Question 1

How do I calculate hydraulic cylinder force?

Accepted Answer

Cylinder force is calculated using F = P × A, where P is pressure (bar or psi) and A is the piston area (πd²/4). For push force, use the full bore area. For pull force, subtract the rod area from the bore area. A 100mm bore cylinder at 200 bar produces approximately 157 kN of push force.

Question 2

What is the formula for hydraulic cylinder speed?

Accepted Answer

Cylinder speed V = Q / A, where Q is flow rate (liters/min or GPM) and A is the piston area. For extension, use bore area. For retraction, use the annular area (bore minus rod). Higher flow rates or smaller cylinders result in faster speeds.

Question 3

How do I calculate hydraulic pump flow rate?

Accepted Answer

Pump flow rate Q = (D × N × ηv) / 1000, where D is displacement (cc/rev), N is RPM, and ηv is volumetric efficiency (typically 0.85-0.95). A 50cc pump at 1500 RPM with 90% efficiency delivers approximately 67.5 LPM.

Question 4

What power motor do I need for my hydraulic pump?

Accepted Answer

Motor power P = (Q × p) / (600 × η), where Q is flow rate (LPM), p is pressure (bar), and η is overall efficiency (typically 0.80-0.90). Always add 15-20% safety margin and consider peak pressure requirements.

Question 5

How do I calculate pressure drop in hydraulic hoses?

Accepted Answer

Pressure drop depends on flow rate, hose length, diameter, and fluid viscosity. The Darcy-Weisbach equation is used: ΔP = (f × L × ρ × v²) / (2 × D). Keep velocity below 6 m/s in pressure lines and 2 m/s in suction lines to minimize losses.

Question 6

What hydraulic oil viscosity should I use?

Accepted Answer

Common hydraulic oil grades: ISO VG 32 (light duty, cold climates), ISO VG 46 (general purpose, most common), ISO VG 68 (heavy duty, hot climates). Viscosity affects efficiency, wear, and heat generation. Optimal operating viscosity is typically 16-36 cSt.

Question 7

How do I size a hydraulic reservoir?

Accepted Answer

Rule of thumb: Reservoir capacity should be 2-3 times the pump flow rate (in LPM for liters, GPM for gallons). This allows adequate cooling time, air separation, and contamination settling. For mobile equipment, 1-2 times is acceptable due to space constraints.

Question 8

What is the difference between single-acting and double-acting cylinders?

Accepted Answer

Single-acting cylinders have one port and extend or retract by hydraulic pressure, returning by gravity or spring. Double-acting cylinders have two ports, allowing hydraulic control in both directions. Double-acting provides more force on retraction due to reduced annular area.

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ISO VG	cSt @ 40°C	Application
22	22	Low temp
32	32	Light duty
46	46	General
68	68	Heavy duty
100	100	High temp