A popular disbelief involving Hydraulic Hose is that if the piston seal is leaking, the cylinder will drift. While a leaking piston seal can be the real cause of cylinder drift, the physics involved are frequently misunderstood. Truth is, f the piston seal is completely taken 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.
In this particular condition, as a result of unequal volume on either side from the piston, fluid pressure equalizes as well as the cylinder becomes hydraulically locked. Once this happens, the cylinder can move as long as fluid escapes from your cylinder via the rod seal or its ports.
Exceptions towards the Rule – There are 2 exceptions to this particular theory. First is a double-rod cylinder (Figure 1) where volume is equal on both sides from the piston. The 2nd exception involves a load hanging on the double-acting cylinder (Figure 2). In this arrangement, the quantity of pressurized fluid on the rod side can easily be accommodated on the piston side. But since the cylinder drifts, a vacuum will experience on the piston side as a result of unequal volumes, and depending on the weight in the load, this vacuum may eventually bring about equilibrium that arrests further drift.
This is simply not the final in the cycle, but it’s essential to a minimum of grasp this theory before continuing. Notwithstanding both of these exceptions, in case a double-acting cylinder’s service ports are blocked by way of a closed-to-actuator spool (Figure 3), and the piston seal does bypass, pressure could eventually equalize for both sides in the cylinder. At this point, a hydraulic lock is effected without any further drift can happen, unless fluid is able to escape from the cylinder or cylinder circuit.
Loss of Effective Area – As a result of loss in effective area as a result of pressure now acting on the rod-side annulus area, the static pressure in the cylinder must increase to support exactly the same load. Remember, force developed by a cylinder is actually a product of pressure and area. For instance, if the load-induced pressure on the piston side from the cylinder was 2,000 PSI and zero on the rod side when the directional control valve closed, assuming no leakage beyond the spool, the equalized pressure might be 3,000 PSI depending on the ratio in the piston and annulus areas.
New call-to-action – Now consider so what can happen if the circuit has a service port relief valve (Figure 4) set at 2,500 PSI. As pressure equalizes throughout the piston seal and the increasing static pressure on the piston side in the Front Flange Hydraulic Cylinder reaches the cracking pressure from the port relief, however the cylinder will still not retract. A comparable situation can take place in circuits with a load control (counterbalance) valve installed. In this particular circuit, shown in Figure 5, the directional control valve features a float center spool (service ports A and B available to tank).
As previously mentioned, in the event the piston seal leaks, unequal volumes of oil on the rod and piston sides from the cylinder indicates hydraulic lock can prevent any noticeable drift. But once again, because of the lack of effective area because of the identical pressure now acting on the piston and rod-side annulus areas, the static pressure inside the cylinder must increase to back up the same load.
The magnitude of the 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 of the counterbalance valve, the valve will open allowing oil from the piston side in the cylinder to circulate towards the tank as well as the cylinder to retract.
Diagnosing Cylinder Drift – Therefore, as the cause in the symptom in both examples is the leaking piston seal, the physics is fundamentally distinctive from the typical belief. And in case the idea is understood, a pressure gauge can be a great tool for establishing the reason for cylinder drift. Either in of those examples, if the cylinder is drifting however, there is no equalization of pressure throughout the piston seal, the directional control valve or load control valve is the source of rldvub problem.
What is the maximum pressure range for your 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 from the cylinder.
Push or pull-or both (double acting)? The solution to this inquiry may need Lift 48″ Farm Jack if 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 rather important to size the rod diameter properly in order 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 burden 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