A popular misconception involving 10ton Electric Hydraulic Ram is that if the piston seal is leaking, the cylinder will drift. While a leaking piston seal can be the root cause of cylinder drift, the physics involved are frequently misunderstood. Simple truth is, f the piston seal is entirely taken off 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 each side from the piston, fluid pressure equalizes and also the cylinder becomes hydraulically locked. Once this occurs, the cylinder can move only when fluid escapes from your cylinder through the rod seal or its ports.
Exceptions for the Rule – The two main exceptions for this theory. The very first is a double-rod cylinder (Figure 1) where volume is equal for both sides in the piston. The 2nd exception involves a load hanging on the double-acting cylinder (Figure 2). In this particular arrangement, the volume of pressurized fluid on the rod side could be accommodated on the piston side. But since the cylinder drifts, a vacuum will develop on the piston side as a result 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 conclusion from the cycle, but it’s important to at the very least grasp this theory before continuing. Notwithstanding those two 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 could eventually equalize for both sides of the cylinder. At this time, a hydraulic lock is effected and no further drift can take place, unless fluid is permitted to escape through the cylinder or cylinder circuit.
Loss in Effective Area – As a result of loss in effective area because of pressure now acting on the rod-side annulus area, the static pressure within the cylinder must increase to support the identical load. Remember, force developed by a cylinder is really a product of pressure and area. As an example, if 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 what can happen if this type of circuit has a service port relief valve (Figure 4) set at 2,500 PSI. As pressure equalizes across the piston seal and also the increasing static pressure on the piston side from the Hydraulic Power Station reaches the cracking pressure of the port relief, however the cylinder will still not retract. An identical situation can take place in circuits with a load control (counterbalance) valve installed. In this circuit, shown in Figure 5, the directional control valve includes a float center spool (service ports A and B open to tank).
As previously mentioned, in the event the piston seal leaks, unequal volumes of oil on the rod and piston sides in the cylinder indicates hydraulic lock may prevent any noticeable drift. But once again, because of the loss in effective area as a result of exactly the same pressure now acting on the piston and rod-side annulus areas, the static pressure in the cylinder must increase to aid the identical load.
The magnitude with this pressure increase depends on the ratio from the cylinder’s piston and annulus areas. If the rise in static pressure exceeds the set maximum load from the counterbalance valve, the valve will open allowing oil through the piston side in the cylinder to flow to the tank and also the cylinder to retract.
Diagnosing Cylinder Drift – Therefore, while the cause of the symptom in both examples is the leaking piston seal, the physics is fundamentally distinct from the typical belief. And if the idea is understood, a pressure gauge can be a great tool for establishing the reason for cylinder drift. In either of these examples, in the event 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 way to obtain rldvub problem.
What exactly is the maximum pressure range for the application? Remember pressures can vary greatly greatly depending on the specific job the device is doing. Cylinders are rated 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 query may require Double Acting Hydraulic Power Unit in the event 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 rather important to size the rod diameter properly to avoid 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 stress at the rated design pressure from 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
E-mail: [email protected]