Hi

Alex I fitted the balanced double acting axle pump designed for the supper simplex to mine, and it works very well, Its drawing were published in the magazine a good few years ago. I'll try and look up the issues for you or you could send me a PM and I'll get the details to you.

Cheers

Stew

Hi Alex

I was faced with the same dilema on my latest pump. The key is having accurate drawings, accurate measuring and accurate O rings. I had one out of the three so opted to machine 8 O rings into the end of my piston, just to be sure! If its made correctly the O ring will just 'nudge' in.

Alex, I think this is the most appropriate. I speak from experience – although it is not fully double-acting, it does produce plenty of water and is especially good for learners as it can recover the water level very quickly.

It is more complicated, but no gain without pain.

In other words, it is more than master of the job – and that cannot be bad!

hi alex,

as you have noted the original design doesnt work the way it should. it was criticised in ME at the time and subsequently, and a revised design eventually produced which was later used for Super Simplex.

there is little point machining down stainless to a good finish and fitting an 'O' ring for the double acting ram if the pump doesnt work as a double acting pump, so there is no point using the original defective Simplex design!

you will also have found the rather stupid method of fitting the pump body to the loco which for removal requires either removing the boiler or taking apart the valvegear and rods and dropping the wheelsets. i am sure you can think of a much better method of locating the pump body to avoid these problems!

personally i would remove the pump entirely and fit a second injector.

cheers,

julian

Edited By julian atkins on 12/11/2015 11:18:57

I see the problem with the ports, can I suggest moving the oring as far forward as it will go and boring the 5/8 diameter say 20 thou bigger until past the ports, then tapering down to 5/8 before the maximum stroke of the 0ring.

Otherwise, how about a 2 piece piston so you can poke the oring down the bore, hold it in place with a bit of tube, enter the piston from the other end and then bolt the end of the piston in place.

What happens in the original design (and Super Simplex) is that when the ram is going from right to left it sucks in 7/16 * (5/8)^2 * pi/4 = 0.134 cu.in. of water. When it goes left to right, some of this water flows into the annulus between ram and cylinder, 7/16 *((5/8)^2- (3/8)^2) *pi/4 = 0.086 cu.in. The rest, 0.048 cu.in goes into the boiler. When the ram moves from right to left, this 0.086 cu.in is forced into the boiler. This is why I said it was unbalanced, the piston should be sqrt(2) * the ram, in this case 0.53” which is what it is on Super Simplex. However, it pumps water into the boiler on both strokes, so it's a double acting pump in my book, although I might have added 'differential'. The redesign pumps 0.066 cu.in. on the in stroke, and 0.021 on the return, total 0.087, less than the original (about the same as Super Simplex) and still unbalanced. It does however need another inlet valve, so more chance of leaks.

No point saying something doesn't work when there are hundreds out there which do.

Edited By duncan webster on 12/11/2015 16:16:50

The thing about all three designs above is that if the bypass to the back of the piston and the second valve are omitted, and instead the back of the piston is left open to the air, the pump will move exactly the same amount of water, just delivering on push instead of splitting it between push and pull (push delivery being the volume of the cylinder occupied by the piston rod, pull being the volume swept by the piston less the rod volume).

So, I imagine the purpose of the complexity is to achieve a smoother delivery.

Neil

hi duncan,

i didnt say that the original design didnt work. i said that the original design doesnt work the way it should, and was defective.

as previously stated i wouldnt bother with an axle pump anyway and would fit a second injector.

cheers,

julian

If you want the same delivery from a single acting pump then it's just 5/8 bore and same stroke as original but without the differential action. 0.75 bore by 1" stroke is 0.44 cu.in per stroke, much bigger.

To open another can of worms, I reckon the original is too big anyway! Super Simplex had bigger cylinders and a significantly smaller pump, only 72% of ordinary Simplex assuming same stroke (not quoted on drawing above). A recent article in Isle of Wight MES magazine recommended 1/250 of cylinder capacity, on the basis that converting water to saturated steam increases its volume by 250, and you don't run at full regulator 100% cut off, so there is a bit in hand. I'm going for 1/200 on my current loco, but with the possibility of boring it out (coward!).

Yes, you are correct – it was late and I missed out pi. Perhaps it would be better if I missed out on a few more pies!!

Very much agree.

Alex,

if you want me to look at your injector and sort it out i would be happy to do so. it sounds like it is feeding way beyond the spec. not unusual im afraid on some of the cheaper stuff sold by the suppliers. it also should have a full operating range and feed down to 30psi/25psi.

unfortunately Simplex's (and Super Simplex's) cylinders are far too big in bore and encourage lazy driving as full working pressure isnt required, and the valve gear is a bit iffy leading to far less use of 'notching up' to save steam and run at a higher pressure.

the enlongated firebox on both also leads to a tendancy to have a fire that isnt radiant all the time, a fault of the Greenly locos designs. what Jim Ewins referred to as a 'lazy fire'.

you will gather from the above i am not a fan of Simplex or Super Simplex, always referred to in most clubs as 'Complex' instead of 'Simplex'. the axlepump design is but just one factor of this dislike.

cheers,

julian