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Quite a few recent posts have been about pumps and closed (non vented tanks). Sheerline have employed this method in their sub kits, and my article in SC# edition 52 describes the use of these pumps within a WTC.
In short the ballast system does work very well. The air compressed inside the tank and held there by a valve or servo arm with a pinched roller (how I rig up the system) works really well. For diving, the servo arm depresses a micro switch to pump in water and the pinch is released to allow this. Surfacing, the servo swings the opposite way, pinch is again released and micro switch remains off.
The pump I used only is good enough to pump water to a point where the ballast tank is 60% full. At this point the centrifugal pump does still spin, but it cannot pump anymore water in the ballast tank, as the air inside is compressed to a point where the pump cannot overcome it (in my case its only 20 PSI). This is a very good safety system.
My sea trials of my new Thor Alfa suffered at the hands of some electronic problems. A loose wire in some terminal block arched up and blew the fuse going from the battery to the speed control. The speed control through a BEC supplies the Rx with power. Thus, I had no control over servos etc. When did this happen? - Right when I commanded a dive. That is when I commanded the servo to depress the microswitch to the pump. So the pump still had power, and down she went, all the way to 60% full which is about 6% past neutral! Next stop the bottom.
Luckily the sea trial was in an Olympic pool, but it was the middle of winter and rather than go for a swim we pulled her out after about 10 minutes using some pool equipment. The pump was still running. The WTC DID not leak.
The moral of the story - 1) When my ballast tank is 60% full, I should be not trimmed to negative (reduce the ballast tank size) 2)-If I had used a geared pump, the Alfa would have turned into Depth Charge. So when using any pump with a sealed non vented ballast tank make sure that should the pump keep running that you don't have an explosive situation on your hands. A friend here had a tank blow apart his WTC in a test tank for this very reason.
The pump I used, with the flaw (it cannot pump beyond 60%) is avaliabe through the web at Dick Smith Electronics at www.dse.com.au
The part number is p8907 and sells for $14.94 Australian.
The pump does require 12V to work effectively and draws 2 Amps when at the 60% stall mark.
In short the ballast system does work very well. The air compressed inside the tank and held there by a valve or servo arm with a pinched roller (how I rig up the system) works really well. For diving, the servo arm depresses a micro switch to pump in water and the pinch is released to allow this. Surfacing, the servo swings the opposite way, pinch is again released and micro switch remains off.
The pump I used only is good enough to pump water to a point where the ballast tank is 60% full. At this point the centrifugal pump does still spin, but it cannot pump anymore water in the ballast tank, as the air inside is compressed to a point where the pump cannot overcome it (in my case its only 20 PSI). This is a very good safety system.
My sea trials of my new Thor Alfa suffered at the hands of some electronic problems. A loose wire in some terminal block arched up and blew the fuse going from the battery to the speed control. The speed control through a BEC supplies the Rx with power. Thus, I had no control over servos etc. When did this happen? - Right when I commanded a dive. That is when I commanded the servo to depress the microswitch to the pump. So the pump still had power, and down she went, all the way to 60% full which is about 6% past neutral! Next stop the bottom.
Luckily the sea trial was in an Olympic pool, but it was the middle of winter and rather than go for a swim we pulled her out after about 10 minutes using some pool equipment. The pump was still running. The WTC DID not leak.
The moral of the story - 1) When my ballast tank is 60% full, I should be not trimmed to negative (reduce the ballast tank size) 2)-If I had used a geared pump, the Alfa would have turned into Depth Charge. So when using any pump with a sealed non vented ballast tank make sure that should the pump keep running that you don't have an explosive situation on your hands. A friend here had a tank blow apart his WTC in a test tank for this very reason.
The pump I used, with the flaw (it cannot pump beyond 60%) is avaliabe through the web at Dick Smith Electronics at www.dse.com.au
The part number is p8907 and sells for $14.94 Australian.
The pump does require 12V to work effectively and draws 2 Amps when at the 60% stall mark.