Why do most showers have 1/2 BSP-P threads?

[Ron Lowe]

Why do most showers have 1/2 BSP-P threads?

BSP-Parallel threads work best with a sealing washer, like you get on washing machine connectors / taps / hoses and on garden taps / Hozelock fittings. ( These are usually 3/4" BSP-Parallel ).

My new Grohe shower valve has 1/2" BSP-P female threads cut into the casting. And from my googling, this is fairly normal.

To connect these to normal pipework, you need to use 1/2" BSP male ( AKA Male Iron ) to 15mm fittings. But to get these adapters to fit into the shower valve in a watertight way, you need to ***really*** pile on the PTFE tape. ( There's no way to use a sealing washer in the shower valve casting. )

Now, this just seems a bit crap to me. You really shouldn't need to lard on PTFE tape like this to make a connection watertight. Any design which relies on larded-on gloop or PTFE is a broken design.

IMHO, if you are relying on the thread itself as the pressure seal, the design should be using a Tapered Thread, not a Parallel one. That's what tapered threads are for! ( Or use a regular compression fitting, or have a Male BSP spigot to which you can fit a female-with-washer like washing machines have, or any other decent method of connection. )

It seems to me that the use of a parallel thread in this way is not the best.

[Dave Liquorice]

You mean like wot you find on taps? With which you use a tap connector, complete with fibre washer?

[mark]

Use a BSPT male to 15mm copper adapter. Mark

[Ron Lowe]

Exactly.

But in the shower casting, there's no way to use any form of washer, just thread tape. That's my complaint!

[Ron Lowe]

[...]

Yes, that's exactly what I'm doing, as I said :-)

My point it that BSP-P without any form of washer, and relying on tons of thread-tape is a crap design, yet it seems commonplace.

[Dave Liquorice]

Sorry, must be having a thick moment. Why won't a tap connector fit? The fibre washer seals between the flange on the pipe connector outlet pipe and the outer end of the shower units casting. Exactly like a tap...

[Ron Lowe]

Because a tap has a male thread which you screw a female ( nut ) fitting ( with washer ) onto. ( Same as the back of a washing machine. )

The shower has a female connection, cast into it. You need to use a Male BSP fitting like this:

female thread in the casting does not bottom out onto a nice flat internal shoulder which would accept a washer, it goes straight through into the main body of the valve. An internal washer would drop right into the gubbins.

A larger external washer on the shoulder of the male fitting would bear against a rough surface on the valve casting, not a polished surface, unfortunately.

So the only sealing mechanism is the thread itself.

[The Natural Philosopher]

Is it? Why?

[Doctor Drivel]

Some can take tap connectors which use washers. Look at the thread first.

[Ron Lowe]

Just 'seems' crap, that's all. It offends my engineering sensibilities.

Sure, it does work, but it's a bit 'yuck'. Like making an electrical connection by twisting the wires together then wrapping them in insulating tape.

In all other fields[1] where I have to make fluid tight connections, there is a specific designed sealing mechanism, and the thread is purely a mechanical device for holding the actual sealing mechanism in place. ( Eg: olives, washers, flared pipe ends, JIC type cone seats, etc etc. )

If the thread IS to be the sealing device, then tapered threads are used.

Thread tape is used sparingly, and only on seals which are designed to use it. Not larded on. If it needs to be larded on, it's an indication that the actual seal is not functioning correctly.

[1] My background is in the oil industry. The seals I normally deal with are typically either for hydraulic oil or other hydrocarbon / gas bearing lines. They are typically 10,000 PSI rated or more, and so are not a particularly good analogy for domestic plumbing.

However, there ARE plenty of well-designed seals in use for domestic plubming: Olives, Solder, Nut-and-Washer, O-ring-based, etc etc.

So with so many good designs available, why use one that relies on larded-on tape? Is it significantly cheaper?

[Baz]

Lowe Engineering Ron???

Baz

[The Natural Philosopher]

Don't be so precious. Showers run at 0 bar, and PFTE tape, or indeed hssians string and putty, is more than good enough. Think how much EXTRA a tepaerd screw fitting would cost, and the problems of getting the screw in bit at the right angle AND done up tight.

A straight screw has two important advantages

- it can stop at any angle

- it doesn't have any exterior housings and the like - a very neat fitting results.

Its also cheap and more than adequate.

In short, it is the correct solution.

[Ron Lowe]

But when the shower is not running, the inlets are at 3 bar.

[Doctor Drivel]

Putty? Oh my God!!!!!

[nightjar]

I have an entire two-factory air line in 1" and 2" steel pipe, working at 7 bar, that works quite happily with parallel threads and an application of PTFE paste. Only two out of about 50 joints had minor leaks that needed to be resealed and it will hold working pressure for 10 minutes without any measurable drop.

Colin Bignell

[Ron Lowe]

On a related Q...

I've always used PTFE tape for these kind of things, eg serewing an external tap into the wall-mounting elbows etc.

Can Fernox LS-X be used as a direct substitute for PTFE tape in these situations? ( I happen to have a tube handy, and am willing to try different things! )

Or should I just stick with PTFE tape?

[Ron Lowe]

Yes, I know.

Our works air system is the same. I think it's pretty much standard for air installations.

( I'm glad I wasn't doing the installation: those guys were *sweating* cutting the threads on the bigger pipes. )

It just seems there are better ( to my thinking ) ways that are commonplace elsewhere in domestic plumbing systems.

[mike]

"Ron Lowe" wrote in news:44a2b8ed$0$663$ [e-mail]:

You can use LS-X for _anything_ ; it's the mutts.

But be sparing, I know a guy who put too much on, and it formed a perfect flow restricting washer inside the fitting.

mike

[Dave Liquorice]

So the second question below was answered incorrectly?

Is that "rough surface" flat or a contoured to the shower body shape? How rough is "rough"?

Fibre washers are very good a sealing. You don't even need to tighten them very much, finger tight can do as the expand when they get wet. I'd still nip it gently with a spanner though.

[John Stumbles]

Does seem a bit crap. I thought Grohe were supposed to be good. Most of the shower valves I've fitted have had either 3/4" female threads with a washer to seal (bar type shower mixer valves) or 15mm compression (round often 'traditional' Vicwardian style). The only ones I've come across with female threads and no washer are on fully recessed valves where you can use PTFE tape and it's all hidden.