Hydraulic Pumps and Cylinders
• Hydraulic Pumps will be rated with a pressure and
flow rate deliverable.
• The Pressure is the output pressure of the pump and
the flow rate is the volume of hydraulic fluid the
pump can move in a given time.
• For this class we will not worry about line losses and
head pressure losses and gains. That will be covered
in Hydraulics class.
Hydraulic Cylinders
• Hydraulic cylinders will have a piston diameter (sometimes
just called the cylinder diameter) and a total length it can be
extended to.
• The force the cylinder can exert is dependant on the fluid
pressure supplied to the cylinder and the cross-sectional area
of the piston
– F = P*A
• The Speed at which the cylinder is traveling is dependant on
the cross-sectional area of the piston and the volumetric flow
from the pump
– Speed = Volumetric flow / A
Pascal’s Law
• A fluid at rest creates an equal pressure in all
directions at any one point
• To add to this, the pressure is only dependant on the
density (ρ) or specific weight (γ) of the liquid and the
depth of the liquid (h) at that point
– P = ρgh
– P = γh
γ = specific weight = ρ * g
Density and Specific Weight of Water
• For Water,
– Density
• 1000 kg/m3
• 1.938 slug/ft3
– Specific Weight
• 9810 N/m3
• 62.4 lb/ft3
Pressure on a Submerged Surface
• Calculate the equivalent
force on each wall and
the bottom of a one
foot long section of the
trench shown filled with
6 feet of water
6 ft
2 ft
Example 1: Determine the magnitude of the hydrostatic force acting per meter
length of the wall. Water has a density of 1 Mg/m^3)
Example 2 – Determine the magnitude of the hydrostatic force acting on gate AB,
which has a width of 2 ft. The specific weight of water is 62.4 lb/ft^3)