Union Joint Washers, O-Rings - best practice to fit?

[ClockPie]

I hang my head in shame asking, but realised I don't know the best practice of swapping o'rings and union joint washers! I've obviously changed things before and they've been fine, so just wondering if there is a correct way?

e.g. I've got to remove a vaillant diverter valve that breaks/disconnects 2x union joints to get to the DHW HE. A new diverter valve comes with new washers for diverter valve and o ring for the connection to the DHW HE. (And the DHW HE comes with new washers/o ring for its connections)

But just taking out and removing the diverter valve doesn't magic up new washers

1. Assume that the o'rings and washers are single use and if should be replaced when the item is put back?
2. Are the washers/o'rings put back "dry", or just "wet", or do they need any type of jointing compound?
3. Do the UJs need PTFE or jointing compound when they are don back up compressing the washer?

Sorry for such a basic question on a Sunday morning, but would rather get it "perfect" than just be lucky

 

[Madrab]

Best practice would dictate that any water/gas tight joint that is made by a o-ring seal/fibre washer/rubber washer etc should be replaced when the joint is remade.

Can you get away with using the old washers? Sometimes .... 50-50 that it'll leak.

For a professional it always makes sense to replace, this reduces the chance of a call back.

Rubber O-rings are better to be lubricated - touch of silicone grease to aid installation
Fibre and rubber washer used in flat faced unions would be used dry

 

[ClockPie]

Brilliant, thanks. Looking at toolstation "plumbers grease" to lubricate? Is that the same? (Or alternative product?) https://www.toolstation.com/shop/Plumbing/Consumables/Plumbers+Grease+57+grms/d20/sd2711/p34053 (I have toolstation & screwfix in 1/2 mile 0

Fibre install dry - great - thanks. (Jointing compound on thread for good measure?)

And even at 10% chance of failure I'd replace - so noted - will replace. (I assume fitting, then if having to remove and refit there and then, then reusing is fine? e.g. not single fit only).

I've got a couple of selection packs of various washers and the like anyway, but I'd always want "branded" ones in this instance - this is where DIY suffer. £2.50 each; or £5 for 10x with £6 postage! But I'll male sure I have stock when I tackle this.

Appreciate the reply, thanks again

 

[DP]

Clockpie, am surprised you are asking a question when the spares in question are supplied with appropriate fitting hardware

Fact that you have to source seals and fittings from DIY stores or by post, a pro will have these items as and when needed.

 

[Madrab]

Nope, that grease would be more designed for the tap internals/metal on metal and stuff like that.

O-Rings and the more modern rubbers are more susceptible to perishing using petroleum based greases, a silicone based lubricant is what you are really looking for.

Jointing compound should not be needed on the threads no, the seal is created by the washer, nothing needed on the threads unless they are really tight/dry and then use a lubricant not a jointing compound

 

[ClockPie]

Nope, that grease would be more designed for the tap internals/metal on metal and stuff like that.

O-Rings and the more modern rubbers are more susceptible to perishing using petroleum based greases, a silicone based lubricant is what you are really looking for.

Jointing compound should not be needed on the threads no, the seal is created by the washer, nothing needed on the threads unless they are really tight/dry and then use a lubricant not a jointing compound

Thanks - I did buy that grease as I was passing (and got my free coffee ), so will take it back tomorrow (and get another coffee). Appreciate the answer and me getting it wrong.

Just bought https://www.ebay.co.uk/itm/O-RING-A...910692?hash=item2829ea44a4:g:ccEAAOSwoydWq-Qg