Cheap Screw-Valve Connectors for Water-Based Crafts Recently I have made a lot of crafts involving moving water, especially scenes I sculpt out of clay and then paint/seal. I made a mini pond to put on my table, an old country scene with a working water wheel for a competition and even a small fountain lit with laser lights.

In each of my crafts, I use acrylic aquarium tubing to transport the water where it needs to go, in and out of pumps etc. Up until now, I have simply glued each tube permanently in place, but this has got to change.

There are times when I wish I could just unscrew a valve connection and remove linking tubes, for example to disconnect a pump from an archived project and reuse it, or in more involved projects, disconnect large pieces for transportation to a showcase.

I don’t like using pre-made tube connectors for this, which can also be expensive if I need lots of them.

So I had a genius idea: bottle necks and caps are designed to be water-tight in nature. If I took a bottle, cut off the neck, glued my tube in and drilled the cap for another tube, I could make a screwable connector.

The first problem with this connector is bulk. If I choose too large a bottle cap, than liquid could remain in the junction after draining the piece. The simple solution is to use necks and caps with a similar diameter to my tubing. Airline toothpaste tubes and their caps have proven well-suited to this task.

The second problem is twisting tubes. Directly gluing my tubes to the caps will cause the tubes to twist (and possibly kink) as I screw the caps on. I solved this with some rubber bands and vegetable oil. I snipped the tube near the cap connection and put the free end of the severed tube over the end of a pair of needle-nosed pliers. I heated the end up with a low-heat heat gun and used the pliers to widen the tube neck. Now the little piece of tube still attached to the cap fits inside the end of the free tube. I glued a strip of rubber band around the outside of the cap tube and the inside of the free tube and then pushed them together. They stayed in place after adding a plastic disk to the cap tube cut from a plastic drinks cup. A swab of vegetable oil on the rubber bands makes for a water-tight, revolving jack.

My problem now is where I can find a good/cheap/free source of tiny caps and screwable necks. I am all out of airline toothpaste. I thought about using cork and bottle necks because they sell tiny bottles at the local store with cork stoppers, but when I cut the glass the bottles sometimes crack and break, and the cork leaks without vegetable oil added regularly.

Any ideas?
Here are a couple of simple, inexpensive solutions.  It doesn't beat the free materials cost of recycling used stuff, but it also doesn't require all of the labor to fabricate water-tight connections.  


Materials for the first solution would be under a dime per connection based on roughly 1/4" ID plastic tubing.

Get some metal tubing that fits tightly into the acrylic tubing.  It can even be slightly larger than the inner diameter because the plastic tubing can be warmed and stretched.  Copper tubing is fairly inexpensive, and a small roll goes a long way (a 10' roll of 1/4" OD copper tubing is about $5 and will yield 80 connectors).  Cut some pieces roughly 1.5" long.  

If you use a tubing cutter, the end will be a little rounded, which is perfect.  If you cut the tubing by other means, use a little sandpaper to smooth any rough or sharp edges, including the end, since these will weaken the plastic tubing.  Use a permanent marker to draw a line around the circumference at the halfway point.

Insert a piece half way into one side of the plastic tubing to be joined.  Leave the mark visible.  The water isn't under serious pressure, so if you need to stretch the plastic tubing a little, it will probably be water-tight as-is.

If you needed to warm the plastic tubing, wait for it to cool.  Finish the connection by pushing the other side of the metal tubing into the other piece of plastic tubing until the ends of the plastic tubing meet.  The visible mark will let you know if you're pushing the metal tubing farther into the first piece, which you don't want.  

If that happens, reposition the metal tubing to the halfway point.  Use a plastic zip tie to tighten the plastic tubing on the first side (under 2 cents if you buy a package of a reasonable quantity).  Position it at half the inserted length of the metal tubing, and use needle nose pliers to pull the zip tie tight (pull it tight by hand, then grab the end with pliers close to the lock, and rotate the pliers against the lock for leverage to pull it tighter).  You can snip off the tail.  The zip tie can be used in any case for extra insurance of a water-tight connection.

On the second side, if you want to add a zip tie, use the removable type there, which will facilitate disconnecting and reusing everything without risking cutting the plastic tubing when cutting off a single-use zip tie.
If you need a ton of connectors and want to save all labor, a ready to use solution is double-sided barb connectors.  For small diameter tubing, this would cost just over a dime per connection (in quantities of 50 or more), with zero fabrication.

Image courtesy Home Depot

  

You just work the tubing over the barb.  This is intended for a permanent connection and doesn't require any form of clamp; it isn't designed as a quick disconnect.  You can disconnect it, but you will probably need to warm the tubing to soften it, then push the tubing off rather than pull it off (think Chinese finger trap).  

If it is an application where you will need to connect and disconnect often, I don't know how well the tubing will hold up to that.  If you use these connectors, I would leave the tubing a number of inches longer than required.  If the connection stops being water-tight due to disconnection/reconnection, snip off the worn end of the tubing to connect a fresh end.