Simplex Axle pump

Hi All.
I bought a 5" simplex a while ago and the Axle pump never really worked. Made driving it really hard work.

I stripped it down to find out what was wrong.

It has 3 broken Bolts and a broken tap in the end cap / Glands.
It appears to have been made to the Martin Evans design then sleeved down to 3/8" making it Single acting with just a bit of 3/8 rod as the Piston. The sleeve appears to have been Hammered in looking at the 'Miss' marks.....
The Gland had no packing. Not hard to fix but judging by the state of the one on it, it's time for a remake.

I have the Simplex Book which came with the Loco, The Drawings and the ME Articles. None ae the same design.

My Inclination is to use the design from the book. This is the semi double acting design with 1 water inlet.

Which is the most appropriate for this loco ?

Thanks

Alex.

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 Stew.
That sounds like the one in the My Time Media Drawings I have.

Very long piston with chamfers on the ends.

I'm wondering how to insert the piston without taking chunks out of the O Rings ? ​

Another reason why my pump won't actually pump anything.

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

This is the pump I fitted, I started off with graphite packing but ended up fixing a O rings as fizzy said you have to fit them correctly, the groove has to have a depth about 80% of the thickness of the ring so that it is compressed slightly when assembled.

Cheers

Stew

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!

I have drawings for the Simplex Axle Pump, SuperSimplex Axle pump and the Simplex hand pump....

Simplex Axle Pump

Super Simplex pump

Hand Pump

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

Perhaps Julian could explain why the original doesn't work, it has exactly the same principle as the Super Simplex version, and there are several simplexes in our club which seem to work OK. Basically the same design is used in Henry Wood's Emma Victoria, and that works really well. My only criticism of the original is that it is not quite balanced (piston too big), this was sorted in the Super Simplex design. I can't comment on how easy or otherwise it is to get the pump out.

The hand pump design is really unbalanced, I wonder why he didn't stick to the differential design?

As to fitting O rings, put a decent chamfer at the end of the bore, ideally the entry diameter should be the OD of the uncompressed O ring, which should have about 12% squeeze when in position. Make the angle of the taper as shallow as you can within the constraints of the length of the stopper, 15 degrees is ideal, but might not be achievable

Hi All.

Clive. The top Drawing is the one I plan to build unless I'm swayed otherwise.
The Super Simplex pump looks interesting, That makes the 4th design. To fit this as drawn would be very tight and require pipework mods. The Outlet is much taller than the book design to accommodate the 2nd ball valve.

Julian. I plan to use 3/8 SS Rod for the ram. I don't however have 5/8 SS for the piston. I plan to make the piston from either Nylon of PB.
There is no issue with fitting or removing the Pump. 4 1/4" bolts, 2 pipes and 1 pin. Out it comes with a slight wiggle. Not sure why you'd have to dismantle anything else ?

Stew. That looks like the Super Simplex pump. Works on the same principle as the Book Pump. Just arranged possibly better. It'd be a tight squeeze to fit that in.

Duncan. The issue is not feeding the O rings in. They have to traverse the in/outlet holes as you assemble the pump. That's what eats chunks out of the rings. I guess I could open out the portion that the piston does not traverse.

I'm currently thinking towards Teflon Rings and a 3 or 5 part piston.
I can feed in the Piston and then compress the Teflon to form the seal ?

Thank you all for your comments.

Sheet 6a of the original drawings shows a double acting design by Martin Evans with a smaller bore than the original which should give smoother operation while still delivering more than enough water. I have fitted that to my as yet unfinished Simplex. It does however require different plumbing having two inlets.

There's a photo of the bits on Dr John's site here

Russell.

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.

here is the amended/redesigned Simplex axle pump from ME 7th March 1980.

in the write up Martin Evans acknowledged that the original Simplex design was "not, in fact, double acting".

this was the pump we fitted to a Super Simplex. the actual Super Simplex design as shown above is a design by D. Anderson from ME 4th July 1980 which Martin adopted for Super Simplex's axle pump, but the Super Simplex hand pump uses his re-design of 7th March 1980.

i think it is pretty evident that with only one water inlet the same water that had already been pumped by one stroke re-circulates into the other end of the pump before being eventually pumped out. hence why the original design doesnt do what it is supposed to do. anyway that is how i have always understood it, though i am happy to be proved wrong!

cheers, julian

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

After much deliberation, all 3 pumps have their advantages. The debate in the thread says that all the designs work and are suitable for this loco. ​

I'm going to build the Pump from the Book. Why ?
It's a well tried and tested interesting design with a small revision over the 1968 ME Drawings.

The Super Simplex and Double acting (1980) Pumps will both require Pipework mods. Not a huge deal but extra work. I can see no real advantage with either of these pumps. If anything they have added complexity.

The piston I'm going to make in 3 parts. 2 Discs with a Teflon piston ring that I can squeeze.
I have M14X1 taps n dies for the Gland nut.

Thank you all again for your Input.

Alex.

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

If Duncan's calculations are correct for the original pump then, a 0.75in diameter piston in a conventional pump (I think we all know what that is) with a stroke of 1in, would deliver a smidge more and be a whole lot simpler?

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

I cant see any logic in its design...is it just me?

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!).