A popular misunderstanding involving Gerotor Hydraulic Motor Bmr 200 is that if the piston seal is leaking, the cylinder will drift. While a leaking piston seal could be the real cause of cylinder drift, the physics involved are often misinterpreted. Truth is, f the piston seal is completely 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.
In this condition, because of the unequal volume on either side of the piston, fluid pressure equalizes and the cylinder becomes hydraulically locked. Once this happens, the cylinder can move only when fluid escapes through the cylinder via the rod seal or its ports.
Exceptions for the Rule – The two main exceptions to this theory. The very first is a double-rod cylinder (Figure 1) where volume is equal on sides in the piston. The second exception involves a lot hanging on a double-acting cylinder (Figure 2). In this particular arrangement, the amount of pressurized fluid on the rod side can easily be 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 in the load, this vacuum may eventually bring about equilibrium that arrests further drift.
This may not be the end from the cycle, but it’s vital that you a minimum of grasp this theory before continuing. Notwithstanding both of these exceptions, in case a double-acting cylinder’s service ports are blocked with a closed-to-actuator spool (Figure 3), as well as the piston seal does bypass, pressure could eventually equalize on both sides of the cylinder. At this time, a hydraulic lock is effected with no further drift can occur, unless fluid is permitted to escape from your cylinder or cylinder circuit.
Loss in Effective Area – Because of 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 support the same load. Remember, force created by a cylinder is actually a product of pressure and area. For instance, if the load-induced pressure on the piston side in the cylinder was 2,000 PSI and zero on the rod side if the directional control valve closed, assuming no leakage past the spool, the equalized pressure could be 3,000 PSI depending on the ratio from the piston and annulus areas.
New call-to-action – Now consider what can happen if this 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 of the Pneumatic Press Cylinder reaches the cracking pressure of the port relief, however the cylinder will still not retract. A comparable situation can happen in circuits having a load control (counterbalance) valve installed. Within this circuit, shown in Figure 5, the directional control valve has a float center spool (service ports A and B available to tank).
As previously mentioned, when 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 in effective area as a result 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 of this pressure increase depends on the ratio from the cylinder’s piston and annulus areas. If the increase in static pressure exceeds the set maximum load in the counterbalance valve, the valve will open allowing oil from the piston side from the cylinder to flow for the tank and the cylinder to retract.
Diagnosing Cylinder Drift – Therefore, whilst the real cause from the problem in both examples is definitely the leaking piston seal, the physics is fundamentally distinct from the overall belief. And if the idea is understood, a pressure gauge can be a useful tool for establishing the reason for cylinder drift. In either of those examples, if 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 way to obtain rldvub problem.
What is the maximum pressure range for the application? Keep in mind pressures can vary greatly depending on the specific job the device is doing. Cylinders are rated for nominal (standard) pressure and test pressure to make up variations. System pressure must not exceed the nominal rated design pressure in the cylinder.
Push or pull-or both (double acting)? The reply to this query may need Power Pack Hydraulic System if 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 vital that you size the rod diameter properly to avoid rod buckling. In a pull application, it is essential to size the annulus area (piston diameter area without the rod diameter area) correctly to move 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
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