How to Choose the Best Sealing Components?
Seals have a direct impact on equipment performance. When used properly, they prevent fluid leakage, extend cylinder life, minimize friction and energy consumption, and improve actuator positioning accuracy. Seals are designed to prevent leaks with minimal friction and wear. Many parameters affect how well they work.
When selecting seals and testing them to verify performance, engineers must consider all the many factors. While the prospect may seem daunting, practical experience with many of these factors can help engineers avoid common mistakes and replicate proven successes. Depending on the application, some are more applicable than others. Here are some considerations that engineers should keep in mind when looking for optimum sealing performance.
Sealing components need the pressure to function. Remember that pressure can deform the seal and change the fluid film in which the seal.
Consider the effect of the rate of pressure rise. A rapid rise in pressure may result in a leak when fluid bypasses the seal. Consider how changes in pressure can affect the fluid film. Films become thinner at higher pressures.
Consider potential pressure spikes from valves, pipes, and other sources. Remember the role of pressure relative to the dynamic profile. Pressure conditions may vary significantly in various motion sequences.
Underestimate hardware expansion or internal deformation caused by pressure. Changes in mating hardware can seriously affect sealing performance.
Misjudging the effect of pressure on internal contamination. Higher pressures give more impetus to contaminants and accelerate wear and debris production.
Concentrate testing only at peak pressures or high system pressures. Pressure can actuate seals, and sealing systems may not be properly actuated at low pressures. Assume that the test pressure is exactly the same as the application pressure.
Sealing Components (type U)
The sealing system must absorb the load or force in order to properly guide the piston or rod. If possible, incorporate bearings or wear rings to handle most of the load and limit rod or piston deflection.
Understand that for partial tests that replicate only part of the machine, the engineer may need to convert the load to displacement. Due to dimensional differences between the test stand and the actual application, isolated tests cannot simulate the specific loads applied to the wear ring.
Please note that scarf cuts on wear rings work better on the unloaded side of the bearing. This ensures maximum material coverage of the wear ring and subsequent load distribution.
Velocity plays an important role in many applications. Variations in duty cycle, motion parameters, and acceleration can all significantly improve or reduce seal performance.
Understand that variations in operating cycles (e.g. linear cycles) can introduce different failure modes. For example, systems with slow rod extension and fast contraction behave differently compared to systems with fast extension and slow contraction. The latter is more susceptible to inter-seal pressure traps. In such cases, special seals may be required to reduce pressure build-up between the seals.
Note that velocity has a significant effect on fluid film thickness and therefore on sealing effectiveness, leakage, friction, and wear. As velocity decreases, leakage increases.
Ignore the fact that velocity can significantly change fluid properties. Rising temperatures, decreasing viscosity, and chemical separation and degradation are all associated with higher velocities and they often lead to premature failure.
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