# Pump stage in a steam engine?

1. Jun 16, 2006

### pivoxa15

My textbook shows a PV diagram for a steam engine with the pump stage having no change in volume and with only a vertical increase in pressure. How can that be done. I can only imagine pumping a substance by pushing it inwards hence increasing its pressure but also reducing its volume. How can there be no reduction in volume?

2. Jun 16, 2006

### Danger

What do you mean by the 'pump' stage? I've never heard that term in relation to a steam engine.

3. Jun 16, 2006

### Cyrus

Well, you can do this by putting heat into the system while maintaining a fixed volume. It would help to have more text and a picture though. What do you mean by a "steam engine"? Please provide more information.

4. Jun 17, 2006

### rcgldr

http://travel.howstuffworks.com/steam1.htm

The boiler tank contains very hot water and steam under high pressure. The average pressure stays about the same, depending on the amount of heat (power input) applied to the tank, and the speed and load on the engine (power output). The amount of water decreases over time requiring the engine to be refilled. Through valves, the high pressure is used to move a piston (both directions usually), and is then released. The loss of steam is replaced by the super heated water boiling and replacing the steam released on the exhaust side of the piston.

5. Jun 18, 2006

### lalbatros

Assuming a condensing steam cycle:
In the liquid phase, the compressibility is very small.
Therefore the slope is very steep, but not really a vertical.
Practically, it doesn't change much to consider it as vertical: the work to pressurize the water is negligible.