Hydraulic cylinders

Hydraulic cylinders are used to perform work in a bevy of different situations and applications every day. Whether it’s the plow truck clearing the road, a utility vehicle fixing an electrical issue, or a compactor at the local recycling center—hydraulic cylinders are in motion almost everywhere.

With hydraulic cylinders, there is more than meets the eye. To contain the pressurized fluids in a hydraulic cylinder system and keep it in motion, a complex configuration of high-performance seals in two basic categories are required: 

(1) static seals and 

(2) dynamic seals (supported by guide rings).

Let’s examine some specific types of seals in each category. Static Seal. A seal that is not subjected to any type of movement when pressurized. This includes O-rings, D-rings, back-up rings, cover seals and gaskets. One of the simplest examples of a static seal is the O-ring.

O-rings are very versatile and available in various sizes. When placed into the cylinder housing and squeezed by a casing, the O-ring creates a physical barrier between the housing and the casing. Commonly used with back up rings for pressures over 1500 p.s.i., O-rings in nitrile rubber (NBR), fluoro rubber (FKM) and ethylene propylene diene (EPDM) are suitable for use in a multitude of different mineral oils, water and water-based fluids and air. Other compounds such as Polyurethane (TPU) and silicone also have uses in a static environment.

How do hydraulic seals work?

A hydraulic seal is a relatively soft, non-metallic ring, captured in a groove or fixed in a combination of rings, forming a seal assembly, to block or separate fluid in reciprocating motion applications. Hydraulic seals are vital in machinery. Their use is critical in providing a way for fluid power to be converted to linear motion.

Dynamic Seal: A seal that is subjected to axial and/or radial movement when pressurized. This includes piston seals, rod seals, rotating seals, wipers/scrapers and oil seals.

Piston seals: prevent pressurized fluid from leaking across the piston as the system pressure pushes the piston and rod assembly down the cylinder bore.

Rod seals: hold pressure in the cylinder by preventing fluid from leaking out. Leakage through the rod seal can reduce equipment performance and in extreme cases cause environmental issues.

Wipers: also known as scrapers, prevent contaminants such as dirt, dust and moisture from entering the cylinder as they retract back into the system. Contamination can cause significant damage to the rod, cylinder wall, seals, and other components, and is one of the primary causes of premature seal and component failure in a fluid power system.

Guide Ring: Resin-bonded fabric, guide tape and engineered plastics that guide the piston in the cylinder bore and rod in the cylinder head of a hydraulic cylinder. Guide rings are used to prevent damage from side loading as they prevent metallic contact between axial and rotational components from contacting one another. In addition, guide rings also help to trap contaminants sub-surface before they reach the most critical sealing elements.

Choosing the right seal is critical in assuring the best performance for hydraulic cylinder applications.

How do you seal hydraulic threads?

Loctite 5452 thread sealant is for use on high-pressure hydraulic and pneumatic metal fittings. It cures four times faster than anaerobic sealants on stainless steel or inert metals. It works on any size NPT, O-ring boss, or JIC fitting, and prevents rotation and leakage.

Can you weld hydraulic cylinder?

Weld repair in hydraulic cylinders can be a challenge because of oil saturation. Low hydrogen welding materials will not seal oil-contaminated metals. The first pass should be done with a 6010 or 6011 stick rod using a whipping motion.