Troubleshooting Of Regulating Valves

Other troubleshooting of regulating valves

01 Change the flow direction, solve the problem of promoting customs, and eliminate the surge method

In order to improve the cut-off effect, the two-position valve is usually used as a flow closed type. For liquid media, due to the unbalanced force of the flow-closing type, the valve core is pressure-closed, and it has the effect of promoting closing, also known as the suction effect, which accelerates the speed of the valve core, causing slight water hammer and causing system surge. The solution to the above phenomenon is that as long as the flow direction is changed to flow open, the surge can be eliminated. This kind of problem can also be considered to solve the problem of the valve not working properly due to the promotion of closing.

02 Ways to prevent plastic deformation

Plastic deformation causes one kind of metal surface to scratch or even stick the metal surface of another kind of parts, causing the valve to jam, malfunctioning, dragging the sealing surface, increasing leakage, and the two parts of the threaded connection biting and rotating. Failure to move (such as the upper and lower valve bodies of the high-pressure valve). Plastic deformation is related to temperature, mating materials, surface roughness, hardness and load. The high temperature anneals or softens the metal, further aggravating the plastic deformation trend.

The methods to solve the valve failure caused by plastic deformation are: high-hardness materials are used for the parts that are easy to scratch, with 5-10Rc hardness differences; two parts are changed to different materials; Increase the gap Increase lubricant; Repair damaged surface, improve finish and hardness: When the thread bites and cannot be rotated, it has to be welded at once.

03 Increase sealing grease method

When the flow coefficient of the valve is too small due to inaccurate calculations or increased output, and the flow cannot be guaranteed when the valve is fully opened, the bypass has to be opened to pass part of the flow. Usually the bypass flow rate is less than 15-20% of the maximum flow rate.

Here is a way to open the bypass: due to the small flow resistance of the closed flow type, the flow coefficient is 10-15% larger than that of the open flow type. Therefore, the method of changing the flow direction can be used to change the normal flow open to flow closed use, even if the valve Pass 10-15% more traffic. In this way, the bypass can be avoided, and the stability problem can be ignored due to the wide opening.

04 Overcome fluid damage

The most typical valve is a double-seat valve. The fluid enters from the middle and the valve core is perpendicular to the inlet. The fluid bypasses the valve core and flows out into two upper and lower beams.

The fluid impacts on the spool, making it lean toward the outlet side, causing friction, damaging the guiding surface of the spool and the bushing, and causing malfunction. High flow may also cause the spool to bend, erode, or even break in severe cases.

The solution: increase the hardness of the material of the guiding part; increase the middle size of the upper and lower balls of the valve core to make it thick; use other valves instead. If a sleeve valve is used, fluid flows from around the sleeve and the lateral thrust on the valve plug is greatly reduced.

05 Method for overcoming the rotating force generated by fluid to make valve core rotate

For the valve core of the "V" shaped port, due to the asymmetry of the medium inflow, the tangential force of the valve core acting on the "V" shaped port is inconsistent, generating a rotating force that makes it rotate. Especially for valves with DN≥100, it is stronger.

As a result, the valve may be disconnected from the actuator push rod, and the springless actuator may cause the diaphragm to twist.

The solutions are: turn the valve core by an angle in the opposite direction of rotation to balance the tangential force acting on the valve core; further lock the connection between the valve stem and the push rod, and add an anti-rotation splint if necessary; The valve core with the V"-shaped opening is replaced with a plunger valve core; adopts or changes to a sleeve type structure; if the rotation is caused by resonance, the problem can be solved by eliminating the resonance.

06 Adjust the friction force of the butterfly valve plate to overcome the opening jump method

The butterfly valve with soft sealing such as "O" ring, sealing ring and lining is adopted. When the valve is closed, due to the deformation of the soft seal, the valve plate is closed in place and wraps the valve plate, which can achieve a very ideal cutting effect.

But when the valve is about to open, the force of the actuator to open the valve plate is continuously increasing. When the friction force of the soft seal on the valve plate is equal, the valve plate starts. Once activated, this friction force decreases sharply.

In order to achieve the balance of force, the valve plate opens violently. When the unbalanced torque of this force and the medium of the corresponding opening is balanced with the opening torque of the actuator, the valve stops at this opening. The opening degree of this violent and sudden take-off can be as high as 30-50%, which will cause a series of problems.

At the same time, due to the large changes of the soft seal when it is closed, it is easy to produce permanent deformation or be crushed by the valve plate, strain, etc., which affects the life.

The solution is to adjust the friction force of the soft seal against the start of the valve plate, which can not only ensure that the required cut-off requirements are met, but also enable the valve to start relatively normally.

The specific methods are as follows: adjust the amount of interference; reduce the difficulty of opening the valve plate due to excessive closing by limiting the position or adjusting the pre-tightening force and output force of the actuator.