The Role of the Hydraulic Manifold System
An electrohydraulic servo control system, in the TRT device, belongs to one of eight systems. According to the instructions of the main control room, to realize the TRT open, stop speed control, power control, roof pressure, and process detection system control, to realize the functional control of the above system, will eventually be reflected in controlling the speed of the turbine, to control the opening of the calm leaf, and control the opening of the blade is the hydraulic position servo system. The accuracy and error of the control system directly affect the control of each stage of the TRT system. Therefore, the role of this system in TRT is very important.
Composition of the hydraulic valve block system
The system consists of the liquid control unit, servo oil cylinder, and power oil station.
The liquid control unit includes the speed regulating valve control unit and the transmission calm vane control two units, each unit is composed of an electrohydraulic servo valve, electric solenoid valve, fast shutdown solenoid valve, oil circuit block, base, etc.
The servo cylinder is a double-piston rod structure, with very little friction and good sealing performance. The power oil station is composed of an oil tank, variable oil pump, oil filter, cooler, pipe valve, detector table, etc.
The command signal issued by the automatic control system, compared with the actual position signal of the cylinder in the servo controller, become the error signal amplification, into the electric-liquid servo valve, the servo valve into hydraulic oil flow to push the cylinder, the feedback signal from the position sensor, until equal to the command signal, the cylinder stop moving, stop in the specified position, is stable on the opening.
The linear movement of the cylinder, through the rotating movement of a set of crank switches into the valve plate, changes the operating angle of the valve plate or the static vane.
Through the above analysis, with the continuous change of the system signal, the opening degree of the transparent calm leaf will also constantly change, and through the change of the static leaf opening degree, controlling the number of revolutions, the gas flow, and the turbine output can be achieved.
The action of the 6 surfaces of the hydraulic valve block
The conventional hydraulic valve block is generally a hexahedron, that is, the existence of 6 surfaces, today we according to the design method of the general valve block see the role of the 6-surface hydraulic manifold.
1. Top and bottom surface
The top and bottom surface of the valve block are mainly superimposed bonding surface. The surface has a common pressure oil port P port, a public oil return port T port, a leakage oil port L port and 4 fixed bolt holes.
1、 The right side
The right side usually contains components that often need to be adjusted. Such as belonging to the pressure control valve overflow valve, relief valve, sequence valve, and such as belonging to the flow control valve, throttle valve, speed valve, etc.; because these valves in the hydraulic system operation process, need to adjust often, so on the right side, for everyone to adjust, after all, the left-handed is less!
3. Front side
When the number of pressure control valves and flow control valves is large, they can not be arranged on the right side, so some such valves can only be adjusted on the front side; because the front side is also a convenient side.
4. The back side
The rear side is obviously the most inconvenient operation of a surface, so we can put some electromagnetic reversing valve, check valve and other valves do not need to manually adjust the valve arranged on this surface.
5. Left side
We generally set the output oil port of the connection actuator on the left side, in addition, there are some external pressure gauge port, accumulator connection oil port, pressure relay oil port and other backup oil port, can be set on the left side.
Of course, the above content is in the more ideal case. In the actual design process, I believe that not many people will follow the above method to make the layout, mainly due to the limitations of various sizes
Processing requirements of hydraulic valve blocks, including size error, shape position error, surface roughness
1. Should each size be marked with a tolerance?
First to throw a question, is every size to consider the machining accuracy?
In fact, no need, then what part needs to have the processing precision requirements? Simply put, only where there is an assembly relationship, you need to pay attention to the processing accuracy, especially with the accuracy requirements of the surface.
Take our common shaft parts, for example:
General radial dimensions will have accuracy requirements, because of the need to cooperate with the corresponding hole (such as bearings);
In the axis up, and there is no matching requirements, so the size only retains the free accuracy, that is to say, the tolerance is not marked, because there is no axial coordination.
2. Review of processing error knowledge
I believe that after reading our problem, some friends will be what error, accuracy, tolerance and other concepts around the dizzy, so we first review the processing error related knowledge.
So-called processing error includes: size error, shape error, position error.
1. Dimension error: the difference between the actual size and the ideal size after processing.
2. Shape error: it can be further divided into macro geometry error and surface roughness.
3. Position error: the deviation between the actual mutual position and the ideal position of each element on the workpiece.
Just talk about the error, not to say the tolerance, is a kind of rogue behavior, so what is the relationship between the error and the tolerance?
The relationship between error and tolerance: tolerance is the allowable range of error (emphasized, it is a range). As long as the error (the error is a value, not a range) does not exceed the tolerance, then the part is qualified.
That is to say, the error is the value that people measure after processing good parts, and the tolerance is artificial to judge the workpiece qualified and unqualified and develop a range, as long as the error falls within this range, calculate qualified, otherwise it is unqualified.
3. Processing error associated with the valve block
The processing error related to the valve block is nothing more than the above-mentioned size error, shape error, surface roughness, let's take a look at it one by one.
1、dimension error
As we know, about the valve block processing, the most processing element is the hole, so we should pay attention to the size error of the hole.
The relationships between dimension error, tolerance grade, and part size are shown in the following table:
among:
IT12~IT18, for sizes not matching the requirements;
IT11~IT12, for less important fit sizes;
IT9~IT10, for only general required fit dimensions;
IT7~IT8, used for slightly more accurate matching dimensions;
IT6, precision fit dimensions for important parts;
IT2~IT5, used for particularly precise parts fitting dimensions;
IT01~IT1, for standard high precision dimensions;
For the valve block, our hole diameter is generally between 3 and 30 m m (that is, the basic size of the lefmost column), so focus on the parameters in the dashed box.
2. Form and position tolerance requirements
The perpendiculality tolerance between the six surfaces of the valve block should be 0.05mm and shall not exceed 0.1mm;
The tolerance of parallel degree between the relative surfaces (i. e., parallel faces) is 0.03mm;
The planar tolerance of each surface is 0.02mm;
The perpendicular degree tolerance between the thread and its fitting surface is 0.05mm;
The tolerance of the perpendiculality of all holes to the end surface is 0.05mm;
3. Surface roughness requirements
Here we will also review the surface roughness correlation.
The common parameter Ra to evaluate the surface roughness, which represents the average deviation of the contour arithmetic (do not understand, please ignore), note that its unit is um;
Ra50, Ra25, generally means the rough machining surface, in fact, is the roughness of the raw material surface;
In Ra12.5, it generally indicates the roughness of the non-mating surface, such as the terminal shaft end surface of the shaft parts, and the chamfer; except for the chamfer in the insertion valve hole.
Ra6.3, generally indicates the roughness of the unimportant mating surface, such as the installation surface of pillars and supports.
Ra3.2, indicating the roughness of the mating surface of the general parts.
Ra1.6 indicates the tooth surface of ordinary gear, transmission thread working surface, positioning pin hole, etc.
Ra0.8, Ra0.4, indicates the working face roughness required to maintain coordination for a long time.
Ra0.1 indicates the roughness of the instrument track, cylinder piston rod and cylinder head contact surface.
Ra0.05, high requirement air tightness moving parts.
Ra0.012, measuring block and other standard high precision measuring tool surface roughness.
We use a "surface roughness comparison block" to intuitively understand what the different surface roughness is a state;
We go back to the valve block, and the roughness requirements of its various parts vary:
The roughness of the surface of the valve block and the holes for the embedded hydraulic valve shall not be greater than Ra0.8;
The roughness of the sealing surface and the O-ring groove shall not be greater than Ra3.2;
The roughness of the general oil channel is not greater than Ra12.5.
The surface where the block joins the block does not have significant scratches.
Finally, for beauty, processed cast iron and steel valve blocks can be surface galvanized.
