Victor's Industrial Supply Advice

How to Replace the Seals on a Hydraulic Cylinder

If one of the hydraulic cylinders on your tractor, forklift or any other equipment is leaking, you can top it up with extra fluid for a while, but that's just a temporary fix, and eventually you may want to invest in hydraulic cylinder repair. Here's a look at the process.

1. Release the Pressure

Ideally, you don't want to work on the hydraulic cylinder while it's pressurised, so removing pressure needs to be your first step. Take off all the hydraulic lines and loosen the gland at the end of the cylinder.

2. Remove the Gland

The gland is usually where you see the hydraulic fluid leaking out of the cylinder, and you need to fully remove this. You can use a screwdriver to take off the hardware, but if there is caked on debris, you may also need to tap the gland with the end of the screwdriver to get it loose.  

3. Stabilise and Pull Out the Piston Rod

At this point, you need to pull out the piston rod. This can be challenging with very large hydraulic cylinders, so you may want to stabilise the cylinder. Some people use winches for large cylinders and just steady smaller cylinders between breezeblocks. While pulling out the piston, keep everything as straight as possible. Try to avoid scraping the inside of the cylinder and damaging it. Once the piston is out, be careful with it. Try to prevent it from getting unnecessarily dirty or scratched.

4. Unscrew the Retaining Bolt

Before the piston is fully free, you need to remove the retaining bolt holding the piston to the rod. You may need to apply some heat, especially if a thread-locking substance was used the last time this cylinder was taken apart. Once everything is free, put it in order so that it will be easy to put back together. Then, replace all the seals and o-rings that you see. Just slip off the old ones and put on the new ones.

5. Put It Back Together  

When all the seals have been replaced, you simply need to put your cylinder back together. Basically, follow the steps above in reverse. Note that pushing some parts together may be slightly harder because the new seals create a tighter fit. Once everything is assembled, connect the hydraulic lines and fill it up with hydraulic fluid. At this point, your leak should be gone. If you need more help, consult with a hydraulic cylinder repair specialist.