Directional control valves are one of the basic components of hydraulic systems. As its name signifies, it is used to direct the fluid within the system to various hydraulic parts. For example, a lever operated valve that we use to open/close a cylinder or operate a hydraulic motor is a simple directional valve. These valves can be various types: Mechanical, electrical, hydraulic or pneumatic operated, spool type or cartridge type in a hydraulic block.
Especially in spool directional control valves, “carry over” fittings are used to carry the pressure line from one valve to another valve. In fact, by using this part, we separate the tank line and the pressure line from each other. For example, if we want to control the function that we operate with a valve from another part of the machine, we can use such connection. Below is a schematic illustration of the fitting’s connection between two valves. In connection, the tank ports of both valves must be connected to tank. The capacity of these valves should also handle flow supplied by the hydraulic pump.
In the picture above, flow from the pump enters first valve’s port P (pressure). When the first valve is not in use, the fluid continues to P port of the second valve through carry over which is attached to N port. Thus, flow is provided for the functions that second valve will control.
Pictures are used for educational purposes.