Automatic Top Up Unit (ATU) is used to compensate for oil volume and pressure loss in API 53B systems. Sometimes such combined system is refered to as 53B Modified.
ATU is recommended for use when calculations show that frequent manual oil top ups would be needed - more often than once per 30 days. Frequent top ups are usually needed when pressure in the system is high, so even a mechanical seal in a perfect condition will exhibit some leakage. The higher the pressure, the more frequent oil top ups are needed. With higher pressure, maintenance is not only more frequent, but also more difficult. Frequent and difficult maintenance would mean higher running costs and lower reliability in general. In this case an ATU will greatly decrease maintenance and increase reliability of the system.
One top up unit will provide oil for several Plan 53B accumulators. In such a system, instead of manual top up of each accumulator by an operator, lube oil is added to the bigger, for example, 300 liter tank. Tank volume is selected according to the number of mechanical seals and the pressure in the system. There is no pressure in the tank, so the fill up is simple, and safer.
The ATUs as shown are powered by electrical motors. When instrument air is available, an ATU may be manufactured to be pneumatically driven as well.
The offered ATUs monitor mechanical seal condition and their own condition as well.