How to select O-Rings
There’s an increasing range of size and material used to make O-Rings in the rubber, plastic and metal industry. The production of O-Rings has gone up recently. The demand of O-Rings is also on the rise. This means that O-Rings are now used for countless reasons. Therefore, you can easily get confused when selecting the best O-Ring for your home/ work use.
In this guide, I give the best tips to use when selecting the right O-Ring for your intended purpose. Please read on.
What is an O Ring?
Also called Toroidal Seal, an O-Ring is a doughnut-shaped object (a torus) that is crafted from an elastomer, and can be used as a seal to stop the flow of fluids.
O-Rings are often simplified and economical products that ship in several forms and can be used for several uses. For instance, you can use an O-Ring as a static seal to replace a sealing washer. You can also use the product as a both single and double acting dynamic seal. Others prefer to use the O-Ring to radially seal cylinders from either internal, external or axial positions.
O-Rings can be manufactured effortlessly, in both small and large volumes depending the required size. This is thanks to their circular form that can be elastic and often features an ring-shaped cross section.
Here some of the common factors to consider when selecting O-Rings:
• The size of the object being sealed – inches or metric
• Predicted applied pressure
• Anticipated temperature levels
• Application type – static or dynamic application
• Type of material – solvent, abrasive, caustic, acid
• If dynamic – speed of moving surfaces
Different instances when you have to select an O-Ring
When replacing an old or damaged seal
• Start by measuring the cross-section “W” to determine if it’s an imperial size (BS 1806), a metric size (BS 4518), or any other metric standard.
• Measure the inside diameter (I.D.) readings of your cylinder using a Vernier caliper to get accurate readings. Bear in mind that an O-Ring is usually differentiated by its I.D. x section – say, 5 x 16. This means you can use these I.D. readings to select the closest O-Ring that’ll fit.
• If you’re not sure, select a sighly larger O-Ring size, given it can easily compress to fit a smaller I.D. – but I advise landing the exact O-Ring size.
When the O-Ring is missing and only have housing metalwork
If somehow you’re lacking an O-Ring but have the shaft, rod or piston, you can use the procedure above to get the right O-Ring.
When at the design stage
• In this instance, you have a series of options. Opt for ex-stock O-Rings both in size and material.
• Ask for customized products when you lack alternatives.
• Stick to commonly preferred material finishes and durability.
• Know how and where the product will be used, whether static or dynamic. This will determine the size and material you’ll select.
For example, temperatures will determine the material of the O-Ring, while the applied pressure will decide the rubber hardness, size of groove and the extrusion gap of the product. This means that if the pressure applied is high, opt for a minimum gap. Alternatively you have to include the back-up washers, and larger grooves.
When factors are unknown
• In this case, I advise performing a rather overall assessment.
• Choose the largest O-Ring section to match the nominal groove I.D. – allows for extreme temperature withstanding and high pressure torelance. It’ll also tolerate several metalwork sizes, and surfaces.
• You should also deliberate how to install the O-Ring – where up to 7% range is allowed, but about 4% of the outside diameter is recommended.
• Apply a considerable squeeze to the cross-section to improve its effectiveness. Avoid applying too much pressure on dynamic uses.
• Maintain the deformation size recommended at the depth of the groove.
• Mind the sizes used when you seal dynamic applications
• Remove all sharp edges and try using fitting tools as well as desirable lubricant when installing
How to select the material used
O-Rings are mostly created from an elastomer called Nitrile 70 Shore ‘A’ (NBR 70). The elastomer can seal a larger part of normal applications, such as water, petrol and oil. These fluids alongside balmy chemicals that record up to 1000 C as well as 1500 psi, offer mating surfaces and adequate housing metalwork.
Bear in mind of the following:
• Low temperatures – often below -350C
• High temperatures
• Hightened pressures
• Hazardous chemicals
The industry is also increasingly demanding for peculiar materials – certified to be used alongside Food Machinery (FDA), and Potable Water (WRC).
About Lusida Rubber Products
Lusida rubber products is an excellent manufacturer of industrial rubber, plastics and metal components. The company is established in the US, where it’s registered and operates, but maintains its manufacturing facilities in China. Lusida supplies quality industrial products to OEMs such as O-Rings, oil seals, custom molded rubber, fabric reinforced hoses, seals, gaskets, extruded profiles and much more. Lusida Rubber can help you develop your products from concepts to prototype to final production.