Bladder-Type Accumulators 
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Bladder-Type AccumulatorsNew Offerings: Stainless Steel Bladder-Type Accumulators - 2.5 through 15 gallon.
An OverviewThe typical bladder accumulator makes use of the considerable differences in the relative compressibility between a gas and a fluid. A typical design consists of a gas proof elastomer membrane enclosed within a steel shell. The membrane contains compressed gas (normally dry nitrogen) and separates the gas from the hydraulic fluid. The compressed gas provides a pneumatic spring action to force stored hydraulic fluid from the accumulator into the system as needed. The steel shells are typically manufactured of homogenous seamless steel tubing with both ends formed hemispherically by spinning or forging. The shells are then heat treated and stress relieved to obtain the desired mechanical properties, as required by ASME Code Section VIII, Division 1 pressure vessel requirements. Corrosion resistance can be achieved with the use of stainless steel, but is more commonly obtained by plating the shell interior with nickel or coating with an epoxy or phenolic compound.
The typical bladder-type accumulator is a bottom repairable design, in that the bladder is inserted into the shell through a bottom opening in the shell. This opening allows the installation of the oil port body/poppet valve assembly to seal the accumulator. Optional top repairable designs are available, along with various gas stem sizes (7/8" & 2”) if desired. Tobul’s parts and bladder kits are interchangeable with most major manufacturers. Due to the limited volume capacities, it is common to find banks of bladder-type accumulators connected to a manifold in order to provide the desired quantity of fluid to a system. Unfortunately, this can cause physical space limitations in certain applications. Generally, bladder-type units are connected to a system by threading a pressure connection directly into the fluid port of the accumulator. Various sized porting must be specified and may entail the use of special adaptors or bolt-on flanges to achieve desired fluid connections. Illustrations are representational and not necessarily indicative of how any particular model will be built. Bladder-Type AccumulatorsBottom Repairable ModelsBottom repairable bladder-type designs (Tobul model designation TBR) are the most commonly found units in the marketplace. Fluid capacities are generally limited to a small variety of sizes (one pint to fifteen gallons/approximately .5 Liter to 57 Liters). Pressure ratings of these vessels are generally 3000 PSI (207 Bar), 5000 PSI (345 Bar) or less. Specially rated units, though, can contain up to 6600 PSI (455 Bar).
Bladder-Type AccumulatorsTop repairable modelsTop repairable bladder-type designs (Tobul model designation TBRT) are readily available in the marketplace, but much less commonly seen than bottom repairable units. TBRT’s are more expensive than TBR’s since an additional gas port body and anti-extrusion ring is necessary to completely seal the accumulator shell.
Top Repairable Versus Bottom Repairable?The distinct advantage of a TBRT (Top Repairable) unit is the fact that a unit may be repaired (i.e., bladder replaced) without dismounting an accumulator from the system. As long as the unit can be isolated and the system pressure relieved, the top gas port assembly can be accessed and a replacement bladder installed. Note: It is extremely important to follow ALL guidelines for maintenance and repair of any pressure vessel! Please contact Tobul sales & service engineering (803-245-5111) for assistance with any questions. Please download a copy of Tobul’s Operating and Maintenance Procedures from this site prior to beginning any procedure on any Tobul accumulator. Illustrations are representational and not necessarily indicative of how any particular model will be built.
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Common bladder-type accumulator capacities are one pint, one quart, and one through fifteen gallons (1, 2.5, 5, 10, 11, and 15). Bladders are commonly constructed of a particular elastomer (Buna-N, Butyl, EPR, Viton, etc.) specified to achieve a desired compatibility with the system fluid (hydraulic oil, water glycols, etc.) and elasticity throughout the operating temperature range (typically -20°F to 200°F). Normally, a spring-loaded poppet valve assembly is utilized to prevent extrusion of the bladder. This commonly limits the fluid flow rate to a maximum of 220 gallons per minute into the system from the accumulator, but higher flows can be obtained with a special poppet valve assembly.
