Renewable Oil Services Limited are the UK’s largest supplier of oil products and oil exchange services to the wind turbine industry covering both the onshore and offshore wind markets.

The company, have been carrying out gearbox and hydraulic oil exchanges on wind turbines across the UK and Ireland for over 10 years using their specialised oil pump trucks. Back in 2013 they were the first company worldwide to carry out a vessel-mounted combined gear and hydraulic oil exchange on an offshore wind turbine using their own specially designed and manufactured vesselmounted pumping system

In-House Developments

Specialised trucks and offshore units are fully bunded and have an in-house developed oil heating and filtration system. This system allows the company to pre-filter and heat the new gear oil products to between 40ºc and 55ºc, allowing them to pump the viscous 320ct new gear oil products up 180 metre hoses to the nacelle and into the gearbox. With truck or vessel in place at the base of the turbine, they start with winching hoses up to the nacelle. From there they connect the waste oil hose and pumping system to the gearbox drain point (or points) and drain the full system of the old oil.

Next Steps

The next step, depending on the contamination level and oil sample results of the gearbox oil, will determine the level of system flushing required.

Level 1 – a basic oil exchange with no flushing required where a routine oil exchange is taking place with no or minimal contaminates currently found within the oil sample.

Level 2 – an oil exchange with single flush if low to moderate levels of contaminates are found in the oil sample. For this, a pre-defined system volume quantity of oil is used, and the quantity will vary depending on the turbine and gearbox type – the new oil is pumped up to the gearbox via a closed system.

The reason for carrying this out in a closed system is so that you do not have to open the gearbox lid as this is one of the main ways in which contaminates can be introduced into the gearbox itself.

To achieve this closed system they use specialised fittings to connect to the gearbox keeping the gearbox lid sealed and contaminate free – the oil enters the gearbox at between 40ºc to 50ºc to allow the operation of any internal system thermostats to open fully, allowing the flow of oil to pass through all of the gearbox auxiliary systems freely (oil coolers, filter blocks, etc).

The oil is then circulated and flushed through the gearbox and ancillary systems with the use of the gearboxes’ own internal or external gear oil pump for a set time period – once complete, the flush oil is then drained from the gearbox via the sump drain point as before.

Final Steps

Once the gearbox has been emptied, along with any flushing requirements, the filters are replaced with new units and then the gearbox and associated systems are refilled with new clean oil to the specified levels. This is carried out via a pump and hose system filling the gearbox using a closed system to ensure the new oil pumped directly into the gearbox is contaminate free.

The procedures and principles for the gear oil exchange are also applicable for the wind turbine hydraulic systems and can be carried out on the turbine at the same time as the gearbox oil change. The hydraulic oil change is also carried out in a closed loop system with various options of flushing depending on the contamination level of the oil.


Also in the case of glycol coolant exchanges a similar principle is adopted using in-house specialist pumps and hoses which are used to drain the glycol system. Systems are then refilled using a specialist glycol pump unit to progressively fill the systems, taking care not to create bubbles in the new glycol and minimising the risk of system airlocks