1. Fluid Power Hydraulic Cylinders
Tim Hague
Nick Burdg

2. 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.

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

4. Types of Cylinders Ram Single Acting Telescopic Spring Return
Double Acting

5. 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

6. 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.

7. 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.

8. 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.

9. Telescopic Cylinders
Most commonly seen in high reach Fork Lifts

10. 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

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

12. 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.

13. 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.

14. Basic Double Acting Cylinder

15. 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

16. 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.

17. Cylinder Construction

18. 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

19. 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

20. Cylinder Mounting

21. Cylinder Mounting

22. 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

23. 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)

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

25. Data for Different Cylinder Sizes

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

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