External gear pump bearing block installed in wrong direction

[Rob47]

Hi, see attached picture. The cavity where the arrow points to is installed on the suction side of the external gear pump.
Is it possible that if the cavity is installed on the outlet (wrong) side of the gear pump, the other side of the gears will wear out very quick due to the high pressure on one side???

I ask, because i have a pump with gears that are very bad worn out on one and the same side. On that side the bearing block is also worn out and damaged. The mechanics took the pump apart but they didn't pay attention to see if one bearing block with the cavity, was not properly installed by the manufacturer. I suspect one of the bearing blocks was not properly installed by the manufacturer, so there was a high pressure build up on one side of the gears. The other surfaces of the gears and pump are smooth and aren't damaged.

 

[HPost]

No pic to see...

 

[Rob47]

Oh sorry. Here is the picture.

 

[HPost]

That cut out should be on the inlet side of the pump.

The 2 grooves you can see are to allow oil to drain away from the bearings and keep them cool

You can also see the blue plastic back up part that supports the seal. It is on the low pressure side, with high pressure coming from the cut out on the other side of the bearing block.

 

[Rob47]

Ok, but if the cut out (grooves) of one of the bearing (bushing) blocks is on the outlet side of the pump that means that on that side there will be high pressure, which will force the shafts of the gears to the other side. Am i correct??

 

[Rob47]

Here a picture of what i mean

 

[HPost]

The separating forces of the gears will push the shafts apart. That is the highest force in the pump and it takes a lot of oil pressure to push the shafts back towards the middle of the bearings.

Some pump manufacturers direct high pressure oil from the outlet to offset this force and balance the shaft. Some don't...

Anyway, you can also see how high pressure oil is taken from the outlet and directed to the seals. External gear pumps have chronic volumetric efficiency at low pressure. As the pressure rises, the high pressure oil gets behind the bushes (bearings) and pushes them against the gears. Oil is also directed to the seal to energize it...

 

[HPost]

I just saw your picture...

There is no oil feed to the end of the shaft. That is also why the grooves are there.

The pressure, by the very nature of fluid dynamics, will leak from the teeth pockets and down the side of the gears and into the bearings. To prevent the build up of pressure the oil is allowed to drain away through the big grooves. The lowest pressure in the pump is at the inlet and so the pressure will move from high pressure to low pressure.

If that big cavity - the one with the arrow in you first picture - was on the outlet, there would be loads of flow to bearings, making the pump really inefficient.

Which side of the gears is worn? The drive shaft side or the other side?

 

[Rob47]

The drive shaft side of both gears are worn. The sides of the gears and the sides of the axles of the gears are worn. I suspect the bushing (bearing) block of the other side of the gears was not installed correctly. The big cavity with the grooves was installed on the outlet side of the pump. Therefore on that side, high pressure oil was pushing against the sides of the gear axles, towards the driveshaft side.

 

[73lafuite]

I think that if the bezel has been mounted upside down it must be noted that the black seal extruded side opposite the blue plastic.

On the other hand if the idle pinion is drilled in the center a bad fitting would mean that the pump does not provide flow.

An axial force on the driving pinion is forbidden !!!

There have also been abnormal wear on some brands of pumps if the outlet pressure was <2bar. When the circuit put the pump in bypass we managed to have 3 to 4bar counter pressure.

 

[HPost]

There is always the possibility that the pump was not built properly. That is to say that the bushes were installed correctly, but there was some excess thrust on the bush?

It doesn’t look like the pump was built with bushes upside, but that’s an educated guess based on the picture.

Could also have seen high pressure. That being the case, the ID of the pump body will have deep grooves where the gears have contacted the housing.

 

[Rob47]

Many thanks HPost. The picture i posted is not the picture of the pump. It's an example to show the bushing cavity. The actual pump is worn out on the drive side of the gears. The gear axles contacted the housing on the drive side and are worn out. The side of the gears contacted the bushings on the drive side. Gear side area and bushings are worn out. Sure there was excess axial thrust on the gear axles on the other side. I forgot to take pictures of the pump. Next monday i will be back on the work site and take pictures. T