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The union features a solder cup and male 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 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
- Lead-free*
- Dezincification resistant
- Silicon Performance Bronze® alloy
- ASME B16.18 design standards
- NSF/ANSI/CAN-61 and 372
Copper Fittings Installation Instructions
Manufacturer Resources
Product Specs
- All Application(s):
- Lead-Free
- All Basic Material:
- Lead-Free
- Classification:
- Solder Pressure Unions
- End Connection:
- Threaded
- Metal End Connection Type:
- C x M (NPT)
- Product Group:
- Fitting
- Product Type:
- Solder Pressure Unions
- System Use:
- Commercial Plumbing, Fire Protection, Heating, HVAC, Industrial, Irrigation, Lead Free*, Residential Plumbing
- Product Subgroup:
- Union
- Department:
- Plumbing
Nibco BF6035L – Frequently Asked Questions
1) What does C x M mean on the Nibco 733-4-LF union?
C x M means one end is a solder cup that takes copper tube and the other is a male NPT thread. So the union transitions a soldered copper line into a threaded connection, such as a valve, pump, or threaded steel nipple. If you need both ends solder, a C x C union is the fitting to specify instead.
2) What pipe sizes does the Nibco 733-4-LF union come in?
Seven sizes, all nominal copper tube: 1/2, 3/4, 1, 1-1/4, 1-1/2, 2, and 2-1/2 inch. The solder cup takes copper tube of that nominal size and the threaded end is the matching male NPT size, so a 3/4 inch union solders to 3/4 inch copper and threads into 3/4 inch female NPT.
3) Why use a union instead of just soldering a coupling into the copper line?
A union gives you a joint you can break apart later without cutting pipe or reheating a soldered joint. The 733-4-LF has a nut and two mating seats, so you back off the nut and separate the line to pull a pump, valve, or water heater for service, then reassemble. A coupling is permanent. Put a union on each side of any component you expect to replace.
4) Can the Nibco 733-4-LF union be used on hydronic heating and HVAC piping, not just domestic water?
Yes. The 733-4-LF is rated for commercial and residential plumbing, heating, HVAC, fire protection, industrial, and irrigation service. That covers hydronic supply and return, chilled water, and makeup water lines. It is a solder pressure fitting, so it belongs on pressure piping, not on DWV.
5) How do you solder a union without damaging the seat?
Take the union apart before you heat it. Solder the cup end onto the copper tube on its own, with the nut and the threaded half backed off and clear, then let it cool and reassemble. Heating the assembled union can distort the ground seat and leave you with a joint that weeps under pressure. Nibco publishes copper fitting installation instructions covering the procedure.
6) Will the Nibco 733-4-LF meet a spec calling out ASME B16.18 cast copper alloy fittings?
It will. The 733-4-LF is a cast fitting built to ASME B16.18 design standards, which is the solder joint pressure fitting standard engineers cite on copper drawings. Pair that with the NSF/ANSI/CAN 61 and 372 lead-free certification and it covers the two lines that usually appear together in a plumbing spec section.
7) Can I use this copper union on galvanized steel pipe?
Not directly on the solder end, no. The 733-4-LF solders only to copper tube; the male NPT end will thread into a galvanized female fitting, but joining bronze to galvanized steel sets up galvanic corrosion at that joint. On a copper to galvanized transition, use a dielectric union instead. The 733-4-LF is the right choice where the threaded side is brass, bronze, or a valve or appliance port.
8) Do I need thread sealant on the male NPT end of a bronze union?
Yes, the male NPT half needs PTFE tape or a pipe thread sealant rated for the system, same as any tapered thread joint. The union's own seal is the machined seat between the two halves, tightened by the nut, and that seat is metal to metal, so no dope goes there. Sealant only belongs on the NPT threads.
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Can I return it if it doesn’t work for me?
Yes—ZenSupply offers a hassle-free return policy. If the product isn’t the right fit,
reach out to our support team for a return authorization or setup a return by following our return instructions.
Does the Nibco BF6035L come with a warranty?
Absolutely. The Nibco BF6035L is backed by a manufacturer’s warranty.
For full warranty terms, check the product documentation or Contact Us.
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