In my experience, as static seals, sandwiched firmly between carefully machined metal parts such as lids on IP rated enclosures, the cut and shut rings are very good indeed, as good as the continuous kind.
But then in this sort of application, a bead of mastic can also be good, and cheaper.
For moving seals on sliding shafts, OK if the shaft moves piston like, you may see occasional breakages if the shaft is rotating though, and not so good against pressure either.
Extending the technique, in the time honoured method of "limits of the possible can be found by going beyond and coming back quickly hoping no-one was looking", attempts to make replacement rubber drive belts for cassette players and so forth in this cut and shut way are something of a disaster, lasting about 5 mins before coming undone at the glue join.
There may be better and worse choices of glue for the rubber.
I presume you need an odd size not within stretch of a standard.
if you mean between the pump body and the end casting, and tightly sandwiched then so long as the cord diameter is chosen to give a good squashing out of round, without meaning it will not close, it should be fine (SAE reccommend crushing 10 to 20% of diameter,. and allowing 20-30% for sideways expansion (so for example a 3mm cord in a channel 2.5mm high in the seal direction (16% compression), but 3.5-3.8 wide to allow for the necessary distortion).
I have had success with these rules with designs to 5m immersion testing. It may do more, that is the limit of our test rig. ? ). ~If it was a motor seal I'd be more worried, those need a few % of stretch around the shaft, and that puts the glue join at a disadvantage.
A kit of made in China "O" rings will be made to a low price not a high quality. Automotive and aeronautical stuff will be full spec in most cases, able to deal with wear, temperature, chemical attack and pressure etc. I would not trust a cheap selection box of "O" rings for anything critical. Perhaps some distributors will sell selections of different sizes guaranteed to be made to a higher standard, like R.S. perhaps. Do "O" rings have a British Standard?
There are two sets of UK standards for O rings, with metric BS 4518 and Imperial BS 1806 these define cord size and ring diameter, in terms of fitting standard slots . There is an ISO series of sizes used in Aerospace that the Germans like to use as well, that are not compatible with the UK series, so we need two sets of boxes.
The choice of cord material is not defined in these standards, but nitrile rubbers are the workhorse for general use, silicone has better corrosion resistance, PTFE for some really nasty chemicals, but it is not so elastic, and viton if it is a moving seal .
The comment I have seen is that if the stored hot water temperature is too high eventually the hot end O ring will shrink and a leak will develop.
This pump is probably around fifteen years old and works fine apart from the leaking O ring. I don't have a vernier caliper rule to measure the O ring and the house is being sold, so the customer said get a new pump at a cost of £320 then call back to fit it to avoid any hassle with the purchasers of the house.
If there was more time and the customer was not selling the house I would considered measuring the O ring and ordering some online or calling st the bearings wholesaler next to the electrical wholesaler I use.
A couple of quid to get some O rings plus some Nylock nuts versus fifty quid for a service kit or three hundred and twenty quid for a new pump.
It comes down to how long you can reasonably extend the life of a fifteen year old pump and at what cost with customers expectations to be considered as well, you could fix the O ring leak only for something else to go wrong.
I bedded the O ring back in with some silicone grease and tightened the end plate down in sequence, but it still leaked.
I was considering if a O ring kit on the van could give a quick fix with one visit.
The problem with kits is that there are hundreds of sizes available, and a kit covers only some of them. The place to go is usually a hydraulic fittings supplier who will probably have a very wide range of sizes. Powertran in Newtownards is probably worth a ring,
Tel028 9181 3427
Graham is very helpful and you can probably persuade him to post some to you for a few quid. You will need to measure the ring diameter, (ruler), and for a static seal the approximate diameter (measure the groove width).
