Plumbing Basics, Part 1

This article was first published in 2005.

Whether you’re playing with a turbo boost control system, an intercooler water spray system, a fuel system or a turbo, there’s one aspect you’ll always need to consider: plumbing. We’re not talking high-end, expensive stuff here – braided line and special anodised fittings and silicone hose. Instead, in this series we’ll cover the sort of cheap bits and pieces you can buy from industrial and truck suppliers and put together to make all kinds of systems – from those that control boost to those that supply fuel.

This week we’ll cover small diameter hose and fittings and next week we’ll take a look at the different valves you can use with this type of plumbing. In the third and final part, we’ll examine large diameter plumbing.

Hose

In most automotive applications, the rubber hose designed for EFI systems is a good general purpose hose. That is, it can be used in fuel systems, boost control systems and water sprays. It’s not as cheap in the latter systems as thin-wall “vacuum” tube (or vinyl tube), but it’s also much more durable in the hot environment of an engine bay. Fuel hose also has great resistance to puncturing and abrasion, so it’s good for applications where you don’t want leaks, even if the hose inadvertently rubs against a metal component.

Fuel hose is available in a wide variety of imperial sizes, including ¼ inch, 5/16^th inch, 3/8 inch, 5/8 inch and so on. (To get these dimensions in mm, divide the top of the fraction by the bottom and then multiply by 25.4 – ie 3/8 inch is 9.5mm.)

In some cases, the fittings on which you want to place the hose may be a fraction too large for any of the available fuel hose sizes. If that’s the case, use a heat-gun to warm the end of the hose until it is slightly softened and then push it onto the fitting.

Clamps

The most widely used clamps are worm-drive – those that everyone knows as normal hose clamps. When buying worm-drive clamps, make sure you’re getting stainless steel clamps – some are just plated mild steel and they’ll corrode. Worm-drive clamps also vary a lot in build quality – a brand name clamp will almost always be better than a cheapy no-brander. Buying clamps individually can get quite expensive – better to see if a bulk lot of clamps is available rather than going down to the local petrol station and buying them one at a time as the need arises!

Many OE manufacturers use spring clamps instead of worm drive clamps. In the applications in which manufacturers are using them (constant hose diameter, constant fitting diameter) they work very well, even on high pressure fuel systems. However, if you change hose brand, or use a fitting with a different diameter barb, this type of clamp can become unreliable. You may find that to get it on the hose, the clamp needs to be stretched beyond its normal elastic limit, or conversely, that when placed on the hose its clamping force is insufficient. Always keep these clamps as you come across them, but be wary of using them unless their fit is perfect.

You’ll find that on very small diameter plumbing there are no worm-drive clamps available that are small enough to fit. In these situations there are three alternatives – use the abovementioned spring clamps, use cable ties, or use super glue. What?! One example where super glue (ie cyanoacrylate) works well is where a car has been converted to forced aspiration.  The very small diameter hoses (say with an internal diameter of 4mm) that previously carried vacuum (so pushing the hose more firmly on their fittings), now carry boost. You don’t want them to blow off so you need a way of positively holding them in place. However, because the hose diameter is so small, the magnitude of the forces that are developed is also small – superglue or small cable ties work fine in these applications. Gluing the hose on will obviously make it rather hard to remove, so don’t do this if you expect to be frequently taking the hose off!

No Clamp?! Some manufacturers are now using hoses in their fuel systems that don’t have clamps. Instead, the fuel hose consists of an inner hard plastic tube and an outer protective rubber covering. The inner plastic tube appears to be factory heated before being pushed over the fitting where it hardens to form a permanent assembly. To replace the hose, use a sharp knife to carefully cut along the hard plastic tube, allowing it to be pulled off. Normal fuel hose and a worm drive clamp can then be used as a replacement. It’s important to realise that this type of OE hose can be kinked badly without this being apparent – the inner hard plastic hose kinks but the outer rubber covering still looks fine. You’ve been warned!

Using Worm Drive Clamps

Nothing could be simpler than using a worm-drive clamp, huh? Well, not really – there are plenty of ways of stuffing it up. Firstly, don’t use a screwdriver. Instead, use a socket and an extension bar. (Don’t have any small diameter sockets? Go buy them – even just a cheap set will last a long time as they’ll be used only rarely.) Using a socket drive allows you to determine the torque that you’re applying far better than when using a screwdriver, and the socket is much less likely to slip off and damage the hose – something that’s dead-easy to do with a screwdriver.

Secondly, make sure that the clamp is not positioned right at the end of the hose – instead, it should be located back from the hose end by about one-quarter of the width of the clamp.

Thirdly, use a penetrating spray lubricant (RP7, WD40, etc) on the worm and thread before fitting the clamp. This reduces the chance of stripping the thread, and – as with the use of the socket – allows a much better feel for how much torque you’re applying.

Finally, don’t over-tighten the clamp! If the clamp is well fitted, and the hose size is well matched to the fitting, the clamp shouldn’t need to be ultra-tight. (Remember the OE factory spring clips used on EFI fuel hoses mentioned above – they’re often not very tight at all yet they seldom leak.) Even if it’s not very tight, the clamp won’t come loose as the springiness of the rubber hose will hold it in tension. If you start seeing the hose bulge out from each side of the clamp, chances are that you’re over-tightening it.

T-Pieces

If the plumbing run that you’re working on needs to split in two, you’ll need a T-piece. T-pieces can be found in boost control systems; fuel supply systems running multiple pumps, pressure regs or fuel rails; and intercooler sprays with multiple nozzles.

The best T-pieces are formed from a single piece of brass. These are relatively rare and can be differentiated from brass T-pieces made from multiple pieces by the absence of silver solder joins. A one-piece brass T-piece is nearly indestructible! At the other end of the spectrum are plastic T-pieces. Even those made for automotive fuel use (eg of nylon) can easily fail, especially if you need to remove and replace the hose a few times.

T-pieces are made in as wide a variety of sizes as hoses, although it’s harder to get brass T-pieces for very small and very large diameter hoses.

The flow behaviour through a T-piece is dependent on its orientation. If the flow is up the vertical arm of the T, equal flow will be available at each of the upper outlets. But if the flow is enters through one of the upper arms, much more flow will go through the other upper arm than out through the vertical part of the T. (The actual flow split also depends a lot on the rest of the system, so this rule of thumb doesn’t always hold true. But it usually does.)

This asymmetric flow behaviour can be very useful. For example, the on-road behaviour of a boost control system can be quite dramatically changed by the orientation of the T-pieces in the system. Together with variable nozzle sizes, it can also be used to direct more water through one intercooler spray nozzle than another.

In short, keep in mind the orientation of the T-pieces when installing them, and if it could be advantageous, try them in different directions.

Barbed Fittings

The T-pieces described above uses three barbed fittings onto which the hoses are pushed. ‘Barbed’ simply describes the bumpy end of the fitting that’s designed to make it harder for the hose to slide off. However, pretty well all ball valves, needle valves, one-way valves, pressure regulators, pressure relief valves (and so on!) don’t have barbed fittings. Instead, they use female threaded fittings. So how do you attach a hose to these valves? The answer is to use barbed fittings called hose tails.

Barbed hose tails have the hose barb at one end and a male thread at the other. These threads are normally either BSP or NPT in type. In addition to the type of thread, the internal diameter of the fitting varies. So for example, if you ask for a “¼ inch BSP barbed hose tail” you’ll get one to suit ¼ inch hose. But what about the diameter of the threaded bit? Well, that can vary!

Long experience and many return trips to industrial plumbing suppliers has taught me that you should always either buy the valve and barbed fitting together (that way, you know the thread type and diameter are right) or you should physically take along the valve when buying the hose barbs.

Like T-pieces, barbed hose tails are available in brass or plastic. For much the same reasons as already mentioned, brass is preferable and since the construction of a hose tail is much simpler than a T-piece, you don’t need to look so hard at quality – any brass one that fits will do.

Some valves don’t require male fittings – instead they need female. This is less common but it certainly can occur so until you physically sight the valve, never presuppose that just a male barbed hose fitting will be needed.

Sealing Threads

Most threaded fittings use a tapered thread design. That is, as you screw it in, it gets tighter and tighter. This is important to know as beginners have been known to get out a big spanner and just keep on tightening until the thread bottoms out – or the fitting fractures!

Sealing of the thread can be done with Teflon thread tape, cheaply available from any hardware store. Wind the tape on the male threaded fitting in the opposite direction to that which you’ll be screwing it – this prevents the thread tape being nicely unwound as you screw the fitting into place. Apply only two or three layers of the tape - you don’t need to wind on a heap. In fact, putting on too much thread tape is a big negative as the chances of the tape getting into the flow path is greater. For the same reason, make sure the wound-on tape doesn’t cover the internal opening of the fitting. (Because of the chances of it getting into the system, some authorities recommend that you don’t use thread tape at all. However, if you’re careful in the application, this can’t happen.)

With thread tape applied, a tapered thread fitting should be tightened to only a snug level – not super tight. Brass is much weaker than steel so it’s not hard to shear off a threaded fitting, especially if you hold the valve in a vice and use a large spanner.

Conclusion

The difference between a plumbing system that leaks, gets holes abraded in hoses, fails in service because a hose pops off, or has cracked fittings, is all in the parts selection and the workmanship. It costs no more and takes no more time to get it right!

Next week – all types of valves

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