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A booster cylinder, also known as a supercharger, amplifies liquid pressure, similar to a step-up transformer in an electrical circuit.
The schematic diagram shows the structure of a single-acting booster cylinder, which consists of a double-acting cylinder and a single-acting cylinder. If friction losses are not considered, the booster’s amplification factor (pressure ratio) is equal to the ratio of the effective working areas SA and SC of the two pistons.
As shown in the diagram, when pressurized oil (pA) enters port A and oil returns from port B, the combined piston moves clockwise, and pressurized oil (at pressure pC) flows out of port C. At this point, the charging valve is closed. When the reversing valve operates to the right, oil enters port B and returns from port A, causing the combined piston to move clockwise. The pressure in chamber C drops, causing the charging valve to open and oil to be replenished from port C to the single-acting cylinder. At this point, no high-pressure oil is output. The pressure increase ratio, i, can be derived from the following formula:
From SApA = SCpC ⇒ pC = pASA / SC = pAi
Since area SA > SC, i > 1, which amplifies pressure pA to pC.