Simplex Axle pump

[Alex CollinsParticipant @alexcollins55045]

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.

[Alex CollinsParticipant @alexcollins55045]

[Stewart HartParticipant @stewarthart90345]

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

[Alex CollinsParticipant @alexcollins55045]

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.

[nigel jones 5Participant @nigeljones5]

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.

[Stewart HartParticipant @stewarthart90345]

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

[Clive IndiaParticipant @cliveindia]

Posted by Alex Collins on 11/11/2015 19:11:30:

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

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!

[Clive IndiaParticipant @cliveindia]

Posted by Alex Collins on 11/11/2015 19:11:30:

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.

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

Simplex Axle Pump

Super Simplex pump

Hand Pump

[julian atkinsParticipant @julianatkins58923]

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

[duncan webster 1Participant @duncanwebster1]

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

[Alex CollinsParticipant @alexcollins55045]

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.

[Russell EberhardtParticipant @russelleberhardt48058]

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.

[duncan webster 1Participant @duncanwebster1]

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.

[julian atkinsParticipant @julianatkins58923]

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

[duncan webster 1Participant @duncanwebster1]

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

[Alex CollinsParticipant @alexcollins55045]

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.

[Neil WyattModerator @neilwyatt]

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

[Anthony KendallParticipant @anthonykendall53479]

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?

[julian atkinsParticipant @julianatkins58923]

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

[nigel jones 5Participant @nigeljones5]

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

[duncan webster 1Participant @duncanwebster1]

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!).

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by julian atkins on 12/11/2015 15:25:43:

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

Yes, that's the one I made.

Russell.

[Anthony KendallParticipant @anthonykendall53479]

Posted by duncan webster on 13/11/2015 01:04:33: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.

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!!

Posted by julian atkins on 12/11/2015 23:20:45:

hi duncan, As previously stated i wouldnt bother with an axle pump anyway and would fit a second injector.

cheers, julian

Very much agree.

[Alex CollinsParticipant @alexcollins55045]

What I have found running with just the injector was it's far to much and uses a lot of steam. The water level rises and I start to lose pressure. Shut the injector down at ~ 40 psi then the water drops – need more and the injector refuses to pick up. That's what I mean by "it was hard work driving"
Please don't get me wrong, the injectors are good and work well. I'd prefer to have a pump that pretty much looks after the boiler and use the injector only when needed.
I have a 16 oz (no. 2 ?) on there at the moment.

Good progress tonight. The brass is cut to size and roughed out. Decided to leave the bore Blind rather than make an end cap so drilled and reamed it 1/4" short. Still plenty of room for the ports.
All the drilling is done, Gland is made and holes tapped.

[julian atkinsParticipant @julianatkins58923]

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

[Author]

Posts