Hydraulics and Pneumatics flashcards

$P=\frac{F}{A}$: force (N) divided by area (m²) gives pascals; 1 bar = 100 kPa, sea-level air is about 101 kPa (14.7 psi). Note $1{\text{ m}}^2=10,000{\text{ cm}}^2$.

Pressure is equal on both pistons, so $\frac{F_1}{A_1}=\frac{F_2}{A_2}$ and $F_2=F_1\frac{A_2}{A_1}$. A 60 N push on 5 cm² drives a 40 cm² piston with 480 N.

Area grows with diameter squared: $A=\frac{\pi d^2}{4}$. A 4 cm piston has 4 times the area of a 2 cm piston, not 2 times, so square the diameter ratio.

Volume is conserved, $A_1{d}_1=A_2{d}_2$, so the large piston moves less. Six times the force means one sixth the travel; work in equals work out ideally.

$v=\frac{Q}{A}$: flow rate (volume per time) divided by piston area. 200 cm³/s into a 40 cm² piston gives 5 cm/s. Pressure sets force; flow sets speed.

$P_1{V}_1=P_2{V}_2$ at constant temperature, using absolute pressures. Air at 100 kPa abs in 12 L squeezed to 3 L reaches 400 kPa abs (about 300 kPa gauge).

$P_{abs}=P_{gauge}+P_{atm}$, with the atmosphere about 100 kPa. A tire gauge reading 250 kPa means about 350 kPa absolute. Gas-law problems require absolute pressure.

Relief valve: opens to tank to cap maximum pressure. Check valve: allows flow one way only, holding loads. Directional valve: routes flow to extend or retract a cylinder. A pump makes flow, not pressure.