Boiler feed pump ?

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ianrichards
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Boiler feed pump ?

Post by ianrichards » Mon Mar 18, 2019 6:25 am

The time has come for me to think about boiler feed pumps and the various options available.
From my research it appears that you can either go for one that is driven off the crank/prop shaft or one that is independently steam powered.
Are there other options and which is the best to go for?
My boiler is a twin drum water tube boiler and it will be powering a 3.5 hp single engine.
Many thanks as usual.
Ian
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Re: Boiler feed pump ?

Post by RGSP » Mon Mar 18, 2019 8:42 am

You could (of course) use an electric pump, but in my opinion something driven by the main engine is better. The boiler should only generally lose water when the engine is running (whistles excepted), so a pump that runs when the engine runs has a certain logic to it.

Stand-alone steam pumps do have a certain attraction, but remember that the cylinders on such pumps are really tiny, and the steam valve gear is often a bit crude: in other words tiny steam pumps are going to be horribly inefficient. The water loss from the boiler as steam for the pump probably won't exceed the pumped water going in, but the two will certainly not be radically different, and this is confirmed by one or two people who have (rather beautiful) small Weir type pumps in their boats - actually Southworth 12" types I think.
ianrichards
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Re: Boiler feed pump ?

Post by ianrichards » Mon Mar 18, 2019 9:35 am

That's all makes sense.
I'll be on the lookout for an engine driven pump then ... that'll be the difficult enough in itself.
A steam driven pump did look like an attractive proposition, but I'm sure that one less thing to look after/go wrong will be much appreciated later on.
As for electric ... makes absolute common sense, but not on my boat !
Thanks
Ian
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Re: Boiler feed pump ?

Post by loggerhogger » Mon Mar 18, 2019 9:55 pm

Contact Pat Spurlock of Elliot Bay Steam Launch. I think he has castings for one that is gear driven off the shaft.
ianrichards
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Re: Boiler feed pump ?

Post by ianrichards » Mon Mar 18, 2019 10:05 pm

Thanks for that, but the wrong side of the pond !
Regards
Ian
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Re: Boiler feed pump ?

Post by TriangleTom » Tue Mar 19, 2019 2:58 am

Ian,

I've been giving a lot of thought to this lately as I re (x4) design my engine. Given the general difficulty in sourcing a feedwater pump, it doesn't seem that constructing one should be extremely difficult by comparison.

A single-acting pump should be able to work with some heavy steel flanged pipe bolted closed to make the piston, with check valves to serve as the ingress and egress valves for the water. If the pressure side of the piston is opposite the rod end, this should also avoid any issues with rod packing, as any water that escaped past the piston should be able to simply escape out through the rod hole. Lubrication of the piston should be more or less possible through the use of graphite impregnated plastic piston rings, so as not to contaminate the feedwater with oil.
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Re: Boiler feed pump ?

Post by ianrichards » Tue Mar 19, 2019 6:16 am

Tom.
I concur your thoughts, but with everything else I have to do I’d rather like to source a ready built pump. Here enters “plan B. The chap I bought my WW2 era ex WD engine from has a pump that was once attached to it. Apparently it has a couple of parts missing and he has indicated that he will sell it to me. The only problem I see now is getting it to the top of his priority list !
Will update you as/if he comes up trumps.
Ian
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Re: Boiler feed pump ?

Post by RGSP » Tue Mar 19, 2019 9:32 am

It may well be worth putting a wanted advert in "The Funnel". Feed pumps do sit in people's workshops for a whole variety of reasons, but mainly being too good to scrap, and not really worth enough to justify the effort of advertising. Now I think of it, I bet Mark Rudall (as editor of The Funnel) would have some good ideas on where to track down a pump.

Bear in mind you have multiple choices for an engine driven pump:-
1. an eccentric straight on, or bolted onto the end of, the crankshaft.
2. chain, vee-belt, polyvee belt, or toothed belt, drive to a lay shaft, and most people arrange a 2:1 (or something) reduction if doing this, which can make the pump valves operate more reliably.
3. a direct link to the engine cross-head - in many ways the simplest and neatest option.
4. I suppose one has to include a geared drive from the crankshaft, but that needs very careful engineering, and it isn't a nice place for gears at all.

Plumbing might be most easily done using flexible armoured hose, and I know of one very effective installation where a pump piston rod runs from a crank on a lay shaft without any crosshead or connecting rod, so the pump body oscillates instead. Looks a bit odd but works very well.

Dick
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Re: Boiler feed pump ?

Post by ianrichards » Tue Mar 19, 2019 10:02 am

Excellent, thanks. I’m on the case.
Best wishes
Ian
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Re: Boiler feed pump ?

Post by dampfspieler » Tue Mar 19, 2019 1:27 pm

I have a pump unit (Boiler feed pump with an air vessel and condensate pump) at my engine. It is direct driven from the crosshead.

EinZylBoot214kl.jpeg
EinZylBoot214kl.jpeg (95.17 KiB) Viewed 876 times

An injector is also a steam driven pump - i prefer it. There will no steam lost and the feed water preheated.

Dietrich
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