Momentum: Jets, Vanes & Pipe Bends

At a pipe bend, the pressure forces p₁A₁ and p₂A₂ act on the control volume as well, and the reaction the anchor block must supply is whatever balances pressure and momentum together.

Worked: a nozzle on a plate

A 2 in diameter water jet at 50 ft/s strikes a fixed plate normally. A = π × (2/12)²/4 = 0.0218 ft², so Q = 0.0218 × 50 = 1.09 cfs. F = 1.94 × 1.09 × 50 = 106 lb. Replace the plate with a vane that reverses the jet and the force becomes 212 lb.