19 June 2013

The Perfect Pump

It was the best of springs, it was the worst of springs...

'Worst' because the weather in New York has been awful: cold with rain that varied in intensity from a miserable drizzle, to tropical storm Andrea. When I rowed around the harbor this morning, the effect of the weather was evident in all the bare booms -- nearly half the boats didn't have their sails on yet.

'Best', because business has been good and I've been busy building a new iPhone app for a corporate client. I never complain about too much business these days, even if it interferes with sailing and building and finishing my book.

Also 'best' because Helena and I spent a week in coastal Maine, seeing all the beautiful wooden boats from Boothbay Harbor to Camden to Brooklin and the Wooden Boat School.

Me in Wooden Boat's workshop

With all the rain, I've been bailing Cabin Boy more than I've been rowing him. That meant scooping out gallons of water with a cut-off plastic bleach bottle. I've always used that sort of bailer because... well, because everyone else did. And let's face it, what's more appropriate for bailing out a white plastic dinghy than half a white plastic bottle?

But after scooping out a hundred gallons or so over the course of a particularly bad week, I got to thinking that there must be a better way... there must be!

While I was in Maine, I bought a copy of Hervey Garrett Smith's classic "The Marlinspike Sailor". This book was printed in 1956, three years after I was born, and it's a collection of useful and interesting things to make, like rope mats, sea chests, canvas buckets, and... and... plans for an old-fashioned wooden dingy pump.

Actually, the word 'plans' is an exaggeration. Like lots of olde time writers, Hervey assumed his readers were more-than-competent woodworkers who didn't need no stinkin' plans. The book supplies a few drawings of the two valves needed and one of the finished pump, along with some inspirational words, such as these, telling of the first time he borrowed an old-fashioned wooden pump:

The pump raised an enormous stream of water, and after a lifetime familiarity with all sorts of metal pumps I was struck by its quietness. There was none of the screeching, scraping, rusty clatter I had always known, and for the first time in my life I enjoyed pumping.
But a few scant drawings and a few inspirational words were all I needed to start drawing the design for my own pump -- the perfect pump for getting gallons of cold rain out of poor old Cabin Boy. I started working on the it as soon as I got home.

So how does a wooden pump work? Hervey doesn't explain, presumably because everyone in his day knew how they worked. I had no idea, but it didn't take long to figure it out. These are simple machines, whose history is well known. They were invented by a Greek (of course) named Ctesibius -- known as the father of pneumatics -- sometime around 250 B.C.

Simple lift pump
Briefly, all lift pumps have two valves, called the lower and upper valves. On the upstroke of the plunger, the lower valve opens, and the upper valve closes, and the low air pressure produced in the barrel sucks water through the lower valve, into the barrel below the upper valve.

On the downstroke, the lower valve closes, the upper one opens, and water is forced through the upper valve into the barrel above the valve.

On the next upstroke, the water above the upper valve is forced out of the spout, while the barrel below the upper valve again fills with water.

Its all much simpler than it sounds.

I again called on my scrap pile for the needed materials. I had a few old red cedar planks that had once been the floor of a patio deck, I think. The were weathered and too thick for the pump, but running them through the planer took care of both problems.

Machining lumber from old cedar decking
You can see that they cleaned up nicely. Plenty of knots, but none of them were rotten or ready to pop out. This is important, because the barrel of the pump needs to be air-tight when done.

3/4" planks milled down to 1/2" 
To help make the barrel air-tight, I cut rabbets into two of the sides. I should know the name of this joint, but I don't. How embarrassing. If you do, please enlighten me!

Rabbeting joint
Here are the four sides of the barrel cut out and laid side-by-side. You can see the grooves for the side joints, and for the lower valve.

Pump sides, roughly jointed

Here is the simple lower valve. It's basically a check valve, consisting of a wooden block with a hole cut in it, and a rubber flap tacked on top.

Bottom of pump with lower valve
The lower valve allows water to flow in from underneath on the upstroke, but slams shut on the downstroke.

I used copper nails to tack down the rubber, so hopefully they won't rust away any time soon.

Lower valve open
And here is the upper valve, attached directly to the plunger. The 3"x3" square of rubber matches the inside dimensions of the barrel. It is tacked to the top of a 2"x2" square of wood. Both are bored through to accept the plunger, which is a 3/4" oak dowel (the only thing I actually bought for this project.)

Upper valve attached directly to plunger
The rubber is tacked on with more copper nails. Notice the nails are quite close to the plunger.

The rubber bends upwards, opening the upper valve on the downstroke, but lies flat on the square block, closing the valve on the upstroke.

Those are the moving parts.

View of upper valve showing placement of copper nails
Every pump needs a spout. I decided to build mine as a glued assembly that could be screwed into the barrel as a unit. Since I wanted to be able to disassemble the pump in case it needed repair in the future, this was the only part I glued together.

Spout assembly, glued

I recently treated myself to a set of Fuller counter-sinks, so I wanted to use bronze screws to hold the pump together. After drilling and counter-sinking all the holes, I dry assembled the pump to make sure everything fit properly. It already looked pretty darn good, but would it work?!?!

Dry assembled for fit
To make the barrel air-tight, I intended to bed the joints with good old Dolphinite. But you don't want to apply Dolphinite to bare wood because the wood will leach out all the oil, causing the seams to dry and crack (ask me how I know that!) So I had to seal the wood with something like varnish.

Of course, once the varnish can was open, there was no stopping me, so testing had to wait a few days while I gave the pump pieces several coats of exterior varnish.

Once that was done, I bedded and screwed the whole thing together. Naturally, it was a sunny, dry day (I must have scared the rain away), perfect for a photo shoot and test on the front lawn in front of Helena's garden.

Varnished and screwed and bedded together.
Notice the short feet. These are not decorative -- the gaps are needed to let the water flow freely under the pump.

Bottom detail showing water inlets
I forgot to mention the top of the pump. This is just a slightly over-sized square of wood, just big enough to make a jaunty cap. I didn't bed this down for the photo shoot and test, because I wasn't sure if the pump would work. I thought I might have to make some adjustments to the valves, so made the cap easy to take off.

Detail showing top and spout
With the photo shoot complete, it was time to try it out. Sometimes words don't do a thing justice. Click on the video below to watch the thrilling demo...

Video demo - click to watch

So! No adjustments required. I bed down the top cap to keep the water from squirting out, and my olde-time wooden pump was done.

Now if it would only rain...

Next Episode: It's about time


  1. Perfect! .... and a lot saltier than the plastic pumps one can get for kayaks, canoes and other small boats.

    VERY NICELY done John!

    BTW, the joint is a "lap" joint. One piece of wood over"laps" the other.


    1. I knew should have known that name.

      Thanks Bob. A compliment from you means a lot. It's a great little project for anyone with a dingy.

  2. I am a faithful follower of your posts - soon I think they should be gathered in a book! Which I would buy! Not only do you write about so many interesting subjects - but you write very well.

    The post on the pump has got me motivated - have some old red cedar, etc. Really want to make that pump. It will help me get rid of the bleach bottle.

    Best to you-
    Ted Ford

    Rochester, NY
    Reedville, VA

    1. Excellent! I forgot to mention how fast it pumps. The nine square inch barrel means it pumps at least 10 times faster than those skinny hand pumps at the marine store. Almost a gallon a stroke when you get going.

  3. John - it is just BEAUTIFUL - a sculpture - but there is a really cheap plastic one that works very well and fits under a seat! ox guess who?

  4. Well done,Looks & works great.

  5. Well done,looks & works great :)

    1. Thanks. If nothing else, it scared the rain away. Naturally it's been clear and hot since I finished it ;-)

  6. A thing of beauty is a joy forever. Well done!

    1. I agree. Cheap and easy are highly overrated, in my opinion.

  7. Makes you almost wish for some excess water .... beautifully done John.

  8. The prosaic pump becomes art... Beautifully Done!

  9. Thanks! I have a new-found love of red cedar. It's a nice wood to work with, and looks great when varnished, I think.


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