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Do hydraulic cylinders that have been stored unused for a long time need to be operated periodically? What are the risks if they are not operated regularly?
I. Hydraulic Cylinders in Long-Term Storage Require Periodic Operation
Periodic operation is necessary to simulate working conditions, maintain the health of the hydraulic cylinder’s internal components, and prevent various problems caused by prolonged inactivity.
1. Maintaining the Elasticity and Lubrication of Seals: This is the most crucial reason.
- Preventing hardening and deformation of seals: The seals in hydraulic cylinders (such as O-rings, U-cups, and rod seals) are mostly made of elastic materials (such as polyurethane and nitrile rubber). If they remain in a static compressed state for a long time, “compression set” will occur, causing them to lose elasticity and fail to return to their original shape.
- Maintaining lubrication of the sealing lips: Seals require hydraulic oil for lubrication. Periodic operation allows the hydraulic oil to flow over the sealing lips, forming an oil film and preventing dry friction and aging. During prolonged inactivity, the oil film at the sealing lips will dissipate and dry out, leading to dry friction upon startup and drastically shortening the seal’s lifespan.
- Avoid “sticking” of seals to the cylinder: Under pressure and in a static state, the seals may experience slight molecular migration with the smooth cylinder wall, or even a “sticking” phenomenon. During the first start-up, the enormous static friction may directly tear the seals, leading to internal leakage.
2. Prevent hydraulic oil sedimentation and performance degradation
- Oil homogenization: When hydraulic oil is left standing for a long time, the additives (such as anti-wear agents and rust inhibitors) may settle or separate. Regular operation allows the oil to circulate within the system, keeping its components uniform and allowing the various additives to fully exert their protective effects.
- Formation of a protective oil film: Operation allows the hydraulic oil to form a protective oil film on all internal metal surfaces such as the cylinder and piston rod, which is the most crucial rust prevention measure.
3. Preventing Internal Corrosion and Rust
- Draining Condensation: The inside of a hydraulic cylinder is not a complete vacuum; air is present. Temperature changes can cause moisture in the air to condense on the inner wall of the cylinder. Water is a major enemy of hydraulic systems, causing electrochemical corrosion, leading to rust and scoring on the cylinder and piston rod surfaces. Regular operation mixes this condensed water with the hydraulic fluid, allowing it to be processed by the filtration system (if the system has a filter) or distributed evenly, reducing localized corrosion.
- Protecting the Piston Rod: For extended piston rods, regular operation changes the part exposed to the air, allowing the protective oil film to cover the entire rod, preventing certain areas from rusting due to prolonged exposure.
4. Maintaining the Normal Condition of Bearings and Guide Bushings
- Distributing Load: If the bearings, guide bushings, and other supporting components of a hydraulic cylinder are subjected to static loads for a long time, localized plastic deformation or “indentations” may occur. Regular operation changes the contact stress points, ensuring even force distribution.
5. Verifying Usability
Regular operation also serves as a simple functional test. It can confirm:
- Whether the seals are intact (observe for internal or external leaks).
- Whether the piston movement is smooth and free from sticking.
- For servo cylinders with displacement sensors (such as magnetostrictive sensors), it can check if the signal is normal.
II. How to Properly Perform Periodic Actuation?
1. Frequency: It is recommended to perform this every 3 to 6 months. In humid environments or areas with significant climate variations, the frequency should be shortened.
2. Method:
- The ideal method is to remove the hydraulic cylinder from storage and install it on a dedicated test bench.
- If a test bench is unavailable, a simple circuit can be set up using a clean hydraulic oil source.
- Actuation Requirements: Slowly and smoothly move the cylinder back and forth several times (e.g., 5-10 cycles) throughout its full stroke range.
- Final Position: After the actuation is complete, it is best to fully retract the piston rod into the cylinder barrel. This is because the internal space of the piston rod (rod cavity) is usually smaller and more prone to condensation buildup, and the piston rod surface is protected inside the cylinder barrel, maximizing protection against rust and physical damage.
Consider the stored hydraulic cylinder as a “living organism” that needs “exercise.” Periodic actuation is a low-cost, high-return preventive maintenance measure, the purpose of which can be summarized as:
- For seals: Preventing aging, maintaining elasticity, and providing lubrication.
- For metal surfaces: Preventing corrosion and applying an oil film.
- For hydraulic oil: Maintaining uniformity and preventing sedimentation.
- For managers: Verifying the condition and ensuring peace of mind.
Neglecting this simple task may lead to internal damage to a brand-new hydraulic cylinder before it is even put into use, resulting in equipment downtime and economic losses.
★★★Review of selected articles in our hydraulic cylinder engineering newsletters:
- A question: Why do hydraulic cylinder seals fail?
- Complete guide to hydraulic cylinder failure repair!
- Six basic laws of hydraulic systems: from pressure formation to flow distribution
- Causes and solutions for the creeping phenomenon of hydraulic cylinders during operation
- Several practical repair methods for hydraulic cylinders
- Working principle of double-acting booster cylinder
- Working principle of single-acting booster cylinder
- How to perform daily maintenance and care on the hydraulic station?
- Choosing the Right Cylinder for Stamping Equipment
- Three working conditions of the hydraulic cylinder!!! What are the three?