RFRP = (Refractory) Fiber(glass) Reinforced Plastic
Fiber Reinforced Plastic (FRP) = пластик армированный волокном (ПАВ)

"..Originally, valves were made of brass, cast iron, or some kind of metal. Plastic valves arrived in the 1960s, but were not as reliable as they should have been. When plastic is heated, the molecules are aligned, allowing them to flow into each other, creating the solid form of the mold they are poured into. But even then, molecules to molecules are lined up with each other, and it is possible to crack those alignments with enough pressure. It took a while for the contractors to accept plastic valves.

Today, many manufacturers are adding reinforcement filament materials to the plastic to make it stronger and keep it from cracking.

Until plastic came along, brass valves were the valves of choice. Brass valves are still used, though reinforced plastic has taken over as the number-one seller..."
http://www.igin.com/Irrigation/letstalkvalves.html