# Fluid Power Hydraulic Cylinders

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Fluid Power Hydraulic Cylinders
Tim Hague Nick Burdg

Function of Hydraulic Cylinders
The main function of a cylinder is to convert hydraulic power into linear mechanical force. This force performs work or transmits power.

Overview Types of Cylinders Construction and Operation
Cylinder Ratings Formulas for Application Cylinder Features Installation and Trouble Shooting

Types of Cylinders Ram Single Acting Telescopic Spring Return
Double Acting

Ram Cylinders The simplest single acting cylinder One fluid chamber
Exerts force in only one direction Mounted mostly vertically The cylinder retracts by the force of the load due to gravity

Ram Cylinders Ram cylinders are most commonly used in elevators, jacks, and automobile hoists. Can also be used on a scissors lift like the one on the loading dock of KL.

Single Acting Cylinders
Acts much like a ram cylinder Main difference is that the single acting cylinder uses a piston. The leakage flow that goes past the piston is ported the tank.

Telescopic Cylinders Mostly a single acting cylinder
Series of rod segments called sleeves, most common to only have 4 or 5 sleeves in each cylinder The sleeves work together to provide a longer stroke The maximum force is at the collapsed position The speed will increase at each stage, but will not allow as much force.

Telescopic Cylinders Most commonly seen in high reach Fork Lifts

Spring Return Cylinders
Considered a single acting cylinder Pressure applied to the cap end pushes the spring down as the rod is extending When the pressure is removed the spring force allows the cylinder to retract The drain is in the spring chamber and allows the leakage flow past the piston seal

Double Acting Cylinders Types
Basic double acting (differential cylinder) Double rod cylinder (nondifferential cylinder) Tandem cylinder

Double Acting Cylinders
Most common type of cylinder Pressure is applied to both rod end and cap end The majority of the cylinders are basic. This means that there is unequal areas at either end.

Double Acting Cylinders
Rod extension is slower because has a larger area, but allows a greater force because of the bigger area. Retract is faster because of the smaller area, but the force allowed is smaller because of the smaller area.

Basic Double Acting Cylinder

Double Acting Cylinders Double Rod Cylinder
Nondifferential type cylinder Same areas at both ends of the cylinder if the rods are the same size Provides equal force, and equal speed in both directions

Double Acting Cylinders Tandem Cylinder
Two pistons in line with a common rod This allows you to have a greater forces without increasing the size of the cylinder bore Tandem cylinders are used in places where there is insufficient space to increase the size of the cylinder bore.

Cylinder Construction

Cylinder Actuation Fluid routed to and from cylinder through ports in each of the heads Cylinder retracts from pressure to rod end port and the other port connected to tank Cylinder extends from pressure to cap end port and rod end port connected to tank

Cylinder Mounting Main function to anchor the cylinder
Mounting methods include tie rod, bolt mount, flange, trunnion, side lug and side tapped, and clevis Tie rod is most common

Cylinder Mounting

Cylinder Mounting

Cylinder Ratings Ratings include size specifications and pressure capability Size specifications - piston diameter (bore) - rod diameter - stroke length Pressure capability - pressure rating established by manufacturer - rating limits maximum force capability

Formulas For Applications
V (in/min) = GPM x (231 / Area (in²)) Q (flow) = Area (in²) x V (in/min) / 231 F (lbs) = Pressure (psi) x Area (in²) P (psi) = Force (lbs) / Area (in²)

Effects of Cylinder Performance for Changes of Flow, Size, and Pressure

Data for Different Cylinder Sizes

Cylinder Features Basic size and pressure ratings are not the only things that define a cylinder Features such as: - seals - cushions - stop tubes - rod spacers - ports - bleed ports -limit switches

Seals Cast iron is most common piston seal
Long service life is most important characteristic Rubber-like materials are the most common rod seal Rod wiper or scraper keeps foreign material from entering the cylinder and the hydraulic system

Cylinder Cushions Used to slow down the piston at the end of its stroke Basic elements include the plunger, adjustable cushion orifice, and a check valve

Stop Tubes Metal collar that fits over piston rod next to piston
Used primarily on long stroke cylinders Provides better cylinder rod support Majority of applications do not require a stop tube

Tie Rod Spacers Tie rod spacers and center supports improve rigidity of long stroke tie rod cylinders Spacer keeps proper position and prevents excessive deflection Tie rod center support has side mounting lugs and serves as additional mounting location

Ports Internal or external opening in a cylinder or a valve
Designed to allow the passing of fluid into or out of the component Wide variety of port type configurations Straight thread O-ring fittings are highly recommended for leak-free connections Poor installation of tubing or hose to port causes leakage

Bleed Ports Usually cylinders bleed air when ports are vertical on top
Bleed ports are necessary to remove trapped air when the ports are installed on the bottom of the cylinder Desirable on high speed, high performance, heavy load applications

Limit Switches Signal rod position to a control circuit or a safety circuit to limit end of travel Common types -mechanical = mechanical actuation of electrical switch when switch is activated by lead angle on a hardened cylinder cushion - proximity = activated when metal cushion passes close to magnetic pickup of the switch * becoming increasingly popular due to simplicity

Cylinder Installation and Troubleshooting
Cylinder application design » hydraulic engineers Installation » hydraulic technician Proper installation and maintenance is crucial to all components to achieve max efficiency Recognizing and controlling potential problems is purpose of troubleshooting

Design Problem A dump truck to lift 5 ton. Specify a cylinder.
Velocity in retract is 15 in/sec Stroke = 18 in P = 2000 psi

References Eaton-Vickers Text, Industrial Hydraulics Manual 4th Edition 2001