# Axle pump for RH Lady Anne, Fowler, etc.



## Dr. J (Feb 29, 2008)

1. Can anyone give me a rough idea of how many cc's per revolution an axle pump for a coal-fired Lady Anne / Fowler should put out? (Or, for that matter, any other locomotive with roughly the same boiler volume?) 
2. Are there published plans for such a thing?
Thanks
Dr. J


----------



## Semper Vaporo (Jan 2, 2008)

Dunno about the Lady Anne/Fowler, but for any engine:

Steam is water expanded by about 1600 times. Thus, if we assume the steam fills the cylinders then you need to replace 1/1600 times the volume of what the cylinders use in one revolution of the drivers. Assumming 2 double-acting cylinders then it is 4 times the volume of 1 cylinder.

Plus you need to replenish what is lost in leaks in poor connections (if any) in the steam piping, blowby in the valves and cylinders and around valve and piston rod glands, and what is lost when the safety valve lifts to relieve pressure, plus blowing the whistle. ALL of that is totally unknown and will vary based on outside temperatures, air pressure, capabilities of the fireman to maintain pressure without lifting the safety valve, whim of the engineer blowing the whistle, and probably the phase of the moon.

This is why there is a bypass valve. The axle pump runs whenever the engine is in motion. If the bypass valve is open, then the water being pumped 'Bypasses' the boiler clack valve and returns to the tender, so no water is lost and the pump does not continuously pump into the boiler and possibly over fill it. When the boiler gets low on water, the bypass valve is manually closed so the pressure that the axle pump can produce can overcome the boiler clack valve and the water enters the boiler to replace what was lost in running (or blowing the whistle!). As long as the axle pump is capable of putting more water in than is being used to work the pump the boiler water level will go up. When it is again to the proper level the bypass valve is again manually opened to release the pressure from the pump and let the water return to the tender.

Some people claim they can adjust the bypass valve to such a partial opening that some pressure is developed that is enough to push "some" water into the boiler and that amount is enough to replace what has been used... A so called "Sweet spot". If the throttle is set to a particular spot and the engine uses the exact same amount of steam in an average of its travels in a loop of track then there might be a "sweet spot" for the bypass valve for that engine on that day at that ambient temperature on that track with that train in tow with that brand of fuel with that setting of the burner with that setting of the throttle. In reality, the amount of water being replenished to the boiler will be either a bit too much or a bit too little, but it is better than no replenishment at all, so the run can be extended without the engineer/fireman/operator/you having to stop the train to pump water with a Goodall valve or tender pump or to alter the setting of the bypass valve (I can open or close the bypass on my Mikes while they pass in front of me at near top speed for my layout!). Care still needs to be taken to be sure the boiler does not eventually run out of water or get over full.

From what I have seen of axle pumps the ram diameter is usually from 1/3 to 1/2 of the diameter of the drive pistons. The stroke is anywhere from 1/4 to 3/4 of the stroke of the drive pistons. They push enough water to refill the boiler in a short time with the bypass closed. If the boiler is getting too full, then open the bypass. If the pump cannot pump that much water then there are probably too many steam leaks or the fireman needs to turn down the fire, or the engineer needs to lay off the whistle.


----------



## Taperpin (Jan 6, 2008)

Axle pump sizing: bore of 6mm stroke of 5mm will supply roundhouse size cylinders [9/16" [bore] bore can be changed too smaller if stroke is lengthened in proportion. check valve lifts/seats and passages are important as well.


----------



## Steve Shyvers (Jan 2, 2008)

Dr. J, 

My RH Billy's coal-fired boiler is about the same size as you would use on a Lady Anne. It's axle pump has a bore of just over 5/32" and a stoke of 3/16", so its got a lot less capacity than Taperpin advises. It will keep up with steam consumption as long as I can maintain the boiler pressure below 40 psi. Above that pressure it won't pump anything into the boiler. This complicates running because the fire can't be allowed to get too hot, and a hot coal fire is easier to maintain in that condition. Probably I should rebuild the axle pump to follow Taperpin's recommendations. 

Another problem with my Billy, I believe, is that the clack is mounted on the side of the boiler so that steam can leak back through the clack if the water level gets low. This causes the pump effectively to push against a bubble. The cure might be to mount the clack lower on the back head. This will also ensure that the clack ball is always immersed in water, which I believe will help it to seal. It's also important to try to use the largest practical clack ball. (Same goes for the valves in the axle pump and hand pump.) I used a commercial clack (long unavailable) that used a 1/8" ball in a shallow pocket. I rebored the clack body to cut a deeper pocket and a new valve seat for a 5/32" ball. Also the ball lift has been restricted to about 1/64". (The ball needs to lift and then reseat very rapidly. If the lift distance is too great then the ball won't seat and seal fast enough to prevent all the water that was just pumped through the clack to flow back the other direction.) This has all helped a lot. Before making these mods the clack seal was very intermittent, resulting at times in hot water or steam flowing out of the bypass return into the tender water tank. If the water in the tender tank is warm then the clack isn't sealing, and you can bet no water is going into the boiler. 

Steve


----------



## David BaileyK27 (Jan 2, 2008)

Steve, never have the Clack Valve below the water level, it will get muck in it much easier, we always put our clacks in above the water level, steam should not leak back through the Clack,, the 5/32" Ball size is OK but the lift is too small at 1/64" I suggest at least a 1/32" or else you are restrickting the pump flo too much, as to pump sizes we use a 5/32" ram and 7/16 stroke, dont forget that the larger the diameter the ram the more horspower is needed to drive it, so a pump with a long stroke and small bore is better. 
David Bailey DJB Model Engineering Ltd


----------



## David Leech (Dec 9, 2008)

Posted By David BaileyK27 on 19 Feb 2012 09:15 AM 
Steve, never have the Clack Valve below the water level, it will get muck in it much easier, 
David Bailey DJB Model Engineering Ltd 
Hi David,
Now this interests me.
I think that all my locos probably have their clack valves below the water for most of their lives and don't appear to have a problem.
In fact, I would have thought that the pressure of 'water' against the ball was probably a nice thing, rather than just steam.
Secondly, 'why' would muck get in them.
I am pumping (hopefully clean) water through them, and then as the pump pressure reduces below the boiler pressure the ball is forced back against it's seat.
Do you reckon that at that moment there is disturbance or something that can suck any boiler crap back into the valve? 
Depending on the design of the back head, there is not always much room, and check valves tend to be put where they can.
How high do you recommend, and therefor how full should one run ones boiler normally?
All the best,
David Leech, Delta, Canada


----------



## Steve Shyvers (Jan 2, 2008)

David Bailey, 

Thank you for the advice. I'll double-check the ball lift in the clack and adjust accordingly. I concur regarding the pump ram diameter and stroke. I will see if I have clearance to install a larger throw pump eccentric, although I may experiment with a slightly larger ram diameter first. 

When I modified the clack, as mentioned in my earlier posting, I cut the ball seat deeper in part to ensure that the ball moved vertically and not to one side off the seat, and in part so that the ball when on it's seat would sit in a puddle of water, reasoning as David Leech did that the seal would be more effective against water than against lower density steam. 

Steve


----------



## David Leech (Dec 9, 2008)

Steve, 
One thing that I like to see, is a nice vertical clack valve body. 
Again, I'm not sure that it makes good sense, but I like to imagine that the ball 'falls' nice and squarely onto the seat. 
I notice that some of the Accucraft locos have their's tilted, and I wonder if that effects the seating of the ball. 
There has to be enough clearance around the ball otherwise no water would get past, so I imagine the ball leaning against the one wall and then having to roll across to sit in the seat. 
Maybe in reality it makes no difference, as the 'horizontal' clack on the Accucraft Royal Hudson seems to function just fine. 
All the best, 
David Leech, Delta, Canada


----------



## David BaileyK27 (Jan 2, 2008)

David, as we are talking about coal fired boilers the water should always cover the firebox crownsheet, the clack should be mounted above this line otherwise when the engine is not in steam the sediment in the water could get in between the ball and seat and prevent it from being pressure tight, I would also reccomend that clacks are mounted verticle otherwise as you say the ball will fall to one side and not seat as well, all the horizontal check valves I have seen are spring loaded to keep the ball on its seat. 
David Bailey


----------



## Dr. J (Feb 29, 2008)

Thank you all!! A couple of follow-up questions: 
1. Steve Shyvers indicated that boiler pressure should be kept below 40 psi, otherwise the axle pump wont be able to overcome the boiler pressure. This leads me to two sub-questions: (a) I thought "higher pressure was better," in terms of getting the most performance out of the locomotive? In other words, if an engine has a safety that's set to lift at 60 psi, then the ideal boiler pressure would be just a hair under 60. No? (b) Since water is essentially incompressible, and because the axle pump is mechanical, with non-deformable parts, I dont understand why it matters to the pump whether the boiler is operating at 40 or 60 PSI. Unless you're suggesting that the axle pump begins to act as a brake. For example, if one clamped the line somewhere between the ram and the clack, the pressure in the line proxmal to the clamp would immediately rise, preventing the ram from "ramming" any more water, and the axle bearing the eccentric would thus be prevented from rotating, and the engine would come to a stop. As long as the engine continues to roll, it seems to me that the pump has to be pumping, no matter what the PSI. This disregards leaks, of course. What have I overlooked?
2. David Bailey states that the clack should be mounted (a) above the waterline of the crownsheet, as well as (b) vertically. I have a hard time figuring that out. All I can envision is the clack is on top of the boiler, pointed downwards (vertical, although "upside down". The ball would fall away from the seat unless retained upwards with a spring, which would be overcome by the pumping action when the engine was in motion). The only way the clack could be vertical otherwise would be to mount it at the bottom of the boiler pointing straight up - with all the problems with sediment that DB refers to. I am confused.

Thanks, Taperpin (Gordon Watson, I think) for those dimensions. 
Jim C


----------



## David Leech (Dec 9, 2008)

Jim, 
A 'normal' traditional check/clack valve is an inverted 'L' shape, with the inlet at the bottom, and the outlet to the boiler to the side. 
The ball will naturally fall to the bottom onto the seat. 
The bushing on the boiler can be right in the centre and as close to the top as possible to follow David Bailey's suggestion. 
Most of my locos seem to have them to the left or right hand side, about mid level, but they are all alcohol fired. 
I do have an Aster Shay that has the clack on the side of the boiler, right towards the front end. 
As I said, I do have a Royal Hudson that has an 'in line' horizontal clack valve, and I must open it up to verify that it does indeed have a spring. 
However, it is working well, so why tempt fate by opening it up!!! 
As far as boiler pressure, the axle pump does need to overcome this every time it pumps. 
Therefor the higher the pressure, the more work required, however since you are also having more power to the cylinders, it probably cancels itself out. 
I have heard of locos 'limping' when pumping which is probably as David Bailey suggests, the bore is probably too large in relation to the stroke, making it work very hard for that one half rotation of the wheel. 
Two little axle pumps, or a double acting one would help cure this. 
All the best, 
David Leech, Delta, Canada


----------



## David BaileyK27 (Jan 2, 2008)

Dr J, to keep the Clack verticle we have a bush in the boiler which is Horizontal but cut into the diameter near the top part of the outer shell. 
We run most of our coal fired engines at 60 PSI to get a sharper exhaust to keep the fire going and to keep the condensation down in the cylinders, that is why I said that use a small diameter pump with a long stroke, because the higher the boiler pressure then the more horsepower is required to drive it, I run some of my larger coal fired engines at 80PSI such as my K27, C21 and C25 but they have 3/4" diameter cylinders and produce a lot more power, so a larger axle pump is required. 
With a coal fired model engine it is a balancing act between keeping the water in the boiler, keeping the fire bright and keeping the pressure up, so when designing a coal fired engine this all has to be taken into consideration, boiler size, number of flues, size of grate, total heating area, size of blastpipe, and size of axle pump, a lot to think about, I have had over 50 years designing and building small coal fired engines and have learnt a lot during that time. 
David Bailey


----------



## Steve Shyvers (Jan 2, 2008)

Dr. J, 

I didn't mean to imply that the boiler pressure must not exceed 40 psig in all cases. Only that on my coal-fired loco the axle pump could not pump effectively against more than 40 psi, all the causes of which still need to be figured out. If you look at the first photo that I posted in your thread about making a 2-6-0 you will see the coal-fired Billy's clack valve mounted on the side of the boiler. This clack valve matches David Leech's description of an inverted "L" configuration. The water inlet is vertical up through the bottom of the unit, and the outlet is horizontal through the attachment to the side of the boiler. 

Steve


----------



## xo18thfa (Jan 2, 2008)

KN Harris goes into depth on steam calculations. How much steam a certain amount of water will produce at a pressure. How much steam is consumed and all that. After reviewing his book, and if I did the calculation right, a pump with a 5/32" bore and 1/4" stroke will just keep up at 50 PSI. So, 5/16" stroke should be enough.


----------

