Directional Control Valves
Frequently Asked Questions
Frequently Asked Questions
What is the function of a directional control valve? A directional control valve is the extend and retract control for your hydraulic cylinders. It provides a flow path from the pump to the cylinders and a return path from the cylinders to the fluid reservoir. What is the flow pattern for a double acting system? A 4-Port valve is normally required for double acting systems. Let’s look at the two control positions first. In the advance position pressure flows from the pump through the valve from "P" to "A", "B" flows back to "T". In the retract position "P" is flowing to "B", "A" is returned to "T". You need to be aware that when shifting between positions, there is a transitional state. During this transition, there is some "crosstalk" between ports allowing pressure to drop in the pressurized circuit and return to tank. The importance of this information is that you cannot pressurize a system and shift back to the closed center position to hold it clamped. Using the center position to hold is inappropriate because it removes the pump from the circuit and defeats the purpose of a live hydraulic system. What is the purpose of the center position? The center position on 3-Position 4-Port solenoid valves is the resting position with both solenoids de-energized. On manual valves, the center position is transitional and is often unused. Closed center solenoid valves are used to ensure that there is no movement during a power failure (though a small amount of pressure will be lost in transition). The closed center manual valve makes no change in circuit direction in the center position. "P" blocked center in either a manual or solenoid valve is commonly used for decoupling of palletized double acting systems. This allows the pressure to be dropped from both the "A" and "B" hoses for disconnect and reconnect under no pressure. In the center position of this valve "P" is blocked, "A", "B" and "T" are connected.
What is the flow pattern for a single acting system? Single acting systems typically have only two valve positions. In the advance position "P" is connected to "A." In the retract position, "A" is connected to "T" and "P" is blocked, allowing the cylinder springs to push the fluid back to tank. What do I need to watch for when I’m plumbing a system? Remember that hydraulic fluid, like water, will take the path of least resistance. Plan your fluid distribution manifolds and fittings to provide for the smoothest possible flow to and from your cylinders. The best schematically designed control system can be ruined by poor plumbing implementation.
I can get a spool valve locally for a lot less money than your valve. Will it work? You are responsible for the appropriate use of all devices. The use of spool valves invalidates the warranty on any VektorFlo ® pump. If you are using a suitable industrial pump and valve, they may work. The use of spool valves, especially when attempting to use a “center” (or de-energized) function can cause unusual flows and pressures, resulting in unpredictable actions of clamps. The use of a pump with an excess flow invalidates the warranty on any VektorFlo ® item. If you choose to use non-Vektek pumps and valves, you assume the responsibility for selecting appropriate sizes.
All VektorFlo ® directional control valves are rated at 350 bar (35 MPa) working pressure. They typically incorporate international standard mounting and fluid flow patterns. This allows one valve sub-plate to serve as the mounting platform for any of these valves. Plumbing lines are connected to ports on the sides of the sub-plate while hold-down screws secure the top valve. Removal and replacement is easily accomplished without disturbing system plumbing, greatly reducing chances of system contamination. Valve changeovers can be accomplished in minutes, not hours: a tremendous advantage as production downtime costs mount up. Standardized mounting patterns also mean that valve operation can easily be upgraded from manual to electric, again without having to change system plumbing. Our electric solenoid valves are direct bolt-on replacements for our manually operated versions.
NOTE: Maximum system flow rate is 5.7 L/minute for all VektorFlo ® special function valves unless otherwise noted.
Excess flow voids warranty.
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