# Articles

Articles about hydraulic, pneumatic, lube, etc. systems design.
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## 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.

## Hydraulic Load Sensing design FAQ

Of course, it’s free. Next questions are discussed there:

• How can load sensing be beneficial to a hydraulic system?
• What is the typical efficiency of a hydraulic system?
• What are the problems when flow is fixed?
• How is load sensing technology energy effective?
• etc.

## Flushing of the pipes and tubes

To do pipe flushing correctly we need to provide the special conditions to create turbulent flow. This is required to remove particles from the surface inside spindle tubes. For that we need:

1.  High velocity of the flushing fluid (not be less than 2 to 3 m/sec. = 106 ft./sec.)
2.  High temperature of the flushing fluid (a minimum temperature should be 140°F = 60°C)
3.  Low viscosity of the flushing fluid (in the 10 to 15 cSt range at 104°F = 40°C)
4.  The pressure of the flushing fluid should be held to a minimum 3 to 5 bar (22 to 73 psi), measured downstream from the flushing circuit, before the return line filter and sampling port
5.  The flushing time to be 30 min.

Next good references about flushing I found in the internet and want to share:

## Pilot Operated Check Valves or Counterbalance Valves?

Summary:

• When use Pilot Operated Check valves?
• When use Counterbalance valves?
• Design advises for topic valves.

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First of all, Pilot Operated check valves are NOT a cheap solution of Counterbalance valves.

Yes, both of them have next the same benefits:

• Prevent a load from dropping in case of hose or tube failure.
• Prevent a load from drifting caused by directional control valve spool leakage.