A popular misconception involving Small Hydraulic Wheel Motor is that if the piston seal is leaking, the cylinder will drift. While a leaking piston seal could be the cause of cylinder drift, the physics involved are often misinterpreted. Truth is, f the piston seal is entirely taken from a double-acting cylinder, the cylinder is filled with oil and the ports are plugged, the cylinder will hold its load indefinitely, unless the rod-seal leaks.
In this particular condition, due to the unequal volume on both sides in the piston, fluid pressure equalizes and also the cylinder becomes hydraulically locked. Once this occurs, the cylinder can move only if fluid escapes from the cylinder using the rod seal or its ports.
Exceptions for the Rule – There are 2 exceptions to this theory. The first is a double-rod cylinder (Figure 1) where volume is equal on sides in the piston. The next exception involves a lot hanging on the double-acting cylinder (Figure 2). In 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 experience on the piston side because of unequal volumes, and depending on the weight in the load, this vacuum may eventually lead to equilibrium that arrests further drift.
This is not the final from the cycle, but it’s essential to at the very least grasp this theory before continuing. Notwithstanding these two exceptions, when a double-acting cylinder’s service ports are blocked with a closed-to-actuator spool (Figure 3), and the piston seal does bypass, pressure will ultimately equalize on sides of the cylinder. At this stage, a hydraulic lock is effected without any further drift can occur, unless fluid is allowed to escape through the cylinder or cylinder circuit.
Loss of Effective Area – As a result of loss in effective area because of pressure now acting on the rod-side annulus area, the static pressure inside the cylinder must increase to aid the same load. Remember, force developed by a cylinder is actually a product of pressure and area. For example, when the load-induced pressure on the piston side from 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 could be 3,000 PSI depending on the ratio in the piston and annulus areas.
New call-to-action – Now consider exactly what can happen if the circuit has a service port relief valve (Figure 4) set at 2,500 PSI. As pressure equalizes across the piston seal as well as the increasing static pressure on the piston side in the Hydraulic Butterfly Valve Actuator reaches the cracking pressure in the port relief, though the cylinder will still not retract. An identical situation can happen in circuits using a load control (counterbalance) valve installed. In 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, if the piston seal leaks, unequal volumes of oil on the rod and piston sides from the cylinder indicates hydraulic lock will prevent any noticeable drift. But when again, due to the loss of effective area as a result of exactly the same pressure now acting on the piston and rod-side annulus areas, the static pressure inside the cylinder must increase to support the same load.
The magnitude of this pressure increase depends on the ratio in the cylinder’s piston and annulus areas. If the rise 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 flow towards the tank and the cylinder to retract.
Diagnosing Cylinder Drift – Therefore, while the cause in the symptom in both examples will be the leaking piston seal, the physics is fundamentally distinctive from the typical belief. And if the theory is understood, a pressure gauge can be quite a great tool for establishing the cause of cylinder drift. In both of such examples, if the cylinder is drifting however, there is no equalization of pressure over the piston seal, the directional control valve or load control valve is the source of rldvub problem.
What exactly is the maximum pressure range for the application? Keep in mind pressures can vary greatly greatly depending on the specific job the program does. Cylinders are rated for both nominal (standard) pressure and test pressure to take into account variations. System pressure must not exceed the nominal rated design pressure from the cylinder.
Push or pull-or both (double acting)? The answer to this question might require Electric Motor Actuator With Self-Locking when the hydraulic system 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 very essential 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 without the rod diameter area) correctly to go the burden at the rated design pressure in 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
Factory: Wujian Industrial Park, Jiangdu District, Yangzhou, CN
Office: 3107# No.2 Building, Global Financial Center, Wenchang East Road, Yangzhou, CN
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