This is the area that requires possibly the most consideration.
Most manufacturers will offer a vacuum pump of some description on some or all of its ranges, but is it right for your application or needs? In essence there are two types of vacuum pump available. The first is a diaphragm vacuum pump. These are relatively inexpensive, but have limited performance. Typically, vacuum levels will reach 500-600mbarA which means their use is limited to providing improved air removal at the beginning of the cycle, plus it will help to dissipate heat in some load types at the end of the cycle. If that’s all you need it for, then this is ideal.
However, for more effective air removal (important when sterilizing bagged goods or hollow-ware, such as pipette tips, tubing etc), then choosing an autoclave with a liquid ring vacuum pump may be more appropriate. These pumps will achieve a much higher vacuum (typically 30-100mbarA), which offers enhanced air removal, but, more importantly will flash off much of the residual water from deep inside the load during the cooling stage, which gives drier loads, and this can be very important with some load types.