The main features of the rack：
1. Since the rack tooth profile is a straight line, each point on the tooth profile has the same pressure angle, which is equal to the inclination angle of the tooth profile. This angle is called the tooth profile angle, and the standard value is 20°.
2. Any line parallel to the addendum line has the same pitch and module.
3. The straight line parallel to the tooth top line and the tooth thickness equal to the tooth slot width is called the index line (center line), which is the reference line for calculating the rack size.
Features of horizontal rack and pinion piston actuators:
①It is easy to design a double-piston type to double the output torque; conversely, when the output torque is constant, a smaller size actuator can be obtained, which greatly reduces the weight and size;
②The rack and pinion rotate evenly and the rotation gap is small, so the movement is free and the hysteresis is small;
③The friction force of the rack and pinion transmission mode is much smaller than that of the sliding friction mode of the crank connecting rod, and the efficiency can be improved by 20% with the same diameter;
④It is very easy to directly connect with the valve, which simplifies the connection method of the valve and makes the shape of the valve more symmetrical, beautiful and miniaturized. Practice has proved that such quarter-turn piston actuators are used more and more widely, and will become the mainstream of quarter-turn piston actuators.