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Categories : Hydraulic valves
4 spool hydraulic control valve is one of the most fundamental parts in hydraulic machinery. It allows fluid flow into different paths from one or more sources. 4 spool hydraulic control valve consist of a 4 spools inside a cylinder which can be mechanically or electrically controlled. The movement of the spools restricts controls the fluid flow.
The spool type control valve consists of lands and grooves. The lands block oil flow but the grooves allow oil or gas to flow around the 4 spools and through the valve body. There are two fundamental positions of directional control valve namely normal position where valve returns on removal of actuating force and other is working position which is position of a valve when actuating force is applied. There is another class of valves with 3 or more position that can be spring centered with 2 working position and a normal position.
4 spool control valves are generally specified using the number of ports and the number of switching positions. It can be represented in general form as np/ns, where np is the number of ports connected to the direction control valve and ns the number of switching positions.
In addition, the method of actuation and the return method can also be specified. A hypothetical valve could be specified as 4-way, 3-position or just 4/3 Control Valve since there are four ports and three switching positions for the valve. In this example, one port is called the pressure port which is connected to the pump, second port is the tank port and is connected to the tank (or reservoir) and the last two remaining ports are called working ports and are connected to the actuator. Apart from characteristics of valve the fluid suitable for valve, working temperature and viscosity also thought upon before selecting a particular type of valve.
4 spool control valves can be operated by many methods: manually, electrically, pneumatically and hydraulically.
Manually operated valves work with simple levers or paddles where the operator applies force to operate the valve. Spring force is sometimes used to recover the position of valve.
Electrically operated 4 spool control valves make use of electromechanical solenoids for sliding of the spool. Because simple application of electrical power provides control, these valves are used extensively. However, electrical solenoids cannot generate large forces unless supplied with large amounts of electrical power. Heat generation poses a threat to extended use of these valves when energized over time. Many have a limited duty cycle. This makes their direct acting use commonly limited to low actuating forces.
Often, a low power solenoid valve is used to operate a small hydraulic valve (called the pilot) that starts a flow of fluid that drives a larger hydraulic valve that requires more force