A Quick And Dirty Guide ToRotary Positive

Displacement Pumps

Rotary pumps, are a popular choice throughout a vast range of industries.

From pumping liquids with high viscosities like asphalt or honey, or low viscosity liquids like water or ammonia, a rotary pump can do it all.

However, making sure you select the right pump for your needs is key.

In this SlideShare, we are going to discuss the advantages and disadvantages of a wide variety of positive displacement pumps.

General Industrial PumpsThe types of general industrial pumps that we will be going over the advantages and disadvantages are:– Internal gear pumps (with crescent)– External gear pumps (spur, helical,

herringbone)– Progressive cavity– Sliding vane pump– Rotary lobe pump

Internal Gear Pumps(with Crescent)

Advantages DisadvantagesOnly two moving parts. Low speeds usually required.Only one stuffing box. Medium pressure limitations .Positive suction, non-pulsating discharge.

One bearing runs in product pumped.

Ideal for high viscosity liquids. Overhung load on shaft bearing. Constant and even discharge regardless of various pressure conditions.Available with built in safety relief valve.Can operate equally well in either direction.Can be made to operate with one direction of flow with either rotation.Low NPSH required. Easy to maintain.

External Gear Pumps(Spur, helical, herringbone)

Advantages DisadvantagesHigh speed. Four bushings in liquid area.Medium pressure. Four stuffing boxes.No overhung bearing loads. No solids allowed.Relatively quiet.Design lends itself to use of a wide variety of materials.

Single Screw Pumps(Progressive Cavity)

Advantages DisadvantagesHigh solids allowed. Cannot run dry.Dry materials. Not for high temperatures (Stator

swells).High viscosity. Hard to maintain.Versatile - same pump without changing clearance. Can be used for water or syrup.

Expensive parts.

Good for sludge or slurry. More floor space required.Stuffing box exposed on vacuum.

Sliding Vane PumpsAdvantages Disadvantages

Medium capacity. Not good with abrasives. Medium speed. Not best for viscous liquids. Thin liquids. Pressure medium. Sometimes preferred for solvents LPG.Can be made to provide variable capacity.One seal or stuffing box.Develops good vacuum.

Lobe Pumps(Single, Multiple & Circumferential piston)

Advantages DisadvantagesPass medium solids. Timing gears requiredRates high acceptance. More space required. Little galling possibility. Factory service required.

Requires two seals.