How to Measure O Rings

[plumbandplumber]

I recently removed the DHW plate hex on my Vaillant Turbomax to descale it. The o rings were fine, so I just petrol. jellied them and reused.

It did occur to me that if I wanted to replace them, I have large selection boxes of metric and imperial o rings. In the absence of the manufacturer's replacement o rings for that specific application, how would you measure the old ones to choose a replacement? Would you do it by eye, or is there a good o ring measure?

Or would heating engineers and plumbers always use the o rings from the manufacturer of the boiler, etc?


By the way, the Turbomax's hw is now scorching, and as good as new. Did both sides of the plate hex, first with citric acid, then 10 mins with some Spirits Of Salt. There was also rust flakes in the primary side. The acid seemed to dissolve this as well as the scale. Thanks to all for advice on this recently!

 

[BLOD]

I wouldnt use a petroleum based lubricant unless it was recommended by the manufacturer.
I'd stick with silicone grease

 

[Barry98]

Get a cone like they use in jewelers for ring sizing

 

[Barry98]

[DLMURL="http://www.globalrubber.com/cones_18inch.html"]O Ring Measuring Cone - Global Rubber Products Ltd.[/DLMURL]

 

[plumbandplumber]

Thanks for the replies.

The measuring cone only seems to be available in imperial. Would that be OK for most applications?

Will petroleum jelly affect o rings?

 

[Dannypipe]

Petrol and rubber is not a good combination.

The O ring won't be pure rubber. It will have other additives, like silicon.

However, it was a very bad choice on your part to use Vaseline. Silicon grease was the order of the day.

 

[Dannypipe]

If you ever wear latex gloves, while doing work on an oil fired boiler, you will see just how quickly the solvent works. It eats holes in them in minutes, but they are thin. Vinyl gloves aren't effected.

 

[WHPES]

Most O rings are made from NBR rubber which is resistant to oils making them suitable for hydraulics etc so petroleum jelly should be fine. O rings are not made from natural rubber.

 

[Dotty]

I always use silicon grease. Petroleum jelly is saved for breaking in the apprentices.

 

[R1CKY]

Just do it by eye, or if it is a planned job, order the manufacturers o-rings ready.

 

[stevetheplumber]

o rings only come in two sizes to big and to small even when you have two multi boxes of them

 

[vern]

o rings only come in two sizes to big and to small even when you have two multi boxes of them

Lol100% agree Steve

 

[R1CKY]

o rings only come in two sizes to big and to small even when you have two multi boxes of them

Never a truer word spoken!!

 

[REDSAW]

o rings only come in two sizes to big and to small even when you have two multi boxes of them

my box is the same!!

who has the chuffin box of 'o' rings that fit the jobs then????

 

[Dotty]

I did have a box of o rings. They learned the art of flight when I gave up on having every size except the one I needed every single time I looked.

 

[GrahamM]

Most O rings are made from NBR rubber which is resistant to oils making them suitable for hydraulics etc so petroleum jelly should be fine. O rings are not made from natural rubber.

Would have to disagree.
Most generic o-rings will not be of the more expensive Nitrile rubber and will be susceptible to attack from petroleum grease.