Pumps galore!

[mtompson]

In the attached image of a basic steamplant, I'd like anyone's opinion on the need for a pump (or pumps) at positions A and/or B (if at all). I appreciate the need for more detail, but at this stage I'm trying to learn how it all works at a high level. I have seen many mentions of an air/water pump around the condenser (probably 'B') and would like to hear what people think. Many thanks for your time.

[mtompson]

'A' is simply the exhaust, I don't expect to see any kind of pump here.

[barts]

The pump at B is indeed typically called an air pump; it scavenges any air and removes the condensate from the condenser, causing a vacuum (pressure below atmospheric) to form therein. This is needed for engines that expand the steam sufficiently to bring the exhaust pressure below atmospheric; these are typically multi-cylinder engines (compounds and triples), but uniflow engines also need such.

For those of us w/ single cylinder engines that expand the steam only a few times, the pressure in the cylinder when the exhaust valve opens is far above atmospheric and a condensate pump is a unneeded complication and waste of power; it's far simpler to allow a slight back pressure in the condenser to return the condensate to the hot well.

I've run Otter that way for many years; it works well.

[mtompson]

That’s great, thanks for that.

[Lopez Mike]

I've had much the same experience as Bart. Most small steam power plants would benefit much more from more insulation than adding complications.

Mike

[mtompson]

Thanks Mike, as I’m learning, I guess I’ve focused on larger systems, compounds, expansion etc, it’s really good to understand the small systems in comparison. Fascinating stuff.

[barts]

At the (slight) risk of re-purposing this thread, one of things we're often trying to do is to increase the amount of available steam so that we can run a bit faster, or have the power plant be a bit more tolerant of less than ideal firing. Some changes that can help, in rough order of increasing complication:

* Increase boiler firing rate... typical approach is to add a stack blower that uses a small amount of steam from the boiler to increase stack draft. Of course, those of you exhausting up the stack as per locomotive or Lake Windermere practice have this already covered

* Add a feed water heater; these heat exchangers use the exhaust steam to preheat the water before it enters the boiler. This is basically a relatively simple plumbing project. This is of more help on single cylinder steamboats, since the exhaust temperature is higher there, but can also help any plant when the hot well temperatures are relatively cool.

* Add an economizer... this is usually tubing, typically located at the exhaust end of the boiler, that adds additional heat to the water before it enters the boiler proper through the boiler check valve(s). It effectively increases the boiler heating surface area. Note that during start up, you'll have steam forming in this tubing; it must always be open to the boiler during operation. An additional check valve in the feed to the economizer should be used to prevent problems w/ the hot steam flowing backwards towards the feed water pumps, injector, etc.

[mtompson]

Thanks Bart! All good stuff. I might make up a new diagram with all these 'options' and some notes. It's amazing how many combinations there can be on these steamplants!

[mtompson]

For discussion only!

[mtompson]

This is a nice one which no doubt many have seen as it often pops up in searches. Notice no return to the hotwell (feed and filter tank here) after the feed pumps and then this being activated by a float switch, not sure how common this was in original ship steamplants.