A gear pump is a rotary pump consisting of two meshing gear wheels in a suitable casing whose contra-rotation entrains the fluid on one side and discharges it on the other.
It is a positive displacement pump that uses two meshing gears to pump both low and high viscosity liquids. The two gears draw liquid into the enclosed housing through the inlet, trap the liquid between the gear teeth and then propel the liquid through the outlet. Gear pumps may require occasional maintenance for optimal performance, the frequency of which is best based on past performance. Maintenance on most gear pumps can be accomplished without removing the driving component and plumbing.
1.) Remove the gear pump casing screws with the Phillips screwdriver. The screw configuration may vary based on the manufacturer and may require the use of a flat-bladed screwdriver or hexagonal wrench to remove the screws. Consult your pump manual for the correct tool.
2.) Remove the pump casing. Gear pumps that have not seen regular maintenance for an extended length of time may not open easily by hand. In these cases, insert the edge of a flat-bladed screwdriver into the seam in the case’s housing and gently apply pressure until the casing comes apart.
3.) Check for wear on the tips of the gear teeth. A new gear pump has a clearance of between 0.005 inch and 0.007 inch between the gear teeth and the gear chamber wall, just enough to insert a piece of thin wrapping paper. More clearance than that indicates wear due to scrubbing against the gear chamber wall, which can occur when the pump heats up and the metal gears expand outward, or can be the result of bearing wear.
4.) Examine all of the bearings for signs of wear. Severely worn bearings are egg-shaped and allow the gears to move around within the gear chamber. If bearings are worn, they should be replaced using a bearing puller, which is a device that uses a collet to remove bearings from inside of the bearing bore. New bearings should then be greased and replaced. Alternately, the entire bearing assembly can be replaced on some models of gear pumps.
5.) Inspect the pin that holds the gears onto their shafts. This pin prevents the gears from coming loose, and if they are sheared off they will cause the pump to stop working completely. The pin can be sheared off if a foreign object enters the pump and jams the gears or if a bearing becomes worn enough to stop rotation within the pump. If the pin is damaged or sheared off, replace the pin and thoroughly clean the inside of the gear chamber.
6.) Examine the pump cover for bulges. Extreme pressure inside the pump, as well as a powerful blow to the drive shaft that enters the pump, can cause bulges in the pump cover, which allow liquid to bypass the pumping process (called slippage). If bulges are found, the damaged pump cover should be replaced by removing the screws that hold it in place and installing a new pump cover.
7.) Check the pump for signs of general wear caused by improper use. If the gear pump has been used to pump an abrasive liquid, the shaft may have visible scouring marks. Likewise, if the gear pump has been used to pump certain chemicals not compatible with the metals that make up the components of the pump, the gears and shafts will bear etching and deterioration may be present. Thoroughly rinse the inside of the gear chamber, removing the chemicals and abrasive fluids. In severe cases where the gear pump has been used to pump chemicals and abrasives for an extended period, the pump components may not be salvageable and will require replacing.