Thread: O-ring sizing

Ron,
O rings are specced according to their ID, section diameter and material.

Thanks Rick. I guess the material info is impossible to answer.

I can measure where they fit and try to get some from an auto parts place tomorrow.

Ron

The easy way is to go and buy the grab kit of O rings from any reputable parts dealer, not super cheap, then guess and giggle. The kits have about 10 or so each of 20-40 different sizes in them depending on if you buy the small kit or the larger one. they are a small red box like a lure box from a tackle box. In a pinch they are worth their weight in gold.

Depending on how good you are with the verniers its simply a case of identifying the seal faces, the diameter it has to seal across then measure the space it needs to fill add 10% for dynamic seals and 20% for static... for example...

A piston has an outside diameter of 26mm and a groove with a diameter of 24mm lathed around it the groove is 1mm wide. For this seal you will need a 25mm diameter 1.1mm wide O ring. If it was a static seal like a flange joint you would use a 25mm diameter O ring with a width of 1.2mm.

hope that helps.

Dave, problem is that every time I seem to need an O ring, it isn't the stock size in the grab kit...........

gab kits are fine on farms! work gives us grab kits for our equipment, 99% of the time it aint in a grab kit.

ron measure the o ring as close as you can, this should be enough for a bearing supplier to sorce you the correct one. my guess would be that it is metric, also i bet i have one in the shed. not much help to you here though??

the material for the o ring isnt of concern for this type of o ring, only when you get int really high temps or synthetic oils..

phil

Originally Posted by Blknight.aus

The easy way is to go and buy the grab kit of O rings from any reputable parts dealer, not super cheap, then guess and giggle. The kits have about 10 or so each of 20-40 different sizes in them depending on if you buy the small kit or the larger one. they are a small red box like a lure box from a tackle box. In a pinch they are worth their weight in gold.

Depending on how good you are with the verniers its simply a case of identifying the seal faces, the diameter it has to seal across then measure the space it needs to fill add 10% for dynamic seals and 20% for static... for example...

A piston has an outside diameter of 26mm and a groove with a diameter of 24mm lathed around it the groove is 1mm wide. For this seal you will need a 25mm diameter 1.1mm wide O ring. If it was a static seal like a flange joint you would use a 25mm diameter O ring with a width of 1.2mm.

hope that helps.

The assortment boxes/grab kits come in inch & metric. Don't be without one of each. They usually have a thickness gauge built in. So suck it and see. I can only say "experienta docent". If it fits the groove and can be got into the cylinder without excessive force it probably is OK. Every bloody manufacturer and every bloody design engineer has their own ideas and never consult the poor bastard who has to either make or maintain the gear. Up to your bum in curry faeces in the bilges of a Greek owned, Liberian register, Chinese officered and n----r crewed merchantman and trying to work out what o-rings keep the fuel flowing. Great fun, and people thought we were highly paid.

Don't over-tighten anything using o-rings for a seal, nor under-tighten. There is a happy medium. " Ooh, aye, Gaffer, what torque setting do use?" " Eeh, lad, as mooch as needs", is a good rule.

Originally Posted by Blknight.aus

The easy way is to go and buy the grab kit of O rings from any reputable parts dealer, not super cheap, then guess and giggle. The kits have about 10 or so each of 20-40 different sizes in them depending on if you buy the small kit or the larger one. they are a small red box like a lure box from a tackle box. In a pinch they are worth their weight in gold.

Depending on how good you are with the verniers its simply a case of identifying the seal faces, the diameter it has to seal across then measure the space it needs to fill add 10% for dynamic seals and 20% for static... for example...

A piston has an outside diameter of 26mm and a groove with a diameter of 24mm lathed around it the groove is 1mm wide. For this seal you will need a 25mm diameter 1.1mm wide O ring. If it was a static seal like a flange joint you would use a 25mm diameter O ring with a width of 1.2mm.

hope that helps.

Bzzzzzzzzzzzzttt....

Wrong!

That seal would fail instantly

Challenge me if you wish

Tombraider

Originally Posted by tombraider

Bzzzzzzzzzzzzttt....

Wrong!

That seal would fail instantly

Challenge me if you wish

Tombraider

I don't wish to challenge but I do want to know why. I want this job right because I don't want the oil pump sucking air nor do I want the oil cooler lines leaking.

Ron