A well known misconception involving Hydraulic Ram And Oil Cylinder is that if the piston seal is leaking, the cylinder will drift. While a leaking piston seal could be the real cause of cylinder drift, the physics involved are frequently misinterpreted. Truth is, f the piston seal is entirely removed from a double-acting cylinder, the cylinder is filled with oil as well as the ports are plugged, the cylinder will hold its load indefinitely, unless the rod-seal leaks.
Within this condition, due to the unequal volume on both sides in the piston, fluid pressure equalizes as well as the cylinder becomes hydraulically locked. Once this happens, the cylinder can move only if fluid escapes from your cylinder via the rod seal or its ports.
Exceptions for the Rule – There are 2 exceptions to this particular theory. The very first is a double-rod cylinder (Figure 1) where volume is equal for both sides of the piston. The next exception involves a lot hanging over a double-acting cylinder (Figure 2). Within this arrangement, the quantity of pressurized fluid on the rod side could be accommodated on the piston side. But because the cylinder drifts, a vacuum will develop on the piston side because of unequal volumes, and depending on the weight from the load, this vacuum may eventually bring about equilibrium that arrests further drift.
This may not be the end of the cycle, but it’s important to a minimum of grasp this theory before continuing. Notwithstanding both of these exceptions, if a double-acting cylinder’s service ports are blocked by a closed-to-actuator spool (Figure 3), as well as the piston seal does bypass, pressure will ultimately equalize on sides from the cylinder. At this point, a hydraulic lock is effected without any further drift can happen, unless fluid is able to escape from your cylinder or cylinder circuit.
Loss of Effective Area – Because of the loss in effective area because of pressure now acting on the rod-side annulus area, the static pressure within the cylinder must increase to aid the same load. Remember, force designed by a cylinder is really a product of pressure and area. For example, when the load-induced pressure on the piston side in the cylinder was 2,000 PSI and zero on the rod side once the directional control valve closed, assuming no leakage beyond the spool, the equalized pressure might be 3,000 PSI depending on the ratio of the piston and annulus areas.
New call-to-action – Now consider so what can happen if this type of circuit features a service port relief valve (Figure 4) set at 2,500 PSI. As pressure equalizes throughout the piston seal as well as the increasing static pressure on the piston side from the Small Bent Axis Motor Hydraulic Pump reaches the cracking pressure in the port relief, though the cylinder will still not retract. A similar situation can happen in circuits having a load control (counterbalance) valve installed. Within this circuit, shown in Figure 5, the directional control valve features a float center spool (service ports A and B open to tank).
As previously stated, in the event the piston seal leaks, unequal volumes of oil on the rod and piston sides of the cylinder indicates hydraulic lock may prevent any noticeable drift. But once again, because of the loss of effective area because of exactly the same pressure now acting on the piston and rod-side annulus areas, the static pressure inside the cylinder must increase to aid the same load.
The magnitude of the pressure increase depends on the ratio of the cylinder’s piston and annulus areas. If the increase in static pressure exceeds the set maximum load of the counterbalance valve, the valve will open allowing oil from your piston side of the cylinder to circulate for the tank as well as the cylinder to retract.
Diagnosing Cylinder Drift – Therefore, while the root cause from the problem in both examples is definitely the leaking piston seal, the physics is fundamentally different from the overall belief. And in case the thought is understood, a pressure gauge could be a useful tool for establishing the reason for cylinder drift. In both of those examples, in the event the cylinder is drifting but there is no equalization of pressure throughout the piston seal, the directional control valve or load control valve is definitely the way to obtain rldvub problem.
What is the maximum pressure range for the application? Keep in mind pressures can vary greatly greatly depending on the specific job the system is doing. Cylinders are rated both for nominal (standard) pressure and test pressure to take into account variations. System pressure should never exceed the nominal rated design pressure in the cylinder.
Push or pull-or both (double acting)? The reply to this question may need Piston Best Welded Cylinder Hydraulic Actuator when the hydraulic method is doing “double duty.” (Single-acting cylinders extend the piston under hydraulic pressure; double-acting cylinders extend and retract the piston under pressure.) In a push application, it is extremely important to size the rod diameter properly to prevent rod buckling. In a pull application, it is essential to size the annulus area (piston diameter area minus the rod diameter area) correctly to go the load at the rated design pressure of the cylinder.
Yongxiang Hydraulic Equipment Co., Ltd locates in Yangzhou, CN, and it covers an area of 143,500 square feet. Winning customer trust with innovation, Yongxiang has been aiming to provide customers with safe and reliable hydraulic products, services, on-time delivery, and customer satisfaction while ensuring employee safety, fostering employee relations and driving efficiency improvements.
Jiangsu Yongxiang Hydraulic Equipment Co. Ltd
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