OPEN OR CLOSED

1
OPEN OR CLOSED???

• Open center or closed center?
• Open loop or closed loop hydrostatic?
• Open loop or closed loop controls?
• Confusion of terms!!

2
Open or closed CENTER hydraulics?
3
Open Center hydraulics

• Fixed displacement pump
• Constant flow must go somewhere
• Flow back to tank in neutral
• Circuits must be in series
• Ex cheap christmas tree lights in series
• Not used on C21

4
Closed Center hydraulics

• Variable pump
• Constant line pressure at varying flow
• Loads are in parallel
• Loads can be added later
• Valves must be blocked center in neutral
• Example wall sockets and power grid
• Example C21 most circuits

5
Open or closed Loop HYDRAULICS?
6
Open Loop hydraulics

• Fluid from tank-pump-load-tank
• Typical C21 circuits

7
Closed Loop hydraulics

• Fluid from pump-motor-pump-motor
• Does not return to tank
• Typical hydrostatic transmissions, SPML not C21

8
Open Loop CONTROL Circuit 1
9
Open Loop CONTROL Circuit 2

• Command-Action-Results??
• Does not use results to correct an error
• Ex buggy lift, hooks
• Note limit switch indicates, but does not cause
  any corrective action

10
Closed Loop CONTROL Circuit 1
11
Closed Loop CONTROL Circuit 2

• Not just feedback, but using the feedback to
  cause corrective action
• Never perfect, always will be a small final error
• Ex engine governor speed, module tilt circuit

12
Closed Loop CONTROL Circuit 3

• If feedback goes to 0, loop commands valve hard
  over one way to correct the error
• If feedback goes to 10, valve goes hard over
  the other direction
• This is normal, loop is doing what it has to.
• Do NOT remove any wires on energized closed loop
  control system, EVER.