# Tag Archive: valve

## Valve’s middle position configurations

Here are the practical advises to select the configuration of the middle position of 4-ways 3 positions directional valves. There are more than 250 configurations of the flow ways usually used in the practice, but in this quick review let see the generic configurations only.

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### All ports are separated from each other:

Configuration notes:

• This spool configuration is used where two or more operations are performed by a single pump or an accumulator. Pump output is available for other valves and actuators with this center condition.
• Closed port P prevents the loss of fluid from the pump or accumulator when the spool crosses center. Avoid fixed displacement pumps for this configuration. More info about close circuits you can find here.
• The spool-type valves are not zero-leaking devices. In actual use, leakage oil across the spool lands pressurizes A and B ports, possibly causing a single rod cylinder to extend trough piston/annular area difference. By the same reason this configuration is not for holding applications.

## Open/Closed center circuits

Summary:

• Open/Closed center circuits – what does it mean?
• Which one I use?
• What can happen if I connect my system to wrong center circuit?

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There are two types of valve circuits can be used to control your system: “Open center circuit” and “Close center circuit”.

## Proportional valve calculation

Calculations Notes:

• The formulas and algorithm of calculations you can find by this link.
• Pressure compensated pump with variable displacement is used as a source of pressure and flow.
• The spool lands work as orifices and have the same shape on both sides of the spool land.
• The same orifice coefficient (Cv) is used for both lands.

## Part 1. Proportional control of double acting hydraulic cylinder.

Fig.1. Double acting cylinder control.

The goal of this calculation is a definition of a cylinder velocity at any percent of the operating control signal at the valve’s solenoid (voltage or amperage).
For calculations we need to know: cylinder and valve parameters (take them from manufacturer catalog), values of forces at the cylinder rod (load), and pressure drop at the return line (can be assumed as zero if unknown).

Summary:
1.1. Hydraulic cylinder extension calculation.
1.1.1. Spool lands ratio.
1.1.2. Pressure drops at the spool lands
1.1.3. Balance of forces at the cylinder.
1.1.4. System pressure calculation.
1.1.5. Flow through spool lands: max. and at current voltage.
1.2. Hydraulic cylinder retraction calculation.
1.3. Full stroke time calculation.