An adjusting device for a seat comprises at least one fluid chamber and a valve assembly in fluid communication with the fluid chamber. Each fluid chamber is configured to be installed in the seat to adjust at least a portion of the seat upon inflation or deflation. The at least one fluid chamber comprises a first fluid chamber. The valve assembly comprises a check valve and a 3/2-way valve. A first port of the 3/2-way valve is in fluid communication with the check valve, and a second port of the 3/2-way valve is in fluid communication with the first fluid chamber.