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Tuesday, March 9, 2010

Mechanically Driven Diaphragm Pumps

Many industries are served by mechanically driven diaphragms pumps. They are used in construction, chemical, and water treatment applications.

Construction Industry

Mechanically driven diaphragm pumps are widely used in the construction industry for dewatering applications where pumps may ingest rocks or other debris. A popular make of this type of pump contains a spring on the plunger rod. If the operating pressure exceeds the maximum recommended pumping pressure, the spring compresses and does not more the diaphragm. The spring can compress and thus keep a rock from being pushed through the wall of the pumping chamber or cause the drive mechanism to fall.

In single diaphragm pumps, the pumped liquid can have a lot of inertia if the suction and diaphragm lines are relatively long. A simple accumulator on the suction (inlet) side of the pump enable the pump to draw liquid from the accumulator while it simultaneously draws liquid through the suction line.

During the discharge stroke, the accumulator can refill with liquid from the suction line. If the discharge line from the pump is relatively long, the inertia of the liquid can be great, as mentioned earlier, and can impose severe loads on the diaphragm and drive mechanism. The spring on the plunger and can absorb some of the drive energy early in the discharge stroke and “give it back” during the latter part of the discharge stroke, greatly reducing the inertia loading on the diaphragm and drive mechanism.

Mechanically driven diaphragm pumps in the construction industry operator by a reciprocating plunger, usually secured to plates on both sides of the diaphragm. The diaphragms are customarily fabric reinforced elastomers (usually synthetic rubbers) similar in many ways to the fabric reinforced materials used in pneumatic tires. The diaphragms are normally molded with a convoluted section between the central damaged area and the clamped periphery. This convoluted section permits longer strokes than would be possible otherwise.

These pumps are sometimes duplexed so that the reciprocating means acts alternatively on two diaphragms with one on a section stroke, while the other in on a discharge stroke and vice versa. A connector called a walking bean is pivoted between two diaphragms. As one diaphragm is pushed down on a discharge stroke, the other diaphragm is simultaneously pulled up on a suction stroke. The pumping chambers with inlet and outlet check valve are manifolded together to a common inlet and a common outlet. The principle advantage of the duplex diaphragm pump is its more constant flow (two pressure pulsa times per cycle).