Liquid pistons pump up the vacuum

Vacuum pumps from nash_elmo Industries llc, (formerly Nash Engineering Co.) Trumbull, Conn. (www.nasheng.com), use a liquid-ring design that moves 20 to 23,000 cfm and generates up to 29-in. HgV. They operate safely and reliably in wet and dry environments and require minimal maintenance. Key to their operation is the water ring formed by a whirling rotor offset in a circular housing. Water, the operating fluid in most cases, is forced to the outside of the housing, forming outside walls for chambers created between the rotor blades. A stationary central cone forms the fourth wall. Passages in the inner cone let air or other gas in and out of the chambers. The axis of the water ring is offset from that of the housing, so as the rotor turns, the chambers vary in size, creating compression and suction.