial plumbing and mechanical drawings. The casting alloy is ASTM B584 C84400. Both call-outs are what an engineer or inspector is looking for on a submittal.
7) How do I solder a union without wrecking the seat?
Take it apart first. Back the nut off and sweat the solder-cup half onto the copper tube on its own, with the ground seat and the nut clear of the flame, then reassemble and tighten. Heating a bronze union fully assembled is what distorts the seat and gives you a joint that weeps no matter how hard you crank the nut. The threaded half is female NPT, so that side gets thread sealant, not heat. Nibco publishes copper fitting installation instructions covering the procedure.
8) I need to tie a threaded gas-fired boiler into copper piping. Is the 733-3 the right union?
For the water side of a hydronic boiler, yes, that is exactly the connection it makes: copper tube sweated on one end, female NPT onto the boiler tapping on the other, and the union lets you drop the boiler out later without cutting the piping. It is listed for heating and HVAC service. Sizes run 1/4 through 2-1/2 inch, so match the union to the boiler tapping size.
9) Is the Nibco 733-3 union approved for fire protection piping?
Fire protection is one of the listed system uses for the 733-3, along with commercial and residential plumbing, heating, HVAC, industrial, and irrigation. On copper sprinkler piping the union gives you a serviceable break point at equipment without cutting into the line.
10) What is the Nibco part number for a 2 inch copper to female thread union?
B259150 is the 2 inch 733-3. The adjacent sizes are B259050 at 1-1/2 inch and B259250 at 2-1/2 inch. All three are the same C x F configuration, cast bronze, solder cup by female NPT.
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Does the Nibco B258850 come with a warranty?
Absolutely. The Nibco B258850 is backed by a manufacturer’s warranty.
For full warranty terms, check the product documentation or Contact Us.
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