A well known misunderstanding involving Manufacturer Double Acting Hydraulic Ram is that if the piston seal is leaking, the cylinder will drift. While a leaking piston seal could possibly be the real cause of cylinder drift, the physics involved are frequently misinterpreted. Simple truth is, f the piston seal is completely taken off a double-acting cylinder, the cylinder is filled with oil and also 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 either side in the piston, fluid pressure equalizes as well as the cylinder becomes hydraulically locked. Once this takes place, the cylinder can move as long as fluid escapes through the cylinder through the rod seal or its ports.
Exceptions towards the Rule – The two main exceptions for this theory. The first is a double-rod cylinder (Figure 1) where volume is equal on both sides from the piston. The second exception involves a load hanging on the double-acting cylinder (Figure 2). In this arrangement, the volume of pressurized fluid on the rod side may be easily accommodated on the piston side. But because the cylinder drifts, a vacuum will develop on the piston side due to unequal volumes, and depending on the weight of the load, this vacuum may eventually result in equilibrium that arrests further drift.
This may not be the end from the cycle, but it’s important to at least grasp this theory before continuing. Notwithstanding these two exceptions, in case a double-acting cylinder’s service ports are blocked by a closed-to-actuator spool (Figure 3), and also the piston seal does bypass, pressure could eventually equalize on both sides in the cylinder. At this stage, a hydraulic lock is effected without any further drift can happen, unless fluid is permitted to escape from your cylinder or cylinder circuit.
Loss in Effective Area – Due to the loss in effective area due to pressure now acting on the rod-side annulus area, the static pressure within the cylinder must increase to aid the identical load. Remember, force created by a cylinder is a product of pressure and area. For example, if the load-induced pressure on the piston side of the cylinder was 2,000 PSI and zero on the rod side when the directional control valve closed, assuming no leakage past the spool, the equalized pressure may be 3,000 PSI depending on the ratio of the piston and annulus areas.
New call-to-action – Now consider exactly what can happen if this type of circuit features a service port relief valve (Figure 4) set at 2,500 PSI. As pressure equalizes over the piston seal and also the increasing static pressure on the piston side in the Hydraulic Pump Power System reaches the cracking pressure of the port relief, though the cylinder will still not retract. An identical situation can occur in circuits using a load control (counterbalance) valve installed. In this circuit, shown in Figure 5, the directional control valve has 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 will prevent any noticeable drift. But when again, because of the loss of effective area because of the same pressure now acting on the piston and rod-side annulus areas, the static pressure within the cylinder must increase to aid the same load.
The magnitude with this 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 in the cylinder to circulate for the tank as well as the cylinder to retract.
Diagnosing Cylinder Drift – Therefore, whilst the real cause from the symptom in both examples is definitely the leaking piston seal, the physics is fundamentally distinct from the overall belief. And in case the idea is understood, a pressure gauge can be quite a useful tool for establishing the main cause of cylinder drift. In both of those examples, when the cylinder is drifting there is however no equalization of pressure over the piston seal, the directional control valve or load control valve is definitely the source of rldvub problem.
What is the maximum pressure range for the application? Keep in mind pressures may vary greatly depending on the specific job the device is performing. Cylinders are rated for both nominal (standard) pressure and test pressure to make up variations. System pressure should never exceed the nominal rated design pressure of the cylinder.
Push or pull-or both (double acting)? The solution to this query may need Hydraulic Linear Actuator 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 vital that you size the rod diameter properly to avoid rod buckling. In a pull application, it is important to size the annulus area (piston diameter area without the rod diameter area) correctly to go the stress on 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