A common misunderstanding about hydraulic cylinders is that if the piston seal leaks, the cylinder will gradually lower. However, the reality is more complex. If the piston seal is entirely removed from a double-acting hydraulic cylinder, and the cylinder is filled with oil with its ports sealed, it can maintain its load indefinitely unless the rod seal also leaks.

The only way the cylinder can move is if fluid escapes through the rod seal or the ports. Understanding this concept is crucial for troubleshooting.

Exceptions to this principle include double-rod cylinders, where volumes are equal on both sides of the piston, and instances where a load is suspended on a double-acting cylinder, allowing pressurized fluid on the rod side to be accommodated easily on the piston side.

However, if the service ports of a double-acting cylinder are blocked, and the piston seal bypasses, pressure eventually equalizes on both sides, leading to hydraulic lock unless fluid escapes. Due to the loss of effective area caused by pressure on the rod-side annulus area, the static pressure in the cylinder must increase to support the same load.

For example, if the load-induced pressure on the piston side is initially 2,000 PSI and zero on the rod side when the directional control valve closes, the equalized pressure may rise to 3,000 PSI, depending on the area ratio. If the circuit has a relief valve set at 2,500 PSI, the cylinder may start to lower as pressure equalizes and exceeds the relief valve setting.

Understanding these dynamics, including the impact of pressure differentials and relief valve settings, is crucial for troubleshooting cylinder drift, highlighting the importance of employing pressure gauges in such situations.

In the realm of Car Lift Repair Tampa Florida hydraulic equipment, hydraulic cylinders are nearly as prevalent as pumps and motors combined. Therefore, if you’re extensively engaged with hydraulic machinery, it’s probable that the expenses associated with cylinder repairs constitute a notable portion of your overall operational costs.

According to various studies, up to 25% of mechanical equipment failures stem from design inadequacies. When applied to hydraulic cylinders, this suggests that as many as one out of every four cylinders may not be suitably designed for their operational context.

This doesn’t imply that such Car Lift Repair Tampa Florida cylinders won’t fulfill their intended tasks; they will, but not with a satisfactory service lifespan. Consequently, if you’re encountering cylinders that fall short of their expected longevity, you might need to address one or more of the following four issues:

1. Bent Rods:

Rod bending can result from factors such as inadequate rod diameter or material strength, improper cylinder mounting arrangements, or a combination thereof. Once a rod bends, it imposes deforming loads on the rod seal, leading to increased leakage and ultimately premature seal failure. The permissible rod loading in an existing application can be evaluated using the Euler formula, with detailed instructions provided by Car Lift Repair Tampa Florida.

2. Rod Finish:

The surface finish of the cylinder rod significantly influences the lifespan of the rod seal. If the surface is excessively smooth, lubrication may be insufficient, thereby reducing seal longevity. Conversely, excessively rough surfaces can heighten contaminant ingress and result in unacceptable levels of seal leakage. To prolong Car Lift Repair Tampa Florida cylinder service life, it’s essential to treat the rod surface as a lubricated wear surface. In certain applications, alternative rod surface treatments with superior mechanical properties compared to conventional hard-chrome plating, such as nickel-chrome plating or High Velocity Oxygen Fuel (HVOF) metal spraying, can enhance rod and seal longevity. Additionally, the installation of shrouds or bellows to shield the rod surface and seals from impact damage and contaminants can provide similar benefits.

3. Ballooned Tubes:

Tube ballooning typically occurs due to insufficient wall thickness and/or material strength relative to the cylinder’s operating pressure. Once ballooning occurs, the correct tolerance between the piston seal and tube wall is compromised, allowing high-pressure fluid to bypass the seal. This fluid erosion can accelerate seal wear, while localized heating resulting from pressure drops across the Car Lift Repair Tampa Florida piston further diminishes seal longevity, culminating in premature piston seal failure.

4. Insufficient Bearing Area:

Inadequate surface area on the bearing (wear) bands in the gland and on the piston can fail to adequately support the side thrust transferred to the cylinder, resulting in excessive loads on the rod and piston seals. This leads to seal deformation and, ultimately, premature seal failure.

Recently, a client enlisted my services to conduct a failure analysis on a sizable and costly hydraulic cylinder from an excavator. This cylinder had been replaced prematurely due to rod seal leakage, achieving only half of its expected lifespan.

Upon inspection, it was evident that, apart from the failed rod seals due to ‘dieseling’, the remaining components of the hydraulic cylinder were still functional. The ‘diesel effect’ occurs when air mixes with hydraulic oil and detonates under pressure.

During the retraction of a double-acting Car Lift Repair Tampa Florida hydraulic cylinder under load, the fluid demanded by the rod side can surpass the supply from the pump, creating negative pressure in the rod side. This vacuum often draws air past the rod seals since these seals are primarily designed to retain high-pressure fluid rather than prevent air ingress. Consequently, aeration transpires, resulting in air-oil mixture.

As previously mentioned, the compression of this mixture can lead to explosions, damaging the hydraulic cylinder and causing seal burns. The term ‘diesel effect’ is derived from the combustion process akin to that in a diesel engine.

Dieseling may occur due to the failure to purge air from the Car Lift Repair Tampa Floridacylinder chambers during commissioning. However, in the scenario outlined above, faulty operation of the ‘float’ valve was the root cause of air ingress. The float valve’s role in a hydraulic excavator is to facilitate rapid lowering of the boom or arm under its weight. When activated, this valve connects the hydraulic cylinder ports, enabling retraction under load. Fluid displaced from the piston side is primarily directed to the rod side before surplus volume returns to the reservoir, with an orifice regulating the retraction speed. Malfunction or improper adjustment of this valve can induce negative pressure on the rod side, drawing air past the rod seals and leading to cylinder failure.