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24

2023

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04

Valve driven actuator - rack and pinion hydraulic actuator

Classification:


【Summary description】The hydraulic actuator is powered by high-pressure oil and has the characteristics of large load capacity and high adjustment accuracy. The hydraulic actuator structure includes a blade type structure and a piston type structure. The blade type is divided into single blade type and multi blade type; The piston type includes subdivided gear and rack type, spiral piston, chain type, crank connecting rod type, and multiple actuators. This article briefly discusses gear and rack actuators. The following figure shows a typical gear rack structure actuator.

The hydraulic actuator is powered by high-pressure oil and has the characteristics of large load capacity and high adjustment accuracy. The hydraulic actuator structure includes a blade type structure and a piston type structure. The blade type is divided into single blade type and multi blade type; The piston type includes subdivided gear and rack type, spiral piston, chain type, crank connecting rod type, and multiple actuators. This article briefly discusses gear and rack actuators. The following figure shows a typical gear rack structure actuator.

 

From the perspective of structural principles, both rack and helical hydraulic actuators can be considered as piston type hydraulic actuators. They all convert linear motion into rotational motion through piston motion, where the piston teeth mesh with the gear shaft teeth.

The gear and rack are divided into single cylinder and double cylinder types. The single cylinder type is a rack piston structure, while the double cylinder type is a symmetrical two rack piston structure centered on the gear shaft.

 

The single cylinder type is further divided into single acting and double acting styles. See the figure below.

In real production, we usually refer to it simply based on whether the hydraulic piston is under force. If the movement of the rack piston is driven by hydraulic pressure at both ends, we call it single rack (cylinder) double action. If only one end is moved by force and the return stroke relies on external forces, such as spring return, we call it single rack (cylinder) single action. As shown in the following figure.

 

There is some confusion and ambiguity between practical and academic names. When communicating in business and technology, it is necessary to pay attention to the names on each manufacturer's sample.

The diameter of the rack piston is generally selected according to industry standards, as shown in the following figure,

 

However, when it comes to specific project requirements, engineers will select the preferred cylinder diameter based on the specific requirements.

Different manufacturers' samples will have different definitions on product models based on their own product type spectrum. Some manufacturers define according to cylinder diameter, some define according to output torque, and some define according to product design serial number. Qunmei Electromechanical Company defines the product type spectrum based on the dimensions of flanges and shafts according to the ISO5211-2017 standard.

Regardless of the definition, the key to selecting an actuator is to select the flange and shaft specifications based on the torque required for the opening and closing of the matching valve. Under normal operating conditions, the safety factor considered by the actuator is 30%. Example: Assuming that the valve requires a torque of 1000Nm, then the safety torque is 1000 × (1+30%)=1300Nm。

At the same time, we need to pay attention to the selection of connecting flanges. According to the ISO5211-2017 standard, we should choose F14 flange as the connecting flange. The maximum allowable torque for this specification of flange is 2000Nm

Assuming that the transmission torque is selected using a flat key, according to the ISO5211-2017 standard, we need to cross the flange specifications with the shaft specifications to obtain parameters and select the transmission shaft diameter ∅ 42.

Select F14D42 product specifications based on the sample of Qunmei Electromechanical.

After selecting the base type, the required torque and opening speed are determined based on the actual application conditions to calculate the required hydraulic system pressure and hydraulic flow matching.

Due to the selected product specifications, the actual cylinder diameter specifications and stroke of the actuator have been determined by the manufacturer. By calculating according to the requirements, the system pressure and flow rate can be set, and based on this, the accessories of the actuator can be reasonably selected.

According to the F14D42 model, the full stroke flow rate of the sample is 274 milliliters, assuming that the valve needs to open for 12 seconds. Calculate (274/12) * 60=1370 milliliters per minute. Based on this flow rate, select a suitable matching hydraulic pump according to the motor speed.

Of course, some manufacturers directly provide the start time of each model based on the predetermined hydraulic motor pump on the sample. The methods all lead to the same goal.

In addition, according to the valve opening performance requirements, select control methods and structures that match the actuator, such as switch type, adjustment type, proportional type, buffer type, etc.

For example, assuming that the demand actuator has a buffering function at the opening or closing end, relevant structures can be designed on the cylinder head structure of the actuator to achieve buffering function.