According to the controlled parameters The parameters controlled by a proportional valve include pressure, flow and direction, etc. There are proportional valves that control one parameter (single parameter, single function), and there are proportional valves that control two or multiple parameters. Proportional pressure regulator including proportional pilot pressure regulator, proportional relief valve, proportional pressure reducing regulator, proportional sequence valve, etc., all are proportional valves that input electrical signals to control the pressure parameters (single parameter) of pneumatic system. There are various suppliers of proportional pressure regulator on the shelf, like the ones as Festo, SMC, Proportion-Air, Asco and many more. KaoLu is specialized in supplying high resolution, high pressure range, and high speed regulator series. Proportional flow valve including proportional throttle valve, proportional speed control valve, proportional one-way speed control valve, etc., it is also a single parameter control valve. Also mentioned main players are Clippard, Bosch Rexroth AG, Burkert, etc. KaoLu offers stepper motor driven proportional flow control valve that features high repeatability, high resolution and low hysteresis. Proportional directional (directional flow) valve is a multi (two) parameter control valve, which simultaneously controls the flow rate and flow direction of the liquid flow according to the magnitude and direction of the input electrical signal. Multi-function proportional valve is a multi-parameter control valve, which is a compound valve that combines pressure compensator and pressure valve on the basis of proportional directional valve. According to the magnitude and direction of the input electrical signal, the flow of the circuit and the direction of the oil flow are simultaneously controlled, and because the pressure compensator is installed, the flow of the control circuit is not affected by the load change, regardless of the load change. In addition, due to the combination of the pressure valve, it can also be used to control the maximum working pressure of the hydraulic system to achieve a variety of control functions. Proportional pressure regulator is also a multi-parameter proportional control valve, which combines pressure and flow control together, and through a balance valve (pressure compensation valve), the pressure at both ends of the throttle valve orifice remains unchanged. (2) According to the control method  This mainly refers to the classification according to the electro-mechanical conversion method in the pilot control valve of the proportional valve. Its electric control part has various forms such as proportional electromagnet, torque motor (mobile and suspension type) and DC servo motor. Electromagnetic type refers to a proportional valve that uses a proportional electromagnet as an electro-mechanical conversion element. The proportional electromagnet converts the input current signal into mechanical output, that is, output force and displacement, and then controls parameters such as pressure, flow and direction. Electric type refers to a proportional valve that uses a DC servo motor as an electromechanical conversion element. The DC servo motor converts the input electrical signal into the rotational speed of the rotary motion, and then outputs the force and displacement through the reduction device and conversion mechanism such as screw nut, rack and pinion or cam to control the output hydraulic parameters. The electro-pneumatic type refers to a proportional valve that uses a torque motor and a nozzle-baffle structure as the pilot control stage. Input different electrical signals to the torque motor, and output displacement or angular displacement through the baffle (sometimes the armature of the torque motor is the baffle) connected with it. (3) According to the installation position of electronic amplifier and the proportional valve body  • Separate type (the proportional valve body is separated from the electronic amplifier); • Type with electronic amplifier (electronic amplifier is integrated on the proportional valve body). (4) According to sensor with and without displacement The valve with displacement sensor can reach closed-loop displacement control of the valve, and its steady-state error ( hysteresis, sensitivity) is better than that of the servo valve without displacement sensor (electrical feedback). (5) According to the valve core structure There are spool valve type, poppet valve type and cartridge type structure. For the proportional valve with large flow, the structure of the cartridge valve is mostly used.