At present, the design of valve remote control system for marine hydraulic, explosion-proof requirements and save cable and other factors to consider, valve position indicator oil tankers, tankers are mostly used in indirect measurement technology. The valve position measurement, indicating mechanism are arranged in the electromagnetic valve box area, control liquid volume, flow, pressure or flow parameters such as circuit in the measuring element measurement, using the parameters reflect indirectly control the opening and closing of the valve position and motion state, and instructs the [1].
In recent years, with the large-scale ship and ship automation level of the continuous improvement, the ship hydraulic valve remote control system has been widely used in large ships ballast water system, oil system and oil tanker bilge system in [2, 3]. The system working pressure, control pipe length increased, the valve position indicator especially volumetric valve position indication application problems. This paper analyzes the factors affecting volumetric valve position indicator measuring accuracy and resolution, developed with pressure compensation module volume type valve position indicator.
The 1 volume of the valve position indicator introduction and Application
Volume type valve position indicator is an indirect type valve position measurement technology, mainly through the liquid volume measurement through hydraulic drive to indirect measuring its position. At present, main metering cylinder type and measurement of motor type two kinds.
1) metering cylinder type
Measuring cylinder type valve position indicator is usually composed of piston, screw mechanism, measuring mechanism etc.. Hydraulic oil through the metering cylinder to push the piston to move, the bore defined circumstances, the hydraulic oil flow into the displacement S, after the screw mechanism will shift S into less than 360 ° opening angle, and then through the measuring with dial directly display and converted into electrical signal output.
2) metering motor type
Measure motor valve position indicator usually by measuring motor, gear decelerator, measuring mechanism. The hydraulic oil to pass through the metering motor drive gear motor, determine the motor discharge conditions, the hydraulic oil flow into the speed measuring motor n, through the small gear reducer will turn n into less than 360 ° opening angle, and then through the measuring with dial directly display and converted into electrical signal output.
Volume type valve position indicator will string in the hydraulic control loop, as shown in Figure 1 for the common volume type valve position indicator control circuit diagram. The graph by the valve position indicator (3) will flow through the volume of the valve position indicator of hydraulic oil volume into smaller than 360 ° opening angle, can machine instructions directly through the valve position indicator, also can be converted into electrical signals to the electrical control console to treatment, which can realize the control of the whole valve remote control system.
2 factors affecting volume type valve position indicator accuracy
Due to the adoption of indirect measurement technology, measurement accuracy of the volumetric valve position indicator is very important. Especially in the ship towards large-scale and automation direction development today, the system working pressure, control of the pipeline length increased, therefore, needs to study the various influencing factors. In order to improve the accuracy of volume type valve position indicator, in addition to its reasonable structure, good manufacturability, low resistance, low leakage, system the length of the pipe, pressure and other factors will also have a great effect on the.
Effects of 2.1 pipe length, working pressure
Indirect measurement techniques based volume type oil can not be compressed. In low, control the pressure of pipeline system is relatively short (control volume small) conditions, control oil circuit in the compressed volume is small, can be neglected, that oil can not be compressed. But in the large ship hydraulic valve remote control system working pressure up to 12.5MPa, the control line for 300m, control the volume of fluid compression volume is often greater than the hydraulic drive or accounted for a large proportion, will seriously affect the volume of the valve position indicator indicating accuracy.
Oil compression according to the formula (1) to calculate [2].
Δ V=V Δ P/K (1) in the formula, V is the oil volume, mL; Δ V was under pressure oil volume compression, mL; P stress; K is the bulk modulus of oil, K=0.7 * 103M
In order to study the effect of pipe length and the pressure of system on the oil volume, in the pipe diameter is 6mm, the hydraulic oil bulk modulus is K=0.7 * 103MPa, 7.5MPa, 10MPa, 12.5MPa were calculated under the working pressure, hydraulic oil volume compression amount of V in different pipeline length values, the results as shown in Fig. as shown in figure 2. It can be seen from the figure, the pipeline is long, the greater the amount of compression of hydraulic oil in the pipeline, pipeline hydraulic oil under the same pressure volume compression and pipeline length is linear growth; the more pressure, hydraulic oil pipeline volume compression amount is large, in the pipeline fluid volume compression and pipeline the pressure of the same pipeline length is linear growth. Under the pressure of 12.5MPa, when the pipeline length reaches above 300m, the amount of compression is in 150mL above, when in measurement, will have a great effect on the measurement accuracy.
The volume ratio of hydraulic oil and hydraulic drive compressed volume between 2.2 pipeline
When the pipeline length of variable length, control the volume of hydraulic oil volume compression and hydraulic actuator (hydraulic oil volume measured) ratio is more and more big, the measurement error will increase. By calculating the relationship between volume control hydraulic oil in the compressed volume and the hydraulic actuator working volume ratio, the pressure and the pipeline length effect of volume type valve position indicator measurement accuracy, compression of hydraulic oil
Conclusion：
The pressure compensation module, can greatly improve the measurement precision of volume type valve position indicator, can fully meet the use of large marine valve remote control system requirements. Designers can according to the requirements of specific ships and drive, timely use of pressure compensation module, in order to take the system method, suitable to ensure safety, improve the measurement accuracy and reliability of the system.
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