A common misunderstanding about Automotive Lift Repair Tampa Florida hydraulic cylinders is the belief that a leaking piston seal will cause the cylinder to drift downward. In reality, if a double-acting hydraulic cylinder’s piston seal is completely removed, and the cylinder is filled with oil and the ports are sealed, the cylinder will hold its load indefinitely—unless the rod seal leaks.
Under these conditions, the unequal volume on either side of the piston leads to fluid pressure equalizing, which locks the cylinder hydraulically. The cylinder will remain locked until fluid escapes through the rod seal or the ports. For a clear explanation of this, watch this 8-minute video.
Understanding this principle will reveal a few exceptions. Firstly, a double-rod cylinder, where the volume on both sides of the piston is equal. Secondly, if a load is suspended on a double-acting cylinder, the pressurized fluid on the rod side can be accommodated on the piston side.
However, this is not the entire picture. It’s crucial to grasp this theory before moving on. Despite the exceptions, if a double-acting cylinder’s service ports are blocked by a closed actuator or spool and the piston seal leaks, pressure will eventually equalize on both sides of the cylinder. At this point, a hydraulic lock occurs, preventing further movement unless fluid escapes from the cylinder or circuit.
Due to the reduction in effective area from pressure now acting on the rod-side annulus, the static pressure in the Automotive Lift Repair Tampa Florida cylinder must increase to support the same load. For instance, if the load-induced pressure was 2,000 PSI on the piston side and zero on the rod side when the DCV was closed, the equalized pressure might rise to 3,000 PSI depending on the area ratio.
If the circuit has a service port relief valve set at 2,500 PSI, as pressure equalizes and the static pressure on the piston side reaches the relief valve’s cracking pressure, the cylinder will start to drift downward.
Therefore, while the underlying issue is the leaking piston seal, the physics involved differ from common beliefs. Understanding this theory shows how a pressure gauge can be invaluable when diagnosing cylinder drift.
Automotive Lift Repair Tampa Florida Hydraulic cylinders are nearly as prevalent as pumps and motors combined. Therefore, if you operate a significant amount of hydraulic equipment, the costs associated with cylinder repair likely constitute a substantial portion of your total operating expenses.
Studies suggest that up to 25% of mechanical equipment failures stem from design flaws. Applying this to hydraulic cylinders, it implies that up to one in four hydraulic cylinders may not be optimally designed for their intended applications.
While this doesn’t mean the cylinder won’t perform its intended function, it may not do so with an acceptable service life. If you’re experiencing shorter-than-expected lifespans with your cylinders, consider addressing one or more of the following four issues:
1. Bent Rods
Automotive Lift Repair Tampa Florida Cylinder rods can bend due to insufficient rod diameter or material strength, improper mounting arrangements, or a combination of these factors. A bent rod creates deforming loads on the rod seal, increasing leakage and leading to premature seal failure.
To evaluate the allowable rod loading for a cylinder in your application, refer to the Euler formula, detailed on pages 58 and 59 of Industrial Hydraulic Control.
2. Rod Finish
The surface finish of the cylinder rod significantly impacts rod seal life. A surface that’s too smooth can reduce seal life due to inadequate lubrication, while a rough surface can increase contamination and leakage past the seal.
Treat the Automotive Lift Repair Tampa Florida cylinder rod’s surface as a lubricated wear surface to extend service life. In some cases, alternative surface treatments like nickel-chrome plating or High Velocity Oxygen Fuel (HVOF) metal spraying can enhance rod and seal longevity. Additionally, installing a shroud or bellows to protect the rod and seals from impact and contaminants can also extend their lifespan.
3. Ballooned Tubes
Ballooning of the cylinder tube is typically caused by insufficient wall thickness or material strength relative to the cylinder’s operating pressure. Ballooning disrupts the tolerance between the piston seal and tube wall, allowing high-pressure fluid to bypass the seal. This can erode the seal and cause localized heating, reducing seal life and leading to premature seal failure.
4. Insufficient Bearing Area
If the bearing (wear) bands in the gland and on the piston are too small to support side thrust, excessive load is placed on the rod and piston seals. This leads to seal deformation and premature failure.
Addressing these issues can help improve the durability and performance of your hydraulic cylinders, reducing repair costs and extending their operational life.
I was recently hired by a client to analyze the failure of a large, costly hydraulic cylinder from an excavator. This cylinder had been replaced due to leaking rod seals after only half of its expected service life.
Upon inspection, it was found that aside from the rod seals, which had failed due to a phenomenon known as ‘dieseling,’ the other components of the hydraulic cylinder were still in serviceable condition. The ‘diesel effect’ occurs in a hydraulic cylinder when air mixes with hydraulic oil and ignites under pressure.
When a double-acting Automotive Lift Repair Tampa Florida hydraulic cylinder retracts under load, the volume of fluid required by the rod side can sometimes exceed what the pump supplies. This creates negative pressure in the rod side of the cylinder, often drawing air in through the rod seals. Most rod seals are designed to retain high-pressure fluid, not to prevent air entry, leading to aeration—a mix of air and hydraulic oil.
As explained, compressing a mixture of air and oil can cause an explosion, damaging the Automotive Lift Repair Tampa Florida hydraulic cylinder and burning the seals. The term ‘diesel effect’ draws a parallel to the combustion process in a diesel engine.
Dieseling can result from not purging air from the cylinder during commissioning. In this case, however, the issue stemmed from a faulty ‘float’ valve. The float valve on a hydraulic excavator is meant to allow the boom or arm to lower rapidly under its own weight. When activated, it connects the cylinder’s ports, letting it retract under the boom or arm’s weight.