How do I connect to the male thread of a dielectric coupler?

[PerpetualLeakingRoof]

I'm fitting an Ariston Andris hot water cylinder and I've hit a bit of a problem with the dielectric couplers on the top of the tank. The dielectric coupler is shown on the left of the picture below. It screws down on to the top of the tank and has a rubber washer to seal it to the tank, this is fine.

The problem is connecting the male end of the dielectric coupler to the rest of the pipe work. I bought the brass 1/2" BSP female to 15mm coupler to attach to the male end of the dielectric coupler. The male threads on the dielectric coupler are much to short to compress to the washer that I'll put in the brass coupler. I'd need probably 3 washers to fill the gap internally!

Interestingly, the flexible tape connector has the perfect fitting. The female threads on that are short enough the dielectric connector would compress the washer.

What am I missing here?

I believe these are all parallel threads so should seal using a washer. I've found several examples of people just covering the threads with teflon tape and calling it good, though.

 

[mattylad]

Go to a plumbing shop and get a different brass coupler, take the plastic one with you to confirm it does fit.

 

[PerpetualLeakingRoof]

As often seems to be the case I think I've figured out what I need 5 minutes after posting. I think I need the things shown below. 15mm to 1/2" bsp tap connectors (there's also a compression version but this is fine).

All the tap connectors I've looked at have this shorter section of female thread. My guess is the designers of the water heater expect most people to just run flexible hoses straight to the tap or something.

 

[avonmouth]

As often seems to be the case I think I've figured out what I need 5 minutes after posting. I think I need the things shown below. 15mm to 1/2" bsp tap connectors (there's also a compression version but this is fine).

All the tap connectors I've looked at have this shorter section of female thread. My guess is the designers of the water heater expect most people to just run flexible hoses straight to the tap or something.

View attachment 419306

That won't work as the centre part of that tap connector would have to fit inside the plastic fitting and i don't think it will. A few fibre washers inside your female fitting and ptfe tape or jointing paste will probably sort it.

 

[denso13]

I believe these are all parallel threads so should seal using a washer.

No, just use PTFE tape, you wouldn't use a washer with a straight adapter.

 

[avonmouth]

No, just use PTFE tape, you wouldn't use a washer with a straight adapter.

You wouldn't put a fibre washer inside that female iron fitting ?......i would plus ptfe on the plastic.

 

[denso13]

You wouldn't put a fibre washer inside that female iron fitting ?

No, I wouldn't to be honest.