A well known misconception involving Food Machine Hydraulic Cylinder is that if the piston seal is leaking, the cylinder will drift. While a leaking piston seal can be the cause of cylinder drift, the physics involved are frequently misunderstood. 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 condition, due to the unequal volume on each side in the piston, fluid pressure equalizes as well as the cylinder becomes hydraulically locked. Once this occurs, the cylinder can move only if fluid escapes from the cylinder through the rod seal or its ports.
Exceptions to the Rule – The two main exceptions for this theory. First is a double-rod cylinder (Figure 1) where volume is equal on both sides from the piston. The 2nd exception involves a lot hanging on the double-acting cylinder (Figure 2). Within 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 develop on the piston side because of unequal volumes, and depending on the weight from the load, this vacuum may eventually result in equilibrium that arrests further drift.
This is not the end of the cycle, but it’s essential to at least grasp this theory before continuing. Notwithstanding these two exceptions, when 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 will ultimately equalize on sides of the cylinder. At this stage, a hydraulic lock is effected with no further drift can occur, unless fluid is permitted to escape from your cylinder or cylinder circuit.
Loss of Effective Area – Due to the loss in effective area due to pressure now acting on the rod-side annulus area, the static pressure inside the cylinder must increase to back up exactly the same load. Remember, force developed by a cylinder is really a product of pressure and area. As an example, in the event 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 past the spool, the equalized pressure could 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 includes a service port relief valve (Figure 4) set at 2,500 PSI. As pressure equalizes over the piston seal and the increasing static pressure on the piston side in the Hydraulic Cylinder For Door Hot Press reaches the cracking pressure from the port relief, however the cylinder will still not retract. A similar situation can happen in circuits with a load control (counterbalance) valve installed. In this particular circuit, shown in Figure 5, the directional control valve has a float center spool (service ports A and B available to tank).
As previously stated, when 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 when again, because of the loss of effective area due to the identical pressure now acting on the piston and rod-side annulus areas, the static pressure within the cylinder must increase to support the identical load.
The magnitude of 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 from the cylinder to flow to the tank as well as the cylinder to retract.
Diagnosing Cylinder Drift – Therefore, while the real cause in the problem in both examples is the leaking piston seal, the physics is fundamentally distinctive from the overall belief. And in case the thought is understood, a pressure gauge can be quite a useful tool for establishing the cause of cylinder drift. In either of such examples, in the event the cylinder is drifting there is however no equalization of pressure across the piston seal, the directional control valve or load control valve is definitely the supply of rldvub problem.
What exactly is the maximum pressure range for your application? Keep in mind pressures may vary greatly depending on the specific job the program is doing. Cylinders are rated for both nominal (standard) pressure and test pressure to account for variations. System pressure must not exceed the nominal rated design pressure of the cylinder.
Push or pull-or both (double acting)? The reply to this inquiry might require Elbow Silicone Hydraulic Hose 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, you should size the annulus area (piston diameter area without the rod diameter area) correctly to move the stress on 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
Factory: Wujian Industrial Park, Jiangdu District, Yangzhou, CN
Office: 3107# No.2 Building, Global Financial Center, Wenchang East Road, Yangzhou, CN