Review and Summary

The four important factors that should be considered while designing any fluid power circuit are:

REVIEW AND SUMMARY

• The four important factors that should be considered while designing any fluid power circuit are:

(i) Safety of operation,

(ii) Performance of desired function,

(iii) Efficiency of operation, and

(iv) Cost.

• A hydraulic circuit is the graphic representation of the hydraulic components in a hydraulically operated machine.

• In this chapter, the design, operation, and purpose of the following hydraulic circuits have been discussed:

(i) Control of a single-acting hydraulic cylinder,

(ii) Control of a double-acting hydraulic cylinder,

(iii) Regenerative circuit,

(iv) Regenerative cylinder circuit for machine tool applications,

(v) Pump-unloading circuit,

(vi) Double-pump hydraulic circuit,

(vii) Counterbalance valve application,

(viii) Sequencing of two double-acting cylinders,

(ix) Automatic cylinder reciprocating system,

(x) Synchronizing circuits,

(a) Synchronizing hydraulic cylinders connected in parallel

(b) Synchronizing hydraulic cylinders connected in series 

(c) Synchronizing hydraulic cylinders with flow control valves 

(xi) Fail-safe circuits

(a) Prevention from inadvertent cylinder extension

(b) Overload protection

(c) Two-handed safety circuit

(xii) Speed control circuits

(a) Meter-in circuit

(b) Meter-out circuit

(c) Bleed-off circuit

(xiii) Speed control of a hydraulic motor

(xiv) Hydropneumatic circuits

• Regenerative circuits are used to speed up the extending speed of the double-acting cylinder.

• Sequencing circuits are used for sequencing operations when two or more cylinders are employed.

• Fail-safe circuits are designed to safe-guard the operator, the machine, and the workpiece.

• Speed control circuits are designed to control the speed of the hydraulic cylinders.

• In meter-in-speed (or flow) control circuit, the flow control valve is located in between the pump and actuator. Thereby this circuit controls the amount of fluid • flowing into the cylinder.

• In meter-out speed (or flow) control circuit, the flow control valve is located in between the actuator and the oil reservoir. Thereby this circuit controls the fluid flowing out of the actuator.

• In bleed-off speed (or flow) control circuit, the flow control valve is located in between the pressure line and return line. Thereby this circuit controls the fluid by bleeding off the excess not needed by the actuator.

• In some applications, the hydraulic and pneumatic circuits are coupled to get best use of the advantages of both oil and air mediums. This combination circuit is known as hydropneumatic or pneumohydraulic circuits. Example: Air-over-oil circuit. 

• Hydrostatic transmission is special case of energy transmission system where the mechanical energy of the input drive shaft is converted into pressure energy in the nearly incompressible working fluid and then reconverted into mechanical energy at the output shaft.

• At the end of this chapter, automotive power-steering application of hydro- mechanical servo system and electro-hydraulic servo system are presented.

KEY TERMS ONE SHOULD REMEMBER

Fluid power circuits 

Hydraulic circuits 

Regerative circuits 

Pump-unloading circuit

Double-pump hydraulic

circuit

Sequencing circuits

Synchronizing circuits 

Fail-safe circuits 

Speed control circuits 

Meter-in circuit 

Meter-out circuit

Bleed-off circuit

Hydropneumatic circuits

Pneumohydraulic circuits 

Air-over-oil circuit 

Hydrostatic transmission system 

Mechanical hydraulic servo system 

Electrohydraulic servo system

An accumulator is basically a pressure storage reservoir in which a non- compressible hydraulic fluid is retained under pressure from an external source.

REVIEW AND SUMMARY

• An accumulator is basically a pressure storage reservoir in which a non- compressible hydraulic fluid is retained under pressure from an external source.

• Types of accumulators: The three basic types are:

1. Weight-loaded (or dead-weight) accumulators,

2. Spring-loaded accumulators, and

3. Gas-loaded accumulators.

(i) Non-separator type, and

(ii) Separator type.

(a) Piston type, (b) Diaphragm type, and (c) Bladder type.

• Applications of accumulators : The accumulator circuits are used as :

(i) Leakage compensator,

(ii) Auxiliary power source,

(iii) Emergency power source,

(iv) Hydraulic shock absorber,

(v) Fluid make-up device,

(vi) Holding device, and

(vii) Lubricant dispenser.

• In this chapter, the purpose, construction, and operation of various types of accumulators and accumulator circuits have been described in detail.

• Pressure intensifier, also known as presser booster, is a device which converts a large-volume, low-pressure fluid supply into a proportionately small-volume, high- pressure fluid outlet.

• Pressure intensifier finds its application at places where a liquid of very high pressure is to be developed from available low pressure. Typical applications include hydraulic presses, riveting machines, and spot-welders.

• At the end of the chapter, the purpose, construction, and operation of the pressure intensifier and intensifier circuits have been presented.

• Formulae Summary:

1. Sizing of accumulators :

For weight-loaded type accumulators:

Capacity = P × A  × L

For gas-loaded type accumulators:

2. For pressure intensifiers:

KEY TERMS ONE SHOULD REMEMBER

Accumulators

Weight-loaded type

Spring-loaded type

Gas-loaded type

Non-separator accumulators

Separator accumulators

Piston-type

Diaphragm type

Bladder type

Accumulator symbols

Accumulator circuits 

Sizing of accumulators 

Capacity of accumulators 

Intensifiers

Pressure boosters

Intensifier ratio

Intensifier circuits

Air-over-oil intensifier

circuits

Intensifier symbols