No, ordinary mechanical pumps do not compress water in any significant or measurable way. Water is considered practically incompressible under typical operating conditions for pumps.
Understanding Water Compressibility in Pumping Systems
The concept of "compressing" a substance refers to reducing its volume by applying pressure. While all matter is compressible to some degree, the extent of this compression varies wildly between states of matter and specific substances.
For liquids like water, the change in volume even under high pressure is negligible for most engineering applications. As stated in the provided reference:
"In no instance of an ordinary mechanical pump working against water will the bulk compressibility of the water enter into the model of the pump/water system. For that to be significant you need high explosives machined into shaped charges."
This highlights that for the bulk compressibility of water to become a significant factor, forces far beyond those generated by an ordinary mechanical pump would be required, such as the extreme pressures produced by high explosives.
Why Water is Considered Incompressible
- Molecular Structure: Water molecules are already tightly packed in their liquid state, leaving very little empty space between them. Unlike gases, which have large intermolecular spaces, liquids resist further compaction.
- Energy Requirements: Compressing water by even a small percentage requires immense energy. Pumps are designed to move water and impart pressure to overcome resistance in a piping system, not to reduce its volume.
Practical Implications for Pumping Systems
The incompressibility of water has several fundamental implications for pump design and fluid dynamics:
- Positive Displacement: Pumps typically work on the principle of positive displacement or dynamic (centrifugal) force.
- Positive Displacement Pumps: These pumps trap a fixed volume of water and then force it into the discharge line. Because water is incompressible, the pump must be able to move that exact volume. If the discharge is blocked, pressure will rapidly build to dangerous levels, potentially damaging the pump or piping.
- Centrifugal Pumps: These pumps use an impeller to impart velocity and pressure to the water. The water flows continuously, and its volume does not change significantly as it passes through the pump.
- Hydraulic Systems: The efficiency of hydraulic systems (which use incompressible fluids like oil or water) relies directly on this property. Pressure applied at one point is transmitted almost instantly and equally throughout the fluid, allowing for precise control and significant force multiplication.
- System Design: Engineers can model water flow in pipes without accounting for volume changes due to pressure, simplifying calculations and designs for water distribution, irrigation, and industrial processes.
Water vs. Gases: A Key Distinction
It's crucial to differentiate how pumps interact with liquids compared to gases.
| Feature | Water (Liquid) | Air/Natural Gas (Gas) |
|---|---|---|
| Compressibility | Practically incompressible | Highly compressible |
| Pump Action | Moves volume, increases pressure | Reduces volume (compresses), increases pressure/temp |
| Pressure Build-up | Rapid and dangerous if outlet blocked | Gradual, volume reduces as pressure increases |
| Pump Type | Centrifugal, positive displacement (e.g., gear, piston, diaphragm) | Compressors (e.g., reciprocating, rotary screw, centrifugal compressors) |
While pumps effectively move and increase the pressure of water, they do not compress it in the way that a gas compressor compresses air or natural gas. The primary function of a water pump is to overcome resistance and move the fluid from one point to another, not to reduce its volume.
