Evacuation of a lumped volume

We will now describe the evacuation of a vacuum container in terms of lumped constants. Referring to Fig. 1.5, this means that the volume V of gas is that inside the container, while the gas volume in the pipe and in the pump is disregarded. Also pressure gradients in the volume V will be neglected, and leaks and degassing are supposed to occur only in the vacuum container. 

The evacuation of a distributed volume can be described only through much more complex formulas (see for example ref. [9], p. 84), and this is beyond the scope of this short introduction to the vacuum technology. 

The pump action is usually defined in terms of a pumping speed S  

S is the volume of gas removed from the container each second at the existing pressure pr The pumping speed of many pumps is fairly constant over a few decades of pressure (see Fig. 1.7). 

The pumping speed of a series connection of a pump and a pipe is  

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Robert Boyle (1627-1691) was born in Ireland. He became especially interested in experiments involving air and developed an air pump with which he produced evacuated cylinders. He used these cylinders to show that a feather and a lump of lead fall at the same rate in the absence of air resistance and that sound cannot be produced in a vacuum. His most famous experiments involved careful measurements of the volume of a gas as a function of pressure. In his book The Skeptical Chymist, Boyle urged that the ancient view of elements as mystical substances should be abandoned and that an element should instead be defined as anything that cannot be broken down into simpler substances. This conception was an important step in the development of modern chemistry. 

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