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The union features solder cups. The fitting is used to allow repair to the line without damage. 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:
- Solder
- Metal End Connection Type:
- C x C
- 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 B255550 – Frequently Asked Questions
1) What does the Nibco 733 union connect to, sweat copper or threaded pipe?
The Nibco 733 is a C x C union, meaning both ends are solder cups that sweat onto copper tube. There are no threads on either end. If you need to break into a threaded line, you want a union with an FIPT or MIPT end instead, not this one. The union nut itself is what lets you take the joint apart later, so the joint is soldered but still serviceable.
2) What copper pipe sizes does the Nibco 733 solder union come in?
Eleven sizes, from 1/4 inch through 3 inch: 1/4, 3/8, 1/2, 5/8, 3/4, 1, 1-1/4, 1-1/2, 2, 2-1/2 and 3 inch. Both cups are the same size on a given union, so pick by the copper tube you are joining. The common trade sizes carry MPN B255400 for 1/2 inch, B255500 for 3/4 inch and B255550 for 1 inch.
3) Can I use a Nibco 733 union on a potable water line?
No. The 733 union is cast from ASTM B584 alloy C84400 bronze, and use of that alloy in U.S. drinking water applications has been prohibited since January 3, 2014. For potable water you need a lead-free listed union. The 733 is still appropriate for the non-potable systems it is rated for: heating, HVAC, fire protection, industrial and irrigation service.
4) Why put a union in a copper line instead of just soldering a coupling?
A coupling makes the run permanent. The 733 union is there so you can break the line later without cutting it, which is the point of the fitting: it allows repair to the line without damage to the surrounding piping. Put one on each side of a pump, a control valve, a boiler or a strainer, and that component comes out with two wrenches instead of a torch and a pipe cutter. In an occupied building that is the difference between a 20 minute swap and a re-pipe.
5) Is the Nibco 733 union bronze or wrought copper?
Cast bronze, not wrought copper. The body is ASTM B584 alloy C84400 with material and workmanship per ASME B16.18, and it is dezincification resistant, which matters on hydronic and closed loop systems where water chemistry attacks the zinc in lesser alloys. Cast bronze is the normal construction for a union because the nut and seat need the wall thickness.
6) Will a soldered bronze union hold up on a hydronic heating loop?
Yes, heating and HVAC are among the systems the 733 is intended for, along with commercial and residential plumbing, fire protection, industrial and irrigation service. The dezincification resistant bronze is the reason it holds up in a closed loop, where dissimilar metal and treated water eat cheaper brass. Same fitting works on a chilled water line.
7) How do you solder a union without ruining the seat?
Take the union apart before you heat it. The 733 has three pieces, two solder-cup tailpieces and the nut, and the ground seat and any gasket will not survive a torch. Sweat each tailpiece to its tube separately, let both cool, then bring them together and draw the nut up. Nibco publishes copper fittings installation instructions, and the joint is made to ASME B16.18 practice.
8) Nibco 733 versus a threaded union on a copper system, which is right?
On copper tube the 733 solder union is the direct fit, since both ends are cups that sweat onto the tube with no adapters and no thread sealant. A threaded union belongs on steel or where you are landing on a threaded valve or pump flange. Mixing the two means adding a copper-to-thread adapter, which is another joint and another leak path. Match the union to the pipe you are actually running.
9) Do I order a 733 union by copper tube size or by the fitting outside diameter?
Order by nominal copper tube size, the same number you call the pipe. A 3/4 inch 733 takes 3/4 inch copper in both cups. Copper tube is sized nominally and runs 1/8 inch larger on the actual outside diameter, so do not measure the tube OD with calipers and order that number, you will end up a size up.
10) Can I use a Nibco 733 union on a fire sprinkler line?
Fire protection is one of the listed system uses for the 733 union, alongside industrial, irrigation, HVAC and heating. On a sprinkler system the union gives you a takedown point at the riser or at a device without cutting the copper. Any fire system installation still follows the authority having jurisdiction and the system design drawings.
11) Is copper the right choice for a LEED or sustainable plumbing project?
Copper is reusable at end of life, which is what makes it count on sustainable projects, and it carries the durability and low maintenance that keep it in service for decades. The 733 union is manufactured in an ISO 9001 certified facility. For a distributor or a specifier building out a green spec, the recyclable copper system with serviceable union points is a defensible package.
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Does the Nibco B255550 come with a warranty?
Absolutely. The Nibco B255550 is backed by a manufacturer’s warranty.
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