Water Cooling Fittings and Tubing Size
I'll attempt to explain some of the differences in various fitting types and make a quick recommendation with respect to tubing size.
Before getting into the details on fittings, it's important to know what tubing size you plan to work with. Water cooling tubing in North America, is specified by it's inside diamater (ID) and comes in 1/2", 7/16", or 3/8". Larger diameter flows better but is bulkier and has a larger bend radius than smaller diameters.
Industry guru Cathar had this to say about tubing size, which I completely agree with...
"Been rolling the whole tubing size idea around in my head, and thinking about trade-offs and the like.
I like the idea of 3/8" ID tubing, but I just can't shake the feeling that for >4LPM that it starts to become an increasingly significant source of restriction for those who wish to make use of strong pumps capable of pushing the higher flow rates. It's not that 3/8" tubing is bad at all for coping with moderate flow rates, it's just that it could be better. For example at 6LPM, 7' of 3/8" ID tubing is offering pretty close to 1mH2O of pressure drop all by itself.
But 3/8" is attractive because it's very light, and it bleeds air-bubbles fast.
1/2" tubing is fat and unattractive. Unless flow rates are getting past the 6LPM mark, air-bubbles don't bleed very well. It's heavy, and it requires fairly thick walls (1/8") before it can turn good radii without kinking, but this wall thickness comes at a cost of making it stiffer to turn, thus putting more leverage on the water-block's all important thermal contact. However, it takes around 13.5LPM before 7' of 1/2" ID tubing offers 1mH2O of pressure drop, so really it's almost overkill.
So I looked to the middle-ground, that being 7/16" (~11.1mm) that has 3/32" wall thickness for a total of 5/8" OD. Per length of tubing it's about 2/3's the weight of the 1/2" ID (3/4" OD) tubing. Being a thinner ID it is able to be bent into tighter radii without kinking, allowing for the use of the 3/32" wall thickness, which means that it also becomes easier to turn those radii. It offers 1mH2O of pressure drop at 9.5LPM for a 7' length, which pretty much puts it still as a very attractive offering.
Then I took into account stretching the 7/16" ID tubing over 1/2" OD fittings (barbs) with 10mm ID orifices. Due to the "lip effect" the 1/2" ID tubing actually offers nearly 3x the transitioning resistance at fittings as the 7/16" tubing whose ID more closely matches the ID of the fitting. Over a typical full system when fitting resistance is taken into account, the 7/16" ID tubing offers almost the same amount of tubing + fitting resistance as the 1/2" ID tubing.
Results were obtained using the pressure drop calculator from http://www.pressure-drop.org.
This all got me to thinking that really what us 1/2 inchers may really want to be doing is fitting 3/32" thickness walled 7/16" ID tubing over our 1/2" barbed systems, and pretty much be enjoying no extra system resistance, but gaining the benefits of lighter tubing that is easier to bleed (bleeds very well at a predicted ~5LPM), easier to bend, isn't as bulky, "hangs" less off water-blocks, and is significantly cheaper due to less wall material being used."
7/16" tubing over 1/2" barbs has the additional advantage that it forms a perfectly water tight seal without the need for clamps of any kind (although clamps are still recommended to prevent accidental tube/fitting separation).
You can buy 7/16" tubing at Jab-Tech or Petra's.
Wondering what threads you water cooling gear has? If it's not specified, it may be listed here on the XtremeSystems forum sticky.
Pipe fittings generally come in two variations, tapered threads where the base of the thread is wider than the end, and parallel threads. With tapered threads, both the male and female ends are tapered and thus form a very tight seal as the fitting is tightened. This kind of thread is not common in water cooling but some online retailers sell tapered fittings which won't work well at all in parallel threads.
Notation for these threads are:
- NPT: National Pipe Tapered Thread
- BSPT: British Standard Pipe Tapered Thread
Note how the threads taper from top to bottom on this NPT fitting...
Again, avoid these kinds of fittings in water cooling systems.
Obviously are parallel and are the most common in water cooling gear. However there are variations of this style of thread as noted below:
- NPSM = National Standard Free-Fitting Straight Mechanical Pipe Thread (19 threads per inch at 1/4)
- BSPP = British Standard Parallel Pipe Thread (18 threads per inch at 1/4)
Note that since the threads per inch are similar (19/inch for NPSM and 18/inch for BSPP) these two types of fittings are interchangeable where thread depth is less than half an inch. This applies to all water cooling fittings and gear meaning that BSPP fittings can safely be used in NPSM blocks and vice-versa.
Here is a good resource on thread standards.
Seal and Tightening:
Parallel threads generally rely on a rubber O-ring for a water-proof seal. The O-rings provided with the barbs mentioned below are ideal. The O-rings that came with my swiftech blocks are too large to be used with G1/4 barbs and I was unable to repurpose them when I switched all my fittings over to nickle plated brass G1/4 high-flow.
As for tightening the fittings, I find that "hand tight" provides a leak-proof seal. Perhaps another half turn with a wrench or socket wouldn't hurt. As long as it's not so tight that the O-ring is deformed you should be good.
Plumbing tape is generally not required. If it has an O-ring use it and forget the plumbing tape. If it doesn't have an O-ring, first ask yourself why, and then if there's simply no way around it, use plumbing tape.
If you are putting a fitting into a curved surface such as a res (i.e. a Dangerden plexi res) then you will need plumbers tape because an O-ring can't seat against a curved surface. I have such a res and actually epoxied the threads before attaching the barb for a more permanent seal.
Now for block fittings, there are a few considerations:
Material: Plastic vs. Metal
Plastic fittings can be nylon, poly(something), or acetal. Most Swiftech stuff comes with platic barb fittings. The main consideration in using these kind of fittings is that if you are using the above recommended 7/16" tubing over 1/2" barbs that are plastic, you will NOT be able to easily remove the tubing once it is on. In fact, you will probably have to heat up the tubing to get it soft enough to put it on and then you will likely have to cut it off.
Metal fittings are typically nickel plated brass. They look good and have the aforementioned benefit of allowing 7/16" tubing to slide onto 1/2" barbs forming a good leak-proof seal (even without clamps) yet the tubing can still be pulled of with some force without damaging the fitting or tubing.
Design: Barbs, Perfect Seal, Push-to-Connect, Compression
I don't have experience with the push-to-connect or compression style fittings. my advice on this is to use the Dangerden high-flow 1/2" barbs with G1/4 BSPP threads on as much of your gear as possible.
EK also makes similar barbs but the flanges on these barbs are wider making them inappropriate for use with many Swiftech blocks.
There is also a 9/16" version available for anything with those threads. The high-flow barbs are actually bored out to the maximum possible bore of about 7/16" making them a perfect match for that tubing. And, as I said above, the nickel plated brass allows the tubing to be slipped on and off without damage yet forms a great water tight seal without clamps.
I would avoid the perfect seal fittings if you are using 7/16" tubing... I expect the lip would make it near impossible to get the tubing over and the turbulence caused on the inlet side would hurt flow.
Good places to buy are:
- Petra's Tech Shop
- Performance-PC's (in fact, I ordered a lot of my stuff through here and the DangerDen high-flow 1/2" fittings were included with most of my gear)
Finding other G1/4 fittings:
Outside of the common barbs mentioned above, finding British threaded fittings in the US/Canada can be a PITA. None of my local plumbing suppliers even know what G1/4 BSPP is. Naturally most american fitting suppliers carry NPT or NPSM fittings. If you want a good selection of G1/4 fittings, I definitely suggest:
- Farnell Export (a UK based company with excellent e-commerce site and UPS next day delivery).
I needed some odd fittings: G1/4 to G3/8 adapters for my Remag flow meter and some good G1/4 elbows and these guys had it.
Here's a pic of the elbows which are great from the perspective that they have an 11mm ID (high flow) and are more of a smooth 90-degree bend than some typical milled elbows. While no one wants to use elbows in their loop if it can be avoided, sometimes they are a god-send for tricky tube routings.
You may need these couplers, if you want to use the elbows above...
I bored mine out to 3/8" at a machine shop (you could probably do 7/16" if you have a good machinist).
I had to steal some O-rings from some of my high-flow barb fittings to mate the couplers.
Coolsleeves are a useful product that wrap your tubing with a plastic spring like coil to prevent the tubing from kinking through tight bends. Coolsleeves comes in a variety of colors and sizes to match any application.
Here is an appropriate use of coolsleeves (considered tight spacing to maximize the bend radius)...
Here is a more relaxed spacing (limiting the effectiveness)...
Here is an application of coolsleeves that is doing absolutely nothing (due to the huge spacing in the coils) to prevent the tubing from kinking...