Measurement and Uncertainty Analysis of Pressure Losses in a Push-to-Connect Elbows and Couplings

Published

July 17, 2025

Author(s)

Lingnan Lin, Natascha Milesi-Ferretti, Glen Glaeser, Kyu Young Kim

Abstract

Measurement and Uncertainty Analysis of Pressure Losses in a Push-to-Connect Elbow and Coupling The data on pressure losses in an elbow and a coupling are reported for Reynolds number (Re) from approximately 104 to 105. Both fittings selected for testing are commercially available, made of lead-free brass, with a push-to-connect design for use with copper or plastic pipe, and have a nominal tube size (NTS) of ¾. The pressure loss was determined by measuring the pressure distribution upstream and downstream of the fitting, from which hydraulic grade lines were established. The results show that the pressure loss coefficient of the elbow decreases with Re before leveling off at 1.0 when Re exceeds 40000. A corresponding correlation was developed. In contrast, the pressure loss coefficient of the coupling is independent of Re, with an average value of 0.007. The equivalent lengths for both fittings are also reported. The equivalent length of the elbow ranges between (0.8 to 1.1) m, while that of the coupling ranges between (4.5 to 7.5) mm. An extensive uncertainty analysis is provided. The uncertainty tends to be larger at smaller Re. A key finding is that additional tapping locations upstream are recommended to reduce the uncertainty associated with the pressure loss measurement. Increasing the upstream tapping locations from three to five can result in a reduction of the expanded uncertainty by up to 75 %.

Citation

Technical Note (NIST TN) - 2342

Report Number

2342

NIST Pub Series

Technical Note (NIST TN)

Pub Type

NIST Pubs

Download Paper

https://doi.org/10.6028/NIST.TN.2342

Local Download

Keywords

Pressure, Flow, Water, Fittings, Plumbing, Coupling, Elbow

Citation

Lin, L. , Milesi-Ferretti, N. , Glaeser, G. and Kim, K. (2025), Measurement and Uncertainty Analysis of Pressure Losses in a Push-to-Connect Elbows and Couplings, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.TN.2342, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=959529 (Accessed October 13, 2025)