Tender Hand Pump for 3/4" Scale Locomotives
Tender Hand Pump
The Live Steamer, March-April 1950
The design of this pump is unconventional in that most tender pumps are horizontal, some requiring a slot in the tank top for the handle to work in, and all requiring a detachable section of the tank top to install the pump.
This vertical design allows a normal tank top, as the whole works drops in thru the water hatch which need only be 1-1/8 inch by 1-1/2 inch in size. The pump is held to the tank bottom by a 1/4 inch nut and a lock nut around the delivery union with a thin rubber joint to make the tank watertight.
This pump is for 3/4 inch scale engines, but can be used for 1/2 inch scale engines also. If the tank is not deep enough for the latter, a sump could be built into the tank bottom to give the extra height needed.
Note to construction: No castings are needed, the pump body being a block of brass 1-1/4 inch long, 1-1/8 inch wide, 1-1/4 inch high. It can have the corners rounded off after boring, to cut down weight if desired. On the top of the block, mark out the center of the cylinder bore which is 3/8 inch from each side in one corner. Mark the position of the discharge pipe hole and fulcrum stand, which is 5/8 inch from cylinder centre on the long cide and 3/8 inch in from it. At right angles to these centres and along the narrow side lies the valve box centre 1/2 inch from fulcrum centre. Now we can do some metal butchering.
Set up in four jaw with cylinder centre dot running true. Centre, drill 1/4 inch thru, follow with a 5/8 inch drill. Now set fulcrum dot to centre. Centre, drill 17/64 inch and tap the top end 5/16" x 24 for 3/8 inch depth. In all tapping or reaming in the lathe either hold the tools in the drill chuck or use the tail centre in centre of tool, turning the same with a wrench. It is never safe to use the lathe power on these jobs.
Now with a round nose tool, take a skim off the block just to leave a smooth seat for the valve bonnet & fulcrum to seat down on. Chuck a bit of 1/2 inch brass rod, project 3/4 inch from chuck, turn down 1/4 inch of it to 3/8 inch diameter & thread to fit valve chamber. Run a narrow parting tool in to relieve the end thread and face the collar where it seats on the block. Using this for a mandrel, screw block on and operate for the suction chamber by drilling 5/16 inch for 1/2 inch & tapping 3/8 inch as before, but do not bottom this hole. Remove block, turn down the bonnet where square will be filed, to 3/8 inch diameter leaving a 1/16 inch washer on it & part off.
Pull out more stock and make the suction valve seat. Thread as before, centre, drill 11/64 inch, ream 3/16 inch and face off lightly. Mark off in six for filing the hex and part off. File hex and screw the seat into the block and run a 1/4 inch drill in the bottom for 3/16 inch depth to take the gauze strainer. From the same stock turn and thread the end of the fulcrum post 5/16" x 24, relieving the last thread as before. Now the height of this post is the lowest possible in the drawing, but should be made as high as the tender depth will allow, so the bell crank that the handle fits on comes up into the hatch at the top of the stroke, otherwise the hatch may prevent the handle swinging full stroke. The jaw is square in section and is filed after it is found where the post tightens up. The bell crank should be brass or stainless steel and pins the same. The double links are offset to form a jaw at the top end.
The cylinder is a 1-7/8 inch length of 5/8 inch brass rod (cast stick turned down is better) with a 1/2 inch reamed hole thru it. However, you can't just saw off 1-7/8 inch of 5/8 inch rod. Chuck it and poke a hole thru it and ream it, because a chuck won't hold a 1/6 inch thick shell against the stress of drilling and reaming without violent distortion. SO use a longer bit of stock, face, centre, drill 1/4 inch for 2-1/4 inch, open out with 31/64 inch drill and ream 1/2 inch, part off. Smear with soldering paste, also inside of block, insert leaving 1/16 inch short of bottom edge. Heat up and sweat solder around each end. At 1/2 inch up from the bottom of the block and at the point where a line crossing the cylinder would also cross the valve box, put a center dot on the cylinder side. Drill the crosshole 11/64 inch and tap for plug in outside. Screw plug in and run reamer thru to remove any burrs.
Now we want the standpost or pillar. This is from the 1/2 inch diameter brass rod. Turn the end down to 1/4 inch for 1/2 inch and thread 1/4" x 20. The pillar portion is reduced to 3/8 inch diameter as a matter of taste. Part off at 1-1/4 inch from collar to end. If it is a free fit in the cylinder, a couple of center punch dots will raise enough burr to hold it in place while you run a ring of solder around the bottom. Don't be too generous with heat or solder, or it will run into the bore and cause a rise in your own temperature.
The piston can be brass, aluminum, or stainless steel and is fitted as tight as you can get the cylinder to go on, then drill 5/16 inch for 3/8 inch deep and with a threading tool put in four 1/32 inch wide water sealing grooves. Now with a strip of finest emery cloth over the face of an 8 inch file, polish it down until it is is a free sliding fit in cylinder bore. The wrist pin should be a water tight fit.
We now need the delivery pipe. This is in one piece with the discharge union. Make this fit a standard compression coupling union nut and cone, also a locknut to suit.
All we need now is the baseplate. This is 1/8 inch brass 1-1/8 inch by 1-1/4 inch, with one hole threaded for the discharge union and the other clearing hole for the 1/4 inch stud end of the pillar. Slip it on the pillar, screw the union thread thru the baseplace, entering the pipe end into the pump body and tighten the 1/4 inch nut, solder pipe into the pump body.
To finish, clean the valve seats perfectly so no dirt gets under the valves when you seat them. Use 7/32 inch stainless steel balls, seating them with a light biff with a hammer and brass rod. Now solder a thimble of brass gauze (as used for automobile gas line filters) into the suction valve seat and the job is done. The linkage pins should be soldered in at the ends to prevent any chance of them coming out at a crucial moment when the pump is needed. My own pump has been in the tender since 1942 and pumped lots of water, not having any other form of feed and the plunger only leaks the odd drop, so why worry about packing.