Sunday, 26 February 2012

Yesterday I finished off the new test system, consisting of a test stand with pressure transducer and load cell, and fill cart with quick disconnect. Here are a few photos:

The system is reletevely simple but cuts down on the amount of peroxide handling and will reduce the risk considerably. I have discussed the system previously, but basically the manifold on the cart controll the 3 steps required to fill the stand tank. Firstly the vacuum valve is open (while the other 2 are closed) and the vacuum pump turned on drawing a vacuum in the system. Once at about -80KPa the pump is turned off and the valve shut. The fill valve is then opened sucking liquid into the sytem which makes its way into the tank. when there is no more liquid it sucks air which serves to suck the remaining liquid in the line into the tank. Once the syustem is at atmospheric pressure the fill valve is closed and the presure valve (the needle one) is opened filling it to the pressure set by the regulator. There is also a relief valve on test stand which will prevent overpresurisation .

I practised filling and dumping distilled water through the system quite a few times, and although I quite happy with its performance, there were a few issues. Firstly it is impossible to disconnect the quick disconnect over about 200PSI, which makes it useless. It makes sense that you cant disconnect it under pressure, but I thought I might be able to force it doesn't budge. I need to look for a better one, perhaps sometihng designed for hydraulics. Secondly I am concerned about the amount of liquid left in the run tank after it is completely emptied. I measured it by tanking the valve off the tank and found it to be 200ml. Afterwards I found out that nitrous tanks are designed to be run on an incline, whoever I am not sure how you know which way to angle it, as you cant see where the syphon is inside the tank. The next door neibour at the workshop suggested marking where it is when you put it in the tank and measuring the number of rotations. I suppose I can handle loosing 200ml each test but I would prefer not to. It wouldn't be so bad if I was running a few tests. Lastly I am not so happy with the time taken for smooth flow to start when opening the run solenoid after a fresh fill. There is quite a but of air and water which comes out in pulses and it takes about 3 seconds to settle down to smooth flow. There also must be a fairly large pressure drop across the solenoid and check valve because even at 800PSI the water coming out seems a bit gentle. I think the check valve might be restricting the flow which makes it look weak with water, but the flow rate of peroxide will be much less os it should be alright.

We also mounted the new test stand on a proper concrete slab which was already in the car park for the workshop. There are female anchors there now so we will be testing out there from now on. The small area we did previous tests at suited us before but all the grass and confined space make me nervous for tests with more concentrated peroxide. Hopefully I can give the new test stand a go this week sometime. I still haven't got the electronics going yet. After the its time to start working on a flight engine!

I have been giving some thought to switching to using lab view for controll and data logging. Ever since using robolab as a kid I have disliked graphical programming languages but after doing some research into just how powerful it is and how manny people use it I am nearly convinced. The icing on the cake was when I found out that you can use a arduino instead of their expensive DAQ's. I have always prefered the DIY aproach as I think you learn more that way, but you need to decide what you really want to accomplish and focus on that.

We also concentrated a batch of peroxide yesterday. I got a neibour at the workshop to make up a large stainless steel tank so I can concentrate more peroxide at a time(at the moment I am using a bowl), but unfortunately iy wasn't finished so we only have a few letires for this week. I have also invested in two really good respirators for use around the peroxide. I haven been able to find anything saying that the peroxide vapour is bad for you (in low concentrations) but the vapour has been concerning me and I thought it was a good precaution to take.

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