Steam & Excursion > Coffin FWH - a whole heap of questions

1: Some sources say that Coffins are an open system, and others say it's a closed system. I'm sure there were different models etc., but as for what we would think of as the "standard" Coffin setup, which is it?

1.5: In the case of open type heaters, what would be the actual consequences of valve oil being introduced into the feedwater supply? Is it simply a case of it building up a layer on heating surfaces/gunking up anything it manages to find it's way into?

2: Is the entire system powered by the single centrifugal pump? If so, those things must be more powerful than I thought. Since there's no hot water pump, the only other thing I can think of is maybe part of the unit acts as an injector?

3: Toward the top of the heater, there are 2 square-looking hatches. Are these just for inspection/maintenance or is there something cool under there?

4: There's obviously more piping going to it than just what's there for the exhaust steam and water, I presume one of them is a live steam line for when the engine isn't running, but is there anything else at play in one of these that might be interesting to know about?

YES!
For locomotives, the Coffin systems are the 'closed' version.

It use a high-pressure, centrifugal pump designed for overcoming boiler pressures.
And, yes it's a 'closed' heat exchanger.

The condensate from the cylinders collects in the heat exchanger and is fed
by piping rearward, to a tall separating tank in the tender's water space.
The separating tank has an internal, tall pipe, open at the top and acts as
an oil skimmer --- feeding the skimmed oil below, to the tracks. 
There is an oil-free water overflow pipe from the bottom of the separating tank,
upward & into the tender's cistern --- and yes, it tends to be warm water.

Its common to see the tops of the separating-cylinders exposed on the tender's 
water-deck, behind the coal slope-sheet. The exposed tank top appears to
sit about 8-inches above the water-deck.  There is a removable top to the separator
for maintenance and probably 'de-gooping' of the drip pipe😃.
When cooled, used superheat valve oil becomes thick, and very tenacious.

The more common Elecso system is also a 'closed' system, and uses a 
similar separating tank in the tender's water space, where the oil collects
& is skimmed off, and water-only goes back into the tender water space.

After being still & collecting for a few minutes, the oil floats to the surface,
and out of these separators.

The 'open' systems, like Worhinghgton's also use a skimmer syphon inside
their heat exchanger spaces.  It also leads down to drain on the roadbed.

You may also see the large pipes that feed the exhaust steam to the heaters,
 low, at the cylinder saddle under the smoke box. These pipes are fitted with oil
separators.... that feed the oil drips down to the roadbed, and send the clean steam
to the heaters' mixing tanks.

​W.

( The last I had checked, decades ago, Coffin corporation was in business 
   up near the Boston area...)



Edited 4 time(s). Last edit at 01/28/23 07:43 by wcamp1472.

Wes' last line got me curious.  Coffin Turbo Pumps, Inc. is alive and well in Englewood, N.J.  They still focus on making high pressure pumps for boiler feeds.

https://coffinpump.com/about/history/

 

Thank you for all the information, I really appreciate it.

> ( The last I had checked, decades ago, Coffin
> corporation was in business 
>    up near the Boston area...)

I believe they were actually going to rebuild the pump for 3713 if I'm remembering correctly.

High pressure and centrifugal don't belong in the same sentence.

Out 

callum_out Wrote:
-------------------------------------------------------
> High pressure and centrifugal don't belong in the
> same sentence.

That was kinda my line of thinking that made me want to ask, I haven't really been able to find much reference material online.

I mean Carver would hang up on me every time I wanted to talk about a 125 psi centrifugal
on a prefill circuit. It'd be hard to imagine a decent size 200 psi plus pump.

Out 

 Coffin made a lot of money selling high pressure centrifugal pumps and
pump systems...

Do your research before flapping your gums.. or banging the keys..

​W.

Do the same, I speak from experience. The Coffin pump is hardly what one would call a "centrifugal" pump, it is a highly
specialized piece. 

Out 
 



Edited 1 time(s). Last edit at 01/28/23 19:04 by callum_out.

callum_out Wrote:
-------------------------------------------------------
> High pressure and centrifugal don't belong in the
> same sentence.
>
> Out 

Sir Frank Whittle had a different opinion.

Whittle didn't have anything to do with centrifugal pumps anymore than Coffin did. They both use a turbine design
which is at best a rotary pump. A centrifugal pump is a low pressure single stage device which simplitiocally scoops
and flings liguids. The impeller design and operating clearances determine maximum pressure and it ain't nowhere
steam boiler numbers.

Out 

Contrary opinion based on 43 years of experience. VLCC (Very Large Crude Carriers) AKA Supertankers have Coffin Feed Pumps feeding two boilers outputting over 50,000 HP worth of steam with superheat outlet pressure of 875 PSI with drum pressure over 1,100 PSI fed from a Coffin Feed Pump with turbine driven single stage pump impeller with operating speeds approaching 10,000 RPM. Also had Coffin Feed Pumps of ex-Sealand SL7 converted to FSS for MSC of USN these were 120,000 Shaft HP with 875 PSI superheater outlet pressure and drum pressure up to 1,200 PSI using a slower speed unit with larger diameter impellers running around 6,000 RPM.

Don Allender

callum_out Wrote:
-------------------------------------------------------
> Whittle didn't have anything to do with
> centrifugal pumps anymore than Coffin did. They
> both use a turbine design
> which is at best a rotary pump. A centrifugal pump
> is a low pressure single stage device which
> simplitiocally scoops
> and flings liguids. The impeller design and
> operating clearances determine maximum pressure
> and it ain't nowhere
> steam boiler numbers.
>
> Out 


Take a look at the design of the early centrifugal flow turbojets some time.

callum_out Wrote:
-------------------------------------------------------
> High pressure and centrifugal don't belong in the
> same sentence.
>
> Out 

Centrifugal pumps are quite capable of working at high pressure.  A very long time ago when I was a marine engineer I had to oversee four, two stage Main Feed Pumps that the relief valve was set to 900 psig to feed a boilers operating at 600 psig.  I was also trained on feed pumps of similar design to feed 1200 psig boilers. I never got into the pressure/temperature relationships of the impellers but the eye of the impeller was fed with hot feed water from the DFT (Deaereating Feed Tank) via a booster pump which took the feed water at 15 psig and about 150 degrees and boosted the pressure to roughly 50 psig and discharged into the impeller of the feed pump. Each boiler had about 14,000 to 16,000 Horse Power and the ship had 24,000 total shaft horse power.  And yes the pumps were centrifugal pumps that used a spinning disk to sling the water outward and the first stage had porting to feed the output of the first stage into the eye of the second stage.  I had the opportunity to see them completely disassembled several times.



Edited 2 time(s). Last edit at 01/29/23 07:17 by SR-RL_Nr_10.

OK, so now, who's on 1st and who's on 2nd??!!!  Just an observer here and the input is interesting and learning more about the Coffin Feedwater units that the Rock Island used on their 4-8-4 5000's is making more sense.  Thanks to all for the input!

If you read it on the internet it must be true!!!

Here is a link describing a typical marine feed set up:

https://www.brighthubengineering.com/marine-engines-machinery/46136-what-is-a-boiler-feed-pump/

>>The turbo-feed pump is a two stage horizontal centrifugal pump, which is driven by an impulse turbine.<<

The ship I was an assistant engineer on also had two reciprocating feed pumps, one for each boiler.  They were designated as "emergency" feed pumps and were usually aligned directly from the feed bottom to the boiler via the economizer (feed heater).  A couple of shots of cold water out of the feed bottom would drop your steam drum pressure about 5 psi within seconds.  The impulse turbine had about five or six stages, and unfortunately I've forgotten it's rated HP.

The reaction turbine has a series of buckets on the end of the rotor and the steam would swirl around three times (three stages) before being exhausted to the auxiliary exhaust steam system.  The forced draft blowers, fuel pumps, other small steam driven pumps and fans were all driven by reaction turbines. The main feed pumps and the Ships Service Turbo Generators (SSTG) were all driven by reaction turbines.



Edited 1 time(s). Last edit at 02/01/23 05:49 by SR-RL_Nr_10.

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