Accumulator (Koomey)

An accumulator or Koomey unit is a unit used to hydraulically operate Rams BOP, Annular BOP, HCR and some hydraulic equipment. There are several of high pressure cylinders that store gas (in bladders) and hydraulic fluid or water under pressure for hydraulic activated systems. The primary purpose of this unit is to supply hydraulic power to the BOP stack in order to close/open BOP stack for both normal operational and emergency situation. Stored hydraulic in the system can provide hydraulic power to close BOP’s in well control operation, therefore, kick volume will be minimized. The accumulator should have sufficient volume to close/open all preventers and accumulator pressure must be maintained all time. According to API RP53, your reservoir tank should have a total volume at least 2 times of usable volume to close all BOP equipment.

Pressure based on 3,000 psi surface stack system that you should check on BOP remote panel and koomey unit is listed below:


• Manifold pressure at +/- 1,500 psi

• Accumulator pressure at +/- 3,000 psi

• Annular preventer at +/- 500 – 1,500 psi

• Rig Air at +/- 100 – 130 psi


There are 4 main components of the Koomey unit as follows:

• Accumulators

• Pumping system (electric and pneumatic pumps)

• Manifold system

• Reservoir tank


According to API RP 53, there must be 2 or 3 independent sources of power that will be available for each closing unit. Typically, you will these following sources:

• Hydraulic with pressure charged in the bottles.

• Pneumatic

• Electric

The diagram below demonstrates how the accumulator is lined up for the surface stack.



Please remember that the diagram is for learning purpose. It may or may not match with your rig configuration. However, the concept of it is the same.


A: Pressure regulator is used to maintain pressure at annular side at 500-1500 psi

B: Pressure regulator is used to maintain the manifold pressure at 1,500 psi

Blue line for opening equipment as VBR’s, Blind/Shear Rams, Annular, HCR.

Red line for closing equipment as VBR’s, Blind/Shear Rams, Annular, HCR.


Cormack, D. (2007). An introduction to well control calculations for drilling operations. 1st ed. Texas: Springer.

Crumpton, H. (2010). Well Control for Completions and Interventions. 1st ed. Texas: Gulf Publishing.

Grace, R. (2003). Blowout and well control handbook [recurso electrónico]. 1st ed. Paises Bajos: Gulf Professional Pub.

Grace, R. and Cudd, B. (1994). Advanced blowout & well control. 1st ed. Houston: Gulf Publishing Company.

Watson, D., Brittenham, T. and Moore, P. (2003). Advanced well control. 1st ed. Richardson, Tex.: Society of Petroleum Engineers.


Tagged , , . Bookmark the permalink.

About DrillingFormulas.Com

Working in the oil field and loving to share knowledge.

46 Responses to Accumulator (Koomey)

  1. Abbas Mousaei says:

    i’m a company man in NISOC in Iran, and i have a presentation on wendsday about Koomey unit that what’re parts and how it work, if you have a document about that please send me, Please help me, thank u

  2. VINOD says:

    HI SIR ,

    i want to know about a bop control system inspection. what is mean by 2 year inspection and a 5 year inspection. what are main parts which we concentrate in inspection and is there any specific format for these type of inspection.

    • 2 year inspection = you must inspect that equipment every 2 years

      5 year inspection = you must inspect that equipment every 5 years

      Depending on which equipment, you may need to read the manufacture recommendation. It should tell you about how often of inspection is.

  3. Fred Godbout says:

    I would like any information concerning an accumulator function test as well as information concerning the accumulator pre-charge. Thank you!

  4. Mohammed Tammam says:

    i know that the fluid reservoir contain fresh water and lubricant and nitrogen is gas which used to charge accumulator bottles but i need to know which type close and open rams,Hcr & annular
    is it nitrogen or fluid reservoir and how
    Thank you

    • Nitrogent is pressured up the bladder inside the accumulator bottle. Typically, the pre-charge pressure is 1000 psi.
      Once 1000 psi pre-charge pressure is accomplished, reservoir fluid will be injected into the bottle to certain pressure as 3000 psi. Reservoir fluid can be hydraulic oil or environmentally fluids (the preference fluid for operators).

  5. Christina Roeyland says:

    Do you know if there excist a Koomey Unit Course for Wellbay Trainees?

  6. will jesus says:

    Excelente las recomendaciones; pero me darían alguna información de lineas y conexiones superficiales así como tipo de anillos de bridas y preventores.

  7. Tejas says:

    I want to know which grade of oil or Hydraulic fluid is used in the accumulator unit.

  8. Ujwal shetty says:

    Hello sir,
    How to check or inspect koomey unit, wheather its working properly?? Can we check during rig operations without any shut down??

    • You can check the Koomey unit by checking accumulator pressure. It should stay where the manufacture designs as 3000 psi. Moreover, when you function test BOP, you should see that the electrical and pneumatic pumps should kick in when pressure drops.

      Can we check during rig operations without any shut down?? – While drilling, only thing you can do is to observe pressure and when you do the BOP test, you can test the function as I say earlier.


  9. Fabrizio says:

    Hello to all

    Are the Koomey units still available on market?
    I cannot find any offial websitefo the Koomey company

    I need to buy in EUROPE

    any help? Thanks a lot


  10. Haq Nawaz says:


    Haq Nawaz

  11. Sanya R. says:

    Ujwal shetty,

    I had one experienced with Koomy inspection and function test with third party team audit which required from our client(This is required when new rig up)as I was AD at land rig(Thailand).

    when you installed Koomy unit inspect shold be following as below:
    1. Physical inspection of all quipments in unit.
    2. Function of equipment such as electrical main control signal and alarm(pilot lamp, oil level etc) must be activate if working properly which you need to test in all situation that all alarm response.
    3. Electrical & Pnuematic pump function which normally electrical is primary used and will be autometically working and control by pressure switch by after working pressure(3000 psi) in bottle drop to 2,700 and pressure switch will be activate electrical pump to pump hydraulic fluid from Resevoir tank and used to pressure up bladder nto 3000 psi, also you need to test Pnuematic pump by shut off electrical pump and when pressure drop to 2700 psi Pnuematic pump will be activate (same as electrical pump process)but for this pump there is time limit to increase pressure for audit which your pump must be working to build up in this time (sorry I cannot remember within 2 minutes or not.)
    4.Check for nitrogen by connect gauge valve to show audit team all bottles are fill up 1,000 PSI.
    5. Rig Air supply(for us using 125 psi)
    6. System pressure Manifold pressure at +/- 1,500 psi, Accumulator pressure at +/- 3,000 psi, Annular preventer at +/- 500 – 1,500 psi
    7. Bypass system working properly.
    8. Remote control system.
    9. Connection hose and supply to BOP stack(Power aplly to system) to check hose leaking and condition(all connections must be secure)
    10. Valve activate to control are correctly, Close and Open (have to physical check at BOP stack during activate valve)

    all above only some of inspection and function test required which you may get more information from client that you working for.

    Sanya R.

  12. Rehman says:

    I want to know accumulator pressure in rig move OR transportation procedure of Koomey unit.


  13. Matt A. Anderson says:

    I’m a Well Control Coordinator at a Drilling Contractor Company in Kuwait.
    Please I need Your Help.

    in the Pre-Spud Testing of the Koomey Unit we Charged the Accumulators to 3000 Psi.
    The Pressure then starts dropping by 100 psi per 3 Minutes .
    NO internal or External Leakage Observed.

    What is Causing the Pressure Drop ??

    PS: the Accumulators are precharged at 800 Psi.

  14. Ahmed Nasser says:

    which accumulator valves shall be opened and which one shall be closed while drilling?


    we are trying to do drowdown test on accumulator unit and after closing all rams & opening all again .we got pressure less than 1000psi which is not acceptable for client ,we didnot find any leak upto now and we still investigating ,what do expect reasons for that

  16. Sunny Thomas says:

    Please guide me about ;

    What shall be the minimum wall thickness of Koomey bottle and Koomey lines ?
    How often the wall thickness inspection to be carried out ?

  17. jeff says:

    Where can I find documentation for BOP/Ram closure times. Well I know 60 seconds or less to close annular and 45 seconds or less to close Ram Type preventers. Where do I find the documentation for the procedure as far as….Push the Function Button, start counting when Readback pressure starts to rise again stop counting.

    API RP 53 12.3.2 in not very clear nor is
    API RP 53


  18. manish dwivedi says:

    i want know why accumulator pressure sat at 3000 psi(slandered) it may be 3500 ,2500,4000 psi

    manish dwivedi

  19. Bob says:

    Matt A. Anderson

    Matt… You have a 4-way valve leaking…remove the top-side bung on each end of the accumulator and look through with flash-light… you will be able to see which valve is leaking


  20. velu says:

    dear All,
    we would like to buy some koomey spareparts, where we can get, is it possible to get any conformity certificate ?



  21. okolie james says:

    i am a rig mechanic, pls explain more how to adjust the manifold pressure, accumulator pressures on a koomey unit

  22. saeed salman says:

    *. Perform Function test.
    *. Adjust; Ann: 1200 PSI – Man: 1500 PSI – Acc: 3000 PSI
    i. When we open (keeping the 4-ways valve in open side)
    1. The annular pressure decrease (while opening), build-up back to 1200 PSI and drop suddenly to 800 PSI.
    2. After taking the 4-ways valve from open side to neutral side, immediately pressure up to 1200 PSI.
    I can’t understand what happened ,my expected 4 way valve not working properly ,so what do you think about this issue ,please let me know as soon as possible
    Saeed Salman
    well sit supervisor (ENI)

    • Luigi says:

      Dear friend, I was also a ENI C.Man.
      on your accumulator or annular BOP you have a leak. The leak can be on 4 way valve of annular BOP or on annular BOP piston seal. Open the plug on oil tank and check for returnu, you can see from the pipe below the 4 way valve. If is the valve you listen noise an the 4 way valve. Or you disconnect the hose to annular and plug then operate the 4 way valve, if the pressure still drop is the valve leak otherwise is the piston seal on BOP.

    • FARMAN says:

      also possible to check annular regulator it not working properly

  23. mp3juice says:

    Great beat ! I would like to apprentice whilst you amend your web site, how could i subscribe for a blog site?
    The account helped me a acceptable deal. I were a little bit familiar of this
    your broadcast provided shiny clear idea

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.