Taking the mystery out of hydraulics

Analyses a farm machinery essential

ALMOST every piece of agricultural machinery around the farmyard is equipped with a hydraulic cylinder or ram.

Essentially, a hydraulic ram is used to convert oil flow into powered linear movement, in either one direction (singleacting ram), or two directions (double-acting ram). Rams provide the power to machinery that has allowed output to increase exponentially in the last 100 years.

For the purpose of this article, we will look at a double-acting ram. This is a ram that provides powered linear movement in two opposing directions, like the ram on a shear grab for example, which uses hydraulic power to both open and close the grab.

A double-acting hydraulic ram has two internal chambers, one for providing power in each direction.

There are a number of internal seals which prevent the oil from passing from one chamber to the other. When these seals fail, the oil moves between the chambers, causing unwanted linear movement in the ram.

This can often be observed on an attachment like a front-end loader. If the loader is left in a raised position for a period of time, it will slowly creep down. This is generally caused by oil escaping from one internal chamber to the other due to worn or damaged internal seals.

However, changing these seals is not a difficult task once you know a bit about the internal workings and follow the simple steps I go through here.

As with any hydraulically operated implement, safety comes first. Remember to never work under an unsupported load or object.

You will need to fully remove the ram from its working position to disassemble it, so ensure the ram is not supporting any weight or load that will suddenly shift as you remove the connecting pins.

It is a good idea to have someone working with you. Take two minutes to assess and neutralise the possible risks before you begin the work.

Step 1

Using a stilson wrench, unscrew the gland from the main body of the ram.

Step 2

Having fully unscrewed the gland, draw the entire rod out of the main cylinder. Any oil within the ram will flow out at this point, so have a suitable container ready to catch this oil. Take care not to mark or scratch the polished surface of the rod. There are seals sliding on this polished surface and any imperfections will quickly ruin them.

Step 3

Having drawn out the rod, inspect the internal bore of the main cylinder. It should be clean, smooth and free of imperfections and scoring. Any marks or scoring on this inner bore will play havoc on piston seals.

Step 4

Unscrew the piston from the rod. Ensure the roll pin or grub screw is removed before attempting to loosen the piston.

Step 5

Having unscrewed the piston, the gland which was loosened in Step 1 can now be slid off the rod.

Step 6

Inspect the general condition of the gland. Check the condition of the primary O-ring. If it is nicked or scored in any way, replace it. They are inexpensive and there is little point in going to the effort of removing it if you are not going to replace it.

Step 7

Check the secondary O-ring (at the tip of the screwdriver), Again, replace if damaged in any way.

Step 8

Inspect the scraper seal on top of the gland. This is a hard nylon seal which plays the important role of wiping the rod clean as it slides back into the ram. This prevents ingestion of dirt and foreign matter into the ram and hydraulic system. Replace if necessary.

Step 9

Inspect the condition of the piston. It should be clean, smooth and unmarked, with undamaged faces on to which the seals are seated. Pop off the piston seals and assess their condition.

Step 10

Verify that the piston seals are undamaged, replace if necessary.

Step 11

Inspect the condition of the wear ring. There is an O-ring seated behind this wear ring — ensure that it too is undamaged. Remove the wear ring to fully assess the condition of the O-ring. Again, replace as necessary.

Step 12

When inspecting the condition of the components, ensure that the work area is clean. Although these seals can withstand great hydraulic pressure, they are quite easily damaged.

Clean and wipe down all components thoroughly before reassembly, so as not to introduce dirt and contamination into the hydraulic system.

Be thorough in your inspections — any minor imperfection on a seal is enough to cause leakage. If in doubt, replace.

To reassemble the cylinder, simply reverse the steps. If parts need replacing, they can generally be purchased at any industrial and agri component stores.

Having reassembled the ram, replace it into its working position, fit the hydraulic hoses and you’re back in action.