The pump works flawlessly, the hoses are perfectly crimped, and fresh HV oil sloshes in the tank. Suddenly, you notice a dark, greasy stain growing under the machine, and the cylinder slowly begins to drop under the weight of the load. Sound familiar? Very often, the reason for downtime of a machine worth hundreds of thousands of zlotys is a piece of rubber that costs... two zlotys in retail.
Hydraulic seals are the silent heroes of every system. They endure friction, extreme pressure spikes, and temperatures. However, when they fail, the system loses its "tightness," and you lose money. BRhydraulic experts have prepared a practical guide from which you will learn what seals are made of, how to avoid errors during their installation, and why a black O-ring is not always the same as a green one.
1. Anatomy of tightness – what seals your machine?
In hydraulic power systems, there is no single universal seal. Different working environments require different solutions. Most often, you will encounter three groups:
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O-rings: Classic, round rings. They are used almost exclusively for static (immobile) seals, for example, under flanges, in connectors, or under plugs.
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Shaft seals (Simmerrings): Rings with a metal insert and a characteristic spring. Their task is to seal rotary motion – you will find them primarily on hydraulic pump and motor shafts.
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Piston and rod seals (in cylinders): Complex systems mounted on the piston and gland. The wiper (the first one you see) removes dirt from the extending rod, and the internal seals retain oil under pressure of around 250 bar.
2. Not all rubber is equal – what are seals made of?
This is the most common pitfall in workshops! Choosing a seal solely by its dimensions is asking for trouble. The material it is made of matters.
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NBR (most often black): Standard rubber. It is inexpensive, flexible, and works well with mineral oils. Its weak point, however, is temperature – above 90°C-100°C, it hardens, crumbles, and leaks oil.
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FPM / FKM / Viton (often green or brown): Seals for special tasks. They withstand temperatures around 200°C and contact with aggressive chemicals. If you are replacing an O-ring in a place that heats up significantly, Viton will be an excellent choice.
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PU (Polyurethane – often blue, yellow, or red): Extremely resistant to abrasion and pressure. Most internal seals in heavily loaded cylinders are made from this material.
3. Why do seals fail? Three main sins
Seals rarely fail "on their own." In 90% of cases, their premature wear is the result of one of the following factors:
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Installation errors: Installing O-rings "dry" or using a screwdriver to push the seal into the cylinder gland. A microscopic cut on the seal's lip during installation will immediately turn into a leak under pressure.
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Diesel effect and oil "boiling": If air is trapped in the system (e.g., in a cylinder), under the influence of a sudden pressure increase, it rapidly compresses and self-ignites. This miniature explosion literally burns the seals from the inside!
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Scratched rod: Even the toughest polyurethane cannot beat sharp scratches on a chrome-plated rod. A scratch acts like a microscopic knife that cuts off pieces of the seal with each cycle.
BRhydraulic tip: How to correctly measure an O-ring to buy a new one? Always measure the internal diameter and the cord thickness (cross-section). Avoid measuring the outer diameter, as a worn O-ring is often stretched or flattened! Use calipers gently so as not to compress the rubber.
Summary
In hydraulic power, there is no room for compromise with seals. Using a cheap substitute made of the wrong material always results in re-disassembly of the component, loss of expensive oil, and machine downtime.
If your valve is leaking, the pump is losing oil from the shaft, and the cylinder is dropping – visit the BRhydraulic.eu store. Not sure what to choose? Contact us – we will help you seal the system once and for all!
