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Vertical steam driven boiler feed pump

Problem under steam

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Stephen Lawson15/03/2011 10:07:07
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I was given this 4" high vertical pump and after a little cleaning and lubrication it appeared to run well on compressed air and after fitting to a horizontal marine boiler, it did the business - on air.>>

On raising steam, the pump failed to run and just rested in one position. No proding or forced action could encourage it to run. Adjustments of the steam valve stroke also failed to get any movement.>>

Back on air it runs well !>>

Disassembling the valve chests at the top end, I could not understand the complicated double steam valves and fail to comprehend how it should work.>>

Is there anyone out there who can tell me the name of the pump, perhaps has a set of drawing that will help me or has previous experience of the little beast ?
This pump is quite different to that in Model Engineer started in Vol.204 No. 4368


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Richard Parsons15/03/2011 10:53:37
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Steve when you ran it ‘on air’ was it pumping water? If so was it pumping against a ‘head of water’? If it is a ‘yes’ to both questions then when you stopped running it on steam did you get any condensate out of the steam cylinder?


Finally how big (in diameter) is the pump cylinder compared to the power (steam) cylinder? Think about this. The boiler pressure is say 50psi, the steam pressure in the cylinder will be lower due to restrictions in the pipe work, valves and steam passages. If the cylinder pressure was say 35 psi and the cylinder was 1 square inch. If the pump cylinder was also 1 square inch could it push water against 50 psi? Pumps like this, work because of Braham’s hydraulic principle. Think of the little pump on your hydraulic pump and the large ram on your car jack.

good luck it looks a nice pump

Dick
Stephen Lawson15/03/2011 12:15:30
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Many thanks for you reply Dick.
I think several points you raise may be discounted but I am no expert by an means.
 
As part of my attempts to diagnose the problem, when running the pump on air, I half filled the boiler and pressurized it with air to 60 PSI. The pump was able to inject water into the boiler as seen on the water level guage.
 
On steam, the pump piston was hard at one extreme and required considerable manual force to move it off the stop. On release, the piston jumped back to the same position it had been forced from.
 
The steam passages in the valve chest appear quite complex and difficult to follow. There are two slide valves, one on top of the other. The first and nearest the steam inlet is operated by the valve rod seen in the photographs. The other side of this port face and between it and the cylinder is another slide valve which can only be operated by movement of the first. The port face of this second valve is on the side of the cylinder. If only I could ascertain how it is designed to operate, I might then be able to understand the prblem.
 
The fault symptoms do not alter if one or both the water inlet and outlet are disconnected.
 
 
 

Edited By Stephen Lawson on 15/03/2011 12:17:39

Richard Parsons18/03/2011 16:08:44
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645 forum posts
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So it works OK on air, which will not be hot! At say 60 psi the temperature of wet steam is 153°C (308°F)-. If you heated air to about that temperature would it still run? If it will not something has expanded and is sticking. From what you write you could only move ‘things’ a little way.
The two part valve may be a way of obtaining ‘cut off’ without eccentrics. Can you measure the how far the inlet side valve moves before it picks up the lower cylinder side valve?

You may find this site handy when doing your expansion calcs?
Sorry but I have to strip down a water pump which ‘Captain Klutz’ has dropped from the veranda onto a slab of concrete. More B****y welding to do!. These folk break things faster than I can mend them.
mgj18/03/2011 22:43:02
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I would bet Richard is right - having had the problem in reverse running in a Metre Maid chassis on air. After a bit it starts to run hard because its all getting cold.
 
Places to look- probably where something in bronze/brass runs in something iron. Some sort of sleeve or channel where there is a close fit.? Polish/oil up a shaft or two where they go through a gland?
 
Less likely in the pump because being water cooled as it were that wouldn't change much.
 
If it is differential expansion the guide would be does it run better after a time on air . If it does, then you know that is the problem.
 
Just a thought - you did use  a lubricant? And if so, it was getting out of the displacement lubricator and into the works?
 

Edited By mgj on 18/03/2011 22:44:47

Edited By mgj on 18/03/2011 22:45:24

Stephen Lawson19/03/2011 10:14:41
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Thanks again Dick and thanks also to MGJ
 
I agree temperature has got to be the main suspect cause of the problem.
 
As a means of progressing my investigation, I intend detaching both valve chests from the pump, bolting them together, applying (A) air and (B) steam to check the operation of the slide vavles by moving the valve rod by hand. Does this sound feasible ?
 
I will keep you posted.
 
Steve
Ian S C19/03/2011 10:34:44
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steve, does the pump have enough head clearance? It might be OK on air, but a few thou expansion on steam is what it sounds like. Ian S C
Stephen Lawson19/03/2011 10:42:16
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Many thanks Ian,
That' s another very valid point that needs to be checked.
 
Steve
AndyP19/03/2011 11:29:31
189 forum posts
30 photos
Steve,
The description of this sort of pump which made sense to me was that the second slide valve (that which controls the inlet of steam to the main piston) is a shuttle operated by the steam admitted by the first slide valve which is controlled by the valve rod you can see.
Does that shed any light on how it is supposed to work or just muddy things further?
 
Andy

Edited By AndyP on 19/03/2011 11:35:58

Stephen Lawson19/03/2011 11:56:29
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14 forum posts
13 photos
Hi Andy,
 
I think you are right about the shuttle.
 
Would I be right in thinking then that the shuttle is designed to work "opposite" the first slide valve to apply steam to the correct end of the piston as the slide valve alone would be at the wrong end ?
 
Hope that makes sense.
 
Steve
AndyP19/03/2011 16:52:14
189 forum posts
30 photos
Steve,
 
Yes, that is my understanding, I have never had one of those in bits though so it is all theory.
 
Cheers, Andy
Stephen Lawson20/03/2011 16:31:37
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Progressing with investigation.
Having removed steam valve chest and shuttle chest from the cylinder, I re assembled them temorarily of the cylinder and applied air to the steam inlet.
By operating the valve rod by hand, I was able to observe the shuttle move up and down correctly.
Brian Selby13/01/2012 19:13:37
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9 forum posts
19 photos
Hi Steve
 
Just started on here, looking at this pump and the top half and trunk is pure LBSC Westinghouse pump, whereas the LBSC pump was an air pump this one seems to have been converted to a boiler feed pump. I have made two of these pumps at the same time one works perfectly on air and steam, the other fine on air and tetchy on steam, the problem with it was the different expansion of the metals for the shuttle valve and its housing. Another issue was the gasket I had made needed cutting away to fully clear the ports for the shuttle. Plans for the pump are obtainable from My Hobby Store ( no association)
 
Brian
Stephen Lawson13/01/2012 22:33:53
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Thanks for you contribution Brian,
The pump remains a problem on steam but fine on air.
It is part of a display illustrating a marine boiler and five stationary engines but I doubt I will ever run it on steam again.
Steamshy05/03/2012 21:12:46
38 forum posts
2 photos

Hi Steve,

Most pumps of this type will run on air ok, but needs a fair ammount of warming before it will run on steam properly, It may have a glissard type valve or D valve, these types of valves can be problematic when not warmed properly, Keep trying with plenty of lubrication on shaft.

Andy

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