Читать книгу Hydraulic Fluid Power - Andrea Vacca - Страница 82

The system contains a solenoid valve (SV; which will be further described in Chapter 8), which when energized opens an accumulator to the piston chamber of a linear accumulator. For simplicity, the accumulator can be seen as a constant pressure source. In reality, the pressure inside the accumulator will decrease as the accumulator releases flow, as it will be better described in Chapter 9.

When the valve is energized, the flow rate across it is defined by the orifice equation:

The pressure inside the cylinder is given by the external force:

Therefore, the actuator speed is

In order to reduce the actuator's speed, there are possible alternatives:

1 Increase the piston diameter.

2 Decrease the valve size, thus reducing the valve coefficient k.

3 Reduce the accumulator pressure.

4 Add an orifice in series with the valve (see figure below).

All mentioned solutions are reasonable; however, solutions 1, 2, and 3 require modifications to the existing components. Solution 4 can be a simple way to modify an existing system.

The flow rate through the orifice and the valve can be written as

d_eq is the diameter of the equivalent orifice given by the series connection of SV and O2. The desired speed of the actuator corresponds to the following flow:

The equivalent series orifice diameter results:

Assuming that both orifices have the same flow coefficient (C_f = 0.7), the diameter of orifice O2 results: