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Post by andyhigham on Sept 13, 2020 16:22:40 GMT
To keep other threads clear I have started this thread to discuss axle pumps. My thoughts :- 2, 3 or 4 pumps will give smaller and a more even resistance With a short connecting link the angularity will cause a lot of side force on the ram causing friction and increasing resistance, a longer connecting link will reduce the angularity. Another approach would be "desaxe" the ram being offset from the crank (eccentric) so at the point of maximum pressure the ram and connecting link are closer to a straight line. My race bike engine uses this arrangement to keep the con rod straighter during the power stroke. Has anyone tried a rotary or gear pump?
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dscott
Elder Statesman
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Post by dscott on Sept 13, 2020 17:14:21 GMT
Yes I am trying 2 smaller opposing pumps on my much modified Simplex. Fowler Complex. They are off the 5 inch Hunslet and bolt onto a brass plate. This slides up into 2 2 BA bolts and is secured by 2 underneath.
Should anything happen to them they just slide down to get attention. Pipework joined at the bottoms as well. One pumps the other fills. And so on.
David and Lily.
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Post by andyhigham on Sept 13, 2020 17:54:20 GMT
I would also say the pump(s) should be timed in phase with the cylinders
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Post by Roger on Sept 13, 2020 20:17:41 GMT
I'm not convinced that you need to go to the complication of more than one pump in 5" gauge, I've never noticed any lumpiness in running. I can see why it might be an issue on smaller gauges or light locomotives though. The one fitted to SPEEDY is way too big in my opinion, based on looking at other similar sized locomotives. Obviously a larger pump than necessary is going to make it harder to work.
Side loads are an issue if you don't have adequate lubrication, so I've made a decent sized reservoir to feed the ram. If you only oil the outside of the ram at the start of the run, it's not really giving the bearing a reasonable chance of a long life.
It ought to be possible to have a smaller pump if you have effective Superheaters.
Another thought is that if you do opt for two pumps, it might make sense to fit two bypass valves. Then you have the option to run just one pump with the bypass fully closed and the other fully open so that it's as efficient as possible. Since pumps are sizes for maximum loading, you'd probably find that you only need to run one anyway unless you're pulling a huge load.
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Gary L
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Post by Gary L on Sept 14, 2020 0:37:20 GMT
I'm not convinced that you need to go to the complication of more than one pump in 5" gauge, I've never noticed any lumpiness in running. I can see why it might be an issue on smaller gauges or light locomotives though. The one fitted to SPEEDY is way too big in my opinion, based on looking at other similar sized locomotives. Obviously a larger pump than necessary is going to make it harder to work. Side loads are an issue if you don't have adequate lubrication, so I've made a decent sized reservoir to feed the ram. If you only oil the outside of the ram at the start of the run, it's not really giving the bearing a reasonable chance of a long life. It ought to be possible to have a smaller pump if you have effective Superheaters. Another thought is that if you do opt for two pumps, it might make sense to fit two bypass valves. Then you have the option to run just one pump with the bypass fully closed and the other fully open so that it's as efficient as possible. Since pumps are sizes for maximum loading, you'd probably find that you only need to run one anyway unless you're pulling a huge load. Roger is right about Speedy. My Speedy had a standard (i.e as drawn) axle pump, and that could definitely give a jerky motion when working hard. So a smaller bore would have been a good idea; pity I never thought of sleeving it... particularly since it spent most of its time pumping through the bypass, which because of an inadequate balance pipe meant that the left hand tank would regularly cascade water out of the filler when running. Paddington, on the other hand, is drawn with 2 pumps and a pair of massive eccentrics to drive them. No doubt this would give a smoother motion, but -word to the wise- I discovered that it was impossible to access the pumps without dropping the driving axle; not what I call maintenance-friendly- so they had to go. Bridget's pump can be taken out by removing four bolts and disconnecting the eccentric- very much superior, even if I don't use it. Maintenance needs to be designed-in at an early stage. There are plenty of reasons for and against axle pumps, and I'm sure we are bored with the arguments that get us nowhere (there was one on another thread recently) but I don't like to hear the alleged unreliability of injectors given as one of them. My experience is that injectors are much easier to maintain and at least as reliable as pumps. Most pumps don't have Roger's clever rubber thingy, so have a tendency to sticking valves which, depending on location, can be a royal pain to unstick. If an injector fails mid-run it isn't the end of the world. You have a backup supply system, and if that fails you put the fire out- but I've never needed to resort to that. Gary
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uuu
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Post by uuu on Sept 14, 2020 6:48:01 GMT
If you're a masochist, you could go for a steam pump disguised as a Westinghouse brake pump. These seem to be an order of magnitude more difficult to get reliable than either an axle pump or injector.
I'm not sure I buy into the the multi-pump idea. Each one increases complexity and with it the chance of failure. A loco with a correctly sized and configured axle pump is a joy to drive (as is one with a reliable injector).
How about a five-cylinder, single eccentric one, shaped like a radial aero engine?
Wilf
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Post by steamer5 on Sept 14, 2020 7:13:15 GMT
Hi Wilf, How about a 6 cylinder swash plate driven one?
My Dads loco has all bases covered....2 injectors, twin axel pumps, Westinghouse pump, & a hand pump one day I’m going to have to figure out how to drive it!
Cheers Kerrin
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smallbrother
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Post by smallbrother on Sept 14, 2020 8:58:40 GMT
I've had 2 x 5" and 2 x 7.25" locos with single axle pumps and I can't ever recall any difference whether the pump was filling the boiler or not. I generally used these pumps on a downhill section so maybe that helped overcame any additional resistance?
All very efficient, made driving a piece of cake, I can't see what the problem is. I had reliable injectors on all of them so it was up to the driver how they wanted to manage the run.
I got a number of youngsters happily doing laps on all these locos which would have been far more risky without such pumps.
Pete.
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Post by eightpot on Sept 14, 2020 14:15:24 GMT
My experience is that small injectors can be fiddly in getting started and in operation. Having once been shunted from behind by another loco whose driver was more concerned with getting his locos injector to work rather than observing signals, I'll admit to being a teensy bit biased! Pump-wise I rather like the Martin Evans semi-displacement type as used on his 'Simplex' design. I fitted one of these on my LBSC 'Speedy' many years ago and it has given complete satisfaction. However, I have made provision with the water inlet elbow to have a removable screw or bolt that can be removed to unstick the inlet ball valve with a bit of wire if necessary. With that one freed the loco can then be moved to get some water into the pump in order to hydraulically unstick the delivery ball if required. I make the same arrangement of a screw in the floor of water tanks under hand pumps for the same reason.
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Gary L
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Post by Gary L on Sept 14, 2020 16:53:39 GMT
I've had 2 x 5" and 2 x 7.25" locos with single axle pumps and I can't ever recall any difference whether the pump was filling the boiler or not. I generally used these pumps on a downhill section so maybe that helped overcame any additional resistance? All very efficient, made driving a piece of cake, I can't see what the problem is. I had reliable injectors on all of them so it was up to the driver how they wanted to manage the run. I got a number of youngsters happily doing laps on all these locos which would have been far more risky without such pumps. Pete. That, I accept, is a very good reason for having a (modest sized) axle pump! -Gary
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uuu
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Post by uuu on Sept 14, 2020 17:24:25 GMT
Or, if you're a miserable old fart, for not having one.
Wilf
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waggy
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Post by waggy on Sept 14, 2020 18:07:19 GMT
I’d agree with Roger re a bypass per pump, not only could you offload one but having a visible bypass return into the tank would let you know if one pump had failed for whatever reason.
Waggy.
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Post by Jim Scott on Sept 14, 2020 20:53:42 GMT
Side loads are an issue if you don't have adequate lubrication, so I've made a decent sized reservoir to feed the ram. If you only oil the outside of the ram at the start of the run, it's not really giving the bearing a reasonable chance of a long life. It ought to be possible to have a smaller pump if you have effective Superheaters. Roger
I haven't seen much in the way of comment on water pump lubrication and I can’t recall a design that incorporates an oil reservoir but it sounds like a good idea. As both you and Andy say, side loads could be appreciable on a compact axle pump arrangement and lack of lubrication could cause a costly failure. In fact this was probably a contributory factor in a mechanical failure of my Maid of Kent which resulted in the loco being derailed - but that's another story...
So everyone, what is the current practice, is it just an initial squirt of lubricating oil at the off? If so, are there any issues with the oil being wiped off by the soft packing or ‘o’-ring seal or washed out by water leakage? Is there any evidence that very small amounts oil could get into the boiler and if so does it pose a problem?
Regarding superheaters, replacing the rather poor originals in my very old Maid of Kent with radiant ones significantly reduced (almost halved) the water consumption.
Jim S
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JonL
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Post by JonL on Sept 14, 2020 21:04:56 GMT
Are we looking at the wrong thing here? Maybe an axle driven pump is still viable but not of the piston displacement type? What about the kind used in automotive oil pumps? Or a diaphragm? Peristaltic? (My apologies if my spelling is wrong)...
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Post by cplmickey on Sept 14, 2020 21:49:21 GMT
I haven't seen much in the way of comment on water pump lubrication and I can’t recall a design that incorporates an oil reservoir I've never thought lubrication was necessary - I only oil the eccentric. Pumps are generally brass with brass, or brass with gunmetal and the packing or o-ring will be lubricated by the water. Ian
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Post by coniston on Sept 14, 2020 21:53:28 GMT
Are we looking at the wrong thing here? Maybe an axle driven pump is still viable but not of the piston displacement type? What about the kind used in automotive oil pumps? Or a diaphragm? Peristaltic? (My apologies if my spelling is wrong)... Some interesting ideas Nobby, but I guess it comes down to the rotational speed of the axel and the relative difficulty of manufacture against the 'old fashioned' piston pump. Nut let's see where this goes. Chris D
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Post by coniston on Sept 14, 2020 21:56:16 GMT
I’d agree with Roger re a bypass per pump, not only could you offload one but having a visible bypass return into the tank would let you know if one pump had failed for whatever reason. Waggy. That's all well and good but for a tender loco it means yet another water connection plus for either there is the complication of an additional valve and pipework. Would it not be better for both pumps to be unloaded rather than unequal loading between them? just a thought and worth some more discussion no doubt. Chris D
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Post by John Baguley on Sept 14, 2020 22:25:16 GMT
I've driven a couple of 2½" Gauge locos that have twin pumps with a bypass each so it has been done. I found them quite good as you could leave one bypass closed most of the time to keep the boiler topped up as you were running and then close the second bypass when you needed a bit more output. Both of the locos had the returns to the tender commoned to one pipe rather than have two separate returns.
John
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uuu
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Post by uuu on Sept 15, 2020 6:23:56 GMT
Doesn't having separate bypasses spoil the whole point of having two pumps. If one of them is man enough to keep the boiler topped up most of the time, then you'll be running with just that one and have all the supposed rough running it brings.
Wilf
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Post by keith1500 on Sept 15, 2020 7:04:33 GMT
Re: lubrication. On my Speedy every now and then I drop the eccentric strap from the pump piston with draw it and check the O ring then a good smear of plumbers silicon grease and reassemble. Quick and simple.
Same with hand pump.
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