What is a gear pump?
Gear pumps are the most common type of positive displacement pump. They are considered fixed displacement pumps, meaning that an unchanging volume of liquid moves through at a constant rate provided the pump speed is constant.
Gear pumps generally work within the following ranges:
- Flow rate ranges between 1 and 1,500 gpm
- Total head (pressure) ranges between 10 and 2,500 psi
- Horse power ranges between 0.5 and 2,000 hp
- Viscosity ranges from clear liquids to 2 million SSU
How do they work?
Gear pumps work by using a rotating set of gears, which are spur or helical for standard types, and herringbone gears for specialty applications. The moving gears create suction at the inlet port of the pump that draws the fluid into the gears. The rotating gears then move the liquid between the teeth of the gears and the walls of the casing and direct the fluid flow to the discharge port, where the pressure continues to build as the volume of the casing gets smaller near the outlet of the pump.
There are two main types of gear pumps, which both consist of a drive gear (the gear that pushes) and an idler (the gear that is pushed). External gear pumps, which are usually found in lower flow applications, use two side-by-side spur, helical, or herringbone gears that mesh together; while internal gear pumps consist of a smaller idler gear that fits inside of the larger drive gear. The internal configuration contains a crescent-shaped internal barrier that helps direct flow through the pump. Both types often contain built-in pressure relief valves to protect the pump and the system in the event that a valve in the discharge piping is inadvertently closed.
Gear pumps are designed to have very tight clearances and are ideal for thicker, high viscosity fluids such as automotive oils, plastics, paint, adhesives, or soaps.
Lobee Pump manufacturers stainless steel, bronze, cast iron, and nickel alloy gear pumps with capacities to 90 GPM and pressures to 150 psi. The company’s stainless steel gear pump models LOE and LOX are built for chemical processing, mining, pulp & paper and other processing markets. Lobee's LOM, LOS, LOS heavy duty bronze pumps can handle a wide range of applications including harsh chemicals, coolants, fuel oils and more.
Maag is a world-wide manufacturer of gear pumps for chemical, industrial, high pressure applications. The company’s external gear pump line includes its chemical and industrial pumps, elastomer extrusion pumps, thermoplastic extrusion pumps, polymer production pumps, and more. The Maag chemical and industrial gear pumps are used where operational safety as well as precise and consistent transport are crucial, such as in the highly demanding chemical and pharmaceutical processes and other industrial applications. The pumps can handle viscous and high temperature fluids.
Maag also manufactures the EnviroGear S1 seal-less internal gear pumps. The EnviroGear S1 pump design reduces maintenance costs up to 50%, eliminates fluid leaks, has a long wear life, includes dry run capability, allows for max fluid viscocity to 50,000 cst, and handles max temperatures to 500 degrees F. The internal gear pump can also handle flow rates up to 200 gpm and max discharge pressure to 200 psig.
The EnviroGear S1gear pumps are magnetically coupled and mechanically sealed for environmentally conscious fluid handling. The pump works with thin fluids in addition to hard-to-seal viscous fluids. The gear pump is used in bio-fuels, petro-chemical, soap, chemical, resin, and printing applications.
VARNA designs and builds a low flow rear pump for smooth and continuous flows in the chemical, metering, dosing, and medical applications. The TG-300 model pump has a max flow to 400 ml per minute and viscosity ranges up to 600 cSt. The pump features a 24VDC brushless motor with integral drive electronics.
Though gear pumps may seem simple enough, properly sizing them can be complicated. Author suggests that it actually takes five pump curves to correctly size a gear pump.
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