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How to choose the control valve? The detailed selection knowledge of control valve


Pressure reducing valve is by regulating, reduced the inlet pressure to a needed discharge pressure, and to rely on the energy of the medium itself, make the valve outlet pressure automatic remained stable. Pressure reducing valve is by changing the throttling area, change the kinetic energy of the flow velocity and fluid, different pressure loss, so as to achieve the goal of decompression. Then, by means of control and adjustment system, the pressure fluctuation behind the valve is balanced with the spring force, so that the pressure behind the valve remains constant within a certain error range.

(1)    The outlet pressure is almost equal to the inlet pressure, without reducing pressure

This failure phenomenon is shown as: import and export pressure reducing valve is close to equal, and outlet pressure does not change with the rotation of the regulating handle to adjust. Causes and elimination method is as follows.

① Because of the main valve core or body hole sink groove edge burr or the gap between the main valve core and body hole card has dirt, or because of the main valve core or valve hole shape tolerance is out of tolerance, hydraulic pressure tight, the main valve core card died in the maximum opening (Max) position, because of the opening, the oil does not decompress. According to the above situation, respectively adopt deburring at this time, clean and repair the valve hole and valve core precision of the method to be ruled out.

② Because the main valve core and valve hole with too tight, or during assembly to pull the valve hole or valve core, the valve core stuck in the maximum opening position, at this time can choose a reasonable gap. J type pressure reducing valve fit clearance is generally 0. 007 ~ 0. 015mm, before the appropriate grinding valve hole, and valve core.

③ The main valve core short damping hole or blockage in a seat holes, lost the function of automatic adjustment, the main valve spring force will push the main valve to the biggest opening, into a straight shine, inlet pressure is equal to the outlet pressure. Available phi 1. omm wire or with compressed air blowing through damping hole, and the cleaning and assembly.

④ For the J type pressure reducing valve, damping parts with damping holes are pressed into the main valve core, in use may be due to insufficient interference and rushed out. After flushing out, make the pressure of the oil inlet cavity and the oil outlet cavity equal (without damping), and the bearing area of the valve core is equal, but the oil outlet cavity has a spring, so the main valve core is always in the position of maximum opening, making the outlet pressure equal to the inlet pressure. At this time, it is necessary to reprocess the damping parts with larger outer diameter and re-press the main valve core.

⑤ JF type pressure reducing valve, hole leakage from factory is blocked with oil plug. When did not screw out the oil plug and use, the main valve cavity (spring cavity) trapped oil on the core, leading to the main valve core is in the biggest opening without relief. Type J tube valves are the same. J plate valve if the design installation plate did not make L port connected to the oil tank will also appear this phenomenon.

⑥ J tube type valve, repairing and when it is easy to install the valve bonnet in the wrong direction (wrong 90 ° or 180 °), the leaked oil mouth closed, can't discharge of oil, ditto trapped oil phenomenon, the main valve in the biggest opening decompression. Fix the valve cover assembly in the correct direction.

⑦ To JF type pressure reducing valve, cover direction installation is wrong, will make the output oil hole and drainage hole, resulting in no pressure reduction, also must pay attention to.

(2)    The outlet pressure is very low, even if the pressure regulating handwheel is tightened, the pressure will not rise

① Pressure relief valve in and out of the oil port is connected with the reverse: on the plate valve for the installation plate design is wrong, the tube valve is wrong to take over. The inlet and outlet of the j-type pressure reducing valve is just the opposite of the inlet and outlet of the y-type overflow valve. When using the valve, please pay attention to the steel mark (Pl, P2, L, etc.) near the oil port, or consult the hydraulic components product catalog, do not design wrong and connect wrong.

② The oil inlet pressure is too low, through the valve core throttle orifice, from the oil outlet output pressure is lower, at this time should find out the reason for the low oil inlet pressure (such as overflow valve failure).

③ Pressure relief valve downstream circuit load is too small. Pressure can not be built up, at this time can consider in the downstream of the reducing valve series throttle valve to solve.

④ Pilot valve (cone valve) and valve seat mating surface due to contamination retention and poor contact, not close; Or the pilot cone valve has serious scratches, with the valve seat matching hole out of circle, gap, resulting in the pilot valve core and valve seat hole is not close.

⑤ When disassembling and repairing, cone valve or cone valve is not installed in the valve seat hole. To this, can check the conical valve assembly or close.

⑥ On the main valve core damping hole blocked by dirt, as shown in figure 3-21, P2 cavity oil but can not by damping hole e into the main valve spring chamber, P2 of the feedback of the oil cavity pressure less than the guide on the cone valve, make the lost to the main valve outlet pressure pilot valve adjustment. After the damping hole is blocked, the main valve P. The cavity loses the function of oil pressure p3, making the main valve become a direct moving slide valve with weak spring force (only the main valve balance spring). Therefore, when the pressure of oil outlet is very low, it can overcome the force of the balance spring and make the throttle of reducing valve turn down ymin. In this way, the pressure of oil inlet p1 is reduced to p2 through the throttle of ymin. Long damping holes should be unobstructed.

⑦ Pilot valve spring (pressure regulating spring) mistakenly installed as a soft spring, or because of spring fatigue permanent deformation or broken and other reasons, resulting in p2 pressure adjustment is not high, can only be adjusted to a low fixed value, this value is far below the maximum pressure reduction valve adjustment.

⑧ Pressure adjustment handle due to thread injury or effective depth is not enough, can not screw to the end and make the pressure can not be adjusted to the maximum.

⑨ Bad seal between valve cover and valve body, serious oil leakage. The cause may be o-ring leakage or damage, pressing screw not tightened and valve cover processing end plane error, generally convex around, concave in the middle.

The main valve core because of dirt, burr, etc., stuck in the small opening of the position, so that the export pressure is low. Can be cleaned and deburring.

(3)    Unstable pressure, high pressure oscillating pendulum, and sometimes loud noise

According to relevant standards, the pressure swing of type J pressure reducing valve is ±o. LMPa, JF type is ±o. 3MPa. If it exceeds this standard, it means that the pressure pendulum is large and unstable.

① J type and JF type pressure reducing valve as the forerunner, pilot valve and relief valve and general, so causes pressure oscillator is large and the elimination method can be reference to the relevant part of the relief valve.

② Under the rated flow using the relief valve, the main valve oscillation phenomenon, often can appear to make the pressure reducing valve is not regulated, the oil outlet pressure appear "booster a step-down step-up step-down repeatedly repeatedly" cycle, so be sure to choose suitable pressure-reducing valve specifications.

③ Drainage mouth L the back pressure is big, also can produce the phenomenon of pressure oscillator is and is not regulated, the appropriate drainage pipeline oil return alone.

④ Spring is not good (bad) heat treatment deformation or stiffness, cause a large pressure fluctuation, replaceable qualified spring.

(4)    The oil outlet pressure rises automatically after the working pressure is set

In some pressure-reducing control loops, the outlet pressure of the pressure-reducing valve is used to control the oil pressure of electro-hydraulic directional valve or externally controlled sequential valve, etc. When the electro-hydraulic directional valve or externally controlled sequential valve reverses or works, the oil outlet flow of the pressure-reducing valve becomes zero, but the pressure still needs to maintain the original set pressure. In this case, since the valve outlet flow is zero, the flow through the relief port is only the pilot flow. Because the guide flow rarely, generally within 2 l/min, so the main valve decompression mouth basically close to the seated position (the opening minute), pilot flow by triangle groove or oblique cone flow, if the main valve core with too loose or too much wear, leakage increase. According to the flow continuity theorem, this part of leakage must also flow from the main valve core damping hole, that is, the flow through the damping hole is composed of pilot flow and leakage, and the damping hole area and the main valve spring cavity oil pressure is unchanged (the spring cavity oil pressure is determined by the pre-compression amount of the adjusted pressure regulating spring), in order to increase the flow through the damping hole, will inevitably lead to the increase of the main valve lower cavity oil pressure. Therefore, when the pressure relief valve outlet pressure is set, if the outlet flow rate is zero, the outlet pressure will increase due to the main spool with too loose or wear too much.

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