Vacuum Pumps

llustration 1: Variable speed vacuum pump system. Source: Scott Sanford

llustration 1: Variable speed vacuum pump system. Source: Scott Sanford

The installation of a variable speed drive (VSD) vacuum pump, sometimes called a variable frequency drive, usually saves between 50 and 65 percent in electricity costs with the same or better vacuum regulation. The VSD can be adapted to blower or, in some cases, rotary vane vacuum pumps. They work by changing the speed of the vacuum pump according to readings from a pressure sensor mounted on the vacuum line near the receiver jar.

The VSD is basically a dedicated computer capable of many adjustments, so it may be possible to improve vacuum regulation over the typical pneumatic vacuum regulator that only has a vacuum level adjustment. Adding a VSD to a vacuum pump is usually economical for a dairy that milks a total of 6 to 8 hours or more per day. Typically a VSD is not  an economical option for small dairies with short  milking time and thus shorter vacuum pump run times.

Dairy farms with either single or three phase electric power can use variable speed drives. Converting a vacuum pump to variable speed entails installing a Variable Frequency Controller, changing the pump motor to a 3 phase motor and installing a pressure transducer near the receiver jar. The existing pneumatic vacuum regulator is removed or set about 1 inch of mercury higher than the set point vacuum level to act as an emergency vacuum regulator. If a farm was using two vacuum pumps, often one can be shut off and maintained for a backup.

For smaller dairies, there are some other ways to cut energy costs. First check to make sure your current vacuum pump is not grossly oversized. A long held belief has been that more vacuum pump capacity was better. Research has since shown that a vacuum pump sized at 3 cubic feet per minute (cfm) per milking unit with a 35 cfm base capacity for up to 32 milking units is usually adequate even accounting for a milking unit falloff. Your local dairy equipment dealer can aid you in determining if your vacuum pump is sized correctly. Vacuum pump capacity is approximately 10 cfm per horsepower is a rough rule of thumb. If your current vacuum pump has larger capacity than needed, it may be possible to change belts and pulleys to slow the pump down or you may be able to trade it in for a smaller pump head. Keeping drive belts in good condition and tight reduces belt slippage and thus electricity usage.