Pump 2

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Home made bilge pump

Apparently, making one's own bilge pump is part of the kayaker's folclore. Here's what I invented...

Though they may be mechanically more resistant, I wanted to avoid the use of non-return valves:

The valves would represent a (too) large part of the total budget!

There's still quite a bit of experimentation to be done, but the neoprene valves proved themselves quite efficient. And neoprene is one of those elements that are frequently available to kayakers. And there are other sources too - think eg. mouse pads) Other material could be used, such as inner tubes (car).

Complete diagram of the construction. The color table refers to each part in the drawing. Note that the longer tubes are the drainage type (thinner walls). Don't try the normal (water supply) pipes - the wall is too thick and you'll have difficulties fitting the inner valve.

Having used the pump for a while now (have seen the use), I noticed that rarely it's completely extended. That means that the full weight of the water is lifted needlessly.

I made a slightly shorter version (5cm less) by shortening both the 50mm and the 40mm tubes (to 440 and 490mm respectively). This seems slightly more practical. Experiment!

I've been asked why I didn't simply use a 50 mm cap at the end of the outer tube (instead of the reduction, then a 40 mm cap).

Though that is possible, there are two reasons I didn't do that:

- The reduction acts as a stop for the inner tube movement, and avoids hitting the lower valve when pumping. If you decide to use a 50 mm cap, shorten the inner tube so as that it can't reach the lower valve.

- I wanted both valves to be of the same size, in case I wanted to take along a spare (and not two).

The valves (clear green in the composite drawing) are probably the only complicated thing to build. Use a 8 or 9 mm drill to make the 6 holes in the two caps. Try to distribute them evenly.
Mind drilling PVC can be treacherous. The drill will go through very suddenly and will try to pull the piece from your hand. Clean the borders of the holes after drilling. If you want to optimize the holes, use a triangular file to change the form.

The valve itself, is a neoprene disc which fits in each cap, but not a press-fit. If the disc is too large, pressfitting will compress the neoprene and it will stay open.

First tests showed that the violence of the water flow tended to dislodge the discs. I decided to contact glue a small ring (yellow in the drawing) to the neoprene. This way they are still easily removable, but stay put.

The three diagonal cuts are made with a sharp knife (cutter). It's easier to cut neoprene if you first cover it with masking tape. You can then draw the lines on the tape, and the tape will keep the neoprene from deforming.

Construction pictures

A nice trick to mark a tube correctly is to wrap a piece of paper around it. When the borders coincide, use the border as a ruler to mark the cut.

The top cap of the 50 mm pipe must be drilled to fit the 40 mm inner pipe, but not too large, so the inner tube can't escape. Few of us have 41 mm drills, so I just drilled using 3 or 4 mm, and rounded the hole with a file.

The 40 mm elbow was way to loose to just glue it on directly, so I wrapped a strip of PVC in between (mind - not polyethilene, which cannot be glued with the same product).

Done. The couple of mm of the PVC strip that showed were easily removed with the cutter.

Before glueing the 50 to 40 mm reduction (brown in the composite) to the pipe, I used it as a compas to mark the valve discs,

From the same neoprene, I cut a 15 to 20 mm wide strip, long enough to glue around the inner pipe. In fact, I cut it somewhat longer to make a 45 degree scarped union.

Don't forget to slip the 50 mm cap on the inner pipe before glueing on the neoprene strip!

Glueing together the strip ends, and we obtain this ring.

Then we glue it on the inner pipe. (all with contact glue)

Glued to the pipe, and with the valve in place. I did not the valve cap to the inner pipe, to be able to do cleaning if necessary (the outer valve isn't glued either)

The two valves - somewhat dirty from intensive use last saturday. Note the cuts and the rings (see composite - orange). The valves tend to stay somewhat open, but that didn't result very important. Even air flow closes them.

Here the complete pump, disassembled for cleaing. Note the float ring around the outer pipe - important! I couldn't find that thermal isolation material for 50 mm pipes, but the 40 mm one stretches fine.
Note that this project is not sponsored by the brand on the pipe!

And the complete, assembled pump. Each action pumps somewhat over 0.8 litres - a complete bucket is less than 10 movements - half a minute!


(c) John Coppens ON6JC/LW3HAZ mail