Axle Pump

[drjohn]

Well, I think at last I've found a couple of reasons why the pump shaft bent.

1) The piston was a margin too long and was covering the outlet holes in the pump, and also, for whatever reason, the pump wasn't exactly in line with the centre of the eccentric driving it.

And 2) the 3/16" copper pipe I got from Oz, has quite a small bore.

So today, having re-vamped the pump and installed it on the new stretcher (see the images bit), I put some water in the tanks and connected the compressor to feed the boiler. At 50 PSI, with the wheels doing about 100RPM, the water jet out of the bypass was virtually good enough for water-cutting - Sheesh! And the "bark" from the exhaust was spectacular, but I doubt sustainable at speed.

My calculations say that with a 7/16" bore and 1/2" stroke, the pump is delivering about 1.3ML per rev. Doesn't sound a lot, but with the bypass closed, the boiler feed pipe was getting too hot to handle with the pressure. So tomorrow, I intend sleeving the pump and fitting a 1/4" ram, single acting, which should pump about 0.4ML per rev, and hopefully get round this problem of Australian copper tube.

DJ

P.S. Guess who won't be buying copper thingys from Oz - either boilers or tubing!!

[drumkilbo]

Well done DJ, you just need some track now !

Ian.

[Shawki Shlemon]

Hi DJ
I see you are upset with us , but when ordering copper tubing one should mention size and wall thickness as they come in different wall thicknesses.My lips are sealed about the other issue.The other issue on the pump I always try to make the by pass as large as the supply to the boiler so that if the boiler is full all pump outlet can be bypassed .As you say may be the double acting pump was /is too big for the size of the boiler .I am sure you will solve the problem and I hope that the does NOT end up in the fish tank , it deserve better than that .

[drjohn]

Hey Shawki, I'm not upset with ALL 'borigines, only a couple! ;D

DJ

[nigelh]

Hi guys,
might seem a very basic question, but what material should be used for the axle pump eccentric strap ? The drawing specifies BMS for the sheave but no mention for the strap! Is steel on steel OK here?
Also, has anyone found the need for a split sheave ? (Apart from forgetting to put it onto the axle before fitting the wheels and axleboxes!)
thanks - Nigel

[jgb7573]

I would use a dissimilar metal for the strap. These are usually supplied as iron or gunmetal castings, though you can machine them from solid too.

[nigelh]

Thanks, John - steel on steel didn't seem right for this sort of work!
I don't seem to have a casting for the strap (it is many years since I bought them!) so will try and find some solid to machine it from.
cheers
Nigel

[nigelh]

Question for John - how has your sleeved (to 1/4" bore) pump performed, John ?
I am soon to start on my pump and would be interested to hear if that bore is sufficient?
cheers
Nigel

[drjohn]

Hi Nigel

The sleeve didn't work against boiler pressure - it wasn't moving enough water to overcome airlocks, so I went back to the original design with a shorter piston and it seems fine - yet to be tried for earnest on the track.

DJ

[nigelh]

Thanks, John - sorry your mod didn't work but, hey, that's the only way to find out, I reckon!
Looking forward to hearing (and seeing some pictures) how she runs on the track.
cheer
Nigel

[drjohn]

Nov 26, 2009 7:37:14 GMT nigelh said:

Looking forward to hearing (and seeing some pictures) how she runs on the track.

Me too! ;D ;D

DJ

[nigelh]

Just a small step forward, for me, but have now completed my axle pump eccentric sheave and strap.
Would love to attach a piccy of it but can't see how to !! Help !
Nigel

[nigelh]

found how to do it -- IIDRTFM comes to mind !!
Nigel

Attachments:

[jgb7573]

Looks good Nigel.

[nigelh]

Thanks John; machining marks show I've got a lot to learn about tool sharpening but it's a good start, for me. Now working on the pump casting - interesting exercise finding ways to hold it, square & securely, in the 4 jaw!
Will post a piccy or two when I've got something to show.
cheers
Nigel

[nigelh]

Hi folks, I'm now making progress on the pump body but cannot fathom out how to cut the delivery ball seats - I'm working to sheet 2 of Martin Evans drawings. The seats are shown as "upward pointing" vee shape and appear to require a hollow ground (on the end) cutter.
Could some kind soul explain to me how they have made theirs ??
Many thanks,
Nigel

[davidm]

I'm afraid that I cheated with mine and cut the seats square with a D bit. I wonder if a slot drill would do as good a job? Anyway its a good idea to form the seat with a clout on a sacrificial ball of the same size as the one that you'll use for real.

David

[nigelh]

Thanks David - I presume they worked ok ?
Much easier than trying to make a special tool.
cheer
Nigel

[jonkett]

I was planning on making a D-bit with a 10/15 degree slope as it only has to scrape a small amount of material to form the seating.

Of course if this is a load of ******** I hope someone will put me right.

[drjohn]

For all the ball seats, I drilled the hole for the water a smidgen undersize, made the seat with a 4 flute end mill, then ran a final cut with a reamer to make sure the hole the ball was going to sit on was round, and used a sacrificial ball to donk the seat. Seems to work fine.

DJ