Senin, 02 November 2009

Hydraulic servo cylinder

Feature and Operation
This kind of servo cylinder is called following cylinder too, which can be used for adjusting the blast volume of a blower fan. It consists of three sections: rotary sealing, distributing spool and main cylinder body. The main functions and features of each section are as follows:
1. Rotary sealing section—it can lead high pressure oil P, return oil (O) and lubricating oil (T) into or out of the main cylinder body rotating at high speed. So the section looks like a rotary valve containing a spindle rotating at high speed and a stationary case supported by rolling bearing. It should be higher in precision and too much internal leakage as well as extra temperature rise after a longer working period is not allowed. For the service life of its rolling bearing is limited, normally it must be rejected after two or three years running.
2. Distributing spindle section--it acts as a directional valve with negative overlap. Normally its inlet line (P) always is opened and return line (O) closed; and lubricating line (T) always opened. As the negative overlap causes a very small opening in return line, accordingly certain return oil flow rate can be used for circularly cooling the main cylinder. Since the blaster fan is located in flue, high ambient temperature could bring the main cylinder too hot. In order to protect sealing and cool the oil circulating outside the body must be implemented, and thus enable the power package normally running at lower pressure so that its service life will be prolonged.
3. Main cylinder body section--it is a differential cylinder with 1:2 ratios of its upper and down area. When high pressure oil (P) is simultaneously led into the upper and down chambers, larger chamber will become cylinder chamber and smaller one acts as a pump supplying the larger one with oil; when the oil returns to tank from the larger one, the smaller one acts as a cylinder. This function causes the cylinder running in both directions for the same time and having the same acting force against outside.
4. Servo cylinder operation: as the distributing spool moves in, inlet line P connects to the upper and down chambers of the cylinder, while the return line O is fully closed. In this case, the large chamber brings the shell of the main cylinder moving backward until the distributing body and spool return to their original positions; Otherwise, as the distributing spool is pulled forward for a stroke, the inlet line P only connects to the upper chamber and the return line O opens fully so that the cylinder body will move forward until it returns to its original relative position. For the shell of the main cylinder moves with the moving direction and stroke of the spool, it is called as “following-up”. Actually servo cylinder is a hydraulic amplifier which can generate power force by tons with a small drive signal source.

Notice to users
1. According to the above, negative overlap condition can cause a servo cylinder running under state mode at lower pressure which we call as medium level pressure value determined by the negative overlap state of the distributing valve group and oil viscosity. The value will fall with temperature rise, which mustn’t be lower than 1.7MPa at the least for it can influence stability of fan blade angle so as to generate vibration. 2.5MPa to 4MPa are recommended. When adjusting the fan blade angle, there will be oil pressure pulse, △ t<10s and Pmax<8MPa. But the pressure of ground power package should be stabilized at 8MPa which was set up by a relief valve. If the setting of the relief valve is lower than the peak value of the pressure pulse, the setting up will be failed and sealing damaged by the pull rod. So correct operation of the power package is very important for the servo cylinder’s normal running.
2. Hydraulic oil in a ground power package must be kept clean.
3. The sealing in a servo cylinder are made of heat-stable rubber and screws made of high strength steel.

Order 名称
Description 规格
Size 数量
Quantity 备注
1 O形圈 ¢27 x 2.65 1
2 O形圈 ¢70 x 5.7 2
3 O形圈 ¢135 x 5.7 2
4 O形圈 ¢170 x 5.7 4
5 O形圈 ¢12 x 1.9 3
6 铜垫 1

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