Lunchbox Sessions: Interpreting Hydraulic Schematics

Introduction

• Speaker: Carl from lunchboxsessions.com
• Topic: Interpreting hydraulic schematics with pressure valves.

Types of Pressure Valves

1. System Relief Valve

   • Located near the pump outlet.
   • Active when cylinders are deadheaded (no flow path).

2. Pressure Reducing Valve

   • Drawn in an open position with the pilot on the downstream side.
   • Reduces pressure downstream.
   • Prevents over-clamping of workpieces by keeping pressure at a minimum level.

3. Sequence Valves

   • Similar symbol to relief valves but outlet does not return to tank.
   • Normally closed; allows flow in one direction only.
   • Requires a bypass check valve for opposite flow direction.

Schematic Analysis

• Features of the circuit:
  • Fixed displacement pump.
  • Left directional valve (tandem center) takes pump flow back to tank.
  • Right directional valve (closed center) has ports blocked at neutral.

Circuit Operation

• Clamp Cylinder Movement:

  • Activated when the clamp cylinder reaches the end of stroke.
  • Pressure builds to allow the drill cylinder to extend.

• Mimic Feature:

  • Visual representation of cylinder movements.
  • Demonstrates the sequence of operations in the machinery setting.

• Sequence Valve Function:

  • Prevents the drill cylinder from extending until pressure builds on the clamp circuit.

• Pressure Reducing Valve Action:

  • Activates to reduce downstream pressure once the block is clamped.

• Retracting Cylinders:

  • When both cylinders are retracted, only the drill cylinder moves first due to the sequence valve on the clamp.

Summary

• Sequence valves are used in conjunction with pressure reducing and relief valves to control the operation of hydraulic circuits effectively.
• Relief valve activates only under deadheaded conditions when no motion is possible.
• Importance of understanding schematic symbols for hydraulic system design and operation.

Closing

• Resources available for further learning:
  • Hundreds of interactive resources and live schematics at lunchboxsessions.com.