Author Topic: Stuart Boiler Feed Pump  (Read 62146 times)

Offline K.B.C

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Re: Stuart Boiler Feed Pump
« Reply #120 on: December 12, 2013, 10:18:35 PM »
Hi Florian,

It's interesting to see that you are making gland packing from Teflon, I can't see any great wear on the pump shaft as all the forces are in line.
I have often considered using this method but have stayed with the Graphite yarn, some years ago there was an imported twin cylinder double acting engine from India, I think it was, modeled on the Stuart D10 and had the pistons made from either Teflon or P.T.F.E..
A friend of mine in England was the importer but had so much trouble with them that he had to make and replace the pistons  made from Bronze and fit Silicone "O" rings, he eventually abandoned their import as he had too much trouble with other parts of the engine.

I have just completed my Stuart pump and it runs very well on steam but must say that it doesn't have the control that yours has.
Mine is very greedy on steam but I haven't had it pumping under working conditions yet, so it may well be much better  when it has some work to do.

May I congratulate you on your workmanship and the ball turning tool is the same as one that I made to turn the ball joints on my Flash Steamers prop shaft.
You are quite an insparation and it only makes me try harder with my machining.

Great job keep it up.

George.

Your never too old to learn.

Offline Florian Eberhard

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Re: Stuart Boiler Feed Pump
« Reply #121 on: December 12, 2013, 10:52:26 PM »
Hey George

Thanks for applauding me! I am always happy if I can give something to the forum because I have (earlier more than now) been finding lots of good information, hints and tricks here in the forum too!

As far as i know, "Teflon" is DuPont's brand name for P.T.F.E. So it is acutally the same.
The reason for using it is: Teflon has the lowest coefficiant of friction of all plastic materials. Especially it does not require a certain breaking loose force like most of the O-rings do!
The seal is yet going a little tight and that is why my pump is running very slow. It wouldn't without any load (because the pressure somewhen would drop under the required amount for moving the shuttle)

Your friends problem is the very great coefficiant of thermal expansion that teflon has. So if you have the piston fitted in cold condition(like 20°C), the piston will expand around half a millimeter when you heat it up to lets say 120°C!!

I did not run mine on steam yet, but I just came from the shop and had it running with pressurized air and pumping water. It can bring 11.5 bar water pressure with 4 bar on the steam side!

Next up will be building an oiler and then I can test it on steam.

For your pump: You may want to try putting silicone O-rings on your shuttle valve as well (possibly with making another shuttle valve?).
You will find out that the pump then has a lot more force than without!
If you are going to try, I would recommend to make the O-ring grooves only slightly less deep than they would have to be to get the o-rings flush with the valve (I use something like 0.1mm less in depth but 1,2 times as wide as the o-ring is).
The O-rings also dont get damaged by the ports (even if they are sharp) if the O-rings are only very few more than flush with the outer diameter of the valve.

 :cheers:  Florian

Online steamer

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Re: Stuart Boiler Feed Pump
« Reply #122 on: December 12, 2013, 11:11:33 PM »
Ive had good luck with teflon piston rings in my launch engine
At 165 psi saturated.

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Florian Eberhard

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Re: Stuart Boiler Feed Pump
« Reply #123 on: December 12, 2013, 11:45:21 PM »
Hey Dave

Rings are different! They are quite thin and the expansion with hight temperatures is therefore smaller than the one of a full piston. (the expansion over all of course - the coefficient is the same for both - pistons or rings)

Florian
« Last Edit: December 12, 2013, 11:52:35 PM by Florian Eberhard »

Offline derekwarner

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Re: Stuart Boiler Feed Pump
« Reply #124 on: December 13, 2013, 01:19:42 AM »
Florian........raw PTFE  certainly does have a low CoF & a high temperature range & so is suitable for out model steam applications .......but the same material has near ZERO memory + low strength

If you use this virgin PTFE material for piston rings ...they will expand @ 10 Bar & 150 degrees C & stay there at this new size/profile/dimension

To counter the strength, manufactures add MoS, or glass or bronze powder which significantly improve the characteristics

With respect to memory, one option is to use a Viton o-ring energiser [whilst dynamic, however is essentially a non wearing elementt] to energise the PTFE seal element

Some very interesting reading  here ....www.economos.st .....

I have been using the Economos  philosophy in industrial hydraulic sealing applications here in Port Kembla for 20+ years........... Derek
Derek L Warner - Honorary Secretary [Retired]
Illawarra Live Steamers Co-op - Australia
www.ils.org.au

Online steamer

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Re: Stuart Boiler Feed Pump
« Reply #125 on: December 13, 2013, 03:33:16 AM »
Well...make it how ever you like....Mine have been of TEFLON and have been pushing my boat around for a number of years.

Mine were machined like this



Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Online steamer

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Re: Stuart Boiler Feed Pump
« Reply #126 on: December 13, 2013, 03:47:08 AM »
And to your point Florian....the lap joint allows for the expansion.

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline derekwarner

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Re: Stuart Boiler Feed Pump
« Reply #127 on: December 13, 2013, 05:01:27 AM »
steamer....I do acknowledge that the single L stepped cut seal profile you show is an excellent choice...having a few advantages

1. it does not require a piston of demountable construction to install within a fixed piston seal cavity
2. it also will compensate for linear, axial & volumetric expansion

Raw PTFE is a difficult material to CNC machine.........with your compound step cut I assume the material is reinforced??........Derek
Derek L Warner - Honorary Secretary [Retired]
Illawarra Live Steamers Co-op - Australia
www.ils.org.au

Offline K.B.C

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Re: Stuart Boiler Feed Pump
« Reply #128 on: December 13, 2013, 11:50:27 AM »
My Post No 120.

May I clear up the statement regarding the Teflon piston on my friends imported engines.
The piston were machined from a Teflon bar and they seized under steam,that is why he had to replace the pistons ( pistons as per pic )
Dave,
I see no reason as to why you shouldn't make rings from Teflon and as you have proven they work well, some of my club mates with small Oscillating engines roll up Plumbers P.T.F.E. tape to pack their pistons and although they work but only for a season and then have to be replaced.
George.





« Last Edit: December 13, 2013, 11:57:23 AM by K.B.C »
Your never too old to learn.

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Re: Stuart Boiler Feed Pump
« Reply #129 on: December 13, 2013, 12:17:48 PM »
steamer....I do acknowledge that the single L stepped cut seal profile you show is an excellent choice...having a few advantages

1. it does not require a piston of demountable construction to install within a fixed piston seal cavity
2. it also will compensate for linear, axial & volumetric expansion

Raw PTFE is a difficult material to CNC machine.........with your compound step cut I assume the material is reinforced??........Derek


Nope.....straight teflon.   A friend of mine with another successful steam launch uses the bronze filled version.    Like I said....that's how I made it.
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline K.B.C

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Re: Stuart Boiler Feed Pump
« Reply #130 on: December 13, 2013, 12:20:24 PM »
Florian regarding your post No121


For your pump: You may want to try putting silicone O-rings on your shuttle valve as well (possibly with making another shuttle valve?).
You will find out that the pump then has a lot more force than without!
If you are going to try, I would recommend to make the O-ring grooves only slightly less deep than they would have to be to get the o-rings flush with the valve (I use something like 0.1mm less in depth but 1,2 times as wide as the o-ring is).
The O-rings also dont get damaged by the ports (even if they are sharp) if the O-rings are only very few more than flush with the outer diameter of the valve.

 :cheers:  Florian

I had considered using Silicone "O" rings on the shuttle but on viewing the drawing there are 2- holes that the ring would foul.

Now this is where I disagree with you, you should never allow a Silicone "O" ring to pass over a port.
Silicone "O" rings expand under steam, some people say 100% which I can accept as the grooves are in excess of the "O" ring cross section.
A number of years ago when I started using Silicone rings I did not believe the makers dimensions for grooves.

As an example , for a 1/2" dia piston the recommended groove for the .070" cross sectioned ring is  Min depth .057"  - .060" and the width is .094" - .102"
Now I just did not believe these dimensions so in my wisdom I machined the groove with min clearance with the result that the engine ran well for about 5 mins and then stopped, after cooling it would start again with the same result.

So after some thought I machined the grooves as per the instruction dimensions and to this day I still do so and have never had any trouble, on further discussions with some of my steam loco model maker friends, who do exactly the same agree that the "O" ring under steam completely fills the groove due to the expansive nature of the Silicone  ring and when cool take up the original round shape of the ring.

George.
Your never too old to learn.

Offline Florian Eberhard

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Re: Stuart Boiler Feed Pump
« Reply #131 on: December 13, 2013, 12:35:54 PM »
Hi George

Yes, it is not the best thing to have the o-ring sliding over a port. And that was my point of view aswell before a friend told me it works quite well in small scales. I tried it out and in fact it does work quite good - at least they last for quite some time and may get damaged after a while but not so fast.

Regards Florian

Offline Florian Eberhard

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Re: Stuart Boiler Feed Pump
« Reply #132 on: December 18, 2013, 08:31:20 PM »
Good evening Lady(ies?) and Gentlemen

Another step has been achieved, the drain cocks were completed.

I also had to get the threads into the cylinder - did it without taking any pictures. However, the drain cocks look like I imagined and I am happy with them except the wooden handles - i would rather like them to be a little darker (in about like pearwood - but I don't have any around. I will see, maybe Ill get some...)
I also made another plug for the pump bore (I only made the one for the top when I was machining the pump body):
To get the pump working really well, I decided to use plungers with o-rings instead of the balls.
The plungers have three cutouts to let the water pass through while guiding themselves with the cylindrical extension on the lower side. I milled those cutouts directly in the lathe.

With the finished plungers, I could testrun the pump for the first time! I was using pressurized air instead of steam though but I guess if it runs well on air it will at least run on steam too.
The Pump can do 11,5 bar with 4 bar air pressure!  :cartwheel: I would say that is a SUCESS!!! :whoohoo:

So whats left:
- Cylinder cladding (I am still not shure how to do it)
- building a displacement lubricator
- building a main steam valve
- probably painting it (or blacken part of it?)

I started with the lubricator:
I have found an old drawing of a "full size" displacement lubricator which I want to copy in an according size.
I am going to make it from several parts by soldering them together.

So much for now - I'll continue soon (hopefully :agree: )

« Last Edit: August 15, 2017, 08:59:23 PM by Florian Eberhard »

Offline Roger B

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Re: Stuart Boiler Feed Pump
« Reply #133 on: December 18, 2013, 09:10:57 PM »
That looks good  :ThumbsUp: :ThumbsUp: What sort of speed was it running under load?
Best regards

Roger

Offline Florian Eberhard

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Re: Stuart Boiler Feed Pump
« Reply #134 on: December 18, 2013, 09:23:17 PM »
That looks good  :ThumbsUp: :ThumbsUp: What sort of speed was it running under load?

It was not running anymore then (I closed the valve)
But It can pump against 10 bar (though it is quite slow then...)

 

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