Figure 2 illustrates the general concept in LOS equipment and components recommended by API Standard 614. The actual scope of equipment will be specified by the Purchaser. For instance, the transfer barrier bladder-type vessel (See Figure 1) is required due to the installation of the overhead tank.

If the overhead tank is not specified, the standard bladder accumulator can be utilized within LOSA (Figure 3).

Theoretical Concept
Bladder accumulators operate on a principle of Boyle’s Law of gases. The expansion and compression of the Nitrogen gas contained in the bladder occurrs in a short period of time (less than a minute). This is an adiabatic process, which characterizes the absence of heat transfer in the system, and no heat is transferred from the system. For Nitrogen, the value of Polytropic constant n = 1.4 and Boyle’s Law can be expressed as follows:

P₁V₁ⁿ = P₂ V₂ⁿ
or
P₁ V₁^1.4 = P₂ V₂^1.4— Which represents the adiabatic condition for Nitrogen.

Figure 4 illustrates the relationship between changes in pressure from P2 to P1 and volume from V2 to V1 described in the equation above under adiabatic conditions.

The following designations will be used in further discussion:

V₁ = Size of LOS accumulator required, cu. in. This is the maximum volume of gas in the accumulator bladder at the pre-charge pressure P₁.

V_x = The volume of lube oil to be discharged from the accumulator, cu. in. This is the volume of lube oil demanded by the system. The V_x value is a function of the LOS for the certain type of turbomachinery and can be obtained from the manufacturers specifications.

P₁ = Precharge gas pressure of accumulator, psia. This pressure is always less then the minimum system pressure P₃, psia.

Figure 4. Adiabatic Pressure Chart. The stored fluid energy in the accumulator is a function of the area under the curve P V n = C, where C is a constant.