Fluid Management Pump System

Fluid Management

Welded Bellows Accumulators, Reservoirs and Surge Arrestors

BOA Aerospace has made aircraft, space, and military applications our principal focus. With ISO9000 and AS9100 certifications, our Swiss (BOA AG) and U.S. (Flexial) facilities have been selected to produce products for Pratt & Whitney, Boeing, Raytheon, GE, Lockheed Martin, Hamilton Sundstrand, Rocketdyne, Honeywell, Northrup Grumman, Liebherr-Aerospace, Parker Hannifin and many other aerospace primes, and provide primary components for Airbus, Boeing, Bombardier, Embraer, Eurocopter, and other air- and rotorcraft around the globe.

Welded bellows reservoirs, accumulators (also called volume compensators) and surge arresters differ in function, but share construction similarities. Each has an outer containment, an internal welded bellows separator and ports in one or both ends depending on the application.

The bellows, which serves as a flexible separator, is welded to one end of the containment and has a closed, movable end called a sweeper that slides through containment as the bellows expands and contracts with the system fluid. As needed for the application, the fluid can either be on the inside of the bellows or on the outside between the bellows and the containment with the gas on the opposite side.

Technology Features

  • High Pressure
  • Maintenance Free
  • Titanium
  • Ultra-light-weight Composite
  • Miniature, Unmanned Vehicles
  • Commercial and Military Aircraft
  • Space Systems


Flexial Reservoir

Reservoirs store fluid for delivery, either in a single surge or dispensed over time. The primary function is fill-then-dispense, as opposed to cycles of partial fill and drain. Reservoir delivery energy sources include:

  • Permanently gas pressurized
    Charge gas sealed on one side of the bellows compresses during filling to store expulsion energy.
  • Permanently liquid-vapor pressurized
    Volatile liquid on one side of the bellows partially evaporates; pressure builds up to phase equilibrium.
  • Actively gas pressurized
    A regulated external pressure source supplies expulsion force.
  • Passively spring pressurized
    Delivery pressure is generated by the spring force of the bellows.


Flexial Accumulators

Accumulators are a type of reservoir that accept system fluid and returns it repeatedly. They usually have a fixed gas charge, are fully open to the system, and typically reside in closed fluid loops to perform one or more of the following:

  • Bootstrapping/ Anti-cavitation
    Accumulator positioned immediately upstream from a pump surges fluid into the pump on startup to prevent cavitation. As system pressure and flow balance, the fluid is returned to the accumulator.
  • Thermal volume compensation
    In a closed-circuit fluid system, the accumulator maintains a steady positive pressure by absorbing the temperature driven expansion and contraction of fluid.
  • Pulsation absorption
    Accumulator placed immediately downstream from a reciprocating pump. Pulsations from the pump are attenuated by surging into the accumulator on the delivery cycle.

Surge Arrestors

Flexial Surge Arrestors

Surge arresters are a type of accumulator that includes an orifice between the bellows and the system and dissipates kinetic energy of a flowing liquid when the flow stream is suddenly stopped by a quick-closing valve.

The static gas charge is higher than the normal system pressure which keeps the bellows immobile and loaded against the fluid until hit with a surge. When flow is suddenly interrupted, the fluid diverts through the orifice and into the bellows, displacing the bellows and compressing the gas charge. The high velocity of this event causes heating of the gas charge and partial adiabatic compression that slows and stops the incoming surge.

The gas charge then pushes on the bellows and sends the surge back into the system. But now the orifice slows the return of the fluid while the wall of the arrestor absorbs the heat of compression thus lowering the pressure of the gas. Usually this repeats for several decaying oscillations until the kinetic energy is dissipated, the system becomes static and the bellows is again loaded against the fluid.

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Flexial is the BOA Group brand for Aerospace applications.

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