Heat pump project oil issues

Hi all.
I am working on a heat pump/chiller project.
It is doing both chilling and heating.
Basically a water cooled chiller, but we are taking condensing temp up to 60'c.
We have 2 copeland ZR380 compressors running together, in parrallel(?) common suction and discharge pipes.
Traxoil oil injectors.
Oil seperator feeding an oil resevoir with pressure reducing valve to make the oil, low pressure feed, 2 bar above suction pressure (following problems with using a high pressure oil feed).
Using 140kg of R134a, yes 140kg.
The problem we have is that at high temperature/pressure (60'/18bar) the oil is leaving the compressors quicker than we can get it back.
We have been told that the traxoils are crap, in general, not just our ones.
An american forum has suggested that we need to have an oil/refrigerant ratio of 10:1 minimum, due to the oil mixing with the fridge.

Any comments on this ratio??

I don't want to overfill with oil, but don't want to kill expensive compressors!!

Not my area of expertise but just reading the Traxoil data sheet out of interest I noticed that you changed from a high pressure oil feed to a system at a lower pressure.

Was the high pressure orifice removed when the system was changed? (assuming that one was fitted of course)

I don't know. I'll have a check tomorrow.
Thanks for the reply