News Seals-Shop GmbH
Nov 12 2018
Single-acting vs. Double-acting Piston Seals
As such, it is critical to make sure that the right seal is selected based on factors such as how the cylinder is expected to operate as the piston is pushed down the cylinder bore.
As a necessary component of fluid sealing in hydraulic cylinders, piston seals, also known as piston rings, are designed to seal in fluid, thus preventing the flow of fluid across the piston. This is made possible when the piston seal secures against the cylinder bore from inside the hydraulic cylinder, meaning that pressure will build up on one side of the piston.
Yet, because hydraulic cylinder seals are found in everything from machine tools, trucks and off-highway vehicles to injection mold machines, it stands to reason that a seal will sometimes need to conceal pressure from both sides of the piston.
This demonstrates a scenario where the choice between single-acting hydraulic seals versus double-acting hydraulic seals becomes crucial.
Single-acting vs. Double-acting Piston Seals
Single-acting piston seals are designed to keep pressure on one side of the piston without leakage. Because the seal operates in one direction (unidirectional), the pressure is applied on one side only.
Double-acting piston seals, on the other hand, are designed to conceal pressure from both sides, which means that they are designed to be bidirectional.
Selecting between single-acting and double-acting piston seals has everything to do with the intended use of the system and the direction that the system will be operating in. As such, choosing wisely can make all the difference in the life of a cylinder and thus help avoid unwanted machine downtime.
Helping to make that decision easier is Seals-Shop, with a variety of Trelleborg piston seals to fit just about any application. Made from high-quality materials that are durable in most conditions, Trelleborg seals have the answer to just about any question concerning hydraulic, pneumatic and mechanical seals and, as its online shop, Seals-Shop will help find the ideal seal for any application using their convenient Product Finder. Need installation help? Each product description on Seals-Shop.com includes an easy-to-follow diagram detailing the installation steps for each specific seal. For more information, visit Seals-Shop.com.
Oct 2 2018
O-ring sizes for hydraulic seals
O-rings are particularly well-suited for hydraulics, both for maintenance and new applications. They seal over a wide range of pressures, temperatures and tolerances, require very little space and are lightweight and sometimes reusable. They come in many sizes and materials, often specialized for particular applications. O-rings are particularly important for hydraulic systems since they seal connections by being forced into a channel and held in place by hydraulic pressure. The O-ring is used to prevent leakage and prevent outside contaminants from penetrating the hydraulic system. Following is a breakdown of some specifications, materials and features of O-rings for hydraulics.
There are several essential specifications for selecting the correct O-rings in hydraulic systems. The inside diameter, outside diameter and cross section define the dimensions of an O-ring. The inside and outside diameters are the distances from the center to the O-ring’s inside and outside surface respectively. The cross section is the difference between the outer and inner diameters. O-ring inside diameters and outside diameters can vary significantly, from a few millimeters to a meter or more. Be sure to leave some space when specifying O-ring inside diameter to account for swelling and possible thermal expansion.
Avoid stretching the O-ring more than five percent, if possible, as stretching can cause the cross section of the O-ring to flatten. O-ring cross sections tend to vary less, from a few millimeters to tens of millimeters. When selecting an O-ring for your hydraulic application, it is very important to know the depth of the gland so that the O-ring selected has the appropriate cross section to avoid extrusion and tearing and to ensure a proper seal.
O-rings come in a variety of materials, including nitrile rubber (NBR), ethylene propylene diene rubber (EPDM), fluoroelastomers (FKM) such as Viton®, silicone rubber (VMQ) and others. NBR has excellent resistance to hydraulic fluids and can be used in the temperature range of -35° C to +120° C. NBR is a copolymer of butadiene and acrylonitrile that becomes more resistant to hydraulic fluids as its nitrile component increases, but it also becomes less flexible. Although NBR does not possess good resistance to ozone, sunlight or weather, it has excellent resistance to compression set, tear and abrasion. O-rings made of NBR generally are an excellent choice for hydraulic applications.
EPDM O-rings have excellent resistance to heat, water, steam, ozone and sunlight. EPDM O-rings are particularly useful when sealing phosphate-ester hydraulic fluids and may be appropriate for some applications in place of NBR. FKM (Viton®) O-rings have very high resistance to high temperatures, greases, fuels, silicone oils and many other materials and are well-suited for aerospace applications. Increasing fluorine content in FKM increases chemical resistance while low-temperature characteristics regress. FKM can be used with non-flammable hydraulic fluids and may be an appropriate choice for hydraulic applications under certain circumstances. Finally, VMQ has good ozone and weather resistance as well as good cold flexibility and high heat resistance, though it is susceptible to superheated steam. VMQ O-rings have relatively low tensile and tear strength and are susceptible to wear. Although excellent for many applications, VMQ is not usually used for hydraulic O-rings.
Another set of important O-ring specifications are the maximum pressure and the operating temperature range.
Generally, maximum pressure tends to be expressed in megapascals (MPa) and operating temperature range is expressed in degrees Celsius. Depending on the O-ring material, maximum pressure can be as high as 25 MPa and operating temperature ranges can vary from -40° C to +200° C. It is very important when selecting an O-ring that the maximum pressure and operating temperature range encompass the extremes of the O-ring application. O-ring chemical resistance, flexibility, tear resistance, abrasion resistance, weather resistance and other properties can be compromised if an O-ring is exposed to conditions beyond its maximum pressure or operating temperature range.
Some applications involving pressures greater than 5 MPa may be ideal for a backup ring. When internal pressure becomes too high, an O-ring may extrude and quickly lose material through wear. Seal failure usually follows fairly quickly afterward. A backup ring is a ring of hard, extrusion resistant material that fits between the O-ring and extrusion gap, thus preventing O-ring extrusion. This can be a cost-effective alternative to more durable yet more expensive materials. An alternative to O-rings that can also be used with backup rings is the X-ring, or Quad-Ring®. Quad-Rings® have two sealing areas per side as opposed to the one for O-rings. As a consequence, Quad-Rings® require less deformation to maintain an effective seal. Less deformation means less friction and wear, which gives Quad-Rings® a longer seal life compared to O-rings. Quad-Rings® come in a variety of materials and sizes and can be an alternative to O-rings for hydraulic system sealing.
The specifications of inner diameter, outer diameter, cross section, material, maximum pressure and operating temperature range are critical to identifying the correct O-ring for your hydraulic application. Backup rings can help prevent extrusion in high-pressure applications while quad-rings offer a longer-life alternative to O-rings for particular applications. Although O-rings are usually a very small and inexpensive part of your hydraulic system, they can be critical to its performance and are worth researching and understanding so that the correct O-ring (or Quad-Rings®) is selected and installed. Putting in the time to understand the O-ring that you need now may buy you years of operation for your hydraulic system. If you are unsure of the article number of your seal, product finders or some online-shops (such as seals-shop.com) quite often have the option to search by the aforementioned criteria when applying filters during product selection.
Company information Seals-Shop GmbH
Our customers come from all corners of the industry, including service and maintenance/repair, manufacturing and wholesale distribution. Our products are specifically intended to suit a variety of hydraulic applications, from light-duty linear hydraulic to heavy-duty rotary seals and static applications.
Our broad and diversified product range sets us apart from the rest, notably our extensive selection of FKM seals. On top of everything, all products are immediately available from stock (unless otherwise stated).
|Handelsregister||HRB 757821 Stuttgart|
|Legal form||Gesellschaft mit beschränkter Haftung|
|Type of company||Head Office|
|Fax||+49 711 78648879|
Turcon® is a perfluoroelastomer (FFKM) compound from Trelleborg Sealing Solutions which is matched to the needs of critical sealing environments, combining the media resistance of a PTFE with the elasticity of an elastomer.
Turcite® is dimensionally stable and wear resistant with excellent performance in dry and boundary lubrication.
The engineered plastic based sealing material Zurcon® provides outstanding wear resistance combined with good friction properties, making it suitable for reciprocating, slow rotating and oscillating applications.
HiMod®, a high modulus thermoplastic is suitable for custom molded components, reinforcing rings and Back-up Rings.
The composite bearing material Orkot® consists of technical fabrics impregnated with thermosetting resins and evenly dispersed solid lubricants gives unrivalled performance in dry running conditions.
Key figures Seals-Shop GmbH
Executives Seals-Shop GmbH
Herr Florent Guillomeau
CEO - Chief Executive Officer
Herr Jürgen Bosch
CEO - Chief Executive Officer (Geschäftsführung)
Activities Seals-Shop GmbH
- Service provider
- Moulded parts, rubber
- Rings and washers, rubber
- Diaphragms, rubber
- Packing rings, rubber
- O-rings, rubber
- Rings, rubber, for screw stoppers
- Rings, rubber cord, sealing
- Rings, cellular/foam rubber, sealing
- Rings, rubber, conical, sealing
- Rings, rubber, hexagonal, sealing
- Rings, rubber, flat, sealing
- Rings, rubber, square section, sealing
- Bushes, rubber
- Seals, rubber
- Seals, rubber, for bottles and jars
- Seals, rubber, dam and lock gate
- Rings, rubber, to customer specification
- Tapes and straps, plastic
- Jointings, packings and gaskets, plastic
- Gaskets, ethylene-propylene-diene monomer (EPDM)
- Gaskets, polyethylene (PE)
- Gaskets, polytetrafluoroethylene (PTFE)
- Gaskets, polytetrafluoroethylene (PTFE) filled
- Gaskets, polyvinyl chloride (PVC)
- Gaskets, plastic, for glazing and draught-proofing
- Packing rings, plastic
- Packing rings, vee type, plastic
- Packings, polytetrafluoroethylene (PTFE)
- Oil seals, plastic or synthetic rubber
- O-rings, polytetrafluoroethylene (PTFE)
- Seals, filled polytetrafluoroethylene (PTFE)
- Jointing materials, plastic
- Plastic products, industrial use
- Plastic products for the mechanical engineering industry
- Plastic products for the electrical and electronics industries
- Seals and gaskets, metal
- Packings, metal
- Internal combustion engine components NES
Other classifications (for some countries)
NACE Rev.2 (EU 2008) :
Manufacture of other rubber products (2219)
ISIC 4 (WORLD) :
Manufacture of other rubber products (2219)