Nothing lasts forever and when a hydraulic cylinder begins to develop problems, it is often caused by drift. For example, most business owners believe a double action hydraulic steering cylinder will drift whenever it begins to leak. However, there is more to it than cylinder seal leakage. Let’s delve a little deeper into the physics behind cylinder drift to give you a better understanding of the issue.
Basic Principle of Hydraulics
When pressure is placed on fluid it is not compressed and this is why pressure can be maintained throughout a system. For example, an automotive brake system will fail if a small amount of air is allowed into the fluid system. Air can be compressed and this is why your brake pedal may suddenly go all the way to the floor, if air is not properly bled from the system or if a cylinder seal is leaking.
Leaking Piston Seals
Let’s look at an example of a leaky piston seal in a double action hydraulic steering cylinder. Imagine a cylinder with the piston seal removed and both ports are effectively blocked off. The piston will maintain its position and its load as long as the rod seal is not leaking, even there is no seal in place.
Why Does This Happen?
The piston does not drift because the fluid inside the cylinder seeks its own level and the pressure equalizes on both sides. However, the cylinder is now locked in position, unless one of the ports is opened.
In some cases a double action cylinder can hang up due to drift but further drift is eliminated when pressure on the rod side creates a vacuum on the piston side. This equalizes pressure inside the cylinder.
What Causes Cylinder Failure?
As you can see, drift can be a result of many factors and understanding cylinder drift is important if you wish to take the best care of your equipment. However, the most important thing to keep in mind, is why most cylinders fail in the first place. Here are some common causes:
* Excessive heat – anytime heat builds up inside a system, it can create additional wear on seals. For example, seal components will prematurely harden and become brittle when exposed to heat. This can be caused by not using the right seals or if operating conditions continually are over the recommended ambient temperature.
* Contamination – dirt, grit, water or air can wreak havoc with a hydraulic steering cylinder, lift cylinder and many other types.
* Improper hydraulic fluid – can cause an undesirable chemical reaction which breaks down seals.
* Improper rebuilding – failure to keep cylinders clean while rebuilding is a major reason for failure.
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