The humble O ring. Used to create an effective, reliable seal. It is a small and seemingly insignificant component that is in millions, if not billions, of machines around the world, and even beyond.
It was an O ring that was responsible for the Space Shuttle Challenger disaster in 1986. The shuttle broke apart just over a minute into its flight resulting in the deaths of all 7 crew members.
Although the O ring failure, in this case, was not due to incorrect measurements, it certainly highlights the importance of these small but essential components.
With any machinery, including hydraulic systems, faulty, degraded or wrongly sized O rings can result in leaks, ineffective systems, damage to the other components or even complete system failure.
Why Are O Rings Measured?
Correctly sized O rings are essential to the efficient and safe functioning of your hydraulic system. This simple component is key to creating an effective seal. Get the size wrong, however, and you can end up with leaks, damage and breakdown of the whole hydraulic system.
Knowing, therefore, how to measure O rings so that you can replace them when they break, degrade or wear out is a key piece of knowledge for anyone who works with hydraulics.
Why Is It Important To Measure O Rings Accurately?
As one of the smallest components in a hydraulic system, the differences in O ring sizes can be tiny. Too tiny to measure accurately by eye. Getting it wrong, even by a marginal amount, could lead to air or fluid leaking, lost pressure and system failure. Accurate measuring is of paramount importance to ensure an effective, reliable seal.
How To Measure O Rings Accurately
There is a huge number of O ring sizes due to their widespread use across the world of engineering.
In the UK, we use British Standard sizing (BS) and O rings that have a BS number. This consists of the measurements of the O rings.
There are 3 measures that are considered when sizing an O ring. These are:
- Inside diameter
- Outside diameter
You can measure O rings with a rule, even better and more accurate are vernier callipers. This measurement is usually taken in inches or less commonly millimetres. To measure the outside diameter you measure the distance between the outside edges. For the inside diameter, you measure the distance between the inside edges.
The thickness of the O ring is best measured with vernier callipers. However, when holding the ring between the calliper jaws, you must ensure that you are not squeezing it as any compression will alter the measurement you get and cause inaccuracies.
To help prevent human error when measuring O rings, there are tools that can assist you. Two of the most common are O ring measuring gauges and O ring measuring cones.
O Ring Measuring Gauge
This tool has silhouettes of the different, most common sizes of smaller O rings and spindles at the top which you can place a larger O ring onto and which slide-out giving you a measurement.
O Ring Measuring Cone
These measuring tools are, as the name suggests, conical with the different sizes marked at the different diameters. So you simply slide the O ring over the cone to see which size it is. There are also grooves cut into the cone so you can easily measure the thickness of your O ring.
If you have any questions about when to replace your O rings, to be sure you are accurately measuring them, or to order your replacement O rings contact us at MCH Hydraulics.