Operators of metering pumps know that diaphragm fatigue and rupture often is unavoidable. So, says a Madden Manufacturing blog post, pump users must account for that occurrence when deciding between the two main styles of diaphragm pumps, mechanically or hydraulically actuated.

(Learn more about metering pumps at the Engineering360 product and supplier section.)

In a mechanically actuated metering pump, hardware connects the piston to the primary diaphragm.In a mechanically actuated metering pump, hardware connects the piston to the primary diaphragm. Hydraulic models, which the blog post says are well suited to applications requiring high flow rates and pressures, contain oil between the piston and diaphragm. When the diaphragm ruptures, leaking barrier oil can interrupt the process and be costly to repair. The situation may be compounded in applications that require pumping corrosive chemicals, where a secondary diaphragm is often added to the pump design and adds a second barrier oil.

Metering pumps—whether hydraulically or mechanically actuated--use a motor, worm gears, and an eccentric (or cam) driven by a drive shaft that provides the stroking motion of the pump piston. Piston stroke actuates the pump’s primary diaphragm—when pulled backward, the piston and diaphragm pull working fluid into the pump, and when moved forward, the piston and diaphragm push the fluid out.

The blog says that to avoid the potential damage of leaking oil opt for mechanically actuated pumps, which use hardware rather than oil to connect pistons to diaphragms. A case study presented in the blog describes metering-pump use at a pharmaceutical company. The company used hydraulically actuated pumps, and a diaphragm rupture on one of the pumps released barrier oil into the product, ruining an entire batch. With a mechanically actuated pump, no such waste would have occurred.

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