Three position valve position control circuit

The position control circuit with three position valve is shown in the figure.

Figure a uses the middle closed three position valve circuit, because of the compressibility of air, the positioning accuracy of the cylinder is poor. No leakage is allowed in this circuit and valve.

Figure B shows the circuit with the middle pressurized three position valve. When the valve is in the middle position, because of the double rod cylinder, the two sides of the piston keep the force balance, and the piston stays at any position of the stroke.

Fig. C is the circuit for controlling the single rod cylinder. A pressure reducing valve needs to be installed to obtain the balance of the forces on both sides of the piston. The middle pressurized three position valve position control circuit is suitable for small cylinder diameter situations requiring quick stop in the middle of the stroke.

Figure D shows the circuit with intermediate relief valve. It is suitable for the situation that the piston moves freely by external force and exhausts the air in the cylinder chamber when it is in the stop position for safe operation. Its disadvantage is that the inertia of the piston movement is large and the stop position is not easy to control.

Among them: (a) intermediate closed type (b) intermediate pressurized type (double outlet cylinder) (c) intermediate pressurized type (single outlet cylinder) (d) intermediate relief valve