The Fluid Power Blog

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:

mid_pos_01

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.

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Scheme Editor 6.2

The new version 6.2 of Bosch Rexroth Scheme Editor has been released! And now it contains the Hydraulic library, like they promised couple months ago (see my article)!

Download the software you can by this link: http://www.boschrexroth.com/dnc-scheme-editor (78 Mb.)

Free registration is required for downloading. After launching of installing wizard the automatic updating of the previous version will be made. So you do not need to uninstall previous one. And, don’t forget to restart your computer!

After computer restarting it is necessary to import new libraries. So, finally you get 3 libraries:

Scheme Editor 6.2 Libraries

Scheme Editor 6.2 Libraries

Pneumatics library has been updated to ver. 1.2 and new Hydraulics and Electrical libraries have been added to the Symbol Library list.

I quickly checked new hydraulics symbols and found the library a little bit poor.

Hydraulic symbols example

Hydraulics symbols example

For example, I did not find symbols for hydraulic valves pneumatically operated for one of my applications. But a generic schematic can be done with the existing hydraulic library and for other, more complicated systems, you can use wonderful “Symbol Modeling Tool”.

Resume: Bosch Rexroth is moving forward in the right direction and hopefully this software will continue to develop and libraries will be updated with a new symbols, at least with components what BR has in their assortment.

 

Cylinders conduits flow rate and velocity

Cylinders conduits flow

Cylinder’s flow

These calculations can help you to figure-out conduits’ (hoses, pipes or tubes) ID sizes, piston speed, flow velocity and cylinder’s force.

Calculations Notes:

  • The recommended flow velocity in conduits you can find at the article Recommended flow velocity.
  • The assumption: if you use more than 1 cylinder in calculations, all cylinders have the same parameters (bore/rod diameters, stroke and friction)
  • The assumption: Pressure and Return lines conduits (flow source – flow divider and flow divider – tank) have the same ID size.
  • The assumption: the conduits between flow divider and cylinders have the same ID size.

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