Mechanical Properties
Mechanically, a breast pump is analogous to a milking machine used in commercial dairy production. A misconception is that the breast pump suctions milk out of the breast. A breast pump's job is to trigger the milk ejection response or letdown. Pumps achieve this by using suction to pull the nipple into the tunnel of the breast shield or flange, then release, which counts as one cycle. Thirty to sixty cycles per minute can be expected with better-quality electric breast pumps. The breast pump is not as efficient at removing milk from the breast as most nursing babies. Most manufacturers have multiple sizes of nipple tunnels available. These tunnels range in size from 24mm to 36mm.
There are several types of pump mechanisms. Piston pumps draw a piston through a cylinder to create suction. These are generally considered top-of-the-line units. They have characteristics of low speed, high reliability, low noise, and long life. Rotary vane pumps use a cam with retractable vanes to create suction. These rotary vane pumps are not widely used anymore. Fast diaphragm pumps use a diaphragm that is acted on by a lever, with thousands of cycles per minute. They operate at higher speed and are usually noisier. Slow diaphragm pumps use a large diaphragm operated by a cam or lever to generate suction with each stroke. Pumps have also been designed that use venturi effects powered by a faucet or water stream, wall suction in hospitals, or pumps powered by oral suctioning.
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