Question

A high rise building has a sink on the fourth floor located 2-feet above the floor. Each floor is 10-feet above the other. Calculate the psi at the sink where when the street pressure is 80 psi. The building does not have a pressure reducing device due to fire codes.

Answer 1

The pressure at a certain height is the pressure at sea level plus the hydrostatic pressure.

P = 80 psi + ΔP
where
ΔP = ρgh
ρ is the density of water equal to 62.4 lbm/ft³
ΔP = (62.4 lbm/ft³)(1 lbf/lbm)(4*10 + 2 ft)(1 ft/12 in)² = 18.2 psi

Thus,
P = 80 + 18.2
P = 98.2 psi