by Caevan Sachinwalla

For a number of years now I have been working off and on, on a pump based around a motor driven hand bilge pump, for tank circulation or as the main pump.

I first came across a description of the device in "Dynamic Aquaria, Building Living Ecosystems" 2nd Edition by Adey and Loveland. The pumps were used in a reef display at the Smithsonian Institute.

It took me a while firstly to find a suitable motor which could deliver 30 rpm and as well someone who could construct the bits required, to actuate the hand operated bilge pump. The first incarnation used a $40 diaphragm bilge pump bought from a boating supply shop and a 15W motor. There are picture of the pump here. The pump was used as the main pump on my old 3ft tank, and worked well for about 5 weeks until the rubber diaphragm split and started to leak. After ten weeks of operation it soon became evident that the gear box on the 15W motor was not upto the task. I ended up changeing to a larger 60W motor with a more robust gearbox. I also changed to a different brand of diaphragm pump to see if I could get a longer life out of the diaphragm.

By then I had changed to my current tank and intended to use the pump for added circulation. I tried using the pump a couple of times, each time modifying the stroke of the device to achieve a longer life span from the pump. Nothing really worked.

Eventually the guy doing all the building for me came up with the idea of replacing the diaphragm with a piston, effectively converting it to a piston pump. The plastic used was Delrin. The important thing is the material has to be hydroscopic, some Nylon materials wil absorb water.

These images are of the 2nd last incarnation of the pump.

Front view of the piston pump / surge device.

Side view of the piston pump / surge device.

Top view of the piston pump / surge device.

This unit was run continuously for 3 months on a test tank. After this time the unit was examined, and we found the piston was not quite to the spec of the seals being used, so it was rebuilt.

I am now running this verion on my tank. The outlet and inlet are place on diagonally opposite sides of the tank. The effect is a wave like surge through the tank, causing the coral polyps to sway back and forth to the cycle of the pump.

This has been a project that has gone on for about 4 years, though at one stage a year went past with it just sitting on the shelf somewhere. At times I thought why bother, though in the end I just wanted to see it work. I was also very fortunate to find someone who had the ability to build the bits required and not charge much at all for his work.

By the way, I have only posted this here for general interest. There are cheaper alternatives available, though I would have to say mine is the only one that can claim a fairly sizeable organism can pass through the pump unharmed. The reason I know this is when I was first testing the piston version of the pump, I used two lengths of 25mm flexible hose that had been lying in the garden. I connected everything up and had the inlet and outlet hose in a large bucket of water. I turned on the pump and after a few strokes out popped a fairly large cricket. Before I could rescue him, he got sucked back in again, only to pop out a few seconds later having travelled through the pump. I rescued him the second time and he was fine.

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