Measuring O-rings for replacement

[AndyP]

I want to replace the O ring on a pump action pressure sprayer. I can see it is loose and not providing any seal at all but how do I measure for a replacement taking into account I only have the old worn O ring?

The internal diameter appears to be 24mm and the cross section 4mm

 

[RogerS]

I'd buy something like this set for £1.59 and hope tha one fitted !

https://www.ebay.co.uk/itm/50Pc-Assorte ... SwxOVb0yUp

 

[Malc2098]

Aldi, Toolstation, B&Q, Wickes all well under a fiver.

If your usual UK agent is stuck, let me know and I'll buy and post to you.

 

[AndyP]

Thanks for the offer. But what a waste. I can buy similar kits here but would never use them. More than happy to buy a couple just for what I need. I might even try making one from leather.

 

[RogerS]

Thanks for the offer. But what a waste. ...

You'd be surprised ! So far I've used the kit to mend Hoselock connectors, Nilfisk pressure washer, knapsack sprayer, 5l hand sprayer ! For £1.59 it's a no-brainer for me to have a selection on tap.

 

[9fingers]

When I've needed specific O rings for a job I turn to ebay.

Yes the kits are ok to have around but Andy needs a 4mm cross section which is possibly outside the range of all but the most comprehensive kits.

There are both metric and imperial o rings out there and 4mm is within a gnats tadger of 5/32" so best to check the ring diameters for integral nos of mm and if not do an imperial conversion to fractions of inches to see if the numbers are more sensible.
1/16 and 1.5mm are another close comparison.

It is a bit like measuring up bearings. No one makes odd sizes of bearings in tenths of mm or decimals of inches so always convert to the other measurement units and check for sensible numbers.

Bob

see https://www.ebay.co.uk/sch/i.html?_from ... ng&_sop=15

 

[AndyP]

The actual problem is how much to add on to each dimension to account for wear and tear. I thought of way around this last night that I will try later that will not need replacing the ring at all. I will tell all only if it works.

 

[Rod]

There used to be a Co. in Alton that manufactured o rings but I cannot find the link to them.
I bought a load for my Unimat lathe.

Rod

 

[9fingers]

The actual problem is how much to add on to each dimension to account for wear and tear. I thought of way around this last night that I will try later that will not need replacing the ring at all. I will tell all only if it works.

True wear manifests itself as minute flats on the rubbing surface. More often it is hardening of the nitrile rubber that loses the seal and in rare cases of abuse, strong organic solvents can make the rubber swell and make the surface sticky.
Buying mail order you can always fall back on distance selling laws and return the part as "unwanted or unsuitable" it it is looks unused.

Bob

 

[AndyP]

I have managed to solve this for the moment anyway.
I wrapped a few turns of PTFE plumbers tape into the base of the groove where the O-ring sits.

 

[Duncan A]

In case someone does need to measure up for O-rings more accurately, plenty of info here:
https://oringcalculator.eriksgroup.com/

Bottom line for non-critical purposes:
- Slight stretch on the internal diameter
- Slight protrusion above the groove on the outside diameter
- Enough space in the groove to accommodate the deformation of the O-ring once the equipment is assembled.

Duncan

 

[Woodster]

They use a measuring cone here.

https://www.globaloring.com/how-to-prop ... me-around/