Advice on BSP fittings

[howardclark]

Now I'm a simple lad with no proper training in how to make up fittings. At home I use lots of teflon tape and it seems to work. I've just bought a boat from a man with 30yrs experience boatbuilding and he uses a red semi-setting sealant such as 'calortite' or an equivalent, originally used on gas pipes but the tube says also OK for water etc.
He also liberally smears it on pump face plates and similar items.
Which gives best results?

 

[stamfordian]

hi,
The simple answer to your question is both are ok,however on the bsp fittings there is a golden rule that says you can,t use PTFE tape on pipework above 1 1/4 pipwork.On the pump flanges you can get less messier substitues such as PTFE rope or products such as instant gasket,just boils down to the condition of the flanges ie depth of pits which need to be filled in by the gasket.
Hope this helps generaly should be ok.

 

[mtb]

First it does depend on what your putting through the pipes.

Plumbers hemp is very good when used with past ( get from merchants )

I have stuff called Unasco sealing compound Expensive but good .
Trevor is spot on as well.
Cheers
Mick


http://homepage.ntlworld.com/boats
I want a big steel ex trawler / tug v / cheap or swap for tug

 

[Guest]

The subject of pipe fitting and the threads used is a complete minefield! In this country we have used BS21 threads for many years and this standard has stood the test of time with no metric equivalent. The standard has now been merged with iso7 which describes the basis of the threads.

BS21 threads for pipe fittings can be either parallel or tapered depending upon the job they are to do. The UK preferred method is to use taper male threads with taper female threads and IMHO this gives the best form of seal when using the thread as the seal face. In general a taper taper seal can be made with very little sealant because the taper threads ultimately make contact with each other and it is only the manufacturing irregularities that have to be taken up with the sealant. The modern method of sealing threads is the PTFE tape method which is less messy than Boss white and hemp but does have some limitations. An earlier contributor suggested not using above 1" thread sizes - this is true if you use the widely available PTFE tape sold for domestic plumbing. Above 1" you can use the thicker tape available from heating engineering merchants, this tape is considerably thicker and not quite as easy to use but properly fitted will give a satisfactory joint. I personally would prefer to use a few strands of hemp and a smear of Boss white on joints that are semi permanent particularly if some adjustment is to be made to tightening lengths on assembly.(PTFE does not perform well is backed off from the tight position).

The reliability of taper/taper joints is very high and as mentioned earlier is the preferred method in the UK. However, this is where the trouble starts! The European standard makes it quite clear that female pipefittings can be parallel threaded for atachment to taper male threads. This makes one wonder how the seal is to be effected- the meeting of a taper thread with a parallel thread will create a seal junction of one possibly two threads when the male is fully screwed in. This is in fact what happens until the male is tightened fully whereupon it expands the female thread by deforming the mouth of the fitting to create a longer seal path.

You can see this happening if you buy a cheap imported valve and try to fit a UK fitting to it. The fitting appears to enter almost all the way into the valve before contact is made. Now, IMHO this is a poor way to make a seal but is very popular in the Europe and beyond. In this country some pipefitters prefer the taper/parallel method because it is easier to 'pull in' the fittings particularly on the large stuff. The mechanical strength and the long term seal tightness are however less convincing than the taper/taper method.

So if I have not sent you to sleep with this fascinating subject the advice is -

Use hemp and Boss white (or similar potable variety) on joints that are semi permanent. The down side is that they are more difficult to dis-assemble when the sealant has dried.

Use standard PTFE on smaller threads up to 1"
Use the thicker PTFE on larger threads if this is preferred to Hemp etc.

Note: Joints made with PTFE will always be easier to assemble / dis-assemble due to the lubricity of the tape on the threads.

The best advice however is to make sure that you are using fittings and valves etc that have been manufactured with BS21 taper threads. This might mean that you have to buy British from a distributor stocking either Crane or Hattersley products but IMHO the extra cost is worth it. The additional benefit from this is that the valves will be manufactured from a high quality bronze material which should give excellent performance over many years without the dreaded de-zincification that takes place so readily in the marine environment.

When specifying products of this type you are looking for threads designated RC Where the 'C' designate CONICAL! Ie 3/4" Rc BS21

PZ

 

[Plum]

Excellent advice from princesszena. In my experience it is better to use PTFE tape wherever possible to ensure you can remove the fitting in the future. Because it is often difficult in the confined spaces of boats to apply leverage or grip skin-fittings when removing valves from them, if you apply any form of goo that hardens or grips you may have to resort to sawing of the fitting in the future if you want to remove it.

 

[vyv_cox]

Don't want to be a wet blanket but my company has strict rules about the use of teflon tape, based upon many examples of blockage of small orifices. I know of several cases but perhaps the best:

A Frame 6 gas turbine, something like 40 MW output, suffered a severe failure of combustor liners. Cause was found to be pieces of teflon tape fouling the fuel injector nozzles, causing the flame to be diverted and burning out the liner. Cost about 1 million dollars to fix.

I know of many examples less dramatic, mostly involving fuel systems. If any small clearances, by which I mean a couple of millimetres, are involved, don't use tape. When you do use it, our rule is two full turns absolute maximum.

 

[brian_neale]

I seem to remember problems with PTFE tape "creep" - being so slippery, it can work its way out over time, at least to the point of allowing a leak to develop. Maybe this is one reason to avoid PTFE on large unions? Or the thicker tape helps avoid this?

 

[Plum]

Good point, Viv, something to be considered if thinking of using PTFE on fuel systems or such precision items. On the 1/2 inch to 1 1/2 inch BSP fitting on most boats for seawater, heads, galley I have never had a problem with PTFE particles causing blockages or creeping. What would you recommend as an alternative when you also want the fitting to be easy to undo?

 

[vyv_cox]

I also use PTFE on relatively large seawater skin fittings and suchlike. On smaller fresh water and similar fittings I use clear silicone but this is equally good at blocking things - I once got blobs of it in the fresh water pump valves after resealing the water tank inspection hatch. Use sparingly. I also use Calortite on diesel fittings but nothing at all on anything downstream of the primary filter. No problems with undoing these things mostly, although I once made up a tool with a handle about 5 ft long, in conjunction with 18 inch Stillsons, for undoing a seized skin fitting.

 

[poter]

Re: Advice on Fitting Pipes

Get a qualified fitter......... I'm cheap! ( rate is now £60/hr )
Failing that....... The advice given here is in general correct, BUT... if you use any form of hemp and paste for potable water you must use a product like Boss GREEN or similar to avoid any water contamination. If the installation that you are doing is for the Plumbing side of the boat. The best advice I could give, would be rip it out and start again with plastic, it will last far longer and you will not have any corrosion problems. If the installation is for the mechanical side, PTFE tape will not do the job, you would be better off getting a PTFE string manufactured by Loctite, if the pipework is say 1 1/2" or larger the you can't beat boss white and hemp. IMPO. All the products above are available at your local plumber’s merchants, BSS, Plumbcenter etc.
By the way as far as flanges are concerned you should use a product that is suitable for the type of installation, ie is it high pressure water, gas, steam or whatever, be carefull not all flange sealing products will do the job, also will there be any vibration? if yes then a non-hardening paste will be far better.


have fun.


poter.

 

[jollyjacktar]

Never did trust thouse European blighters

Good on you Duncan. To heck with the iso7 nonsense I will stay faithful to the BS21 standard and not mix my "tapers" and my "straights". Never did see the reason behind going metric anyway and at least pipe threads did not alter with the change over, except for the stuff ups as you have outlined, a decision probably made by the same wally who decided we needed to go metric and to the SI standard and all that in the first place. After all, the British originally tossed out the artificial standards of the metric system before the French Revolution. Now the metric system has come the full circle. Any way the Watt and the Joulle are named after guess what nationality engineers in the first place. I was quite happy with Horsepower, and ft.lbs etc. Made perfect sense and were based on convenient sizes not artificial standards. And really what a silly little unit the Pascal is [=1 Newton per square meter, Newton another British person] when pound-force per square inch at least give a sensible quantity. Note 20 lbs per sq inch is equivalent to 137895.2 Pascals or some such. Pshaaw.

 

[Guest]

Re: Never did trust thouse European blighters

I enjoyed your reply but must admit to now using metres as my general yardstick!!! Anyway what is the matter with Pascals - there OK as long as you have got thousands of them!!

PZ

 

[jollyjacktar]

Short legs

Well, you see I have got short legs [they do not go all the way to my feet], I can pace out 6 chain accurately to within a yard or two, but when I try to pace out a metre, ouch! Probably the seat of my deep resentment.

 

[vyv_cox]

Re: Never did trust thouse European blighters

I'm quite used to megapascals now, using them most days. It's volume/capacity that gets really silly, when a cubic centimetre is 1000 times the size of a cubic millimetre and a cubic metre, if we want to be strictly S.I. is 1,000,000,000 times bigger. Bring back the minim, drachm and gill!

 

[Guest]

Re: Never did trust thouse European blighters

Having my post school education during that wonderful metrication period I find myself using which ever measurement comes closest to a line on the rule. Unfortunately this might mean the width is in inches and the length in millimetres!!!

I am OK with this but others seem to get upset when I give them cutting dimensions!

PZ

 

[jollyjacktar]

And all those freaking zeros

And where to put the decimal point that gets me. In the old system you just multiplied by a number and the new unit was it. Now you fiddle about with zeros and where to put the decimal. One slip and you're drinking litres instead of nips. Well thats my excuse anyway. Yo ho ho, I've only had ben tottles of teer amd that's not bad for an engineer.