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Proportional valve control calculation. Part 2.

February 20, 2017 0 Articles , , 994 Views

Part 2. Proportional control in the regeneration mode.

Regen mode - proportional control

Fig.1. Regeneration mode schematic

See also:
Part 1. Proportional control of double acting hydraulic cylinder.
Online calculator for cylinder proportional control.

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

Summary:
2.1. Regeneration mode schematic
2.2. Regeneration Mode: Cylinder extension calculation
2.2.1. Balance of forces at the cylinder
2.2.2. Spool lands ratio and pressure drops at the spool lands
2.2.3. Hydraulic cylinder extension. System pressure calculation
2.2.4. Flow through spool lands: max. and at current voltage
2.3. Hydraulic cylinder retraction calculation
2.4. Final words….

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Hose Overall Assembly Length

December 18, 2016 0 Articles 561 Views

There are three different ways to measure hose assembly length are used in the practice:

  1. Use value of “Overall length” (Default for Parker’s suppliers)
  2. Use value of “Seat-to-seat length” (Default for RYCO’s suppliers)
  3. Use value of “Cut length” (Default for EATON suppliers)

 

Unfortunately, there are no any standards for the definition of  “Overall Length” value and therefore different manufactures determine different ways of measuring the value of Overall Length. This is why you need to be very careful before ordering hoses with new supplier and you have to specify which length you provide, because sometimes it can be critical.

The normal practice of “Overall Length” measuring please see below:

All US fittings (JIC, SAE, NPSM), except ORFS fittings, are measured up to the end of the nut:

US fittings

DIN, BSP and ORFS fittings are measured up to the end of the sealing head (this rule does not work with RYCO suppliers, but works with Parker and EATON suppliers):

ORFS fittings

SAE flange fittings are measured up to the face:

SAE flange fittings

All male threads are measured up to the end of the fittings:

male threads

All 90 degree fittings are measured to the head center line:

90* fittings

Other elbow fittings can be measured up to the center line of the head face (RYCO) or up to the center line of the seal face (Parker):

0..90* fittings

I recommend to use Parker’s rule for this type of fittings.

And my last recommendation: check the value of Overall Assembly length: it has not to be less than Minimum Overall ASSY Length:

If the Overall Length is not long enough it could hinder the ability of the hose assembly to function properly. Notes from RYCO:

“This is particularly the case when utilising very short hose assemblies, where a shortening or shrinkage of the hose under pressure may result in hose and coupling separation. In addition, small misalignments, vibration and other displacements may induce very high stresses upon the hose/coupling juncture, as there is little capacity for the flexible nature of the hose to compensate.“

Parameters “A” and “B” you can take from manufacturer’s catalog.

Sources:

Valve’s middle position configurations

November 20, 2016 0 Articles 1015 Views

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.

~~~ // ~~~

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

October 10, 2016 5 Articles , , 2513 Views

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.

 

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