Hope it's useful for you guys. I should've been more forthcoming with the detail so that people could do it easier for themselves when needed. I'm sure you'll be fine.
A couple of things that I think I forgot to mention. As I said before, I used a simple digital calliper for measuring the o-rings and seals. Sometimes the seals are completely destroyed so you cannot measure the diameter, but you measure the groove in which they sit, then you know the size. The beauty of the fact that standard AS sizes are used is that the groove or rod will give you the nominal size of the o-ring or seal, and that standard sizes are spread apart enough from each other so that measurement error is ruled out. For instance look at this below. The first column is the AS standard size. The second column is the nominal inner diameter (ID), third is nominal outer diameter (OD), and third is nominal cross section (CS). So, if the rod of a cylinder measures about 1/2 inch diameter as you can see in the picture below, the correct nominal o-ring would be 1/2" ID. The measurement error would have to be more than 1/16" to make the wrong decision for the o-ring. Same with the thickness (cross section) of the o-ring, in this example the distance between two standard sizes is 1/32" for thickness. A decent calliper and a little care when measuring will be enough to decide on the right size o-ring. I'll just add something that most of us knows, the nominal size of a o-ring is not the true measured size. For instance, if the nominal thickness of the o-ring is 1/16" a new o-ring will measure a little thicker. That's because in real life, in application, it needs to be compressed in order to provide a seal.
- Screenshot 2024-03-13 at 09.46.47.png (18.02 KiB) Viewed 1151 times
- Screenshot 2024-03-13 at 09.47.47.png (17.96 KiB) Viewed 1151 times
The site I used for looking up standard sizes for o-rings is this:
https://www.sealanddesign.com/technical/o-ring-sizes/
In my opinion is the easiest site to look up these sizes easily. But then, let's say we measured the rod and thickness of the old o-ring and our conclusion is that we need a 1/2 ID and 1/16 CS. Looking it up gives us a standard size of "-014". The site
herculesus.com
has several ways to look up o-rings. There is a drop down menu where I normally would choose Categories->Seals->Inch->Inch O-Rings and the website gives you these choices
Clearly the category I'm interested in is the 568 O-Rings, so I click on that and get another page with many types of 568 o-rings. This is where it gets interesting and here's where we choose the material the o-ring is made of. After some research my conclusion was to use 70 or 75 Duro Buna-N o-rings. 50 or 60 are too soft, and I did not see a reason to use 90, which are significantly harder. PTFE or Fluorocarbon are for more specific applications. So we click on the 70 Duro category and get a page with a list of many o-ring sizes of this hardness and some filters on the left hand side. I chose the 1/2" ID on the left hand side and that made the list smaller, like this.
Turns out that the o-ring that we want, with 1/16 CS is the first one on the list, which is product 568-014. So nice of herculesus.com, they keep the AS standard size as part of the product name. Once I figured this, for all other sizes of o-rings that I needed, once I figured the AS size, I would just search directly for "568-<size>" and that took me directly to the o-ring of 70 duro hardness of the size I need.
Backup rings are also interesting, they are used to give an extra back support to o-rings, so they are always on the opposite of the o-ring opposite to where the greatest pressure comes. They also follow the size standard. Once you figure this out it's pretty easy.