Chapter 6 Cylinders

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Learning Objectives Describe attributes related to the different types of linear actuators. Identify the different components used in hydraulic cylinders. List the different methods manufacturers use to dampen a cylinder’s stroke. Explain different methods used for sensing a cylinder’s position.

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Learning Objectives Explain the difference between tension and compression cylinder loads. Describe how to compute cylinder speeds. List different types of valves that can be integrated into a cylinder housing. Explain the principle of cylinder regeneration. Identify several items that can cause a cylinder to drift.

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Learning Objectives List the problems that occur when metering-in or metering-out an overrunning load. Explain the different methods used for synchronizing hydraulic cylinders. List unsafe actions to avoid when servicing and diagnosing hydraulic cylinders.

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Types of Linear Actuators Single acting Double acting Single rod Double rod Ram Telescoping

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Single-Acting Cylinders Commonly use fluid pressure to extend cylinder (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Double-Acting Cylinders Use fluid pressure to extend and retract cylinder Also known as “differential cylinder” Area is different between piston’s rod end and cap end (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Double-Acting, Double-Rod Cylinders Same speed and force in both directions Commonly used for steering (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Rams Type of single-acting cylinder Cylinder rod is same diameter as cylinder’s piston (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Telescoping Cylinders Can contain up to six cylinder tubes Will retract to length 20–40% of extended stroke Can be single-acting or double-acting

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Telescoping Cylinders (cont.) (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Cylinder Components and Nomenclature Main components –Piston, gland, rod, barrel, seals (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Piston Rings and Seals Pistons have multiple rings and seals around their outside circumference Piston wear ring prevents piston from rubbing barrel (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Piston Rings and Seals (cont.) Piston seals must maintain fluid-tight seal between barrel and piston Piston seal groups –Metal seals –Double-acting seals –Lip seals

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Double-Acting Seals Seal fluid in both directions Use O-ring with Teflon backup ring (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Lip Seals U-shaped or V-shaped Seal fluid in one direction Less likely to leak (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Glands Guide for cylinder rod “Spanner wrench” used to remove glands (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Rod Rings and Seals Located in cylinder gland Rod seals are inside cylinder gland Rod seals are commonly the lip type Outer rod seal is known as “wiper” or “scraper” seal Gland also includes internal wear ring External O-ring prevents leakage between gland and barrel

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Barrel Many barrels can be honed Honing deglazes and renews barrel Most popular hone is made of silicon-carbide (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Cylinder Rod Must be inspected during rebuild –Look for cracks or nicks –Check for straightness Can be rechromed Hydraulic repair shops can fabricate new

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Cylinder Loads, Dampening, and Speeds Thrust load –Anytime cylinder must push load Tension load –Anytime cylinder must pull load

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Cylinder Dampening Reduce shock loads –Cushioned cylinders –Orifices –Accumulators –Programmable kick-outs (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Cylinder Dampening (cont.) Mechanical limitation on cylinder stroke –Stop tube –External depth stop (Bryan Bell)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Cylinder Speeds Three formulas –Speed (ft/min) = (Flow (gpm) x 19.25)/Area (in²) –Speed (ft/sec) = (Flow (gpm) x )/Area (in²) –Speed (m/sec) = (Flow (lpm) x 0.167)/Area (cm²)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Cylinder Electronic Sensing Examples –Automatic header height on combine –Load control for agricultural tractor’s three-point hitch –Slope control on motor grader –Grade control on excavator –Grade control on dozer Two common technologies for sensors –Potentiometer –Magnetostrictive

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Cylinder Electronic Sensing (cont.) (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Valving Designed for Cylinders Regeneration –Unloaded differential cylinder is extending and its return oil is rerouted to cylinder’s inlet (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Cylinder Drift Occurs when rod leaks down over period of time Valves that can also cause cylinder drift –Thermal-relief –Cylinder port relief –Counterbalance –Lift check –Secondary poppet (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Metering-In and Metering-Out Overrunning Loads Metering-in –Restricts oil flowing into cylinder Metering-out –Restricts oil flowing out of cylinder (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Synchronizing Cylinders Hydraulic cylinders that extend simultaneously to lift load Common synchronizing methods –Master/slave series configuration Master/slave will also use rephasing orifices –Parallel configuration with rephasing relief valves

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Synchronizing Cylinders (cont.) (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Cylinder Safety Compressed air and heat should never be used to remove seized cylinder piston or gland Do not attempt to stall hydraulic cylinder or motor under pressure Do not attempt to mechanically actuate cylinder or motor while it is under pressure (Goodheart-Willcox Publisher)

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Summary Single-acting cylinders use fluid pressure in only one direction. A double-acting, single-rod cylinder exhibits different forces when extending and retracting under a given pressure and different speeds when extending and retracting using a given flow. Telescoping cylinders provide long strokes, and compact lengths when retracted. A ram’s cylinder rod is the same diameter as the cylinder’s piston.

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Summary The gland guides the cylinder rod during extension and retraction. Wear rings prevent metal-to-metal contact during cylinder operation. Piston seals can be metal, Teflon, lip design, or O-ring. Rod seals retain the cylinder’s fluid. Rod wipers prevent outside contaminants from entering the cylinder.

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Summary Cylinder shock loads can be dampened with cushioned cylinders, orifices, accumulators, or programmable kick-outs. Computing a cylinder’s speed requires knowing the cylinder’s area and input flow. Potentiometers and magnetostrictive sensors measure the position of a cylinder. When the cap end and rod end of a double-acting cylinder are plumbed together, the cylinder will regenerate.

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Summary Cylinders can drift due to a bad pressure control valve. A bad piston seal can cause cylinder drift only if the rod points toward the ground. Manufacturers use master/slave series designs to synchronize two cylinders. Rephasing orifices and rephasing relief valves are used to place cylinders back into synchronization.

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Summary Compressed air and heat should never be used to remove a seized cylinder piston or gland. Do not mechanically restrict or stall an operating actuator. Do not mechanically assist an actuator that is under pressure.