BSP straight or taper?

[davidor]

What determines whether you use BSP straight or taper fittings?

As I understand it, male straight to female straight fits (no sniggers now), male taper to female taper fits, and male taper to female straight fits. But why for instance would you use the last option over straight/straight or taper/taper? Does a male straight fit a female taper?
Is there a simple rule for using straight or taper?

Thanks guys.

 

[ricarbo]

The idea is that only one of the two has a taper, it doesn't matter which one. That way the joint goes tight when you wind them together. Straight with straight or taper with taper equals does'nt go tight therefore leaks!

 

[keego]

Is there a simple rule for using straight or taper?

Yes, you can't use a straight or parallel thread on a gas fitting.

 

[chrishutt]

you can't use a straight or parallel thread on a gas fitting.

You can, but only one of the two mating threads should be parallel. The other must be tapered to achieve a seal between the threads.

As mentioned above, parallel to parallel threaded joints will not seal or tighten properly. You can get around it in various ways with water, but not with gas because the regulations are tighter with gas.

In general, male threads are taper and female threads are parallel, so there isn't usually a problem. Parallel threads are used exclusively with union or compression joints, where the threads do not form the seal.

 

[PEDANTICVINDICTIVEMAN]

Just fitted a paralell to paralell thread onto a a gas meter today, jointing paste, tighten up tight tight, no problem at all, it definately wont leak, all stuff and nonsense.

 

[chrishutt]

tighten up tight

If it tightened up they can't both be parallel threads. Think of the threads on a long screw connector for example - needs a lock nut, hemp and sealant to seal.

 

[PEDANTICVINDICTIVEMAN]

No both paralell but both flat faces, it's tightened up so both faces are tight up against each other.

 

[chrishutt]

tightened up so both faces are tight up against each other.

In which case it's a kind of union joint where the threads only provide compression of the two mating surfaces. This is the point I'm trying to make. Also I think you'll find that HSE/Corgi would take a dim view of such a joint, since it may be that the gas fitting is not being used for the purpose intended.

 

[PEDANTICVINDICTIVEMAN]

Yea well I am qauking in my boots, if they aint interested in anything dangerous I have ever reported I dont think they will be interested in this, anyway it's all wrapped in denso to protect it as it's outside, one thing for sure it wont come loose as the solder from the capillary fitting right next to it has soldered the compression nut to the pipe.
I cant even be bothered to report the illegal boiler installation work in the next close by the plumber who isn't corgi, why, same reason as before, whenever I have reported anything you either cant get through on the phone and if you do they aint interested, if you phone up to find out about something you reported a while back to see what happened they wont tell you and come over with a high and mighty attitude, bollokks to them, there only interested in money.

 

[chrishutt]

I share your sentiments (at least on a bad day), PVMan, but you know how these things work - the hordes of cowboy installers get away with the most blatant outrages, yet the full wrath of Corgi/HSE descends on the registered installer who makes some minor error.

For example, a while back an RGI was prosecuted and heavily fined for connecting a gas hob using a tap connector (with the spigot filed back). A case of a male parallel to a female parallel union joint!

Anyway the joint leaked a little (and started a fire ) and so he was hauled up in court - the full works. He was just doing what he thought was the best of a bad job (there is no taper female thread adaptor to copper available in the UK).

 

[PEDANTICVINDICTIVEMAN]

Come on Chris, the joint leaked a "little", not really acceptable, in any circumstances, but I know what you mean, my accountant was saying about their rip off association of chartered accountants, they aint here to help the accountant only to nail them using their own money against them, ridiculous innit.