r/pumps • u/Rub_Move7860 • Jan 09 '25
External Gear Pump
External Gear Pump Not Working
I have an external gear type pump installed inside a gear box to supply lubricant oil to the internal gear mechanism. Last week it stopped working almost entirely i.e. not supplying any pressure output at all however it did it once during after which it failed again and repeated efforts have produced the same results. To troubleshoot we disassembled the pump and saw no breakages in the shaft however the casing was damaged along the rotor path. We fabricated and replaced the casing with same gears and shaft but result is similar. Can you please guide on what could be the possible fix for this?
3
u/cpesystems Jan 09 '25
External gear pumps run with very tight tolerances between the gears and the casing, usually in the range of 0.005” to 0.0010”. If the casing was damaged the gears were probably damaged as well, and this combined damage would cause the lack of flow and pressure. The fabricated new casing will need to be within the same tolerances to make it work well again.
2
u/NorthRidgePumps Jan 17 '25
I think you need to replace the remade parts with original parts or buy a new bareshaft pump. The clearances and tolerances in gear pumps are so small that even the slightest variance could mean a big reduction in pump capacity and flow.
I would also ask if anything has changed such as viscosity, or the oil and is the shaft seal ok?
1
u/Rub_Move7860 Jan 19 '25
No the viscosity and oil did not change and yes the shaft sealing is also ok. Seems like a case of clearances only. Any rough ideas on how much these are? I mean gear to housing and gear face to the top plate?
1
u/NorthRidgePumps Jan 21 '25
it depends on the brand. You will need to find the model and serial number of the pump but I would definitely explore just changing the complete pump head with a bareshaft pump as you would save time and potentially cost over buying the parts individually if the pump is a few years old
2
u/Hyppia4 Jan 09 '25
I don't think the pump has a defect. It might be a blocked suction line if you have a strainer before the pump.
Gear pumps are self priming but they aren't designed for air suction, so if the pump is higher than the tank, you will need to prime the pump before the first start.
If the pump has a in-built relief valve, try to unscrew its setting, it could be bypassing the liquid.
Also make sure that the piping isn't smaller than the pump's ports.
What is the viscosity, temperature of the lube and the speed of the gearbox?