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:
• 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.
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.
Reference book: Well Control Books