Mechanical pump oil discharge through inlet

[zaillian]

I have an old mechanical vacuum pump that is discharging a lot of oil (half a gallon was found after some use) through its inlet, with enough force to move at least a few inches vertically. The pump is used in conjunction with a diffusion pump and the discharge ruined its oil. The pump also creates lot of oil mist, but this is not a problem.

I would like to hear ideas what causes the discharge and how to prevent it.

Possibly the issue is that the pump has been shut off, which after the air has been let into the chamber with the inlet open sucking oil from the pump. Then the issue is solved by making sure the valves are always shut off when filling the chamber with air. Anyone else having had this problem?

 

[berkeman]

What make/model is this pump? Can you link to the datasheet for it? Thanks.

 

[zaillian]

What make/model is this pump? Can you link to the datasheet for it? Thanks.

I may not recall the exact number properly, but will check as soon as possible.

It is one of Leybold's Trivac models, but decades old. Probably the D16 or close.

https://www.leyboldproducts.de/en/p...s/trivac/trivac-b/pumps/691/trivac-d-16-b-dot

 

[Baluncore]

Check the oil is not too high. Someone may have overfilled the crankcase, so it is whipping oil up into a foam with the big end, then throwing it on the piston and rings from below.

Check for leaking valves or broken piston rings.

Maybe slope the inlet line so oil on the inlet side, runs with the flow, back into the mechanical pump.

 

[Lnewqban]

I would like to hear ideas what causes the discharge and how to prevent it.

Copied from
https://www.leyboldproducts.us/medi...tals_of_Vacuum_Technology_EN58774555441f3.pdf

"The TRIVAC rotary vane pumps are produced as single-stage (TRIVAC S) and two-stage (TRIVAC D) pumps."

Could it be that one or both stages of the pump are worn out, by-passing gas and oil through worn vanes and cylinders?
Perhaps old oil that has lost original properties?

 

[Ivan Nikiforov]

Hello! Perhaps a vacuum pump should be used together with a pre-vacuum filter? It is a device designed to capture or absorb oil vapor molecules coming from the pump inlet. In addition, it seems to me it makes sense to check whether the diffusion pump is the source of the oil.

An example of a pre-vacuum filter.
Pre-vacuum traps are used to protect against the reverse flow of oil from the pump to the working volumes.
They are used in combination with a mechanical pre-vacuum pump that works with a diffusion pump.

 

[zaillian]

Clarification, the pump is the Leybold-Heraeus Trivac D30A. A manual is available at manualslib.
https://www.manualslib.com/products/Leybold-Trivac-D30a-8859916.html

View attachment 356832
The pump has an anti-suck back mechanism to prevent the oil from escaping when turned off.

 

[zaillian]

Copied from
https://www.leyboldproducts.us/medi...tals_of_Vacuum_Technology_EN58774555441f3.pdf

"The TRIVAC rotary vane pumps are produced as single-stage (TRIVAC S) and two-stage (TRIVAC D) pumps."

Could it be that one or both stages of the pump are worn out, by-passing gas and oil through worn vanes and cylinders?
Perhaps old oil that has lost original properties?

Interesting and possible. Though the pump was able to achieve an ultimate pressure of approximately 10^-1 TOR in the chamber. A tech stated it is impossible to determine which way the wanes are supposed to go after taking it apart and assembling previously, so a possible fault.

 

[Ivan Nikiforov]

I suggest you check the valve indicated by the green arrow. If it does not work properly, the working chamber of the pump may overflow with oil, which will be intensively discharged through the inlet pipe of the pump. I also suggest you check the oil separator indicated by the purple arrow. If it does not pass air well, excessive pressure may be created inside the oil chamber, which will eject oil through the inlet pipe.