A well known misunderstanding involving Air Hydraulic Long Ram Jack 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. Fact is, f the piston seal is completely removed from a double-acting cylinder, the cylinder is full of oil and also the ports are plugged, the cylinder will hold its load indefinitely, unless the rod-seal leaks.
Within this condition, because of the unequal volume on each side from the piston, fluid pressure equalizes and the cylinder becomes hydraulically locked. Once this takes place, the cylinder can move only if fluid escapes through the cylinder through the rod seal or its ports.
Exceptions for the Rule – There are 2 exceptions for this theory. First is a double-rod cylinder (Figure 1) where volume is equal for both sides of the piston. The 2nd exception involves a load hanging on a double-acting cylinder (Figure 2). In this arrangement, the quantity of pressurized fluid on the rod side could be accommodated on the piston side. But because the cylinder drifts, a vacuum will experience on the piston side due to unequal volumes, and depending on the weight from the load, this vacuum may eventually result in equilibrium that arrests further drift.
This is simply not the final of the cycle, but it’s important to a minimum of grasp this theory before continuing. Notwithstanding those two exceptions, when 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 will eventually equalize on both sides from the cylinder. At this stage, a hydraulic lock is effected without any further drift can occur, unless fluid is permitted to escape from your cylinder or cylinder circuit.
Lack 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 within the cylinder must increase to support the identical load. Remember, force designed by a cylinder is actually a product of pressure and area. As an example, when the load-induced pressure on the piston side in 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 could be 3,000 PSI depending on the ratio from the piston and annulus areas.
New call-to-action – Now consider exactly what can happen if this circuit includes a service port relief valve (Figure 4) set at 2,500 PSI. As pressure equalizes across the piston seal and the increasing static pressure on the piston side from the Hybride Solar System For Home reaches the cracking pressure of the port relief, nevertheless the cylinder will still not retract. An identical situation can occur in circuits using 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 ready to accept 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 can prevent any noticeable drift. But once again, because of the lack of effective area due to the same pressure now acting on the piston and rod-side annulus areas, the static pressure inside the cylinder must increase to support the identical load.
The magnitude of the pressure increase depends on the ratio of 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 of the cylinder to circulate towards the tank and the cylinder to retract.
Diagnosing Cylinder Drift – Therefore, whilst the real cause of the problem in both examples is definitely the leaking piston seal, the physics is fundamentally distinctive from the typical belief. And if the idea is understood, a pressure gauge can be quite a great tool for establishing the reason for cylinder drift. In both of those examples, in the event the cylinder is drifting but there is no equalization of pressure throughout the piston seal, the directional control valve or load control valve is the supply 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 device does. Cylinders are rated for 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 solution to this query may need Hydraulic Rubber Hose Pipe 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 rather important to size the rod diameter properly in order to avoid rod buckling. In a pull application, you should size the annulus area (piston diameter area minus the rod diameter area) correctly to maneuver the burden at 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
E-mail: [email protected]