The cylinder is made of a seamless tube or casting that has a true, smooth interior surface. The piston circumference has a mechanical seal, usually in the form of œ0-ring or œT- ring seals. The piston rod on double acting cylinders is chromed or hard surfaced and polished and passes through an end cap. The piston end cap provides mounting for the cylinder end. Ports into the cylinder are positioned in the end caps. System relief pressure and piston diameter determine the piston capacity within design limits. The piston speed is determined by the volume of the oil flow.
When valving directs the
circuit pressure to the piston end, oil at the rod end is directed to the
reservoir as the rod extends. To change direction, the oil under pressure
is directed to the rod side of the piston and oil on the piston face is
directed back to the reservoir.
In (Fig. 15), cylinder A with a capacity of ½ gal. would
take 6 seconds to stroke fully with a flow rate of 5 G.P.M. Cylinder B
with a capacity of 1 gal. would take 12 seconds at 5 G.P.M. Equal
pressures at 5 G.P.M. would allow cylinder B with twice the piston area to
move double the weight of cylinder A. With these examples, we can see how
pressure affects capacity and volume affects speed. Engineers designing
hydraulic systems choose components which will perform their jobs
according to the needs of the equipment. Pump volumes, cylinder and line
capacities, valving, and operating pressures all need to be
[Source: Simplicity publication, Hydraulic Systems Training Information, #840172, Principles and Operation of Tractor Hydraulic Systems]