GEAR PUMP - HOW TO WORK THIS PUMP AND ITS TYPES
- A gear pump uses the meshing of gears to pump fluid by displacement. They are one of the most common types of pumps for hydraulic fluid power applications.
- Gear pumps are also widely used in chemical installations to pump high viscosity fluids. There are two main variations:
- external gear pumps which use two external spur gears
- internal gear pumps which use an external and an internal spur gears (internal spur gear teeth face inwards, see below).
- Gear pumps are positive displacement (or fixed displacement), meaning they pump a constant amount of fluid for each revolution. Some gear pumps are designed to function as either a motor or a pump.
Fluid flow in an external gear pump
External gear pumps are similar in pumping action to internal gear pumps in that two gears come into and out of mesh to produce flow. However, the external gear pump uses two identical gears rotating against each other -- one gear is driven by a motor and it in turn drives the other gear. Each gear is supported by a shaft with bearings on both sides of the gear.
1. As the gears come out of mesh, they create expanding volume on the inlet side of the pump. Liquid flows into the cavity and is trapped by the gear teeth as they rotate.
2. Liquid travels around the interior of the casing in the pockets between the teeth and the casing -- it does not pass between the gears.
3. Finally, the meshing of the gears forces liquid through the outlet port under pressure.
Because the gears are supported on both sides, external gear pumps are quiet-running and are routinely used for high-pressure applications such as hydraulic applications. With no overhung bearing loads, the rotor shaft can't deflect and cause premature wear.
Materials Of Construction / Configuration Options:
As the following list indicates, rotary pumps can be constructed in a wide variety of materials. By precisely matching the materials of construction with the liquid, superior life cycle performance will result.
External gear pumps in particular can be engineered to handle even the most aggressive corrosive liquids. While external gear pumps are commonly found in cast iron, newer materials are allowing these pumps to handle liquids such as sulfuric acid, sodium hypochlorite, ferric chloride, sodium hydroxide, and hundreds of other corrosive liquids.
- Externals (head, casing, bracket) - Iron, ductile iron, steel, stainless steel, high alloys, composites (PPS, ETFE)
- Internals (shafts) - Steel, stainless steel, high alloys, alumina ceramic
- Internals (gears) - Steel, stainless steel, PTFE, composite (PPS)
- Bushing - Carbon, bronze, silicon carbide, needle bearings
- Shaft Seal - Packing, lip seal, component mechanical seal, magnetically-driven pump
How Internal Gear Pumps Work:
Water flows from left to right in this internal gear pump
1. Liquid enters the suction port between the rotor (large exterior gear) and idler (small interior gear) teeth. The arrows indicate the direction of the pump and liquid.
2. Liquid travels through the pump between the teeth of the "gear-within-a-gear" principle. The crescent shape divides the liquid and acts as a seal between the suction and discharge ports.
3. The pump head is now nearly flooded, just prior to forcing the liquid out of the discharge port. Intermeshing gears of the idler and rotor form locked pockets for the liquid which assures volume control.
4. Rotor and idler teeth mesh completely to form a seal equidistant from the discharge and suction ports. This seal forces the liquid out of the discharge port.
Materials Of Construction / Configuration Options:
- Externals (head, casing, bracket) - Cast iron, ductile iron, steel, stainless steel, Alloy 20, and higher alloys.
- Internals (rotor, idler) - Cast iron, ductile iron, steel, stainless steel, Alloy 20, and higher alloys.
- Bushing - Carbon graphite, bronze, silicon carbide, tungsten carbide, ceramic, colomony, and other specials materials as needed.
- Shaft Seal - Lip seals, component mechanical seals, industry-standard cartridge mechanical seals, gas barrier seals, magnetically-driven pumps.
- Packing - Impregnated packing, if seal not required.
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