Actuators

Question 1

Function of actuators

Answer 1

To convert hydraulic energy into mechanical movement.

Question 2

Three basic types of actuators

Answer 2

Linear rotary and semi rotary

Question 3

Piston cushions

Answer 3

When the piston is moving to the right, deceleration begins when the solid metal plunger enters the main orifice and begins to restrict the exhaust oil flow.
During the exhaust stroke if the oil flows through the adjustable restrictor.
When the piston moves back to intake oil the one way return valve opens and also assists with pushing the piston back to the top of the cylinder.

Cushioning can be fitted to one or both sides of the linear actuator to prevent damage to the cylinder end caps.

Question 4

Semi rotary actuator

Answer 4

The example if the semi rotary actuator is the steering gear from the QE class.

Six pressure chambers are formed. There are two manifolds formed each of which connects to three alternate chambers. Hydraulic pressure in one of the manifolds will cause torque. To be applied in the opposite direction. Connections between each of the manifolds and the suction and delivery ports of a variable delivery pump enable torque to be applied in either direction as required.

Question 5

Rotary actuators

Answer 5

Full rotary movement is achieved by hydraulic motors.
They are used extensively for capstans, winches, windlasses, Davits and some lifts.

Question 6

Radial piston hydraulic motor

Answer 6

1. Oil is pushed into the cylinders via face value (P) ports. Forces it to move down the piston.
2. But as they’re constrained by the can track, forcing the needle roller bearings to roll along the cam track and thus turning shaft of the motor.
3. As the piston reaches the bottom of the cam profile and starts to move up the other side. The cylinder passes over a return port (R) and oil is exhausted away to return back to the tank.
   4.the motor can be reversed by swapping the (P) and the (R) we can do this by using a DCV

It’s lubricated by small amounts of leakage between the face valve ports and the rotor ports. The leaks are drained away to the header tank.