Fluid Power Control

Module:03 ~ Hydraulic SYSTEM COMPONENTS FLUID POWER Module:03 ~ Hydraulic SYSTEM COMPONENTS Sources of Hydraulic Power Construction and working of pumps – Variable displacement pumps Actuators: Hydraulic cylinders, performing linear motion Hydraulic motors, performing continuous rotary motion Hydraulic rotary actuators, performing limited angular Control Components: Pressure Control Valve Direction control valve Flow control valves

Pressure Control Valves control components FLUID POWER Pressure Control Valves What is a PCV?

Pressure Control Valves control components FLUID POWER Pressure Control Valves Why do we need a PCV in hydraulic circuit? Limiting maximum system pressure at a safe level. Regulating/reducing pressure in certain portions of the circuit. Unloading system pressure. Assisting sequential operation of actuators in a circuit with pressure control. Reducing or stepping down pressure levels from the main circuit to a lower pressure in a sub-circuit

Pressure Control Valves control components FLUID POWER Pressure Control Valves Types: Pressure-relief valve. Pressure-reducing valve. Unloading valve Pressure-sequence valve.

Pressure-Relief Valve FLUID POWER control components - PCV Pressure-Relief Valve What is a Pressure Relief Valve for? Comparison with a fuse in an electrical system. Construction and Working Principle.

Pressure-Relief Valve control components - PCV FLUID POWER Pressure-Relief Valve Spool (1), Housing (2), Spring (3), Spring seat (4), & Adjusting knob (5). max

Pressure-Relief Valve control components - PCV FLUID POWER Pressure-Relief Valve SUMMERY: The pressure at which the valve begins to open is known as cracking pressure The pressure that exists at full pump flow can be substantially greater than cracking pressure. It is the maximum pressure level permitted by the relief valve. Spring stiffness determines the difference between full pump flow pressure and cracking pressure.

Pressure-Relief Valve control components - PCV FLUID POWER Pressure-Relief Valve Points to note: It limits the maximum pressure in a hydraulic circuit by keeping it below a preset level. It provides protection against any overloads; or it limits the force or torque produced by hydraulic cylinders or motors. It can bypass fluid anytime, or all the time, without intervention by maintenance. A well-designed circuit never bypasses fluid unless there is a malfunction. This eliminates most overheating problems and saves energy. Note the external adjusting screw varies spring force and, thus, the pressure at which the valve begins to open (cracking pressure) also varies.

Pressure-Relief Valve control components - PCV FLUID POWER Pressure-Relief Valve Graphical Symbol

Pressure-Relief Valve control components - PCV FLUID POWER Pressure-Relief Valve Symbolic Representation of Partial Hydraulic Circuit Typical Hydraulic Power Pack

Pressure-Relief Valve control components - PCV FLUID POWER Pressure-Relief Valve A relief valve is not needed if a pressure-compensated vane pump is used.

FLUID POWER control components - PCV Pressure-Relief Valve A pressure-relief valve has a pressure setting of 140 bar. Compute the power loss (kW) across this valve if it returns all the flow, 0.0016 m3/s, back to the tank from a pump. 50 bar 100 bar

Pressure-Relief Valve FLUID POWER control components - PCV Pressure-Relief Valve A pressure-relief valve contains a poppet with an area of 4.2 cm2 on which the system pressure acts. During assembly, a spring with a spring constant of 3300 N/cm is installed in the valve to hold the poppet against its seat. The adjustment mechanism is then set so that the spring is initially compressed to 0.5 cm from its free-length condition. In order to pass full pump flow through the valve at the pressure-relief valve pressure setting, the poppet must move 0.30 cm from its fully closed position. (a) Determine the cracking pressure. (b) Determine the full pump flow pressure (pressure-relief valve pressure setting). (c) What should be the initial compression of the spring in pressure-relief valve if the full pump flow is to be 40% greater than the cracking pressure? 50 bar 100 bar

A Typical Hydraulic Circuit where a pressure Reducing Valve is needed. FLUID POWER control components - PCV Pressure-Reducing Valve 50 bar A Typical Hydraulic Circuit where a pressure Reducing Valve is needed. What is a Pressure- Reducing Valve? Why is a Pressure- Reducing Valve used in a hydraulic system? 100 bar

Pressure-Reducing Valve control components - PCV FLUID POWER Pressure-Reducing Valve How does it work? ..\video\Edited\Function of a Pressure Reducing Valve in a Hydraulic System.wmv

Pressure-Reducing Valve control components - PCV FLUID POWER Pressure-Reducing Valve APPLICATION

Graphical Symbol Pressure-Reducing Valve control components - PCV FLUID POWER Pressure-Reducing Valve Graphical Symbol

control components - PCV FLUID POWER Pressure-Reducing Valve APPLICATION Draw a hydraulic circuit for controlling two double acting cylinders by two separate 4/3 solenoid operated spring centered closed neutral DCV. Assume actuator -2 will be operated at reduced pressure.

Dumps excess fluid with little or no pressure. control components - PCV FLUID POWER Unloading Valve Normally closed type Dumps excess fluid with little or no pressure. It unloads the pump.

Application of unloading valve control components - PCV FLUID POWER Application of unloading valve in a punching press

Application of unloading valve in a punching press control components - PCV FLUID POWER Unloading Valve Application of unloading valve in a punching press (High-Low circuit)

control components - PCV FLUID POWER Unloading Valve

control components - PCV FLUID POWER

Operation of UNLOADING VALVE control components - PCV FLUID POWER TANK PORT PILOT PORT PUMP PORT

UNLOADING VALVE With as an Integral Part control components - PCV FLUID POWER UNLOADING VALVE With CHECK VALVE as an Integral Part

** APPLICATION OF UNLOADING VALVE ** control components - PCV FLUID POWER ** APPLICATION OF UNLOADING VALVE **

control components - PCV FLUID POWER

** APPLICATION OF UNLOADING VALVE ** control components - PCV FLUID POWER ** APPLICATION OF UNLOADING VALVE **

Unloading Valve ¬ Points to note: control components - PCV FLUID POWER Unloading Valve ¬ Points to note: It allows rapid discharge of pressurized oil near atmospheric pressure. These valves are very reliable and seldom require maintenance, adjustment or replacement. An unloading valve requires no electric signals. This eliminates the need for maintenance. An unloading valve is used to perform operations such as stamping, coining, punching, piercing, etc.

Application Sequential Valve: control components - PCV FLUID POWER Sequential Valve: Application A machining operation where the work-piece must be clamped with a certain force before the cutting tool starts moving to make contact with the work-piece.

control components - PCV FLUID POWER Sequential Valve: B B P A P A A

control components - PCV FLUID POWER Sequential Valve: B P A

control components - PCV FLUID POWER Sequential Valve: B P A P

control components - PCV FLUID POWER B P A P Sequential Valve

Application Sequential Valve: FLUID POWER control components - PCV Sequential Valve: Application The Hydraulic Circuit for a clamp cylinder to extend first to hold a work-piece and then a second cylinder to extend to bend the work-piece in the desired shape.

control components - PCV FLUID POWER Sequential Valve: Application