Some questions on water treads
 

#1 Can you make a taper thread with a normal tap?

#2 Where is the size of the thread measured on bsp/npt fittings?

#3 What's the difference between NPT and bsp?

#4 Is ID and OD used on barbs?

#5 Are quick connect fittings like these more restrictive than the respective barb size?

1 no

2 you cant really do it like that, read this http://www.ajfittings.com/performance_charts.htm

3 NPT= national pipe thread : bsp = british standard pipe

4 barbs are rated for tubing ID

5 yes

To be more specific about #3, the NPT thread is angled, where the BSP thread is straight, like a screw. The former will form an acceptable seal, while the latter will require a seal.

You can buy NPT taps. They are slightly conical. The nice thing about threading your own parts with NPT is that you get to choose how far in the fittings will turn before coming up tight. If your fittings stick out too far, you just tap another turn or two. If you have the opposite problem, you're stuck with it.

Ok Then, another 2 questions.

#6 Are quick connect fittings SIGNIFICANTLY more flow restrictive than the same sized barb?

#7 How can a seal be made with bsp fittings?

6) Don't know. :D

7) When Ben said acceptable he was being to scientific. It is NOT an acceptable seal by a long shot. It still needs to have sometype of sealant on it. This same sealant should work fine on strait threads aswell.

#6: relatively, yes, but in the greater scheme of things, maybe.

#7: a sealer is still required, yes. Teflon tape works well for me. The BSP is not one I'm too familiar with, but I believe that a rubber at the bottom of the threaded portion makes the seal.

I was asking question #7 because last time I tried, teflon tape didn't seal with a straight thread

and it won't, because it's not designed to.;)

Yeah use something liquid that will seep into the threads like silicone, plumbers good, or whatever.

ahh, yess...but this is where things get confusing. See, there are 2 different British standards for pipe threads. There is BSP ( British Standard Pipe ), which as you said is straight, no taper. Then there is also BSPT. ( British Standard Pipe Taper ) What I have found in my rather limited dealing with these standards is that many, many times people get them mixed up. That is, a fitting will be tapered & the person, no knowing any better will just label it a BSP. The things are not interchangeable with NPT threads, but they are very close. The taper is slightly different. the included angle of the threads on a NPT fitting is 60 deg, while the BSP uses 55 deg. The pitch ( the distance from crest of one thread to the next ) is the same...but the diameters are slightly different.

As far as sealing with the "straight" variety of BSP....I think that plumbers dope or a lot of teflon tape would work fine.

So, according to the tables I measured this thread on this barb to be 1/8".

Judging from its shape, it is a BSPT fitting since it is tapered. I have an NPT tap of the same size. Making an experimental thread in wood, it resulted that the barb fits in the tread. Are the TPIs of BSPT and NPT the same?

Given that there is a slight variation in taper angle, will the NPT tap make an acceptable seal with a BSPT fitting?

I'm having trouble finding an NPT tap. I've tried the local hardware stores and they only carry standard taps. So I have 3 questions.

8, Will a standard 'straight' tap work with an NPT fitting?

9, Anyone have a link where I could buy some of these NPT taps?

10, As I look at the threads on this 3/8 fitting I notice the material is quite thick. Has anyone tried removing the existing threads and replacing it witha slightly smaller thread?

The BSP & BSPT threads are similar to, but not interchangeable with American NPT pipe threads. The thread pitch is different in most sizes, and the thread angle is 55° instead of 60° angle found on NPT threads.
I am not saying that it absolutely will not work. However, considering you will be pumping water through this around some expensive parts, a real BSPT tap might be in order. I can warn you, tho....they are not easily found in the states.

8- No

9- I can't believe that any hardware store would NOT have any of these. Instead of asking for a 1/4 NPT tap, try just asking for a 1/4" pipe tap. I know I have seen these at Lowes/Home Depot. The sales guy might not know what they are...

10- would be easier to just buy a fitting with a smaller thread. There are 3/8" fittings that have a 1/8" NPT thread on them. These I have seem in McMaster Carr....have not seen them at any typical hardware store.

Just adding a tidbit... What you have there in the pic Hara is NOT a quickconnect fitting...

The picture shows a straigth barb with a locking ring, put the tube on and tighthen the ring, no need for a clamp to secure it... And that one is not anymore restrictive than any other barb, because the internal diameter is the same for the same size of tubing... It's a bit more bulky on the outside thoo...

A quickconnect fitting is more restrictive than a straigth barb undoubtedly... how much is dependent on the construction... there are ones supposed to be "less" restrictive then a "normal" quickfitting... dunno how much difference it makes thoo...

Yeah, I've always asked myself why they're telling me that that kind of fitting is restrictive :shrug:

I use PTFE tape on my British manufactured rad and it's fine, just have to put more on than an NPT jobbie...

What sealents (better than teflon tape) do you recommend? On my Maze 3 I found some yellow paste.

look for something called Thread Sealant, i know loctite make some stuff + i'm sure your local plumbers store has something similar, this stuff is the biz for threads.. much better than teflon tape, seals up to 10k PSI or something scary (think thats for air tho, 2000 or something for liquids).. but if u wanna make a seal in a thread, thats the stuff u want :)

Does it work with plastic/metal combo though? Say a Poly top with metal barbs, or a metal top with poly barbs, or even Poly top with poly barbs?

Should be ok, at least the one i have which is a british product called 'Jet Blue' deals ok with (that i've tried) acrylic/poly - copper/poly, it also seems happy with chrome to chrome. But thats the extent of what i've used it on, but in all honesty i think it'd work with just about anything.

This product from Loctite is made to seal plastic-plastic or metal-plastic threads.
I used it to seal brass fittings onto my DD polytopped Maze3 and GF4 WB's. You can put it under pressure already after half an hour and it's completely dry after 24 hours.
The dryed seal is very flexible (almost like silicone), no need to tighten the thread very strongly (advisable with a polytopped block!), you can easily remove the thread if needed, clean the old seal rests and re-apply a new one...
I paid 8-9$ for it at a local hardware store here in Belgium
http://users.skynet.be/turbokeu/myco...0/pict0183.jpg

CD :)

Is the threading on an Eheim BSP? I know that they're manufactured in Germany and the inlet and outlet threads are not NPT. If it is a European standard that is different from BSP then I can't remember what it is.
The practical relevence of this is, that I tried every way I could to put a 5/8" brass inlet on my Eheim 1250. I knew that the threading was not a perfectly exact match, so I used pipe tape, silicone sealant and an O-ring.
It leaked some initially, then settled down. I was just about to start installing components when it started leaking again. Time to drain, disassemble and fix at the source.
In a truly stubborn effort to use the brass fitting, I tried some pipe thread sealant. Any decent flow pressure and it would leak, too.
So out came the factory fitting, with a double circumference of PTFE tape, and guess what?. Been dry ever since (2 days now), so I can finally start assembling this system.
The moral? Don't try to mix pipe threadings! The difference in my case was very small, and should have worked with the tape and the silicone. But it didn't.
As a result I lost several days off this project, and bought a bunch of stuff that did me no good in the long run.
Sorry to rant, but I'd like to keep some other poor soul from doing this if I could....