Читать книгу Hydraulic Fluid Power - Andrea Vacca - Страница 87

Pilot lines are used to transmit the value of pressure to different locations of a circuit. In such lines, it is very rare to find orifices working as metering or compensator devices. Instead,

Orifices are used in pilot lines to manipulate the pressure signal, according to two possible function purposes: pressure separators or dynamic orifices.

A pressure separator is an orifice used to decouple the pressure in the working line – where the pilot line is connected – and the pressure transmitted by the pilot line itself, downstream the orifice.

A dynamic orifice is utilized with to modify the rate at which the pressure information is transmitted through the pilot line. Dynamic orifices dampen the pilot pressure information, acting as hydraulic low pass filters. Typically, dynamic orifices are accomplished with two different layout configurations. In the first layout, they are located next to closed‐end connections of the pilot line. Therefore, they do not affect the operation of the system in steady‐state operation, being crossed by zero flow rate in this condition. This kind of dynamic orifice can be neglected while studying the main steady‐state system operation. In the second layout, the dynamic orifice is used in an additional pilot line connection to the reservoir (bleed orifice). Also, a bleed orifice does not affect the steady‐state operation of the system, but it introduces a constant dissipation by bleeding fluid to tank.

Understanding the function of orifices in working lines and pilot lines is not always simple, particularly for the cases of pressure separators and dynamic orifices. For this reason, this book will often point out the function accomplished by the various orifices present in a certain component or system. In this way, the reader will progressively become more familiar with recognizing the different roles of orifices in hydraulic systems.