Hydraulic cylinders are used in a wide variety of applications on today’s modern equipment. These simple piston and cylinder arrangements are capable of lifting heavy objects or other uses. By using an oil based fluid which is pumped into the cylinder to push the piston and shaft forward or backward a smooth reliable result is achieved.
If you are involved in the construction, agricultural, or any other heavy equipment related business you will eventually face the problem of maintenance or repairs to a hydraulic system. Since downtime means loss of money in most of these applications, and repairs and labor takes time when using commercial repair services, being able to do the repairs yourself can mean the difference in profit or loss.
While the pump itself can be the root cause of your problem the usual problems arise from faulty seals and piston rings in the cylinder itself. After determining the cylinder is not damaged by swelling or by being cracked and the piston rod is not bent itself, replacing the seals and piston rings is a simple task.
The seal around the shaft itself is generally the culprit and the entire assembly must be dismantled to replace this item. Replacing the piston rings also while you are in here is usually done as the repair kit usually includes all rings and seals. If a double application of cylinders is used for power ordering two sets is recommended as the other cylinder will usually need repairing in the neat future.
Before starting to disassemble the cylinder itself it is recommended that you obtain a diagram of the particular cylinder to familiarize yourself with the parts used and also if the disassembly could be dangerous to the novice repairman. Most of the time if the cylinder is only a few feet long this is not a problem but large cylinders sometimes have high tension springs to achieve smoother operation.
By going on-line or visiting your local equipment dealer obtaining a printout of the parts and any particular warnings is usually easily accomplished. This is normally done while ordering the repair kit using model numbers and cylinder numbers as a guide. Often the cylinders are changed or upgraded over the years so having the numbers of the cylinder itself is very important for getting the right parts.
There are different types of cylinders and the way they are held together make each different in their disassembly. Some use long rods which connect the ends together with nuts being used to lock them in place. Others have the cylinder made onto the stationary yoke with the movable yoke end containing the seal around the shaft. This end screws out enabling access to the piston and retaining bolt.
Loosening the hoses or pipes through which the hydraulic fluid travels to and from the cylinder will enable you to pull the shaft out of the cylinder easier. If this is not done a suction will be created when attempting to remove the shaft and piston. This is true also for installation.
Be very careful not to scratch the shaft itself as this will damage the new seal as it travels back and forth during use. The piston is usually attached to the shaft by a bolt or nut and must be removed to replace the seal in the retaining housing. On large cylinders loc-tite or some other thread sealing substance may have been used to prevent the bolt or nut from working loose during operation. If this is the case, heating the bolt or nut carefully will usually help to remove it.
In some cases two cylinders are used on the same hose or pipe arrangement and have a pressure release plunger which goes through the retaining bolt. This prevents the piston from traveling too far by the plunger contacting the end of the cylinder and releasing the pressure. A spring inside can be damaged by heating it too much but sometimes this is unpreventable. Simply replace the spring when reassembling the piston.
After removing the piston carefully remove and replace the seal being sure not to use any sharp objects which will damage the retainer cap or seal itself. This seal may be thin and prone to damage if not inserted straight. If it starts aslant gently tap it out and start over. If you can find an object the same size as the seal to place against the seal itself it will be easier to insert the seal properly.
You may replace the piston rings while it is off of the shaft or after bolting it back on. Be careful when you do this so the new rings will not be damaged. I recommend using a thread locking substance when replacing the bolt or nut because if this comes loose during operation it could ruin the cylinder or even cause injury to someone. Safety is always a factor in these instances.
When the piston rings have been replaced you are ready to insert the piston back into the cylinder. Oil all of the rings and gently work the piston back into the cylinder. It may be necessary to tap the end of the shaft to get the piston into the cylinder but be sure to use a piece of wood on the end of the shaft to prevent the yoke from chipping or breaking.
Screw in the retaining cap or bolts, whichever the cylinder uses, making sure to tighten them sufficiently. Reattach both yoke ends to the respective places and retighten the hoses or pipes and the job is finished. Lubricate the shaft itself before testing out the cylinder.
These are generic tips for most common cylinders and some differences may be encountered. It is very important to obtain a diagram of the particular cylinder and the breakdown of parts before attempting this procedure. Being able to accomplish this task will save you much money and time.
