A Feed Pump and Double-clack for the EIM Steam Plant
Martin concludes the construction of an addition to his popular stationary engine build project, making the replacement clack and staging a first steaming.
We move onto the final stage of our project this month by first constructing a replacement double-feed-clack, the arrangement of which can be found on Drawing DCPL.
Clack Valve Body
Part Six of Six
Item FP35 – 10mm diameter AF hex brass
Refer to Drawing FP35
On the lathe, hold the brass bar in a three-jaw chuck with 25mm protruding and face off.
Turn 6.35mm diameter x 8mm, then using a 1mm wide parting tool set with its left-hand edge against the turned face, undercut 0.5mm deep (1mm on a diameter dial) into the 6.35mm diameter. Chamfer the hexagon 30 degrees x 0.5mm and thread ¼-inch x 32 ME x 8mm.
Using a No 3 centre drill, drill into the face, stopping when the cone formed is just short of the core diameter of the thread (Photo 51).
Part off 21.25mm overall (Photo 52).
Screw the part into a ¼-inch x 32 ME mandrel made up from a short length of stock faced off with a ¼-inch x 32 ME thread run into it, and hold in a chuck.
Face off, bringing the length between the mandrel and end face to 13.25mm. Chamfer the hexagon 30 degrees x 0.5mm. Centre drill then drill 2.8mm diameter through, before reaming to 3mm diameter. Drill 5.5mm diameter x 9.5mm deep, and thread ¼-inch x 32 ME x 7mm.
This method of drilling any hole accurately to depth when using a tailstock that does not have a graduated feed dial or DRO fitted produces a guaranteed result. It only requires a length of tool steel and two identical thickness (around 0.5-0.8mm) steel rules or feeler gauges.
Hold the 5.5mm diameter D-bit made earlier for the valve body valve seats (part FP5A) in the tailstock drill chuck. Adjust so that the tip of the D-bit just contacts a steel rule/feeler gauge laid across the end face of the clack valve body.
Clamp a piece of tool steel in the toolpost, projecting sufficiently to contact the end face of the tailstock drill chuck. Move the saddle to lightly sandwich a 12mm diameter drill plus a rule/feeler gauge of identical thickness between the tool steel and the chuck end face. Clamp the saddle and remove the drill and both rules/ feeler gauges (Photo 53).
Machine the valve seat by feeding in the D-bit until the tailstock drill chuck contacts the tool steel ‘stop’ then remove from the mandrel. Repeat the process for the second clack valve body.
Turning to the mill, screw a union nut onto the ¼-inch x 32 ME thread to protect the coned face. Position the body in the centre of and near to the top of the vice jaws, using a suitable
parallel placed under the flat section of the hexagon, with the top internally threaded face against the fixed jaw. Centre the spindle to the middle of the body on the X axis and to the fixed vice jaw on the Y axis. Clamp the X axis and zero the Y axis, then move the work towards the column 6.75mm before clamping the Y axis.
Centre drill then drill 3mm diameter, breaking through completely into the 5.5mm diameter hole. Drill 6mm diameter x 1.5mm deep, using a slot drill (Photo 54).
Remove the piece and repeat the process for the second clack valve body. Deburr and put to one side.
Clack Valve Cover
Item FP36 – 10mm diameter AF hex brass
Refer to Drawing FP36
This is basically a repeat of part FP11 but note that it has different dimensions – see the drawing.
Central Banjo Body
Item FP37 – 12mm x 16mm x 9mm Brass
Refer to Drawing FP37
Bring the blank to the 12mm x 16mm x 9mm dimensions. Mark out and centre punch two end centres and one face centre.
Hold the blank in an independent four-jaw chuck on the lathe with the 12 x 16 face at least 3mm protruding using a ‘wobbly centre’ in conjunction with the dial gauge (Photo 55).
Centre drill then drill 6.35mm diameter, and with the boring tool used earlier to produce the O-ring recess in the pump cylinder, bore the 8.35mm diameter x 3.5mm recess from 1.5mm to 5mm, measured from the face in the 6.35mm diameter. Bore it out (Photo 56).
Reset the blank with one end at least 5mm protruding and the centre ‘pop’ mark running true, again using a wobbly centre method as before (Photo 57). Face off, centre drill and drill 3mm diameter into the recess.
Turn the 6mm diameter x 4mm stub detail (Photo 58) and then repeat at the opposite end.
On the mill and using suitable parallels, clamp the body with at least 4mm protruding above the jaws. Using a sharp countersink, machine the four 45-degree chamfers at the four locations indicated (Photo 59).
The next step is to silver solder the two clack valve bodies to the central banjo body. Put the three parts in the pickle for 10-15 minutes, drain on removal and wash in clean water.
Make up two 6mm diameter silver solder rings from 0.7mm diameter wire (55 per cent), and fit one of the rings over one 6mm diameter plain stub of the banjo body. Apply flux to the ring, stub and in the recess of one clack valve body.
Fit a spare union nut to the thread to protect it from damage whilst being heated and set it on a piece of steel plate not less than 3mm thick, with a support to provide weight to hold the two parts together. Move the parts into their correct orientation.
Using a small flame alternately heat the plate/lower clack valve area and support/upper banjo body area, generally avoiding prolonged contact in the immediate joint/silver solder ring area. After the flux has become transparent watch the joint area and when a fillet is seen to form allow the flame to briefly cover the joint area to ensure full penetration before removing the heat and allowing the assembly to cool down (Photo 60).
Place in the pickle for 10-15 minutes and rinse in clean water, brushing with a stiff brush to remove any remaining flux residue.
Reflux the joint just completed and the recess of the second clack valve body. This should be placed on the steel plate (recess upwards) so that the remaining plain stub, after having the silver solder ring fitted to it and fluxed, can be placed into the recess,
enabling the two valve bodies to be correctly aligned before the support is placed in position.
Using a small flame alternately heat the plate/lower clack valve area and general area of the banjo body with an occasional sweep over the first clack valve body, but generally avoiding prolonged contact to the immediate joint area previously formed and to the second of the silver solder rings.
After the flux has become transparent watch the new joint area and when you can see a fillet has formed, allow the flame to briefly cover the new joint area to ensure full penetration, before removing the heat and allowing the assembly to cool down (Photo 61).
Again place in the pickle for 10-15 minutes and rinse in clean water, brushing with a stiff brush to remove any remaining flux residue.
Banjo Bolt
Item FP38 – 10mm AF PB102.
Refer to Drawing FP38
Hold in a three-jaw chuck on the lathe with 28mm protruding, face off, centre drill and drill 3mm diameter x 15.5mm deep. Turn a diameter of 6.35mm for a length of 18mm. Thread ¼-inch x 40 ME x 9mm and then part off 22.5mm overall.
Hold on the turned diameter with the hexagon pushed tight to the chuck jaws and face off the head to 4mm thickness. Chamfer the head 30 degrees x 0.5mm.
On the mill, position the bolt in the centre of and near to the top of the vice jaws using a suitable parallel placed under the flat section of the hexagon, with a hexagon head against the fixed jaw. If you have one, set the vice stop against the hexagon head. Centre the spindle to the middle of the bolt on the X axis and to the fixed vice jaw on the Y axis. Clamp the X axis and zero the Y axis. Move the work towards the column by 8.75mm and clamp the Y axis.
Centre drill using a drill with a pilot less than 2mm diameter then drill 2mm diameter, breaking through completely into the 3mm diameter hole (Photo 62). Release from the vice and rotate the hexagon by 120 degrees (two flats), and repeat – centre drilling and drilling 2mm diameter at this second location. Repeat the process producing three holes at 120 degrees to one another. Remove from the mill, deburr and put to one side.
Assembly and adjustment
The seating and assembly of the ball valves is a repeat of the ball valves as described earlier for the engine-driven Feed Pump.
An important note: the setting of the ball lift differs a little to that previously in that after the lift limiting set screw has been ‘bottomed’ gently against the seated ball, the measurement taken between the ball valve cover and the underside of the head has to have subtracted from it 0.65mm for the side connected to the hand pump, and 0.5mm for the side intended to be connected to the engine driven pump.
Connecting Feed Pump to Boiler Double Clack Valve
Remove the clack valve from the boiler bush that takes the supply from
the hand pump. Replace with the double-feed clack and secure with the banjo bolt that has a copper washer fitted under the head and between the body and boiler bush. The original feed pipe from the hand pump should be able to be reconnected to one of the clack valve threads (lift set to 0.65mm), a very small adjustment to the original run.
To connect the engine pump to the double clack requires a 4mm diameter (5/32-inch) pipe to be made up with a nut and cone fitting silver soldered on each end. The method of obtaining the required length and location of any bends was described fully in Part 16 of the construction series of a gas-fired boiler for the EIM Steam Plant, in the February 2020 edition of EIM.
A warning: remember to allow any pipework that has been silver soldered to cool completely before placing in the pickle, for the reasons given in the article.
When completed this pipe should be connected between the vacant double clack valve (with ball lift set to 0.5mm) and the discharge stub which is the lower of the two stubs at the end nearest to the drilling plug on the pump body.
A second pipe is required for the feed-water supply to the pump, requiring a nut and cone to connect to the lowest pipe stub at the pump cylinder end, and a third also having a nut and cone for the bypass return to the feed water supply to the top pipe stub at the end nearest the drilling blank. As constructors will have differing sources of feed-water the pipe run/layout must be decided on an individual basis.
My solution was to bring the hand-pump supply, engine-driven feed-pump supply and bypass return to a common connection point, supported in a plate fixed at the rear of the base to enable orderly connection when setting up, as shown in Photos 63 and 64.
Pump Operation
1) Connect up the feed-water supply to the inlets of the hand and enginedriven pumps. Connect up the end of the bypass pipe to a pipe that may be observed discharging onto the top of the feed tank. Open the bypass control wheel fully (unscrew).
2) Prime/check that the hand pump is working by noting the gauge glass level rise when it’s operated.
3) Raise steam and set the engine in motion, when it has warmed through and is able to run at a steady speed observe the discharge from the end of the bypass returning to the feed tank. 4) Shut the bypass control wheel fully, and confirm that the water level in the gauge glass begins to rise.
5) Open the bypass hand wheel in very small increments, until the water level remains constant. The amount of excess discharge may be observed at the feed-tank end of the bypass pipe and this will act as a guide to how much of a turn should be given to the control wheel.
Now enjoy the fruits of your labours! But a final word of warning – never leave the steam plant running unattended...
References
1) Notes on the Design of a Steam Engine Feedwater Pump, by Kenneth. J. Hemmeingarn. Live Steam & Outdoor Railroad, May/june 2017.
2) Model Stationary & Marine Steam Engines, by K. N. Harris
3) Model Steam Engine Design, by R. M. De Vignier
4) Model Steam Locomotive Construction, by Martin Evans
5) Experimental Flash Steam, by J. H. Benson & A. A. Rayman
6) The American Live Steam Forum.