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3 inch Southworth engine

Running on steam?

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Half centre05/09/2021 17:49:54
32 forum posts
1 photos
Hello everyone - I have built 2 of the Southworth 3 inch vertical pump engines, one for each side on the front plate of my Sweet Pea (I think they are also known as Weir pumps). They work beautifully on air and pump water at atmospheric pressure on my test rig. Both have a hydrostatic lubricator in line with the steam supply. When I put them onto the engine and try using steam its no go? The steam supply for each is an independent feed from an extended manifold and is copious. I have tried running them against boiler pressure, and with the water supply disconnected, the inputs and outputs open to the air. Still nothing. I sometimes get a slight down stroke then nothing. Steam and water jet out from the exhausts?
Has anyone got one of these engines to run and pump against boiler pressure on a 5 inch loco? If so would you have any hints (or magic spells!) you could share with me.
Thank you
Simon Collier05/09/2021 21:37:51
418 forum posts
60 photos

What are you using for the piston seals and gland seals? If using Viton O-rings, you want very light squeeze. They expand when hot and may well get too tight. The official, specified squeeze from charts for a dynamic application is far too much for use in our locos. A friend recently made a pump in the style of a Westinghouse compressor for his 5" gauge engine and it works fine. I have one on my Simplex built by Warwick Sandburg which works, but is very inefficient as a serious water feed. I intend to make one fairly soon.

Half centre06/09/2021 08:53:11
32 forum posts
1 photos

Hi Simon - Thank you for getting back to me - I am starting to realise that these things are a bit of a minority sport.

The rings come supplied in the bag of castings so I am not sure what they are made of, I will phone Blackgates. Your suggestion of rings expanding and tightening in the heat is an excellent explanation of why they run on air and not steam. I am sure you are right about their inefficiency. I am treating them as a bit of mechanical bling - an interesting feature rather then a serious water feed. They do look good perched on the front of the Pea (vanity, vanity!)

Its good to know they can potentially work so I will persevere.

thank you


Jon Lawes06/09/2021 10:23:14
652 forum posts

Might want to check the small shuttle inside the valve chest is still moving freely. I've built one of these and I can get the steam side working fine, but the clacks don't return fast enough to stop backflow of water. I'm perservering!

noel shelley06/09/2021 10:57:08
758 forum posts
19 photos

I have heard it said or read that the mini weir pumps are notoriously dificult to get to work well, requiring great accuracy in the build and also in setting up - this may be idle gossip ? Just a thought. Good luck, Noel.

Jon Lawes06/09/2021 14:49:55
652 forum posts

I'm a complete amateur and mine wasn't too bad. I lapped all the mating faces to try to get a good seal (as there is a plate between the valve chest and the cylinder to provide the crossover between the ports for the shuttle valve) but on the whole its a nice little design to make. As I say, the problem I've had has been with the valves on the water pump side not shutting off quickly enough to pump the water rather than just moving it back and forth. I'll get there.

Half centre06/09/2021 16:32:19
32 forum posts
1 photos

Hi Noel - Thanks for your reply, I have heard that as well. I have DRO on the mill otherwise it would be well beyond my experience / ability to tackle. I think the basics must be correct because they go like the clappers on air, very frustrating they don't run on steam.

Hi Jon - Thanks for getting back to me. I fixed the shuttle valves at an early stage in the make, but you are right it is a key source of problems if you are not very careful. As for the clacks I did not follow the drawings, they looked very fiddly and rather delicate? I made ordinary type in line clacks with a Nitrile ball (its a cold water feed so Nitrile is OK). By ordinary I mean the type that have a deep groove in one face and the ball is pressed against it in the on position allowing the water to flow around it, through the groove and out. In the off positing the ball presses against a seating to stop water flow. They seem to work well and I have had no problems (yet!) with transient back flow - might be worth a try? However without a spring and with no pressure to close them they do let water through, but as they connect the water tank to the pump and then a boiler clack the whole feed water line can remain flooded. Hope that all makes some kind of sense?


David Wasson23/09/2021 00:44:12
149 forum posts
43 photos

Here's the pump I made for my Super Simplex. Works well on steam or air. Really moves a lot of water fast. Will work on high or low pressure. It is a Van Brocklin design, uses no castings. Valves are cross ported and will always self start. (Not just bling!)

Sorry the photo is turned!


Half centre23/09/2021 17:18:57
32 forum posts
1 photos

That's quite some pump David - it looks great and it works. I think I have found the plans for it and if my Southworth pumps continue to be uncooperative I will definitely give it a go.

thank you


David Wasson23/09/2021 17:58:54
149 forum posts
43 photos

Thank you Martin,

Yes, the drawings are available on the net at no charge. I think they are available at the IBLS site. All made from bar stock, no castings.


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