29

2021

-

01

Other troubleshooting of regulating valve

Author:


In order to improve the cutting effect, the two-position valve is usually used as a closed flow type. For liquid media, due to the flow-closing unbalanced force, the valve core is pressed closed, which has a closing effect, also known as a suction effect, speeding up the action of the valve core, resulting in a slight water hammer, causing system surge.

 

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

 

In order to improve the cutting effect, the two-position valve is usually used as a closed flow type. For liquid media, due to the flow-closing unbalanced force, the valve core is pressed closed, which has a closing effect, also known as a suction effect, speeding up the action of the valve core, resulting in a slight water hammer, causing system surge.

The solution to the above phenomenon is to simply change the flow direction to open and the surge can be eliminated. This method can also be considered to solve problems like this that affect the normal operation of the valve due to accelerated closing.

 

Methods to prevent plastic deformation

 

Plastic change causes one metal surface to scratch the metal surface of another part, or even stick together, causing the valve to get stuck, causing malfunction, drag on the sealing surface, increased leakage, and two threaded parts to bite the screw. Faults such as the upper and lower valve bodies of the high-pressure valve not moving.

Plastic deformation is related to temperature, matching materials, surface roughness, hardness and load. High temperatures anneal or soften metals, further exacerbating plastic deformation tendencies.

Methods to solve valve failures caused by plastic deformation include:

The parts that are prone to scratches are made of high-hardness materials, with a hardness difference of 5 to 10Rc;

Use different materials for the two parts;

increase the gap;

Add lubricant;

Repair the damaged surface and improve the smoothness and hardness:

When the thread bites and cannot be rotated, it has to be welded at once.

 

Add sealing grease method

 

Due to factors such as inaccurate calculation or increased output, the flow coefficient of the valve is too small. When the flow cannot be guaranteed even when the valve is fully opened, the bypass has to be opened to allow partial flow. Usually the bypass flow rate is <15~20% of the larger flow rate.

Here is a way to open the bypass: Since the flow resistance of the closed flow type is small, the flow coefficient is 10 to 15% larger than that of the open flow type. Therefore, the flow direction can be changed to change the usual open flow to closed flow, even if the valve Pass 10-15% more traffic. This can avoid opening the bypass, and since it is working at a wide opening, stability issues can be ignored.

 

Overcome fluid damage method

 

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

The fluid impacts the valve core, causing it to move toward the outlet side, causing friction and damaging the guide surfaces of the valve core and bushing, resulting in abnormal operation. High flow rates may also cause the valve core to bend, erode, or even break in severe cases.

the solution:

Improve the material hardness of the guide parts;

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, the fluid flows from around the sleeve, and the lateral thrust on the valve plug is greatly reduced.

 

Method to overcome the rotational force generated by fluid to rotate the valve core

 

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

As a result, the connection between the valve and the actuator push rod may become disconnected, and the springless actuator may cause the diaphragm to twist.

The solutions are:

Turn the counter-rotation direction of the valve core by an angle to balance the tangential force acting on the valve core;

Further lock the connection between the valve stem and the push rod, and if necessary, add an anti-rotation splint;

Replace the "V"-shaped opening valve core with a plunger-shaped valve core;

Adopt or change to a sleeve-type structure;

If the rotation is caused by resonance, eliminating the resonance can solve the problem.

 

Adjust butterfly valve plate friction to overcome opening bounce method

 

Butterfly valves that use soft seals such as "O" rings, sealing rings, and linings. When the valve is closed, due to the deformation of the soft seal, the valve plate is closed in place and covers the valve plate, which can achieve a very ideal cutting effect.

But when the valve wants to open, the force of the actuator to open the valve plate continues to increase. When the friction force of the soft seal on the valve plate becomes equal, the valve plate starts. Once activated, this friction decreases dramatically.

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

At the same time, due to the large changes in the soft seal when closing, it is easy to deform the valve body or be squeezed or strained by the valve plate, which affects the service life.

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

Specific methods include:

Adjust the amount of interference;

By limiting the position or adjusting the pretightening force and output force of the actuator, the difficulties caused by excessive closing of the valve plate can be reduced.