Vertical Southworth Pump

by John

I will post progress in making this 6″ pump. I started making it 4-5 years ago, but put it aside when the horizontal version worked so well. See the previous post to see a video of the horizontal 2 cylinder pump filling the 6″ vertical boiler.

So, 2 workshop sessions later, and I have made the piston rod with steam and water pistons, and the studs which support the steam and water cylinders.

Doesn’t sound like much, for 2 whole sessions of 4-6 hours each, does it? But there it is.

First the studs.

They have to be identical lengths, with an M3 thread at each end. And a central narrower section with a curved end fillets. I decided to CNC the central section, with an Unbrako stud held in an ER collet (left) and a cap screw (right) in the tailstock.

The stud right with M3 threads at each end. At left, the narrowed section with curved fillets. The cap screw fitted nicely into tailstock and the Unbrako thread left into the headstock. The locknuts were required to prevent unscrewing during turning.
The aluminium insert worked nicely on the brass studs. 2000rpm, F50mm/min. 1985 Boxford TCL 125 CNC lathe.

Then the single piston rod, 4mm diameter, with the large steam piston, and small water piston.

The pistons were drilled and tapped, and turned to exact size on the piston rods with a sharp HSS cutter and 0.25mm depth of cut.

The grooves for the O rings were made with a parting tool. Depth determined from a “Machinerys Handbook” table, and the width 50% larger, as specified. Unfortunately I damaged the O rings during insertion into the cylinders. But I had some Viton spares, and filled the sharp edges of the cylinder bores before trying them, with better success.