Pump housings and gears are made of top quality bronze, shafts are from stainless steel 303. Bearings are designed of high performance carbon-graphite material selected for wear resistance and long service life.
Gear pumps are positive displacement pumps. Each shaft revolution displaces a definite amount of liquid relatively unaffected by the back pressure in the discharge line. Shaft speed and flow are directly proportional. Recommended pressure limits are 100 psi for water and non-lubricants, 150 psi for oil and lubricants. Maximum shaft speed is 1750 rpm.
A relief valve is necessary in the system if the discharge line contains any throttling devices, such as a shut-off valve, a spray nozzle or other restrictive device. This will return the liquid to the suction side or to the tank. The relief valve is also available as part of the pump itself (R-model pumps). However, built-in relief valves are only good for intermittent service. If used continuously, the pump will over heat. A built-in relief valve is strictly a safety device against overpressure. It will not work successfully as a pressure or flow control device. For this purpose a separate relief valve in the pressure line must be used.
Service life will be increase substantially if the liquid pumped is clean and has a lubricity value. These pumps have extremely close tolerances. Fine abrasives like sand, silt, or powder in suspension will destroy pumping ability.
Liquids compatible with bronze, stainless steel and the graphite bushing can be pumped. Solvent resistant packings and Teflon® packings are also available.
Temperature extremes are detrimental to service life and should be avoided. Basic metals of construction allow temperature range of _40F to 400F. The acrylic graphite packing is rated to 500F. Freezing liquid in the pump can deform or damage the pump.
Viscous liquids such as molasses or oils require a lower pumping speed, in extreme cases as low ass 200 R.P.M. Liquids with specific gravities heavier than wate such as dry cleaning fluids require an increase in motor horsepower directly proportional to the increase in specific gravity over water.
A rotary gear pump is capable of lifting water on the suction side as high as 20 feet. Though gear pumps are self-priming, a foot valve is recommended. For pumping water directly from streams or ponds, a wire mesh strainer must be used at the beginning of the suction line to prevent stones from entering the pump. Strainer and foot valve are commercially available as combination units. Often used in Diesel transfer.