Archive for June, 2010


High Pressure Air Hose

We have taken delivery of a new 15m high pressure air hose. This hose is made by  Nylex and is called a Super ULTRAFLEX air/water hose. It has an internal diameter of 10mm, external of 16.6mm,  is kink resistant, has a working pressure of 20bar (290psi) and a burst pressure of 80bar (1160psi).

Nylex Super Ultraflex Air Hose

Working pressure 2Mps (290psi)

The connectors used are from the Nitto Hi-Cupla 200 series and are a once touch quick disconnect type. They are very solid and swivel freely.

Nitto HI-CUPLA 200 Male and Female quick disconnect

Fittings connected

We have a second hose being delivered shortly. These will be used for all hoses between the compressor and launcher.

These hoses we purchased for as little as $25 each with the fittings., which is excellent value considering one of the female fittings sells for around $30 each.

Posted by on June 26th, 2010 Comments Off

How to make a 2L Reinforced Bottle

We are trialing using 2L reinforced bottles to power the rocket car. Here is a brief overview of our process.

We start with 3 bottles

- 1 x 2L bottle
– 2 x 2.25L bottles (although 2L would probably suffice)

Start with 3 bottles

The 2 x 2.25L bottles are cut so that one will go over over the bottom of the 2L bottle and one will go over the top. There is an amount of overlap as well where the top and bottom sections overlap to be 3 layers thick.

Cut out sections + 2L Bottle

Close up of the 2 cut sections

The next step is to shrink slightly the 2L bottle. A big pot is required which can be filled to a depth of 3/4 of the bottle + have spare volume so no hot water splashes out when the bottle is inserted. Be careful of this, make sure the pot is big enough.

Bring the pot of water up to about 75 degrees, you can test this by quickly inserting the bottle 2 seconds or so and see if it shrinks slightly. Dont get the water too hot or the bottle will shrink to fast and deform. Once the water is the correct temperate insert the bottle for 2  seconds and check how much the bottle shrinks. Its better to do it a few times rather than have the bottle too long in the water and deform.

Submerge the bottle to past 1/2 way until the bottom section shrinks, then turn the bottle around and do the top as well. Be very careful with the top, you dont want the spout deforming.  What you should end up with is a bottle that is slightly smaller over the entire area (except the bottle throat and cap section).

The next step is to fit the other two sections. Start with the bottom section first, you will find that as its a close fit it wont slide on easily due to the air trapped in the bottom section.  There are a couple of ways around this. One is to use a wooden skewer or similar and push it between the two bottles so the air trapped in the cutout bottom section can get out, or you can drill a small hole in the base of the bottom cutout (not the 2L) bottle and air will get out this way. As we are going to fit a Robinson coupling anyway this hole wont weaken the second bottle.

You can put a bit of PL premium between the two bottoms of the bottles to hold them together but this is optional.

Once the bottom section is on, put the top section over the top of the 2L bottle, we slide the top section underneath the overlapping bottom section. TO do this its easier if you have a wooden skewer and run it around the bottle while you push the top section in, then just push until the top section is in place. You will find that once in place they really dont move. You can add a strapping of fibre reinforced tape if you wish.

Here is a pic of the bottle when finished. Its has already had a robinson coupling added to it.

Completed Reinforced Bottle - Robinson coupling added

If you look carefully you can see the slightly shrunken inner bottle.

Posted by on June 26th, 2010 1 Comment

Reinforced Bottle Testing – 2L@180psi

Work has commenced on reinforcing 2L bottles to increase thrust on the water rocket car.

The first attempt to make a 2L reinforced bottle uses
– 1 x 2L bottle (slightly shrunk)
– 2 x 2.25L bottles

The 2L and 2.25L bottles have the same diameter, the 2.25L is slightly taller though. The  2L bottle was slightly shrunk in hot water to reduce its diameter so the 2.25L would slide over the top of it. One of the 2.25L bottles had the top 1/3 cut off. The other 2.25L bottle had the bottom 1/3 and the the bottle throat section removed.

Then 2.25L bottle without the top was then slid over the bottom section of the 2L carefully lining up the claws at the base. The second 2.25L we had to cut a bit more of the throat away to fit it over the 2L bottle throat flange (for want of a better word). The 2 x 2.25L bottles overlap a little in the middle. It was then just taped this down with fibre reinforced tape to hold all the sections in place

Standard 2L (left) and 2L reinforced (right) bottles.

Reinforced bottle on its side

The bottle was then ready to be hydrostatically tested. A few modifications for safety were made (due to the higher test pressures) to the air hose to hold the hose and connectors in place in case the air hose exploded. Each separate section of hose was cable tied to a brick

Pump to airhose connection hold-down

Airhose to abort valve hold-down

The bottle itself was placed in a milk crate with a 20L water container (full) placed on top to hold it down in case the bottle exploded as a safety cage.

Bottle Testing Cage

There is a valve in the female gardena connector that will close off the airhose if it has pressure in the line but no bottle on the open end. This makes it easy to test the air hose itself for leaks. Safety glasses were put on and the air hose (no bottle) was pressure tested up to 180psi with no leaks. This is the pressure we decided we wont test past until the airhose, connectors and PVC abort valve are replaced with stronger components.

Safety glasses were put on again and the reinforced bottle was filled with water and pressurized to 180psi. There were a few drips from the nozzle (only hand tightened) but the bottle held the pressure fine.

Reinforced bottle hydrostatic test to 180psi

The next version of the reinforced bottle we will grind of the flange of the 2L so that the throat section is more reinforced and use PL Premium to glue the bottle sections together.

The test was very successful, this is the highest pressure we have pressurized a bottle to. It seemed the reinforced bottle could take a lot more pressure before bursting as there was minimal (visually) stretching of the bottle. We are working on replacing the components for the air delivery and will try a further hydrostatic test once these are in place.

Posted by on June 2nd, 2010 Comments Off