O-ring replacement - size advice

[gregcope]

Hi All,

I want to replace an old O-ring.

The ID of its slot is 15mm. It is 2.5mm Dia. Which suggests and OD of 20mm. However the ID of the whole it fits is 19mm.

What size OD O-ring to get?

 

[Plum]

Hi All,

I want to replace an old O-ring.

The ID of its slot is 15mm. It is 2.5mm Dia. Which suggests and OD of 20mm. However the ID of the whole it fits is 19mm.

What size OD O-ring to get?

allowing for 25% compression is OK for a static seal but for a sliding seal 20% max or rotating 10% is what i would plan for

 

[gregcope]

This is a sliding seal. So 20% of 19mm is 22.8mm.

I was thinking 20mm OD - 15mm ID/2.5mm Dia.

 

[Plum]

This is a sliding seal. So 20% of 19mm is 22.8mm.

I was thinking 20mm OD - 15mm ID/2.5mm Dia.

If the id of the shaft groove is 15mm and the id of the bore the o ring slides in is 19mm then an o ring with a 2.4mm diameter cross section would be compressed by 20%ish on assembly.

 

[B27]

It's 20% of the cross section, so a 2.5mm strip of rubber is compressed to 2mm.
It can make a difference if the width of the slot is tight, your round section o ring becomes square section...
If 15 ID x 2.5 xs is too tight, you could try a smaller ID so it's stretched , thinning the section a little.