All Rotary Lobe Pumps Are Not Created Equal

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All Rotary Lobe Pumps Are Not Created Equal

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From the outside, all rotary lobe pumps may look the same. They operate in the same basic manner with lobes that create expanding and contracting cavities that propel fluid from the inlet to outlet port. They handle a variety of fluids and viscosities and can pass solids found in wastewater sludge. 

But there are several design variances that surpass the traditional rotary lobe pump. Design innovations engineered by Vogelsang have improved pump performance, allowed for longer maintenance intervals, and made its rotary lobe pumps easier and quicker to service. The Vogelsang VX and IQ series pumps are ideal for viscous liquids, heavy solids and abrasives.

The truth about lobes

The first of these design improvements are in the rotary lobe tips. Vogelsang broke away from the traditional two- and three-tip lobe design in favor of four- and six-tip designs that make its pumps virtually pulsation free. This lobe configuration is more efficient and allows the pump to last longer. Studies show that efficiency gets steadily worse as two- and three-tip lobes wear. Four- and six-tip designs are more durable and increase pump efficiency.

Other rotary lobe pumps boast replaceable tips as a benefit. But separate tips are difficult to remove and install, and may come loose during operation. It is common for grit to work its way into the track and mechanical fixtures. Tip breakage can cause damage to other components like couplings, shafts, timing gears and lobe cores. Vogelsang lobes are one solid piece of metal or metal with an elastomer wrap, depending on the application.

Insight on seals

Traditional component pump seals are a three-part system with a stationary seat, a rotating seat and a setting device that is either a collar or a threaded device. These have to be manually set, must be kept clean, and cause a mess if the seal fails with pumpage entering the bearing frame and leaking on the floor. Vogelsang engineered the block ring cartridge mechanical seal as a vast design improvement over traditional seals. The hard block ring surface is wear-resistant, especially against fibrous matter. Abrasion affects only the block ring, not the seal itself. This design allows for excellent heat transfer due to the large block ring acting as a heat sink and transferring this to the pumpage and shaft. Due to the greatly improved heat dissipation, the Vogelsang seal is also insensitive to dry running.

Adjustable housing segments

Wear plates and adjustable housing segments are another advancement in Vogelsang’s pump. Its wear plate design allows for axial adjustments of the plate. The wet end consists of three elements. The top and bottom housing segments and the housing ring. The housing ring has a series of adjustment holes to allow the segment to be placed in three locations. The total movement is up to 3 mm. Unlike the competition’s one-piece casting, the three-piece arrangement allows the pump to remain in capacity longer without replacing any parts, saving spare parts cost. It also allows for commonality of wear parts throughout each series of pumps and an increased material hardness.  

Overlooking shaft design ends up being costly

There are several problems associated with step-down shafts that are common in other rotary lobe pump designs. Threaded step-down shafts are prone to breaking due to the resulting shaft fatigue. This is a result of the higher shaft deflection causing metal fatigue that is localized at threads and step-downs on the shaft. Vogelsang’s pump design features a solid shaft that stands up to distress and deflection. Vogelsang uses shafts that are much larger in diameter than other lobe pump models. The larger shaft diameter greatly reduces shaft deflection, which dramatically improves pump life cycle and performance.

Get advanced warning on seal maintenance

Vogelsang has also added a buffer chamber and oil canister to protect the gear case in the event of seal leakage or failure. This gives Vogelsang pump users advanced warning before a seal failure. As long as the oil in the canister atop the pump remains clean, the gearbox and buffer chamber are clear of any foreign liquids. Should the oil become discolored, or pressure can’t be achieved, the pump can be serviced before damage occurs. Adding pressure to the blocking chamber extends the life of the mechanical seals by offsetting the pressure in the wet-end. This keeps the buffer chamber close to the system pressure versus a low-pressure zone like other pump designs.

When looking at rotary lobe pumps, be sure to have these design features in mind and ask questions to make sure the pump you are considering has the most advanced engineering — like the Vogelsang pump.

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