Axle Driven Feed Pump for the Beginner's Locomotive

Axle Driven Feed Pump for the Beginner's Locomotive

An 0-4-0 Switcher of Simple Design in 3/4 inch Scale

by Cliff Blackstaffe

Victoria Society of Model Engineers

The Miniature Locomotive, March-April 1954

This item had best be made and fitted now before we get involved in boiler work. You will notice the pump is not very large being only 3/8 inch x 3/8 inch but the engine is small and with 3 inch wheels it will pump as much water to the mile as a 5 inch drivered Atlantic with a 5/8 inch stroke pump which pretty well evens things up. While a big pump is handy to get the water up quick you can overdo it when the boiler is small, it may take a chill.

The pump shown is fabricated from round and square brass and I doubt if any time would be saved if a casting were used.

The barrel is made from 1/2 inch diameter stock and is 1-3/8 inch over all. Chuck, turn down 3/16 inch of it to 7/16 inch diameter. Reverse and screw cut a 32 thread per inch for 9/16 inch on it. Center, drill 5/16 inch, open out to 23/64 inch and team 3/8 inch. If no reamer, bore as smooth as possible until a bit of 3/8 inch bronze or stainless steel will just slide in. The penalty for a sloppy fit is frequent re-packing of the gland. While the lathe is set up for 32 threads we may as well make the gland and oval mounting flange. The flange is cut from 1/8 inch brass plate (steel would do) 1-1/4 inch by 7/8 inch. In the center put a punch mark and set same running reasonably true. Center, drill 15/32 inch and screw cut to fit barrel.

The gland can be made from 9/16 inch hex brass, but if you're like me I wouldn't find a bit of 9/16 inch hex in my stock pile so I'd just turn it from 5/8 inch round. Divide into six parts and file the hex. If your lathe has no dividing marks on it, by all means divide the front face of the back gear into six and center punch.

Then fit up a pointer to line up with these punch marks. This is extremely useful for making hexs. The gland is only 3/8 inch long and the hex left and the outer 1/4 inch turned off, which looks much neater. Drill 3/8 inch for 7/16 inch in. Open out to 15/32 inch, 5/16 inch deep and screw to fit the barrel. Part off.

The valve box is made from 5/8 inch square brass with an overall length of 1-1/4 inch. Turn down 1/8 inch of it to 1/4 inch diameter to spigot into the delivery valve box. Center, drill 7/64 inch for 7/8 inch depth and ream 1/8 inch. Take the merest scrape of a facing cut off this spigot to insure an even true knife edge seat for the ball. Reverse, center, drill 3/8 inch with a 1/4 inch drill (which will meet the 7/64 inch hole). Take a facing cut off the end to form a true joint surface for the suction valve seat. Turn the end to 5/8 inch round for 1/2 inch long. In the middle of one of the flats drill a 7/16 inch hole to take the barrel. This can be a drill press job and the hole 1/2 inch deep.

The top and bottom valve boxes are turned from 1-1/8 inch brass rod. The top one is faced off for the joint, centered, drilled 1/2 inch depth with a 1/4 inch drill. Leave a 1/8 inch wide flange, run in the parting tool with several cuts until you've turned the top to 5/8 inch over all length. Drill through 7=64 inch and tap 6-32.

The bottom box has a 1/4 inch spigot turned, center drilled, and reamed just like the delivery valve seat. The flange is on the bottom in this case. The 7/64 inch hole goes down through and is tapped 6-32. Now file the flanges oval and in the side of each drill 17/64 inch and tap 5/16-24 (SAE) for the unions. Drill the bottom one 9/64 inch for the tie bolts each side and top one drill 7/64 inch and tap 6-32. The tie bolts can be made from wire nails threaded 6-32 each end and 6-32 hex nuts brazed on to be sure the whole works screws out.

The union parts are easily made. CHuck 5/16 inch round. Run a 5/16-24 thread on for 1 inch, center deeply so the center drill forms the seating for the union cone, drill in for 1 inch with 3/16 inch drill and part off the first one at 3/8 inch long. Apply the center drill again and part off the second one. Now you've done enough lathe work for a little so a change to brazing is in order. Screw the oval flange onto the pump barrel to the thread's end. Run a little ring of flux around the back side of it and stand it on end (thread down), heat up to a medium red applying a little easy-flow wire to the joint. It will creep right around following the flux trail. Clean up the end of the barrel where it enters the valve box. Set it in place being sure the flange is level crossways. Anoint with flux and standing on end brazed up as before. Screw a union piece 1/8 inch into each valve box and run a braze around them. Now you can have a clean up time. While you are at it file the back off the pump body as it is rounded for appearance.

May as well put the pump body into the frame and set the valve box vertical, scribe the two fixing holes, drill them 7/64 inch and tap 6-32. Countersink the frame as we need to use flat head screws to get full clearance of the gland.

The plunger is a 2-5/16 inch length of 3/8 inch drawn bronze or better rustless steel as it polishes up to a hard glaze that doesn't wear the packing. It is slotted in the end to take the pump eccentric rod and has a wrist pin hole drilled 2-1/8 inch from the pump end. The wrist pin can be a bolt with just enough thread so the nut fetches up on the thread rather than pinching the jaw onto the eccentric rod.

Cut a couple of 1/64 inch gaskets to go between the valve boxes and placing the suction ball on its seat insert the seat into the pump body. Now drop a 3/32 inch rod down the discharge seat and with it resting on the suction ball mark level with the discharge seat. Transfer the height of the ball to the outside of the pump body and drill and tap 1-72 for the lifting restricting screw, the bottom side of which should be as near as possible 1/32 inch above the ball. The lift can be checked by a rod put through the No. 6 screw hole in the bottom. Put the discharge ball in place and the box on. Then put a screw down until it touches the ball. Then slack it off one turn (1/32 inch) and measure the distance between the head and the valve box; cut this off the end of the screw.

Now we're about ready to put the pump together so we must seat the balls. Choose a new hard steel bearing ball to do this and examine the seats for the least trace of burr or dirt as if these are at all imbedded into the seat "leakitus" is sure to set in. When all is clean set the valve box or pump body on a block of lead or hardwood and with a 1/4 inch brass drift smack the ball one shart rap which will shape the metal near the seat to a perfectly true fit. Now assemble the valve boxes with stainless balls in them and tighten each tie bolt the same amount.

Pack the gland with a strand of twisted valve stem packing and a drop of oil. Put in the stop screws and solder over the heads to prevent leakage. If you set the bottom of the pump in a dish of water and work the punger in and out you'll be rewarded with little jets of water from the deliver union. Now don't be so pleased with yourself, its a darn poor pump that won't deliver against air pressure so let's prove it further. With the pump full of water hold your finger over the discharge union and press in on the plunger lifting the pump from the water. See if any water leaks back through the suctions valve. The odd drop won't matter. See that the gland doesn't leak and with the pump again full of water but plunger well in hold finger over suction union and pull out plunger noting if the water at the mouth of the delivery union draws in. It shouldn't if this valve is tight. Having made sure the valves are tight the pump may be fitted to the engine for keeps.

Now you can turn to the lathe again and from either 7/16 inch round or 3/8 inch hex brass make the two union nuts these are 3/8 inch overall length, drilled in for 5/16 inch and tapped 24. Use a bottoming tap to get the thread full size to the bottom and turn off the hex each side leaving 1/8 inch wide hex in the middle. Standard compression fitting cones can be used when piping up but for now stick in a couple of blind joints or 3/16 inch rivets to keep dirt out of the pump until ready to pipe up.