The symbol above is a representation of which one of the following?

The symbol shown is the standard graphical representation for a check valve as defined by the National Fire Protection Association (NFPA). In fire protection system drawings, this symbol indicates a valve that permits fluid flow in only one direction, which is denoted by the direction the triangle is pointing. The vertical line within the triangle represents the internal gate or flapper mechanism that prevents backflow, a critical function in systems like sprinkler risers and fire pump connections to ensure water flows towards the fire and not back into the supply.

A. Riser: A riser is a vertical supply pipe, and its symbol is typically a circle with a dot in the center, often labeled "R".

B. Reducer: A reducer is a pipe fitting used to join pipes of different diameters; its symbol depicts a conical transition between two parallel lines.

D. Post-indicator valve: A post-indicator valve (PIV) is represented by a butterfly valve symbol (a "bowtie") with a circle and a vertical line through it, or a circle labeled "PIV".

1. NFPA 170, Standard for Fire Safety and Emergency Symbols, 2021 Edition. Table 5.3.1, "Symbols for Pipe Fittings, Valves, and Pipe," Symbol No. 5.3.1.21, "Valve, Check."

2. Society of Fire Protection Engineers (SFPE), SFPE Handbook of Fire Protection Engineering, 5th Edition. Chapter 20, "Water-Based Fire Protection System Design," Figure 20.20, "Typical wet pipe sprinkler system riser detail," which illustrates the use of this symbol in a system schematic. (DOI: https://doi.org/10.1007/978-1-4939-2565-020)

3. Oklahoma State University, Fire Protection Publications, Fire Protection Hydraulics and Water Supply Analysis, 3rd Edition. Appendix A, "Symbols," provides a table of standard NFPA symbols, including the one for a check valve.