Why Bladder Accumulators?
Bearings in turbo machinery require lubrication while they are running. All turbo machines are equipped with a lube oil system to provide the necessary lubrication at high pressure. These lubrication systems consist of from a high flow-rate pump, a reservoir and an accumulator. Accumulator is a very essential part in lube oil systems, because it supplies the lube oil to the bearings when the pump shuts down due to a power failure or a pump changeover. This prevents the bearings from costly damage and increases the bearing life and overall reliability of the lube oil system.

API Standard 614 Requirements to LOSA
LOSA are designed in compliance with API 614, and in accordance with the ASME Section VIII, DIV. 1 of the Pressure Vessel and Boiler Code. European CE, Canadian CRN, Brazilian NR-13, Chinese SELO, and Malaysian DOSH certifications also available. These accumulators are constructed from a 300 series stainless steel shell and have a nitrile bladder, which forms a barrier between the gas and the fluid. If the working pressure is less than 500 psi, then the design allows a screen welded inside the flange to keep the bladder from extruding out of the fluid port. The screen is welded flush and smooth with the inside of the shell so as not to damage the bladder. If the

pressure is more than 500 psi, then a plug and poppet design has to be utilized. At a low pressure the bladder material does not extrude through the holes in the screen but at a higher pressure the bladder will extrude through the holes in the screen. In a plug in poppet design a fully inflated bladder sits against the poppet andcloses the opening keeping the bladder from extruding out of the fluid port. The minimum shell safety factor needs to be 3.5:1.

Figure 1 shows bladder type accumulators designed
according to requirements of API Standard 614 for installation within turbomachinery Lube-Oil Consoles.

LOSA are installed vertically in the system so that the gas valve molded into the bladder is on the top end and the fluid port is on the bottom end. The accumulator bladder must always be pre-charged with an inert gas that does not react with the bladder material or other components that the gas comes in contact with. Nitrogen is the best option because of its availability, chemical and physical properties, and cost. Nitrogen is very stable and non-reactive even under high pressure. Air should never be used because of its corrosive properties and the explosive situation it may create under high pressure.

The pre-charge should always be maintained between 70-80% of the minimum working pressure of the system. The high flexibility and low weight of the bladder causes the bladder response time to be very quick as compared to the pressure drop in the system. The quicker response enables the LOSA to maintain the pressure and flow of the lubricating oil and prevents the damage to the bearings and other components.

The pre-charge needs to be monitored periodically. The accumulator needs to be completely drained of the lube oil and the bladder needs to be fully expanded within the shell in order to obtain a correct pre-charge pressure reading. Any fluid remaining in the accumulator will cause the pressure to rise, and give an incorrect reading. This also holds true when precharging the accumulator. For measuring the pre-charge, or for actually pre-charging the LOSA, the system should be shut down or the accumulator should be isolated from the pipeline with an isolating valve. Any fluid remaining in the accumulator may be drained through the bleed port.