BARREL AS 5511105 - Caterpillar

Basic Hydraulic System
The power piston is the part of the actuator that does all of th work. Under normal conditions, the oil pressures at both the top and bottom of the piston are balanced, and the piston remains stationary at the "centered" position. The pilot valve plunger controls the flow of oil to and from the power piston. The control land at the bottom of the pilot valve plunger is just large enough to completely cover the control port in th pilot valve bushing when the plunger is exactly "centered".If the signal from the Electronic Locomotive Control Box makes the pilot valve plunger move up, the oil under the power piston can drain past the control land to sump. The higher oil pressure at the top of the piston will now move the piston down until the control land of the plunger will again close the control port. This piston movement will also move the terminal shaft (in the decrease fuel direction), since they are connected together.If the signal from the Electronic Locomotive Control Box makes the pilot valve plunger (and control land) move down, pump oil pressure can now pass through the control port to the bottom of the piston. Even though the pump oil pressure in the circuit above the piston is the same as the circuit below the piston, the piston will move up. This is due to a larger surface area available to the oil pressure at the bottom of the piston than the surface area at the top of the piston. The movement of the piston will now turn the terminal shaft in the increase fuel direction.Feedback Systems
A high degree of stability is necessary to maintain a constant output from the generator set. The stability of a system controlled by the Electronic Locomotive Control Box is increased with the use of a temporary actuator feedback signal that biases (makes a correction to) the Control Box command signal to the pilot valve plunger. Since the Control Box makes an adjustment rapidly to a change in engine load, the actuator can make the engine go into a "hunt" condition (temporary increase and decrease in engine speed) if the corrections are too sensitive. The purpose of the feedback system is to prevent over-correction to the load change.The EG-10P Actuator is different because two feedback systems are used, one mechanical and one hydraulic. Under normal conditions, the mechanical system will correctly control the actuator. However, during cold engine start-up conditions, the addition of the hydraulic buffer system eliminates erratic (variable) speed problems caused by the cold engine oil. The result of the two systems is constant speed control at all times. The explanation for the operation of each feedback system is as follows:Mechanical Feedback System
The temporary feedback signal is accomplished in this system by the addition of linkage and a restoring spring arrangement that applies a secondary force to