Posts Tagged ‘nozzle’


Water Rocket Mist Attachment – Static Test

An interesting development we saw on from Jelo and Thunderrockets was a device called a mist rocket. This is an alternate method of mixing the air and water into the exhaust plume which produces a single air/water thrust and not the normal water then air pulse of a standard water rocket. Also when flown vertically there was a distinctive jet sound.

We though we would give this a try for our water rocket car.

The design uses a PVC pipe to funnel water from the second bottle to the nozzle. The air pressure in the top and bottle bottles are equal. The air in the top bottle pushes the water down the pipe and the air pressure in the bottom bottle forces air through two (2) small holes to mix air with the water just prior to escaping from the nozzle.

This is how we built it and tested it.

First we purchased some 20mm electrical conduit and a conduit cap. The 20mm conduit just fits in the 22mm bottle throat. A 10mm hole is drilled in the centre of the conduit cap and a 10mm internal diameter (ID) nut from our robinson couplings is carefully glued (with 24hr araldite) into the base of the cap, making sure no glue gets on the threads.

20mm Conduit Cap with 10mm ID nut - no glue yet

The conduit cap is then glued (24hr araldite again) to a section of 20mm conduit (longer than the bottle at this stage) and left for 2-3 days to set properly. Once this is set, this section should screw easily onto a standard 10mm robinson coupling thread.

Conduit connected to threaded rod (robinson coupling rod)

The next step is to cut the conduit so that it fits just inside the nozzle cap. The section is screwed onto the robinson coupling between two bottles then marked, unscrewed again and cut to size. The conduit shouldn’t protrude past the bottle lip as this will cause the bottle lip not to seat properly against the rubber washer in the nozzle and the bottle wont hold pressure.

Conduit cut to size of bottle

The conduit section then needs 2 holes drilled near the base of the rod. we used 6mm holes, these are to let air from the bottom bottle mix with water from the top, also if any water does get in the bottom bottle it allows it to escape.

Conduit section with cap and 2 holes drilled near the base

The completed conduit (now referred to as mist attachment) is then inserted into the bottle and screwed onto the robinson coupling. Note that about 10mm of thread was needed on the threaded rod to catch on the nut threads.

Robinson coupling ready for mist attachment

Mist attachment connected to robinson coupling

The the nozzle is screwed into place and its ready to test / launch. Here is the pic ready to test

2 Bottles with robinson coupling and mist attachment - Ready to test

The handy thing with this attachment is that it can be added and removed quite easily for test or launch.

Mist Attachment Test

The test we conducted was a vertical static test with 1L of water (no foam) and 100psi. The bottles used are 2.25L bottles. We were interested to see the following

– If we could reproduce the jet sound that thunderrockets produced on launch
– Examine the exhaust plume to see if it generate a good air / water mix
– Examine if there was any distinct air pulse after the water was ejected from the bottles

We did find that filling the top bottle a little more challenging to ensure water didn’t get in the bottom bottle. We used a small section of hose connected to a funnel to get the water past the 2 holes in the mist attachment, then gently pumped the top bottle.  Here is a video of the test


– We didn’t get the jet sound, even after 2 separate static tests – its a possibility that the rocket needs to be flying through the air to generate the sound, or possibly the holes were too big.
– The exhaust plume definitely had a good mix of water and air and produced a spray similar to a foam launch
– There was no distinct air pulse after the water was ejected
– An interesting observation was that there was minimal (a small amount) splash back in the bottle at the end of the thrust phase.

We will try this test again in a horizontal configuration to suit our water rocket car

Posted by on July 27th, 2010 5 Comments

More Small Diameter Nozzle Testing

We finished off some more small diameter nozzle testing this week. With some interesting results.All Test were performed with a 1.5L bottle with 600ml of water

We will be able to use results to steadily increase the instantaneous thrust on the water rocket car.

Picture Diameter (mm) Pressure (psi) Time to empty bottle Area of Nozzle

Gardena 9mm Joiner

Gardena 9mm

9 140 0.433 63
9 80 0.533 63

8mm Nozzle Insert

8mm Nozzle Insert

8 140 0.533 50.2
8 80 0.734 50.2

7mm Nozzle Insert

7mm Nozzle Insert

7 140 0.467 38.4
7 80 1.000 38.4

6mm Nozzle Insert

6mm Nozzle Insert

6 140 1.000 28

5 x 2.5mm Nozzle Insert

5 x 2.5mm Nozzle Insert

5 x 2.5 (star) 140 1.066 24.55
6 80 1.243 28
5 x 2.5 (star) 80 1.400 24.55

These nozzle inserts may be of use to vertical water rockets as well

Here is a short video of the 5 star patter test at 140psi. All the others were a little boring so I wont bother posting them, the results are above

Posted by on September 18th, 2009 Comments Off

Small Diameter Nozzle Testing

Todays testing was to ensure the smaller diameter discs would not crack or break when high pressure water passed through them. We setup a vertical test stand with a 1.5L bottle and a standard water volume of 600ml.

We first tested the bottle with the 6mm diameter disc inside the nozzle at both 80psi and 140psi
The 6mm disc was then removed and tested again at 80psi and 140psi.

The disc survived the testing without any signs of cracking or stretching

It was obvious even in real time that the 6mm diameter disc slowed the water coming out quite significantly. So we slowed the videos down in VirtualDub (video processing software) and recorded the exact time it took to empty the water from the bottles. The results were

Nozzle Diameter  (mm) Pressure  (psi) Time to Empty Bottle (seconds)
6 80 1.243
6 140 1.000
9 80 0.533
9 140 0.433

Here is a video of the testing

The 6mm nozzle disc has a 44 percent smaller area than the 9mm nozzle.The water took 2.3 times longer to be pushed out of the bottle or 43% slower than the 9mm at the same pressures.

Looks like the size of the nozzle discs we make will slow the water down in proportion to the surface area of the hole. This will provide a longer thrust phase with lower magnitude thrust which is what we need to control our thrust steering problem.

Posted by on September 5th, 2009 Comments Off

Small Diameter + Longer Thread Nozzle

After some previous failures at making smaller diameter nozzles, our new solution involved inserting a disc with a small diameter hole between the bottle and the gasket inside the bottle cap.

Unfortunately we were having trouble with leaks when we had a 1.5mm – 2mm disc inserted in the cap. The cap just didn’t have enough thread to make a good seal.

This week George from Air Command posted a video (definitely worth watching) showing how to use different types of bottle caps as nozzles to increase the length of the thread dramatically. This is just what we needed :)

We scoured the house for empty bottles / pump packs and found one that had the same thread as a drink bottle. We decided to commandeer it for testing … luckily the normal drink bottle top fitted the pump pack so no need to waste the contents of the pump pack :)

Pump Pack Nozzle and Normal bottle cap

Pump Pack Nozzle and Normal bottle cap

Its obvious how much longer the thread is on the pump pack .. The pump mechanism was disassembled. Use a pair of long nose pliers to remove the white disk from inside the cap, then bend some of the tabs on the pump section and it will come apart quite easily. It already has a hole ready for the gardena nozzle.

Pump Pack Dissasembled

Pump Pack Disassembled

Here is  a close up of the difference in size of the nozzle and the normal bottle cap

Normal Bottle Cap + Longer thread Bottle Cap

Normal Bottle Cap + Longer thread Bottle Cap

Top View Comparison

Top View Comparison

You can see on the last pic there was a small 1mm ridge that was filed off to make the top of the green cap smooth. This will allow a nice mating with the Gardena launch adapter. The existing hole was just about perfect, we probably enlarged it 0.5mm and the gardena snaped in perfectly.

Next step is to make the reduced diameter disc. Scouring the $2 shop we found some cheap signs that stick to the back of cars. They are 1mm thick plastic which is slightly flexible. A 24mm disc was drawn on one and cut out. A 6mm hole (can vary based on what size reduced nozzle you want to make) was drilled in the centre and cleaned up.

Cap + Gardena 9mm nozzle + gasket + 6mm disc

Cap + Gardena 9mm nozzle + gasket + 6mm disc

We found that the disc needed to be inserted between the bottle and the gasket (see below), other way around caused leaks.

Reduced diameter disc fitted

Reduced diameter disc fitted

Here it is fitted on the bottle

Nozzle Fitted to the Bottle

Nozzle Fitted to the Bottle

Fitted ready to test

Fitted ready to test

The longer thread nozzle clips properly into the launcher and doesnt pop out as George advised us to look out for which is good. See below

We tested up to 80psi with air only on a 1.5L bottle with no leaks. Next test will be with water to see how the disc stands up to the pressure of the water rushing out.

Posted by on September 3rd, 2009 Comments Off