MechEng said:
Thanks for the information guys.
I am still new to boiler mechanical design. What is a SDNRV? Do you know any sites that explain the functioning of a float switch (I am already picturing something in my head but what to make sure there isn't an easier way)? Also, when you say the boiler doesn't super heat, you mean that function is done in a different set of pipes separate from the boiling pipes like the first picture on
http://en.wikipedia.org/wiki/Water_tube_boiler ? Or that when running steam engines you use wet steam and superheating is only used at powerplants?
I'll try and answer as best I can:
SDNRV - Screw Down Non Return Valve.
On a boiler it's normally called a feed check valve, (because it controls or checks, as in reduces, the rate of feed water supply to the boiler.
Regulators come in several flavours from a simple float mechanism to 3 element controllers either air or electronically operated which measure drum water level, steam flow and feed water flow. e.g. when more steam is demanded the water level in the drum initially rises because the steam pressure initially drops, however that's not what we really want because a float control would say admit less water when in fact we need more water to make up for the excess steam demand and to allow for the fact that the firing rate is increased to keep up with the demand for more steam.
This is a bit esoteric for a model boiler and probably the most sophisticated would be a simple float regulator. Hand regulation of the feed check works satisfactorily for all but the most high powered boilers with fluctuating steam demands.
Yes, a superheater is another set of tubes placed in the flue passage after the steam has left the steam drum and after the heat from the fuel has done it's primary job of boiling the water.
Both reciprocating engines and steam turbines may use either saturated or superheated steam.
In condensing systems it is usual to use saturated steam in reciprocating engines because the water in the steam is used to lubricate the rings and cylinders and obviates the need to try and remove lube oil from the feed water before it goes back to the boiler.
For non condensing engines and most, (very nearly all), turbines, superheating is used because it's extracting more heat from the fuel giving greater power/efficiency and there is no water present to belt the hell out of the turbine blades.
Another very potted explanation but I hope it helps.
Best Regards
Bob