< Axle Driven Pump >
William's axle driven pump is single type. A casting of eccentric strap shrunk and didn't have enough volume to cut. I asked the supplier to exchange it and they sent me a new one which but also shrunk.
So I decided to make a double type pump with smaller eccentricity so as to utilize these shrinking castings.
Sawing off the casting. Note a pair of small bars as a guide to saw straight.
After bolting the pair of straps together, bore it to the final size using a spigot as a gauge.
The spigot will also be used as a jig to hold the straps during surface cleaning.
Metal saw cuts a slot in the strap to catch the eccentric rod.
Outer face of the strap is cut on a rotary table.
The straps was completely machined.
I added funnels to the straps so as to ease lubrication for the eccentric.
Outer shape of the funnel is round but I made it of a hexagonal brass bar. Because hexagonal blank is indexable in a machine vise.
The eccentric is made of bright mild steel round bar. But if you have iron casting of similar size, it is better for the eccentric. To cut the groove to the exact diameter, you have to move the parting tool left and right in every one thou advance.
The eccentric rod is made of a bright mild steel sheet.
The rod is fixed to the eccentric strap with copper rivets. Although the back half of the strap is threaded for screws, it is better to support the screws with nuts so as to resist hardworking.
Section of the pump.
The ram is sealed with an O-ring in the gland.
As forming delivery valve seat in the body is difficult and risky, I made it as a small part and glued it to the body with Loctite 510. (the red part in the section)
The pump body consists of one flat bar and two round bars of brass. They are machined individually and silver soldered together.
Boring the pump body in the lathe. Note a bar of brass is used as a balance weight for turning.
The pump ram was made of free-cutting stainless steel. The ram and the eccentric rod was connected with a small pin. To secure the pin, I used snap-rings which are more reliable than traditional thread and nut.
Accuracy of the ball is most important. You have to get the highest grade of stainless steel ball for valves.
I burnished the seat in the lathe instead of seating with a hammer. If you do this, 1 sec slight push is enough. You can use more accurate chromium steel ball for seating or burnishing.
Ready for assembly. Note the five holes in the side of the pump body. The lower four holes are for fixing the body to chassis, while the upper one is very deep enough to make the two delivery lines merge inside the body. This trick allows you to connect the delivery unions directly to both the boiler and the by-pass valve.
The parts were painted, assembled and fixed between the frames. The picture shows a view from underneath of the frames.