Cylinders Motors Accumulators

The primary function of a hydraulic cylinder is to:

Convert fluid power into linear mechanical motion and force Convert fluid power into rotary motion Store hydraulic energy Filter hydraulic oil

A single-acting cylinder:

Uses pressure on one side only with external force or spring return Uses pressure on both sides of the piston for extension and retraction Has two rods Cannot support a load

A double-acting cylinder is able to:

Extend under pressure and retract by gravity only Provide controlled force and motion in both extension and retraction using pressure ports on both sides of the piston Operate without seals Operate only as a shock absorber

The rod side of a cylinder has:

Greater effective area than the piston side Smaller effective area due to the rod occupying some of the piston area The same area as the piston side No pressure applied

Cylinder cushioning is used primarily to:

Increase cylinder speed at end of stroke Slow the piston near end of stroke to reduce impact and shock Eliminate the need for relief valves Reduce oil temperature

Telescopic cylinders are often used where:

Short stroke is needed in limited space A very long stroke is required but retracted length must be compact Rotary motion is required No load is present

Common cylinder mounting styles include:

Only welded lugs Clevis, trunnion, flange, foot and pivot mounts Steering knuckles Tie rod ends only

Cylinder seals are usually located:

Only on the piston On the piston and rod gland to prevent internal and external leakage Only in the reservoir Only inside the pump

Rod wiper seals are designed to:

Increase internal leakage Keep dirt and moisture from entering the cylinder as the rod retracts Hold system pressure Control flow rate

Hydraulic motors are used to:

Convert rotary mechanical power into fluid power Convert fluid power into rotary mechanical power and torque Store hydraulic energy Filter hydraulic fluid

Gear motors are similar in construction to:

Accumulators External gear pumps used in reverse Cylinders Relief valves

Bi-directional hydraulic motors:

Operate in one direction only Can rotate in either direction depending on flow direction Have no case drains Cannot be used for travel drives

When applying hydraulic motors, important catalogue information includes:

Paint colour only Displacement, speed range, torque rating, pressure rating, mounting and shaft type Only port size Only overall length

Hydraulic accumulators are used to:

Filter oil Store hydraulic energy in the form of pressurized fluid and gas Cool the fluid Vent air from the system

Common types of hydraulic accumulators include:

Piston, bladder and diaphragm types Gear, vane and piston types Leaf, coil and torsion types Friction and disc types

In a bladder accumulator:

The gas and fluid are not separated A flexible bladder separates the gas precharge from the hydraulic fluid Only air is used in the gas side No precharge is required

The gas used for precharging most hydraulic accumulators is:

Compressed shop air Nitrogen, because it is dry and non-reactive Oxygen Propane

Accumulators can be used to:

Provide emergency power, absorb shocks, maintain pressure and supplement pump flow Replace all pumps Cool engine coolant Filter air

Safety regulations require that accumulators:

Be pressurized with oxygen for quick response Have appropriate isolation valves, relief devices, and be depressurized before service Be left fully charged during service Be painted only in bright colours

Motor case drains are used to:

Supply oil to the pump inlet Return internal leakage to the reservoir at low pressure Increase output torque Measure motor speed

If a cylinder drifts under load with the valve in neutral, a likely cause is:

Perfect sealing in the circuit Internal leakage past piston seals, valve spools or load-holding valves Low reservoir level only Correct accumulator precharge

A rephasing cylinder circuit is used when:

Only one cylinder is present Multiple cylinders must stay synchronized through internal porting between stages No load is carried Motors are used instead of cylinders

Hydraulic motors used for wheel drives on mobile equipment are often:

Low-torque, high-speed motors High-torque, low-speed motors integrated with planetary gear drives Direct-coupled to the steering wheel Used only as brakes

A cylinder’s rated pressure and rod diameter determine its ability to:

Generate heat only Resist buckling in compression and withstand internal force safely Change oil viscosity Filter contamination

The ILM Cylinders Motors Accumulators module expects parts technicians to:

Overhaul cylinders and motors in the shop Identify component types, basic functions and key catalogue data for replacements Design new accumulator types Ignore maximum pressure ratings

A double-rod cylinder provides:

Different areas on each side of the piston Equal area and speed in both directions No rod seals Only spring return operation

The stroke of a cylinder is defined as:

Rod diameter multiplied by pressure The distance the rod can travel from fully retracted to fully extended position Cylinder bore area Length of the piston head

Symptoms of a damaged accumulator bladder can include:

Stable system pressures Frequent pump cycling and loss of stored energy capacity Reduced contamination Elimination of relief valve operation

Hydraulic motors differ from cylinders in that motors:

Provide linear motion Provide continuous or limited rotary motion and torque Cannot operate bi-directionally Do not require case drains

Mounting style for a cylinder (such as clevis or trunnion) is critical because it:

Determines fluid type Affects how loads are transmitted into the machine structure Changes system pressure Defines reservoir size

A piston accumulator differs from a bladder accumulator in that:

It has no moving parts A sliding piston separates gas and fluid rather than a flexible bladder Gas and fluid are not separated It cannot be precharged

Maximum safe working pressure of a cylinder assembly is limited by:

Only the rod size Cylinder tube strength, end cap design, tie rods (if used) and mounting hardware ratings Seal material only Colour of paint

Over-running loads on cylinders or motors are typically controlled by:

Check valves alone Counterbalance or brake valves in combination with correct valve circuits Larger reservoirs High-viscosity oils only

Catalogue specifications for a hydraulic cylinder will normally include:

Only overall length Bore, rod diameter, stroke, mounting style, port size and maximum working pressure Only bore and stroke Only paint colour

When precharging an accumulator, it is important to:

Use oxygen for better performance Follow manufacturer instructions for nitrogen precharge pressure and use proper charging equipment Bleed oil from the gas side Set precharge higher than relief pressure

Hydraulic motors used in series circuits share:

Flow and torque equally at all times The same flow path, so speed is affected by load balance between motors No interaction Different fluids

Cylinder stop tubes or spacers are sometimes used to:

Increase stroke beyond design Limit stroke and reduce side loading on rod bearings Seal the rod Increase speed