The Caleffi R51838 is a union nut with a 2-1/2 in connection for Caleffi 5231 series equipment, providing the union joint that lets the host valve or separator be installed and removed without cutting pipe.
Product data compiled from Caleffi North America technical documentation. Last reviewed July 2026.
FunctionUnion Nut
For LineMixCal+ (5231 Series)
Connection2-1/2 in
Warranty2 Years
Key Features
Genuine Union Nut
Correct thread form and depth for the matching Caleffi union tailpiece and body.
Fits 5231 Series
Matched to Caleffi MixCal+ 5231 series high-flow thermostatic mixing valves - confirm your model number before ordering.
Technical Data
| Function | Union Nut |
|---|---|
| For product line | MixCal+ (5231 Series) |
| Fits | Caleffi 523180A, 523188A, 523190A, 523198A (5231 MixCal+, 1-1/2 in and 2 in valves) |
| Description | 2-1/2 in Union Nut for 5231 Valves |
| Connection size | 2-1/2 in |
Related Products
Caleffi R530032 in Union NutCaleffi R530052 in Union NutCaleffi NA107151-1/2 in Union NutCaleffi R315891-1/2 in Union Nut
Frequently Asked Questions
What does the Caleffi R51838 fit?
It is the genuine fitting for Caleffi 523180A, 523188A, 523190A, 523198A (5231 MixCal+, 1-1/2 in and 2 in valves). Match your host model number and connection size before ordering.
2-Year Limited Warranty. Backed by Caleffi North America's limited warranty against defects in material and workmanship for two years from date of shipment. See Caleffi's limited warranty for full terms.
- Type:
- Union Nut
- For Product Line:
- MixCal+ (5231 Series)
- Connection Size:
- 2-1/2 in
- Fits:
- Caleffi 523180A, 523188A, 523190A, 523198A (5231 MixCal+, 1-1/2 in and 2 in valves)
