A Tale of Three Pumps
Rich concludes his experiments with water feed pumps started as a means to overcome a crowded cab on his loco build project, this month returning from vertical to horizontal.
Over the last couple of months I have described my efforts to free up more space in the cab of my locomotive build project by designing new vertical hand water pumps – the loco design having precluded my mounting a horizontal pump out of sight either under the running board or in the water tank.
The very first little pump I made way back in 2009 uses what I will call mushroom valves instead of balls. It works well and has been in regular use to test boilers, superheaters and safety valves and the like without fault since then. Using balls for the valves relies on gravity to a certain extent so they must be used vertically. I wondered if the mushroom-type valve could be used horizontally? Only one way to find out, let’s have a go.
Construction
Starting with the body, a piece of 18mm round brass 2½ inches long, drill right through this time 15⁄32inch, then ream ½-inch. Now tap or screw cut it 9⁄16-inch x 32 TPI to a depth of ⅜-inch (Photo 1). That’s the body done.
The piston is machined as per the drawing at right and follows the same method of construction as the Mk2 pump, except that it is 2½ inches in length (Photo 2). The operating lever and the links are also similar to the
“Using balls
for the valves relies on gravity to a certain extent so they must be used vertically...”
Mk2 and made to the dimensions in the drawing.
The pump mounting I made from a piece of ¼-inch thick brass. Four 3.1mm holes are drilled in the corners for bolting down. Two holes are drilled and tapped M3 for mounting the link bracket, and two holes are drilled and tapped M3 into the sides to take grub screws which secure the pump to the mounting (Photo 3).
The link bracket itself is made from a short piece of ¾-inch x ¼-inch brass bar machined and drilled as per the drawing.
Moving onto the valves, the inlet
valve starts life as a piece of 5/8-inch hex brass 1.18 inches long. Drill right through 13/64-inch. There is no need to ream this time as the O-ring will sit on a flat face. With a 3/8-inch end mill machine down the hole to a depth of
3/4-inch (Photo 4), aiming for a nice flat bottom (Photo 5).
Turn down to 9/16-inch for 280 thou and thread 9/16-inch x 32 TPI. Reverse in the chuck and turn down to 3/8-inch for 1/4-inch and thread
3/8-inch x 32 TPI. Machine a taper seat with a centre drill.
Two holes must be drilled and tapped into the sides of the valve body.
One will be at 2.5mm for a pin to limit the valve lift, and the other on the opposite side at 5/16-inch x 32 TPI for the outlet valve connection (Photo 6). I have included in the drawing another view of the valve body showing the position of the tapped holes.
Mushroom valves
The inlet mushroom valve is made from 5/16-inch round brass as per the drawing. The stem is machined to 175 thou so that it is a loose-ish fit in the
13/64-inch hole in the valve body which will then allow water to flow past it (Photo 7).
The outlet valve, which will be horizontal, is made from 5/8-inch hex brass an inch and 40 thou in length. Drill right through 5mm then with a
3/8-inch end mill open out to a depth of 5/8-inch aiming for a good clean seat. Tap or screw-cut 7/16-inch x 32 TPI to a depth of 1/4-inch. Reverse in the chuck and turn down to 3/8-inch for 270 thou then turn down to 5/16-inch for 145 thou and thread 5/16-inch x 32 TPI. Note the short boss (Photo 8).
The connector is also 5/8-inch hex brass and is drilled through 11/64-inch.
With a 9/32-inch end mill machine a
recess 130 thou deep, the spring sits in this (Photo 9).
Turn down to 7⁄16-inch for 200 thou and thread 7⁄16-inch x 32 TPI. Reverse in the chuck and turn down to 5⁄16-inch for ¼-inch, thread
5⁄16-inch x 32 TPI and create a taper seat with a centre drill.
The outlet mushroom valve is similar to the inlet mushroom valve but differs slightly in size. The spring I wound from some 24 gauge bronze wire to the size in the drawing. I must confess I couldn’t figure out how to draw a spring so I cheated/adopted a cut, copy and paste method. The spring is very light and simply holds the mushroom valve, which is horizontal, in place.
The two O-rings I used came from the assortment box (Photo 10) and are
5⁄16-inch in diameter with a section of 1⁄16-inch.
Photo 11 is a close up of the mushroom valve in place with its lift limit screw. Assembly is straightforward using thread seal on all the threads.
The heading shot shows the Mk3 pump assembled and ready for a test. It performed faultlessly first time and easily achieved a pressure of 160psi. You can view two short videos of the pump in action at https://youtu.be/VVMUU0BV8GM and https://youtu.be/3oqq05zezum
Well there you are – three pumps of different design and construction methods. I think the Mk3 is probably the easiest to make but might not be so easy if it were a smaller-bore version. The original pump I made in 2009 has a bore of ⅜-inch and the mushroom valves are much smaller so this would be fiddly to make especially for these older eyes and fumbling digits...
■ Construction of the Mk1 and Mk2 pumps were described in the March and April 2022 editions of EIM. You can download digital versions or order printed copies of these back issues from www.worldof-railways.co.uk/store/ back-issues/engineering-in-miniature or by calling 01778 392484.