Operatioin of Feedwater Heaters.

nw-mailing-list at nwhs.org nw-mailing-list at nwhs.org
Wed Oct 20 14:26:38 EDT 2004


Inasmuch as none of the steam experts among us has addressed your question, I'll send this rather sophomoric explanation based partly on my recollection from working several summers around N&W steam locomotives and partly on various written sources.

Using the N&W "Y" class locomotives as an example, the Y3's (modernized) through the Y6a's were equipped with Worthington Type BL-2 feedwater heaters, whereas the Y6b's were equipped with Worthington Type SA feedwater heaters.  In addition, all were equipped with an injector as well.

A BL-2 is easily identified as being the large apparatus suspended below the running board on the left side of an N&W locomotive so equipped.  A BL-2 contains all of the devices to pump water from the tender, heat the water, and pump it into the boiler.  It is only necessary to attach the pipes, and it is ready to go.  Facing the side of the locomotive, on the right of the BL-2 the top portion is the steam cylinder, the portion below it is the cold water pump and the portion below it is the hot water pump.  The steam piston and both water pump pistons share a common piston rod so that both pump pistons make a stroke every time the steam piston makes a stroke.  The left side of the BL-2 is the heater where a portion (typically 15 - 20 percent) of the exhaust steam from the locomotive cylinders is mixed with cold water from the tender to heat the water.  When the steam valve in the cab is opened, steam flows to the BL-2 steam cylinder pushing the steam piston alternately up and down, causing the cold water pump to pump water from the tender into the heater, and likewise causing the hot water pump to pump the heated water into the boiler.  Because the cold water pump is a positive displacement piston pump, it can draw water from the tender even when the water lever in the latter is below the inlet to the pump.

In contrast, the SA feedwater heater is a three-component device.  A steam-turbine-driven centrifugal pump mounted on the left side of the locomotive under the cab delivers cold water from the tender to the heater mounted mostly inside the top of the smokebox ahead of the stack.  Like the BL-2, the SA uses exhaust steam to heat the water in the heater. The heated water is pumped into the boiler by a steam-driven reciprocating piston pump mounted on the left side of the locomotive outside the smoke box near its bottom.  Now, back to the cold water pump.  The steam to drive the centrifugal cold water pump is regulated by a steam valve operated by a float inside the heater such that the centrifugal pump only operates as necessary to maintain the water level in the heater.

You can see from this that either type of feedwater heater is controlled by only one steam valve in the locomotive cab.

Injectors are a different animal from feedwater heaters.  They do the impossible by taking steam from the boiler at, say, 300 psi and using it to force water into the boiler against the same 300 psi.  This miracle is wrought by nozzles in the injector body that accelerate the steam though venturis that draw in water from the tender.  The water is accelerated to a high velocity, after which an expanding section converts the velocity energy of the water to a pressure that is sufficient to force the water through the boiler delivery check valve into the boiler.  The injectors on later-day N&W steam locomotives were live steam, non-lifting injectors, meaning that they used live steam from the boiler rather than exhaust steam from the cylinders (exhaust steam injectors were called "poor man's feedwater heaters"), and that they had to be located below the lowest level of water in the tender because they could not raise water from a lower level.  This type of injector was operated by one lever in the cab.  The injector can be seen in many photos mounted underneath the cab, but the most distinguishing feature is often the delivery pipe running from the injector to the boiler check valves on top of the boiler.  Early locomotives had check valves on the side of the boiler, but the N&W practice in later years was to place the check valves on top where they were less likely to be sheared off in a sideswipe accident.

I hope this helps more than confuses.

Gordon Hamilton

----- Original Message ----- 
  From: nw-mailing-list at nwhs.org 
  To: NW-Mailing-List at nwhs.org 
  Sent: Friday, October 15, 2004 10:28 AM
  Subject: Operation of Feedwater Heaters.

  What is involved in the operation of a feedwater heater?  Does the fireman have to operate the cold water pump and hot water pump separately?  Or, do the two pumps turn on with the same control?  How does this system differ from the operation of the injector system?

  Nathan Driscoll

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