Presentation on theme: "Fluid Power Hydraulic Cylinders"— Presentation transcript:
1Fluid Power Hydraulic Cylinders Tim HagueNick Burdg
2Function 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.
3Overview Types of Cylinders Construction and Operation Cylinder RatingsFormulas for ApplicationCylinder FeaturesInstallation and Trouble Shooting
4Types of Cylinders Ram Single Acting Telescopic Spring Return Double Acting
5Ram Cylinders The simplest single acting cylinder One fluid chamber Exerts force in only one directionMounted mostly verticallyThe cylinder retracts by the force of the load due to gravity
6Ram CylindersRam 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.
7Single Acting Cylinders Acts much like a ram cylinderMain difference is that the single acting cylinder uses a piston. The leakage flow that goes past the piston is ported the tank.
8Telescopic Cylinders Mostly a single acting cylinder Series of rod segments called sleeves, most common to only have 4 or 5 sleeves in each cylinderThe sleeves work together to provide a longer strokeThe maximum force is at the collapsed positionThe speed will increase at each stage, but will not allow as much force.
9Telescopic CylindersMost commonly seen in high reach Fork Lifts
10Spring Return Cylinders Considered a single acting cylinderPressure applied to the cap end pushes the spring down as the rod is extendingWhen the pressure is removed the spring force allows the cylinder to retractThe drain is in the spring chamber and allows the leakage flow past the piston seal
12Double Acting Cylinders Most common type of cylinderPressure is applied to both rod end and cap endThe majority of the cylinders are basic. This means that there is unequal areas at either end.
13Double 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.
15Double Acting Cylinders Double Rod Cylinder Nondifferential type cylinderSame areas at both ends of the cylinder if the rods are the same sizeProvides equal force, and equal speed in both directions
16Double Acting Cylinders Tandem Cylinder Two pistons in line with a common rodThis allows you to have a greater forces without increasing the size of the cylinder boreTandem cylinders are used in places where there is insufficient space to increase the size of the cylinder bore.
18Cylinder ActuationFluid routed to and from cylinder through ports in each of the headsCylinder retracts from pressure to rod end port and the other port connected to tankCylinder extends from pressure to cap end port and rod end port connected to tank
19Cylinder Mounting Main function to anchor the cylinder Mounting methods include tie rod, bolt mount, flange, trunnion, side lug and side tapped, and clevisTie rod is most common
22Cylinder RatingsRatings include size specifications and pressure capabilitySize specifications- piston diameter (bore)- rod diameter- stroke lengthPressure capability- pressure rating established by manufacturer- rating limits maximum force capability
23Formulas For Applications V (in/min) = GPM x (231 / Area (in²))Q (flow) = Area (in²) x V (in/min) / 231F (lbs) = Pressure (psi) x Area (in²)P (psi) = Force (lbs) / Area (in²)
24Effects of Cylinder Performance for Changes of Flow, Size, and Pressure
26Cylinder FeaturesBasic size and pressure ratings are not the only things that define a cylinderFeatures such as:- seals- cushions- stop tubes- rod spacers- ports- bleed ports-limit switches
27Seals Cast iron is most common piston seal Long service life is most important characteristicRubber-like materials are the most common rod sealRod wiper or scraper keeps foreign material from entering the cylinder and the hydraulic system
28Cylinder CushionsUsed to slow down the piston at the end of its strokeBasic elements include the plunger, adjustable cushion orifice, and a check valve
29Stop Tubes Metal collar that fits over piston rod next to piston Used primarily on long stroke cylindersProvides better cylinder rod supportMajority of applications do not require a stop tube
30Tie Rod SpacersTie rod spacers and center supports improve rigidity of long stroke tie rod cylindersSpacer keeps proper position and prevents excessive deflectionTie rod center support has side mounting lugs and serves as additional mounting location
31Ports Internal or external opening in a cylinder or a valve Designed to allow the passing of fluid into or out of the componentWide variety of port type configurationsStraight thread O-ring fittings are highly recommended for leak-free connectionsPoor installation of tubing or hose to port causes leakage
32Bleed 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 cylinderDesirable on high speed, high performance, heavy load applications
33Limit SwitchesSignal rod position to a control circuit or a safety circuit to limit end of travelCommon 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
34Cylinder Installation and Troubleshooting Cylinder application design » hydraulic engineersInstallation » hydraulic technicianProper installation and maintenance is crucial to all components to achieve max efficiencyRecognizing and controlling potential problems is purpose of troubleshooting
35Design Problem A dump truck to lift 5 ton. Specify a cylinder. Velocity in retract is 15 in/secStroke = 18 inP = 2000 psi