# Hydraulics Basic Concept of Hydraulic excavators

Excavator System  Pressure     # ∴ ∴ S2 = (A1/A2) * S1    Flow Q = V/t   Where V = liter, t = min, Q = liter/min or lpm The function of main pump
To determine discharging oil amount, Q (strictly speaking, displacement q) under certain working condition. Q = (q * n)/1000 Where q = cc/rev,  n = rev/min ▷Displacement of pump ?

Oil amount in cc discharged  at 1 revolution of pump shaft.

Displacement = cc/rev ▷Displacement of motor ?
Oil amount in cc necessary to rotate motor shaft 1 turn. Motor Shaft Speed = (Displacement ratio) x (pump shaft speed)
Ref) Motor shaft torque = Motor Acting pressure * Motor Displacement Cylinder Speed = input flow / chamber area
Ref) Cylinder Force = Chamber area * Chamber Pressure   Cylinder Speed = input flow / chamber area
☞  Cylinder Force = Chamber area * Chamber Pressure ▶Difference between 2 cases ?
Priority Valve
Priority Valve
☞ Relative speed between A & B or A1 & B1 ? ▶Out of V1 and V2, which one is faster?
☞It depends….   =>   Controllability Design

Power

Power = work / time = (force x Distance) / time 1 PS = 75 kgf.m / sec

▣Power –Lifting Capacity –Working Speed ☞Same power, but…  ▣Power Match ?
▶Engine Output Power ≥Pump Input Power
☞ (T * n)/716.2 ≥(P * Q)/450 1) Pressure = 200kgf/cm^2
2) Pump Input Power = 40PS
3) So, Engine Power ≥ 40 PS
in order not to be overloaded…
By the way, can the pump control the pressure caused by external load on the cylinder ?
If not, what can the pump control ?

▣ Engine Speed drop ?
Case 1. Engine output power is lower than normal
Case 2. Pump input power is higher than normal

▣Power = Torque * Speed = Constant
Case 1. High speed, low torque Case 2. Low speed, high torque Which one do you prefer ?
If you want high speed and high torque together, what is needed ?

▣ Hydmotor input Power = Torque * Speed = Constant
Where
Torque = Max pressure * Displacement
Speed = Input Flow / Displacement

▣Cylinder Digging Power = Cylinder force * Cylinder speed P : cylinder acting pressure
A : cylinder chamber area
F : cylinder force ( P * A )
V : cylinder speed ( Q / A )

If available digging power is constant, F and V have trade off each other. I.e if F increases, V decreases and reversely.
For example, if the chamber area is incresed, digging force F will increase but V decrease..Which way is better for working ?