Hydraulic External Gear Pump

Aluminum housings provide lightness while being designed to withstand up to 250 bar (approx. 3600 psi). The inside must be smoothly machined to prevent gap expansion. Microscopic wear in the housing causes oil to slip back to the suction line (internal leakage), dropping volumetric efficiency.

In gear pumps, the shaft and gear are not separate; they must be integrally machined from a single solid billet for maximum strength. When the teeth mesh, fluid gets trapped. This "Trapped Volume" creates extreme pressure spikes that can break the shaft; relief grooves are machined into the bushings to vent this pressure.

This is not an ordinary bushing; it is a "Pressure Loaded Bushing." The pump's own high-pressure oil is routed to the back of the bushing, constantly pushing it against the gear. Because of this, even if the pump wears down over years of operation, the bushing advances to keep the clearance at absolute zero.

The front and rear bushings sandwich the gears. Under high pressure, the gears deflect radially toward the housing. The bearing capacity of these bushings must be strong enough to prevent the gear tips from galling into the aluminum housing.

250 bar of hydraulic pressure forces rubber to act like putty. These small plastic pieces plug the "weak points" where rubber could extrude, saving the seal from destruction.

If this seal "blows", high-pressure oil bypasses to the low-pressure suction side, the force pushing the bushings vanishes, and the pump fails to build pressure (Volumetric efficiency drops to 0%). A hard "Back-up ring" is used alongside it so the pressure does not extrude and tear the rubber.

Prevents oil from bypassing in high-pressure "Extrusion Gap" areas.

When the bolts are torqued during assembly, the O-ring deforms (squishes) inside its groove to create a seal. A "nipped" or damaged O-ring is the cause of 90% of external leaks.

A 250-bar pump exerts tons of outward pushing force on the covers. If the front cover deflects, the O-rings will blow out, causing external oil hemorrhage. Therefore, covers are designed thick and often ribbed for rigidity.

Prevents the aluminum or cast cover from crushing (embedment) under high torque, thereby maintaining the bolt's preload tension.

The 250 bar of fluid pressure acts like a hydraulic jack, trying to push the covers apart. The bolts counteract this "separating force." If they are not torqued evenly in a cross pattern, the housing will distort, and the internal gears will mill out the aluminum casing, destroying the pump in 5 seconds.

In heavy-duty applications where oil temperatures exceed 80°C, standard NBR rubber cooks and becomes brittle. In such cases, expensive but durable Viton (FKM) seals are mandatory.

The surface roughness of O-ring grooves must be kept extremely low during machining. A scratched groove allows high-pressure oil to bypass underneath the O-ring.

This part bears the mechanical vibrations and weight. Its pilot (register) must perfectly align with the engine housing; angular misalignment will cause the drive shaft to snap under fatigue.

Rubbing against the rotating shaft, this seal is one of the system's weakest links. The seal's lip is pressed against the shaft by a garter spring. If the internal casing pressure spikes, this seal will blow out. The shaft surface where the seal rides must be plunge-ground with zero spiral lead marks.

It is an Internal type circlip, requiring specific pliers (for gripping holes) to install. When sudden pressure spikes occur in the pump, this ring is the only thing keeping the seal in place.

Its half-moon shape allows it to automatically and tightly align when seated in the shaft keyway. In an overload situation where the pump gears seize, this key shears off (acting as a mechanical fuse), saving the expensive diesel engine or pump shaft from snapping.

In high-vibration environments (heavy machinery), "Nyloc" (nylon-insert) nuts or chemical threadlockers (Loctite) are typically used to prevent loosening.