Posts Tagged ‘hydrostatic’

 

Triple Bottle Reinforced Stack – Hydrostatic Test

We have had our triple bottle stack of reinforced bottles ready for a while to hydrostatic test and finally got around to it this week.

Each bottle in the triple stack is reinforced using this method.  We had previously hydrostatic tested individual reinforced bottles to 180psi but not a stack of them. The 3 bottles in the stack are held together using robinson couplings.

Hydrostatic Test of reinforced stack

Our goal was to hydro test to 180psi. The bottles were filled with water, safety glasses were put on and being well back we pumped up to 180psi. This was a pic we took which says 177psi but we did put a few more psi in it to be sure we got to the 180psi. We left it for about 30 seconds before releasing the pressure with the abort valve.

177psi or 12bar

We didnt see any leaks which was good, so it was a successful test.

The triple stack has been fitted to the water rocket car ready for a test run. Based on the success of the last launch day we will probably need to fit a parachute to the car to slow it down, so we will turn our attention to that next.

Posted by on August 20th, 2010 Comments Off

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

Water Rocket Car MkX – Hydrostatic Mishaps

Its always a good idea to hydrostatic test a new setup before a launch day. Considering we hadnt launched these bottles for a few months, it was an especially a good idea to test them first.

The bottles were filled totally with water and pressurized .. no leaks ….  good .. right up to 120psi then … the last bottle ruptured. This was a rip across the middle of the bottle. Pic below

Ruptured Bottle - ripped

Whilst this was not totally unexpected, it was a bit disappointing but easily repaired after a trip to the supermarket for another 2.25L bottle. Also some of the water went into the electronics section so it was left in the sun to dry while we went to the shops.

The new bottle was cleaned and connected into the rocket car and a 40psi air test to check for leaks around the bottle cap. No leaks so the bottles were filled with water to hydrostatic test again.

Again no leaks up to 120psi .. then .. the last bottle (the brand new one) ruptured …

New bottle ruptured

This time spilling about 3L of water directly into the electronic bay .. hmmm .. not good :(
A close look at the ruptured bottle showed it let go right at the thick end of the bottle. Click pic for higher resolution photo

New Bottle ruptured - close up

This is the thickest part of the bottle, so it was either a manufacturing flaw in the bottle or it pressed up against something to make a weak point and ruptured there.

It could have been either that caused the rupture, but when looking closer at the setup, its possible the new bottle alignment guides we installed could have caused this. The way they were setup meant that when the bottles expanded under pressure all three could only moved towards the front of the car. So its possible that all three expanded causing the bottle that ruptured to press agaisnt the back of the servo and possibly cause a pressure spot.

We repositioned and realigned the bottle guides to allow the bottles to expand in both directions and slid all three bottles back in the chassis about another 10mm. This should now allow the bottles to expand without hitting the servo.

Another downside of dumping 3L + of water into the electronics section is that the r/c wouldn’t  work. The electronics bay was pulled apart and dried and all connections checked with a multimeter. It appeared the on/off switch enclosure was still very wet and was shorting, so it was replaced. Another was soldered in and remounted. It is more convenient to access now.

New on/off switch

By the time the electronics was put back together and an unpowered test of the steering done, it was too late to do another hydrostatic test. We will do one tomorrow and hopefully get to do a launch.

Posted by on April 11th, 2010 2 Comments

Water Rocket Car Hydrostatic Test

In order to test the bottles and the connections we setup a hydrostatic test to see what pressure the bottles would take and if there were any leaks. A hydrostatic test is the safest way to test bottles as the water is not compressible so there is not much stored energy in the bottle at high pressures.

The hydrostatic setup is basically our launch setup with the abort valve pipe going into a bucket, or in the case a container to hold the overflowing water. In our setup once the desired pressure is reached and the test complete, the abort valve is turned and the water is sent out to the bucket for collection. The wrocket car never leaves the launcher

Hydrostatic Test Setup

Hydrostatic Test Setup

The wrocket bottles are full totally with water.

Wrocket Car Full of Water

Wrocket Car Full of Water

We pressurized to 60psi and held with no leaks. Approaching 120psi there was a leak from the robinson coupling and water was escaping. IT was more than a few drops so we will take the bottles apart and fix it. We are currently only using a washer at one end, so we will add another at the other end. We wil lalso use a bi tof locktite on one of the nuts to hold it in place on the threaded rod.

Posted by on July 30th, 2009 Comments Off