|
|
Post by runner42 on Aug 18, 2022 7:08:12 GMT
Mention there of an axle pump! DY says it's not needed as the two injectors will do the job but I'm still pondering that. I've driven a 5" B1 with only injectors and it was really good, but injectors seem to be a bit of a black art and what if the magic pixie dust that keeps them working fails? Anyway, is your axle pump based on a published design, or your own? I'm redrawing the DY originals in 3D CAD as I go and after pretty much finishing the tender and bogie, I'm starting on drawing the main frames and stretchers so this might be the time to look at incorporating an axle pump - all ideas welcome! 3D CAD revealed the slight error in the tender drawings that DY notes in his article without actually correcting anything - bit of a pain to have to cut notches in the tender wheel flanges to clear the drag box  The axle pump is an Allan Wallace design, which I posted some considerable time ago. He is of the opinion that most designs by LBSC et al are too large and spends a lot of time pushing the boiler feed water back to the tender. The optimum delivery rate should just be enough to provide an indication of water at the tender return, more or less to show that the axle pump is working. Brian  axle pump by Brian Leach, on Flickr |
|
stevep
Elder Statesman
Posts: 1,073
|
Post by stevep on Aug 18, 2022 8:34:33 GMT
I think that view depends on how many feed systems you have in place. If you have injectors, then it's probably right, but on my Rob Roy, with only the pump and the emergency hand pump, if my water level starts to drop, I want to be able to close the bypass and see the level start to rise pretty soon.
|
|
Neale
Part of the e-furniture
5" Black 5 just started
Posts: 283 
|
Post by Neale on Aug 18, 2022 10:33:51 GMT
Well, my 3D modelling is ahead of my building so I can take a look at how I can fit in an axle pump while assuming a couple of injectors plus tender hand pump as per DY drawings. Belt, braces, and electric trouser hoist...
In the meantime, I'm collecting "gotchas" from threads like this one!
|
|
dscott
Elder Statesman
Posts: 2,440
|
Post by dscott on Aug 25, 2022 6:05:52 GMT
One of the best parts of the Design of Twin Sisters is the TWIN axle pumps.
These are made with a horizontal flange to bolt onto two of the stays, very balanced. castings from GLR Kenions.
I have 2 Heavily Modified Simplexes going through the works which now feature twin axle pumps with easy access plate which they are mounted on. Fowler Complex also has 1 3/8" cylinders and a moved out of the ashpan beck axle and lovely sized ashpan.
Our Gresley O1 has now got twin opposed Tender hand pumps and all the pipework in the accessible box in the back.
It is no good putting any fittings the other side of a baffle. These are 5/8! rams.
Tender body kit from Model Engineers Laser.
Lovely axle pump.
Do you have a dimensioned drawing please?
We will have to go into production of several.
David and Lily.
|
|
|
|
Post by runner42 on Aug 26, 2022 7:54:59 GMT
No dimensional drawing exists or is neccessary. The pump size depends on the bore and stroke that is required and then any measurement stem from these factors. However some guidance is provided in determining the other sizes.
The features of this design are:
(1) The bronze gland provides a long, robust guide for the ram, supporting it just where it is needed most.
(2) There is provision for oil lubrication, just where it is needed. Wear is virtually eliminated; water may be good, but oil is better.
(3) The O ring slides on the OD of the ram, which can be polished easily. With oil lubrication, there is virtually no wear, and zero maintenance.
(4) The O ring seals in both directions. There is zero water leakage outwards, and air cannot be drawn in to reduce the displacement efficiency.
(5) There is no need for an accurate or finely-finished bore in the barrel. It can have a slight clearance, so there is zero wear. Alignment of the gland with the bore is simple, precise and reliable.
It is worth mentioning a few tips for those who want to design their own. Make sure that the O ring gland dimensions are correct. If you are using imperial O rings, the correct squeeze is built in to the nominal sizes, so a 1/16” cross section ring is correct on a ram 3/8” diameter in a gland of ½” diameter (for example). The length of the gland is not critical but it should be at least 1.5 times the O ring cross section (e.g. 3/32” for a 1/16” O ring). O rings are never to be squashed like a gasket.
Between two and four small screws can be used to attach the gland into the barrel. There is not much thrust tending to force the gland out. Four M3 screws for a 5/8” ram is plenty, and two would be adequate for a 3/8” ram.
It is important to minimise the dead volume when the plunger is fully in, to clear air which would otherwise reduce displacement efficiency due to its compressibility. LBSC’s spigot helps in this regard, but where there is room one can run the ram bore right into the valve body at full diameter, so there’s no place for an air pocket to hang up in.
oil cup
Bronze gland
Stainless steel ram (polished)
O ring gland
Poppet valve with O ring
O ring face seals
Brass barrel
Limit the lift of the ball valve to a maximum of around 20% of ball diameter. This is to minimise chattering, which can seriously reduce displacement efficiency. If chattering persists, I would suspect a travelling-wave type of waterhammer in the connected plumbing. A modification to the piping might work. Once I introduced a short length of silicon pipe into an intake line and it fixed the problem by acting as a snubber. However, with a small displacement pump one is far less likely to have a chattering problem in the first place. Another approach is to use an O ring seated poppet valve like the one illustrated.
Naturally, the flow path above the valves, when the valves are lifted to their stops, should be reasonably generous. As a guideline, try to make the minimum cross-sectional area of the slots or gaps equivalent to the area of the bore of the valve seat.
Brian
|
|
Gary L
Elder Statesman
Posts: 1,208
|
Post by Gary L on Aug 28, 2022 18:55:35 GMT
Mention there of an axle pump! DY says it's not needed as the two injectors will do the job but I'm still pondering that. I've driven a 5" B1 with only injectors and it was really good, but injectors seem to be a bit of a black art and what if the magic pixie dust that keeps them working fails? Anyway, is your axle pump based on a published design, or your own? I'm redrawing the DY originals in 3D CAD as I go and after pretty much finishing the tender and bogie, I'm starting on drawing the main frames and stretchers so this might be the time to look at incorporating an axle pump - all ideas welcome! 3D CAD revealed the slight error in the tender drawings that DY notes in his article without actually correcting anything - bit of a pain to have to cut notches in the tender wheel flanges to clear the drag box The axle pump is an Allan Wallace design, which I posted some considerable time ago. He is of the opinion that most designs by LBSC et al are too large and spends a lot of time pushing the boiler feed water back to the tender. The optimum delivery rate should just be enough to provide an indication of water at the tender return, more or less to show that the axle pump is working. Brian axle pump by Brian Leach, on Flickr Sorry to be a bit late, but what is the pintle on the end of the ram for? (I know LBSC said it was to prevent airlocks, but I’m sure his air would have behaved like mine, and can’t be forced downwards by the pintle.) More seriously, as soon as the tip of the pintle enters the outlet port, it obstructs the water (most of it) from passing. Water being incompressible, this would cause a significant inefficiency at the end of each stroke. A better plan, if worried about airlocks, would be to drill the outlet port at the top of the cylinder. Do away with the pintle, whatever else you do. HTH Gary |
|
|
|
Post by steamer5 on Aug 28, 2022 23:35:14 GMT
Hi Gary,
My guess from what Brian wrote is the pintle is the ram, it is sized to provide slightly more water than required for the engine design, water consumption, the larger end is basically support to keep the ram ( well the whole thing is the ram) nicely lined up. The end of the pintle entering the void between the inlet & outlet isn’t going to cause an issue, the inlet valve at the bottom seals shut at the beginning of the stroke, lifting the outlet at the top as the ram advances, if the pintle enters the void at the end of its stroke it will just squeeze a little bit more water out. On the return stroke this may give rise to an increase in vacuum to assist closing & opening of the valves…..this is only a bit of an educated guess.
Cheers Kerrin
|
|
|
|
Post by Jim on Aug 29, 2022 0:24:03 GMT
I was told that the pintle/ram also reduced the risk of cavitation by ensuring any trapped air was squeezed out.
One suggestion I found useful was to include a a non return ball valve at the inlet end of the water pick up pipe especially if there was some distance from the water tank/tender. The valve ensured a column of water was at the inlet valve ready for delivery and to stop it running back down the pipe between strokes.
The photo shows the ram pump on the Burrell with a long delivery pipe going down into the water tank below. The tap is for the water bypass when the pump is no longer needed to dliver water to the boiler. The gap between the end of the bypass pipe gives the driver a visual indication that the pump is circulating water while idle, if all that makes sense.
Jim
|
|
|
|
Post by runner42 on Aug 29, 2022 0:36:18 GMT
Gary,
as I indicated. It is important to minimise the dead volume when the plunger is fully in, to clear air which would otherwise reduce displacement efficiency due to its compressibility. LBSC’s spigot helps in this regard, but where there is room one can run the ram bore right into the valve body at full diameter, so there’s no place for an air pocket to hang up in.
Brian
|
|
Gary L
Elder Statesman
Posts: 1,208
|
Post by Gary L on Aug 30, 2022 12:45:38 GMT
Gary, as I indicated. It is important to minimise the dead volume when the plunger is fully in, to clear air which would otherwise reduce displacement efficiency due to its compressibility. LBSC’s spigot helps in this regard, but where there is room one can run the ram bore right into the valve body at full diameter, so there’s no place for an air pocket to hang up in. Brian Sorry Brian, I didn't make myself clear. Yes indeed, reduce the dead volume, to minimise the size of any air bubbles left behind. In an extreme case (in theory) the pump plunger could just work back and forth compressing and expanding a massive air bubble and never actually getting to move any water, which is obviously not helpful. But consider what happens as soon the pintle enters the outlet port when there is no air in the pump barrel. The stroke has not finished; there is still an appreciable distance for the ram to travel, and there is a quantity of incompressible water in front of the ram looking for a way out of the barrel. But the outlet port is blocked by the pintle, so there is nowhere for this water to go, unless it can squeeze around the sides of the pintle, or squeeze past the ram seals. If the clearances around the pintle are slack, then it does not fulfil the 'dead volume' criterion very well, but the pump will just about work at low speeds. If the clearances are tight, or speeds are higher, you will get a hydraulic lock. In my view, you should, as you say, keep the clearance volume at the end of the stroke to an absolute minimum (as with all pistons), and this will clear the majority of any rogue air bubbles. But no bubbles will linger long in the outlet port, because of the flow of water, so the pintle is redundant at best, and positively harmful at worst. HTH Gary |
|
|
|
Post by runner42 on Aug 31, 2022 7:32:43 GMT
Gary, you appear to be saying that when the pintle reaches the output port that is closes the output port and prevents the residual water from being pumped out, thereby producing a lock up and preventing the ram from operating to its design limit. The amount of water trapped is proportional to the length of the pintle. The assumption here is that the pintle is a snug fit without clearance between it and the output port. Under this scenario the pintle should be short, but equal in length to the output port. In practice the clearance between the output port and pintle is sufficient to provide a escape route for the potentially trapped water. If this is not the case is to engineer a deliberate bleed path as shown in the sketch. I am not au fait with the operation of the fluid in this pump, I can only say that this concept is not new and tends to be a feature of most axle pump designs.  RAM by Brian Leach, on Flickr Brian |
|
|
|
Post by ettingtonliam on Aug 31, 2022 8:38:47 GMT
This concept of the pintle to clear excess air was advocated by LBSC (I think) and so has been around for a lot of years. Yes, it should be a slack fit in the barrel output drilling. Alternatively, file a flat on the pintle. Whether it is necessary or not is open to arguement, but I should think that thousands of locos have been built incorporating it without problems, so lets not overthink this one!
|
|
|
|
Post by springcrocus on Aug 31, 2022 11:51:37 GMT
This concept of the pintle to clear excess air was advocated by LBSC (I think) and so has been around for a lot of years. Yes, it should be a slack fit in the barrel output drilling. Alternatively, file a flat on the pintle. Whether it is necessary or not is open to arguement, but I should think that thousands of locos have been built incorporating it without problems, so lets not overthink this one! It doesn't mean that he was correct, however. I should think that thousands of model engineers have blindly followed whatever he (and others) advocated without question and nobody dared to contradict him. The design below should do the same (supposed) job just as well, and is probably easier to make as well.  Regards, Steve |
|
Gary L
Elder Statesman
Posts: 1,208
|
Post by Gary L on Aug 31, 2022 13:59:48 GMT
This concept of the pintle to clear excess air was advocated by LBSC (I think) and so has been around for a lot of years. Yes, it should be a slack fit in the barrel output drilling. Alternatively, file a flat on the pintle. Whether it is necessary or not is open to arguement, but I should think that thousands of locos have been built incorporating it without problems, so lets not overthink this one! You mean you've never wondered why an axle pump was knocking, or why it makes the loco run rough? Personally I think the LBSC excrescence on the pump ram is a classic example of overthinking. It looks so neat on a drawing too, but LBSC clearly never thought about the fluid dynamics. He certainly never (at least to my limited knowledge) specified that it had to be a slack fit. I'm guessing that these days, we make things to tighter tolerances than LBSC was used to, and he wouldn't have predicted or allowed for that. Yes, filing a flat on the pintle will improve matters a little, but if you were going to do that, why not just remove it entirely? An air bubble might lodge in the top of the pump bore, but it is impossible for them to lodge for long in the exit port. Just think it through. I had more than enough troubles with the LBSC pattern axle pump on my Speedy. Since then, neither of my locos has had one. I removed it from Bridget and the running was instantly transformed. Maybe not quite a Rolls Royce but it stopped sounding like a bag of nails on the track. I also removed the twin pumps from Paddington (not my work). That decision was made even easier when I discovered that the designer had made no provision for servicing. The only way to extract the pumps was to remove the driving axle! Hand pump, yes, wouldn't be without one. Axle pumps- never again! But improvements are possible if you must have one. Reducing the over-large LBSC bore has been mentioned already. Gary |
|
|
|
Post by runner42 on Aug 31, 2022 23:22:55 GMT
This concept of the pintle to clear excess air was advocated by LBSC (I think) and so has been around for a lot of years. Yes, it should be a slack fit in the barrel output drilling. Alternatively, file a flat on the pintle. Whether it is necessary or not is open to arguement, but I should think that thousands of locos have been built incorporating it without problems, so lets not overthink this one! You mean you've never wondered why an axle pump was knocking, or why it makes the loco run rough? Personally I think the LBSC excrescence on the pump ram is a classic example of overthinking. It looks so neat on a drawing too, but LBSC clearly never thought about the fluid dynamics. He certainly never (at least to my limited knowledge) specified that it had to be a slack fit. I'm guessing that these days, we make things to tighter tolerances than LBSC was used to, and he wouldn't have predicted or allowed for that. Yes, filing a flat on the pintle will improve matters a little, but if you were going to do that, why not just remove it entirely? An air bubble might lodge in the top of the pump bore, but it is impossible for them to lodge for long in the exit port. Just think it through. I had more than enough troubles with the LBSC pattern axle pump on my Speedy. Since then, neither of my locos has had one. I removed it from Bridget and the running was instantly transformed. Maybe not quite a Rolls Royce but it stopped sounding like a bag of nails on the track. I also removed the twin pumps from Paddington (not my work). That decision was made even easier when I discovered that the designer had made no provision for servicing. The only way to extract the pumps was to remove the driving axle! Hand pump, yes, wouldn't be without one. Axle pumps- never again! But improvements are possible if you must have one. Reducing the over-large LBSC bore has been mentioned already. Gary I thought you were raising a concern about the pintle to better understand the operation of an axle pump. However, it was not the case you already have concerns about the efficacy of axle pumps in general and setting the scene to provide your objections to their use. A bit of time wasting, it would have been better had you made your concerns known at the outset. I suspect that your pump design was not optimum and therefore not met your requirements. I have experienced good performance with axle pumps so as with many things, there's those for and those against. However one point that you raise that I totally agree that maintenance if required is a major operation, so the design that Allan Wallace provides attempts to minimise the wear areas so maintenance is greatly reduced. Brian |
|
Gary L
Elder Statesman
Posts: 1,208
|
Post by Gary L on Sept 1, 2022 9:50:01 GMT
You mean you've never wondered why an axle pump was knocking, or why it makes the loco run rough? Personally I think the LBSC excrescence on the pump ram is a classic example of overthinking. It looks so neat on a drawing too, but LBSC clearly never thought about the fluid dynamics. He certainly never (at least to my limited knowledge) specified that it had to be a slack fit. I'm guessing that these days, we make things to tighter tolerances than LBSC was used to, and he wouldn't have predicted or allowed for that. Yes, filing a flat on the pintle will improve matters a little, but if you were going to do that, why not just remove it entirely? An air bubble might lodge in the top of the pump bore, but it is impossible for them to lodge for long in the exit port. Just think it through. I had more than enough troubles with the LBSC pattern axle pump on my Speedy. Since then, neither of my locos has had one. I removed it from Bridget and the running was instantly transformed. Maybe not quite a Rolls Royce but it stopped sounding like a bag of nails on the track. I also removed the twin pumps from Paddington (not my work). That decision was made even easier when I discovered that the designer had made no provision for servicing. The only way to extract the pumps was to remove the driving axle! Hand pump, yes, wouldn't be without one. Axle pumps- never again! But improvements are possible if you must have one. Reducing the over-large LBSC bore has been mentioned already. Gary I thought you were raising a concern about the pintle to better understand the operation of an axle pump. However, it was not the case you already have concerns about the efficacy of axle pumps in general and setting the scene to provide your objections to their use. A bit of time wasting, it would have been better had you made your concerns known at the outset. I suspect that your pump design was not optimum and therefore not met your requirements. I have experienced good performance with axle pumps so as with many things, there's those for and those against. However one point that you raise that I totally agree that maintenance if required is a major operation, so the design that Allan Wallace provides attempts to minimise the wear areas so maintenance is greatly reduced. Brian Time wasting? I agree. I’ll stop following your thread. Best wishes Gary |
|
|
|
Post by runner42 on Sept 2, 2022 7:36:03 GMT
I have completed the superheater, the final part was cutting the outputs from the dry header to size so they aligned correctly with the smokebox steam connections. Initially I cut them 1/8" too short which neccesitated making two sleeves of gunmetal to lenghten them so that they aligned without too much stretching of the copper pipes. Had I made the dry header in two halves it would have made installation a lot easier. However, the assembly was straightforward if the sequence was thought out beforehand. The smokebox needs to be affixed to the boiler and installed as an assembly. The steam pipes from the cylinders to the smokebox are added afterwards. Brian  Superheater installed by Brian Leach, on Flickr |
|
|
|
Post by GWR 101 on Sept 3, 2022 12:32:48 GMT
Brian, looks very neat, I have been deliberating how to undertake a similar set-up on my Jubilee. A question if I may please, how is the steam oil delivered to the cylinders ?. Apologies for asking. Regards Paul
|
|
|
|
Post by runner42 on Sept 4, 2022 1:19:15 GMT
Hi Paul, I copied LBSC's solution for his 3 1/2" gauge Doris Black 5 which is to feed the cylinder lubrication in via the steam connections between the cylinder and smokebox. This positioning was driven by the placement of the mechanical lubricator between the frames at the front of the smokebox. Brian  Cylinder lubrication by Brian Leach, on Flickr  lubricator by Brian Leach, on Flickr |
|
|
|
Post by GWR 101 on Sept 4, 2022 7:27:54 GMT
Brian many thanks, I must admit I hadn't considered that. I propose to fit the mechanical lubricator in the same position. Regards Paul
|
|
