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Accumulator Precharge Pressure Formula and Calculator

Hydraulic and Pneumatic Design and Engineering
Fluids Engineering and Design

Accumulator Precharge Pressure Formula and Calculator

In operation, the accumulator pre charge pressure that is somewhat lower than the system operating pressure. As an example of accumulator operation, let us assume a cylindrical accumulator is designed for a preload of 1,300 psi in a 3,000-psi system. When the initial charge of 1,300 psi is introduced into the unit, hydraulic system pressure is zero. As air pressure is applied through a gas servicing valve, it moves the piston/diaphram toward the opposite end until it bottoms. If the air behind the piston/diaphram has a pressure of 1,300 psi, the hydraulic system pump has to create a pressure within the system greater than 1,300 psi before the hydraulic fluid can actuate the piston/diaphram. At 1,301 psi the piston starts to move within the cylinder, compressing the air as it moves. At 2,000 psi, it has backed up several inches. At 3,000 psi, the piston/diaphram has backed up to its normal operating position, compressing the air until it occupies a space less than one-half the length of the piston/diaphram. When actuation of hydraulic units lowers the system pressure, the compressed air expands against the piston/diaphram, forcing fluid from the accumulator. This supplies an instantaneous supply of fluid to the hydraulic system component. The charged accumulator may also supply fluid pressure to actuate a component(s) briefly in case of pump or pressure failure.

Eq. 1
P = V_r / V_a [ ( P_f P_s ) / ( P_s - P_f ) ]

Where:

V_a = Total Accumulator Volume (gal)
P_s = Starting Accumulator Pressure (psi)
P_f = Final Accumulator Pressure (psi)
V_r = Volume of Fluid Removed (gal)
P = Accumulator Pressure (psi)

bbl = 42 gallons

Source:

Reference: Lapeyrouse, N. J., 2002, Formulas and Calculations for Drilling, Production and Workover, Second Edition, Gulf Professional Publishing, Page: 41.

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