Читать книгу Hydraulic Fluid Power - Andrea Vacca - Страница 18

1 1.1 Using following symbols, represent a schematic of a hydraulic system that rotates the hydraulic motor in both directions. All the circuit branches need to be protected from overpressure using proper pressure relief valve(s). Symbols with (*) can have more instances. Use the minimum number of components.Does the system have an “on/off” regulation nature, or does it implement a variable angular speed of the load?

2 1.2 Solve again Problem 1.1. But instead of using the manually operated valve, use the electrically operated directional valve shown below.

3 1.3 Consider the hydraulic system below. It includes two fluid sources (generically represented) that supply two circuits: one circuit is to pilot the actuation of valve 1, and one circuit supplies the main flow through the hydraulic actuator, cylinder 2. What happens to the cylinder 2 when the valve 1 is pushed and held?It extends immediately and remains extended.It extends after a certain time interval, necessary to fill the accumulator.It remains in equilibrium, not moving at all.It retracts immediately, and it remains retracted.Retract immediately and extend after a certain time interval.Motivate your answer.

4 1.4 Consider again Problem 1.3, now with a modification of the hydraulic schematic as shown below. The pilot‐operated valve includes now a spring. Does the behavior of the hydraulic cylinder 2 change? Motivate your answer.

5 1.5 A hydraulic control system uses a 5 kW engine to drive a hydraulic motor (10 cm3/rev, gear type with external drain) and a single‐acting hydraulic cylinder (piston diameter: 80 mm, rod diameter: 40 mm). The single‐acting cylinder is used to lift and lower a gravitational load. The two actuators are independently supplied by two fixed displacement gear pumps (10 cm3/rev) both connected to the thermal engine. Both pumps are protected by system overpressurization through relief valves (pressure setting of 250 bar). Each pump is connected to the actuator through a directional valve that allows both directions of motion for the actuators. For controlling the hydraulic motor, a 4/3 valve is used. Instead, the single‐acting cylinder is actuated through a 3/3 directional control valve. The retraction of the cylinder occurs through gravity. For this purpose, between the 3/3 valve and the cylinder, there is a check valve in parallel with a fixed orifice, calibrated for achieve a flow of 10 l/min during the lowering condition. Both directional control valves are solenoid operated. In rest conditions, no flow is supplied to both actuators, even if no load holding is achieved.Represent the hydraulic schematic of the system, with particular attention to the positions of each directional control valve.