What is Pressure booster? and where is it used?
A pressure booster is a device used to increase the supply pressure from a controller. The pressure boosters are used where plant pressure is not enough for the working of field instruments. A common pressure booster is a 2:1 booster, which means it doubles the pressure.
For example, heavy spring can be used to close the valve against a high upstream pressure; however, the normal controller output of 20 psi cannot open the valve fully. A 2:1 pressure booster makes the system operational.
1-Drive chamber A, 2-piston, 3-booster chamber A 4-switching valve, 5-check valve, 6-booster chamber B, 7-piston rod, 8-drive chamber B, 9-regulator, 10-air source. The pressure is higher in red lines than in green lines.
The figure shows a simple 2 chamber booster. The pressurised air flows into drive chamber A and boosts chamber B, and the air in drive chamber B discharges directly to the atmosphere. The force on the left side of the piston can be twice as great as that on the right side, so the pressure in boost chamber A can become twice as high as the supply pressure. When the piston moves to the end of its stroke, the switching valve changes its position, which causes the piston to change direction. Thus, the booster regulator can continuously exhaust high-pressure air.
A volume booster is typically used to increase the response of a pneumatic controller to the control valve. This is done by increasing the air flow rate to the actuator. Volume booster is used in conjunction with a positioner on a throttling control valve to increase stroking speed. The booster has a fixed deadband (controlled by the seat‐to‐seat dimension of the supply and exhaust plugs) which is factory set during assembly and testing.
The controller applies its output signal to the booster instead of to the control valve. The pilot valve in the booster requires about 1 cubic inch of air to reposition. The air to operate the valve passes through the booster at 35 standard cubic feet per minute, increasing the stroking time of the control valve.
The only operating requirement of the volume booster is the adjustment of the bypass restriction for stable actuator performance. Although systems with different characteristics may require different adjusting techniques, the following adjustment procedure is recommended when using the actuator for throttling control.