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Post by george on Sept 28, 2017 20:07:17 GMT
Hello all, if an axle pump is put on upside down does it hydraulically lock and stop the wheels turning please? George
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smallbrother
Elder Statesman
Errors aplenty, progress slow, but progress nonetheless!
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Post by smallbrother on Sept 28, 2017 20:14:42 GMT
That's a strange question George.
Why would you put it on that way?
Pete.
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Post by andyhigham on Sept 28, 2017 20:25:07 GMT
What do you mean by upside down? If you mean so that the balls fall away from their seats then it will just not pump. I can't see a situation where the pump could hydraulic unless the outlet ball was mechanically prevented from leaving its seat
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Post by george on Sept 28, 2017 21:30:20 GMT
the loco came that way, (its a sweet pea) i have to get the pump off to check it ,but it wont pump water. it seems the most logical place to start.another thing ive noticed is the feed to the bypass valve is on the inlet side of the pump,every loco ive owned has this on the outlet side of the axle pump, but having said that the pipe diagram drawings show it routed from the inlet side.
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Post by manofkent on Sept 28, 2017 21:34:31 GMT
George
I once saw a 5" gauge tender loco. The feedpump had been put on one of the tender axles.
The tender wheels always locked up as soon as the bypass valve was closed. The owner tried weights on the tender, and even laying on it. The wheels would not pump. I concluded that you always need a driven or coupled axle to power a feed pump.
I have never seen a driven axle locking with a pump.
John
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smallbrother
Elder Statesman
Errors aplenty, progress slow, but progress nonetheless!
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Post by smallbrother on Sept 28, 2017 22:04:15 GMT
I would check the balls are the right way up and disconnect the pipes and see if things move freely. After that I would connect a feed and see if it pumps it into the air.
It turned out we had a ball stuck on our Polly 1 loco. It was a right swine to get at but once out and cleaned it all worked fine.
Pete.
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Post by peterseager on Oct 1, 2017 6:33:15 GMT
This problem occurred recently at the Bishops Stortford MES. Problem was caused by the outlet valve not having proper clearance above it to allow the water to pass by on the output stroke. The drawings said to put nicks there. There are nicks and nicks. The original builder had used the small type.
I bought a hand pump at the Guildford Rally which would not work. Turned out that clearance above the inlet valve was not provided.
Peter
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Post by gwr14xx on Oct 1, 2017 6:56:25 GMT
The method I use to produce the 'nicks' is to insert a suitable sized 'Phillips' screwdriver bit into the valve, then use a vice to press in the 4 nicks to the required depth. (Much easier than trying to cut them)!
Eddie.
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Post by george on Oct 1, 2017 16:25:59 GMT
I had the axle pump off today, had it all apart cleaned it and put it back together, it pumped water out of a bucket into the air fine, put it back on and will try in steam in the week sometime, Another problem i found was the blast pipe had not been sealed where it entered the smoke box, cleaned it all out and sealed it, im still not sure about the bypass return pipe being on the inlet side of the axle pump,even though the drawings say it goes there, ive always had the return on the outlet side of the axle pump.but i will wait until ive steamed it to see if there are any more problems.
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smallbrother
Elder Statesman
Errors aplenty, progress slow, but progress nonetheless!
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Post by smallbrother on Oct 4, 2017 17:38:41 GMT
I had the axle pump off today, had it all apart cleaned it and put it back together, it pumped water out of a bucket into the air fine, put it back on and will try in steam in the week sometime, Another problem i found was the blast pipe had not been sealed where it entered the smoke box, cleaned it all out and sealed it, im still not sure about the bypass return pipe being on the inlet side of the axle pump,even though the drawings say it goes there, ive always had the return on the outlet side of the axle pump.but i will wait until ive steamed it to see if there are any more problems. I would say that the water will take the line of least resistance. If it is easier to go back into the tank than push the clack-valve open then it will go back in the tank. If the only available route is via the clack-valve it should work. Good luck! Pete. |
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Post by builder01 on Oct 4, 2017 18:03:33 GMT
Axle pumps are easy enough to test on compressed air. I do it all the time. With 50-100 psi of air in the tank, the axle pump should easily put water in the boiler. You can also test how the "by pass" valve is working. You can steam it if you want, but, compressed air should show what you need to know. (The only thing I cannot test is the injector!)
David
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Post by chris vine on Oct 4, 2017 19:09:16 GMT
Hi George,
to test the pump, before taking the time to have a steam-up, you could try pumping water (like you did) but put your finger over the delivery pipe while pumping. The pressure should easily be able to push past your finger, however hard you press it on.
If it won't do this, then it won't pump against the boiler pressure.
Enjoy,
Chris.
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Post by george on Oct 5, 2017 4:10:14 GMT
This is what this forum is best at, getting good sensible advice, thank you gentlemen.
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Post by runner42 on Oct 7, 2017 6:07:12 GMT
Here is an answer to a question that was not asked, but provided to ensure that the design of the axle pump does not provide too much displacement such that the by-pass valve is always open and continually pumping water back in the tender or side tanks. LBSC, Martin Evans et al provided designs where the displacement volume is 3 times more than required, which puts too much load on the locomotive more than required to keep the boiler at the required level.
To estimate how much displacement (per wheel revolution) is required from an axle pump. The density of water is 1000 kg/m^3. Steam tables show that the density of saturated steam at 700 kPa (100 psi) is about 4 kg/m^3. The ratio is 250 to 1. This suggests that the displacement of the axle pump (per wheel revolution) should be about 1/250th (0.4%) of the displacement of the cylinders. In other words, to completely fill the cylinders with saturated steam at boiler pressure, one needs an axle pump to deliver 1/250 of the cylinder volume.
Using this it shows that many locomotive designs that the displacement volume of the axle pump is greater than 1/250 of the cylinder volume.
Brian
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Post by steamer5 on Oct 7, 2017 7:41:34 GMT
Hi Brian,
Now that's a handy bit of information! Stored away for a rainy day, not that my loco's got axel pumps but Dads has & is likely to come my way one day.
Cheers Kerrin
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stevep
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Post by stevep on Oct 7, 2017 9:50:07 GMT
That's interesting information Brian.
If I understand it correctly, if you have an axle pump that pumps 1/250 of the cylinder volume, then you would have the bypass closed all the time, and the pump would maintain the water level in the boiler.
However, if the water level dropped - say due to the safety valves lifting, then you wouldn't have any spare capacity to re-fill the boiler. So the pump needs to be some factor larger than the 1/250. Any thoughts on what that should be?
Steve
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Post by runner42 on Oct 8, 2017 0:10:35 GMT
That's interesting information Brian. If I understand it correctly, if you have an axle pump that pumps 1/250 of the cylinder volume, then you would have the bypass closed all the time, and the pump would maintain the water level in the boiler. However, if the water level dropped - say due to the safety valves lifting, then you wouldn't have any spare capacity to re-fill the boiler. So the pump needs to be some factor larger than the 1/250. Any thoughts on what that should be? Steve Yes, the bypass should be closed all the time. The only reason for having a bypass is to verify that the axle pump is producing an output by looking at the tender return pipe for evidence of pumping. I agree one should consider the effect of superheat, the cutoff, leakages, auxiliaries such as injectors, safety valves blowing etc. Some of these push the 4% ratio up, and some down, but at least you have a starting point for an engine working continuously at maximum output. You would need to consider how much these variables impact the ratio for your particular design, so it would be inappropriate to specify a general amount. I sure that many would engineer a safety factor amount that would always insure sufficient capacity, but generally you will find that even with this safety margin the pump is producing too much output. Brian |
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stevep
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Post by stevep on Oct 8, 2017 10:01:46 GMT
I think I would be very uncomfortable if I needed to have my pump bypass closed all the time. On my Rob Roy, I have the bypass valve cracked open about a 1/4 turn. If the water level in the boiler rises (which it does when I am driving one notch off mid-gear and not using so much steam), I can open the valve a bit more, and if the water level drops, I can close it a bit.
The bypass discharges just under the filler of one of the side tanks, so I can see the water squirting out, and I tend to adjust the bypass valve to get the right amount of "squirt", based on my experience of driving the engine.
Rob Roy is quite a small locomotive, and I cannot feel any additional loading when I close the bypass - I just see the boiler pressure dropping like a stone. With the bypass open (or partially open), I don't think the amount of work used to drive the water around is at all significant.
Steve
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Post by runner42 on Oct 8, 2017 23:16:30 GMT
I think I would be very uncomfortable if I needed to have my pump bypass closed all the time. On my Rob Roy, I have the bypass valve cracked open about a 1/4 turn. If the water level in the boiler rises (which it does when I am driving one notch off mid-gear and not using so much steam), I can open the valve a bit more, and if the water level drops, I can close it a bit. The bypass discharges just under the filler of one of the side tanks, so I can see the water squirting out, and I tend to adjust the bypass valve to get the right amount of "squirt", based on my experience of driving the engine. Rob Roy is quite a small locomotive, and I cannot feel any additional loading when I close the bypass - I just see the boiler pressure dropping like a stone. With the bypass open (or partially open), I don't think the amount of work used to drive the water around is at all significant. Steve I don't like to perpetuate an issue when I have nothing of importance to add. But we are referring to axle pumps, Rob Roy utilises a crosshead pump and these generally are by necessity smaller. When I built my Rob Roy I intuitively thought that the displacement volume of the crosshead pump would be insufficient to keep the boiler level at the required level, but like yours it is about right. Brian |
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smallbrother
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Post by smallbrother on Oct 9, 2017 7:54:15 GMT
Where fitted, I use the axle pump for short top-ups often when the engine is coasting down a slope. The pressure may be high due to a good blast up the slope, in which case the input of water closes the safety valve. If I have struggled up the hill I can whack the blower on and top up at the same time. I use the injector(s) in the station or on the run as seems fit. I like to use all the available water supplies which means a longer run between topping up the separate tanks. I also try and work out a routine for each track I run on.
No idea if this is "right", but it has worked for several years for me.
Pete.
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