Just William (3.5 gauge 2-6-2)

[JonL]

Possibly, I don't know. But when I open the bypass I often get air bubbling out of the return pipe (whilst in motion), and the pump seems to push air back into the centre feed tank.

But when I apply pressure or suction to each non return valve in turn they are completely airtight?! It's driving me to distraction!

[timb]

Hi Nobby, You say the pump works OK when on the bench but not the track?
Assuming that you are not under steam on the bench, is the differenct the boiler pressure, ie the pump will move water but not overcome the pressure in the boiler to allow it to feed?

Thinking out loud!

Tim

[JonL]

Sept 6, 2020 13:28:14 GMT timb said:

Hi Nobby, You say the pump works OK when on the bench but not the track?
Assuming that you are not under steam on the bench, is the differenct the boiler pressure, ie the pump will move water but not overcome the pressure in the boiler to allow it to feed?

Thinking out loud!

Tim

It sounds quite likely. I'm going to revisit the ram seals. I know I can do better, especially with Roger's aforementioned better materials.

[dhamblin]

When running 'Netta' it is very noticeable the extra resistance / surging once the bypass is closed and the axle pump is pushing water into the boiler. Are you getting that sensation when you try it on the track?

Regards,

Dan

[JonL]

No, it would appear opening and closing the bypass has zero affect on the performance.

Funnily enough I can't believe how much easier it is to turn the wheels now she has had a full day of running in. She wasn't exactly lumpy before but now the wheels spin like silk.

[don9f]

Yes, great photo Jon and well done ! Pity you don’t live nearer as I’m sure the axlepump problem will be an easy fix....I’m in most days 😀

Don

[ettingtonliam]

Thinking completely outside the box, the inlet and outlet valves are the right way round, are they?

[JonL]

Sept 6, 2020 20:16:54 GMT ettingtonliam said:

Thinking completely outside the box, the inlet and outlet valves are the right way round, are they?

It was something that crossed my mind early on as well, I've been back through the two valves on the pump and can confirm they are working in the correct sense!

[ilvaporista]

Sept 7, 2020 7:15:07 GMT JonL said:

Sept 6, 2020 20:16:54 GMT ettingtonliam said:

Thinking completely outside the box, the inlet and outlet valves are the right way round, are they?

It was something that crossed my mind early on as well, I've been back through the two valves on the pump and can confirm they are working in the correct sense!

I managed to invert the connections between the loco and driving truck. Worth a quick check.

[JonL]

Tonight I skimmed the bore on the axle pump and remade the gland to take a fresh o-ring, I also made a new ram. This I fitted with two separate grooves of square cross section to allow the o-rings I installed in there to seal adequately. I also changed the stainless balls for ceramic ones and reseated them.

Running on air there was no change, until I primed it by sucking on the bypass outlet pipe. Suddenly it burst into life, but again not consistently. Once or twice it would stop at random and need repriming. However for the most part is seemed to run well. My only concern was that if I applied finger pressure over the outlet I could stop the flow without a huge amount of force being applied. Below that level the water squirted all over the place like a finger over a hose pipe. I should also confirm the water was coming out of the overflow in hearty squirts that was going all over the shop. It also appears to top up the boiler over the air pressure I was applying through one of the safety valve bushes. I wonder how much pressure a finger over the pipe could overcome?

It's rather odd and annoying that it doesn't self prime, especially as it appears to need to be reprimed if you stop and restart. Maybe there was still a bit of air in the system. I can only think its my workmanship letting this down. Under pressure I can see no air leaks from any fittings. In use it will probably prove to behave differently yet again...

[mbrown]

This may be a silly question, but this puzzle seems to have defeated the sensible questions.... is it possible that the take--off point in the tank is somehow above the water level allowing air in instead of "solid" water? The fact the pulp needs priming suggests an air leak on the inlet side, but you say all joints seem airtight....

The mystery deepens.

Malcolm

[mr swarf]

Just a thought,have you got an anti air lock pin on the end of the ram.
Paul

[JonL]

The under-bunker tank has a small sump on the underside which supplies the axle pump. It's quite low (below the height of the running boards), but I believe its at a height which will not give issues. You have got me wondering if the convoluted route I've taken to keep the pump supply pipe well away from the grate has given me issues?

[JonL]

Sept 8, 2020 20:28:11 GMT mr swarf said:

Just a thought,have you got an anti air lock pin on the end of the ram.
Paul

No, and now I remember such a thing exists I wish I had known earlier when making my new ram! The annoying thing is I made one on my Britannia water pump. I just followed the drawing for this one.

[John Baguley]

Hi Jon,

Just a couple more thoughts:

If you have got rid of any air in the system and you can stop the water coming out of the pump outlet easily with your finger then that suggests to me that the inlet ball valve may be leaking and allowing the water to leak back down the supply pipe on the pumping stroke.

The ram could also still be leaking although you should see that. The O ring grooves should be about 50% wider than the O rings and not the same width. Is the ram a tight fit when you fit it?

Do the balls have too much lift? If the balls have too much lift they will bounce around when the pump is running at any speed rather than seating and making a proper seal on the valve seat. The amount of lift needed to pass the output of the pump is actually very small and the balls only need to lift something like 1/32" at the most.

If all else fails, it might be worth trying some nitrile balls instead of the metal ones. They work best with a conical seat as the usual sharp edge of the normal seat may damage them but it will at least prove if it is the seats that are at fault.

John

[doubletop]

I test water pumps by disconnecting the boiler feed and fitting a safety valve in the line. The pump then runs against the safety so you get an idea of how it will work against boiler pressure. You are also able to test feed rate and the action of the bypass. Run the loco on air and you'll have a simple setup to test the pump and investigate what is happening, make changes and try again.

If you want to check the boiler clack as well, remove from the boiler and make a fitting to have the safety valve downstream from that.

BTW do you have the hand pump and axle pump going to the same clack? That won't work, you'll need a double clack.

Pete

[JonL]

Some good notes there thank you. I suspect the inlet clack and also the amount of lift are good leads here, I do have a way more lift on the delivery clack than you mention, I'll reduce that probably tonight.

[JonL]

I managed to get hold of some brass sheet from my boiler cladding yesterday so tonight I clamped it to a piece of wood and milled out the holes for the safety valves and the steam dome (the real one, the cosmetic cap that goes over the top covers up the edges of this hole.

For milling holes in the sheet I just clamped it down to a piece of wood using as many clamps as I could from my machine clamp set (something I purchased with my Mill and boy am I glad I did, this one if anyone is interested) and then drilled a hole slightly larger than one of my end cutters. This allowed me to then axially cut out a radiused slot for my safety valves to poke through. The dome hole was a bit less pretty; I had to manipulate the x/y of the mill to use a small end cutter to enlarge the hole until it was about the right size for the dome. It wasn't ideal but it was the best I could do with the tools I had other than chain drilling (which I only remembered after, idiot).

[JonL]

An interesting day. I've now managed to get it pumping water, roughly half of the time! However when I opened the clack to check for blockages or sticking I found the new ball bearing is covered in corrosion. It's less than a few weeks old. I am quite unimpressed, I believed it to be stainless steel. I've ordered some silicon nitride ones to replace it.

This explains why it works some of the time, and sometimes was squirting a tiny amount of boiler water back out of the bypass outlet (something I only discovered today by putting my finger into the outflowing water).

I was able to ascertain it was flowing water by touching the clack itself; it was cold when working and hot when not.

[stevep]

I still don't quite understand your problem, as when the bypass valve is closed, there should be no water coming out of the bypass outlet. As I have said before, I think there is an issue with your plumbing.