Accumulator Types

Two types of accumulator are in common use — bladder type and float type (Figure 47). They each have a total capacity (fluid + nitrogen + bladder/float) of 11 gallon although 15 gallon versions are also available. Cameron float type accumulators are available with up to 35 gallon capacity. The volume occupied by the float or bladder is usually taken to be 1 gallon.

The bladder type accumulator contains a rubber bladder that separates the nitrogen from the stored hydraulic fluid. The gas is injected into the bladder through the precharge valve in the top of the bottle and the hydraulic fluid enters the accumulator at the bottom. A poppet valve at the base of the bottle prevents extrusion and damage to the bladder once all the fluid has been expelled.

In the float type accumulator, the gas is introduced at the top of the bottle and is kept separate from the stored fluid by a buoyant float. Escape of the gas through the fluid port at the base of the bottle is prevented by the weight of the float actuating a shut-off valve once all the fluid has been expelled.

The float type design is more complex than the bladder type and although replacing the rubber bladder can be a difficult operation this type of bottle tends to be the most commonly used of the two. Since large numbers of accumulator bottles are often needed, they are installed in banks which have the necessary isolation valving to allow for the re-charging or servicing of individual bottles.

Accumulator Type Gas

Float Type

Figure 47 - Accumulator Types

Float Type

Bladder Type

Figure 47 - Accumulator Types

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Accumulator Drilling Rig
Figure 48 - Charging a Bladder Type Accumulator

Hydraulic fluid volume at 3,000psi equals 6.67 gallons. Hydraulic fluid volume at 1,200psi equals 1.67 gallons. Therefore usable fluid operating under the above pressure; equals 6.67—1.67 = 5gallons

NOTE: If the total volume of hydraulic fluid required to operate the various functions of the BOP were to be 225gallons. The required number of 10 gallon accumulator bottles would be;

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Accumulator Sizing

Determining the total accumulator capacity required for a particular BOP stack is an important consideration in the design of the control system. The particular criteria to be applied depends on the relevant regulatory authority or on operating company policy. However, the following can be taken as an example:

• The accumulators must be able to provide the fluid needed to function as required the BOP functions and still retain a pressure of 200 psi above the precharge pressure.

The operating pressure of accumulators is generally 3000 psi. A minimum of about 1200 psi is required to hold some annular preventers closed and so this is taken to be the minimum acceptable pressure that should remain in the accumulator after operating the stack functions. A precharge pressure of 1000 psi will therefore ensure that a small liquid reserve will remain in the bottles when the pressure in the system falls to 1200 psi. Figure 48 illustrates these situations for a bladder type accumulator.

Using these pressures, the amount of usable fluid in a bottle can be calculated and knowing the total volume of fluid needed by the various stack functions will allow the required number of bottles to be determined. The calculations are different however for surface and subsea accumulators.

Sea water hydrostatic pressure will be added to the initial gas pre-charge pressure of 1000 psi (subsea bottles), this will reduce the overall useable fluid volumes.

This sea water hydrostatic increase on the stack mounted bottles is to overcome any hydrostatic compression on the hose bundles prior to entering the pods.

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Responses

  • natasha
    How to determine accumultor bottle capacity?
    9 years ago
  • mike
    How to calculate number of bottledesign accumulator?
    9 years ago
  • jessica
    What types of accumulators are available?
    9 years ago
  • Tom
    How much usable fluid in a 10 gallon accumulator bottle?
    8 years ago
  • sirja mett
    What type of gas use in accumulator?
    8 years ago
  • MIRANDA
    Why are accumulator bottles mounted on subsea BOPs?
    8 years ago
  • pirkko
    Can hydraulic fluid compressed?
    8 years ago
  • Adonay
    How to calculate the total usable fluid volume for the accumulator bank?
    8 years ago
  • yonatan
    What is precharge pressure 15 stack acc?
    8 years ago
  • patrick
    What is an accumulator in well operations?
    7 years ago
  • Elina
    How to calculate the usable volume of accumulator bottle volume?
    7 years ago
  • luis yarnell
    Why isnt hydrostatic presure used for sunsea bop's?
    7 years ago
  • franziska
    How to calculate useable volume of subsea accumulator?
    6 years ago
  • Giacomo
    How to calculate accumulator reserve?
    6 years ago
  • deborah
    How much fluid will a 11 gallon accumulator bottle hold?
    6 years ago
  • Sara
    How does a nitrogen bladder compress in hydrostatic pressure to allow more fluid to be in the bottle?
    6 years ago
  • joann
    What is the “rule of thumb” for available hydraulic fluid in each individual accumulator bottle?
    6 years ago
  • Gerontius
    How to calculate subsea accumulator precharge?
    6 years ago
  • Wilda Bradshaw
    How often does accumulator bottle have to be recertification?
    5 years ago
  • leyton
    What is BOP accumulator capacoty?
    4 years ago
  • pekka
    Why is minimum operating pressure 200 psi above precharge?
    4 years ago
  • Mike
    Does a 5 gallon accumulator hold 5 gallons?
    4 years ago
  • vanessa
    How to calculate tank oil capacity in hydraulic forging?
    2 years ago
  • davide
    How often should Accumulator bottles be tested?
    1 year ago
  • ELISABETH RUUTU
    How much volume in a 15 gallon koomey bottle?
    10 months ago
  • claudia
    Why does accumulator require more botttles?
    6 months ago
  • rose
    How many usable gallons fluid in an 11 gallon accumulator bottle?
    3 months ago
  • kristin
    What is the recommended precharge for a 15 gallon accumulator bottle?
    2 months ago
  • FELICITA
    What types of calculations does the accumulator does?
    1 month ago
  • semhar
    What types of fluid goes into BOP Accumulator?
    6 days ago

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